A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermo...A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermore,through precise compositional regulation by adjusting the Cu content and introducing Co,the Cu60Ni35Co5 alloy was obtained.The morphological evolution of the solidification front and the variation in solidification rate with undercooling were systematically investigated.By combining metallographic analysis,the BCT model,electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM),the microstructural evolution and grain refinement mechanisms of the undercooled alloys were revealed.This work aims to establish the intrinsic relationship among undercooling,solidification behavior,and microstructure,thereby provides both experimental and theoretical foundations for a deeper understanding of the deep undercooling solidification mechanism and microstructural control.展开更多
The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investig...The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investigated.For this purpose,the Mg-0.6Si,Mg-1.34Si,and Mg-3Si(wt%)alloys were considered as hypoeutectic,eutectic,and hypereutectic alloys,respectively.By decreasing the geometrical modulus of the solidifying section(increasing cooling rate),remarkable grain refinement,refining the dendrite arm spacing(DAS),and modification of Mg_(2)Si particles were achieved.Moreover,the grain size was refined via Si addition in the hypoeutectic range,while coarsening of grain size at high Si concentrations was observed.The results of shear punch testing and hardness measurements demonstrated that the ultimate shear strength(USS)and hardness increased by increasing the cooling rate during solidification.Moreover,Si addition generally improved hardness,while the highest USS level was achieved for the eutectic alloy due to the fine grain size and strengthening effect of the eutectic constituent.However,regarding the hypereutectic Mg-3Si alloy that exhibited high hardness,the shear properties were inferior due to the detrimental effect of the primary Mg_(2)Si particles.Finally,the results were discussed with consideration of the relationship between strength and hardness,for which the critical effect of Si was clarified.展开更多
The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC c...The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC carbides and eutectic(γ+γ′)formation,differential thermal analysis(DTA)was utilized to investigate the effect of cooing rate(10-90℃·min^(-1))on solidification behavior and micro-segregation of GH4975 alloy.According to the thermodynamic calculation and distribution characteristics of precipitates,the MC carbides can act as nucleation sites forγdendrites,but the nucleation ofγdendrites becomes less dependent on the MC carbide primers at higher cooling rates.As theγdendrites grow,the elements including Ti and Nb gradually accumulate in the residual liquid and leads to the formation of more MC carbides near the interdendritic region.Finally,the solidification is terminated with the formation of eutectic(γ+γ′).With an increase in cooling rate,the liquidus temperature rises,but the solidus temperature decreases,and thus the solidification range is obviously enlarged.The dendritic structure is significantly refined by the increase of cooling rate.The secondary dendrite arm spacing,λ_(2),as a function of cooling rate,T,can be expressed asλ_(2)=216.78T^(-0.42).Moreover,the increasing cooling rate weakens the back diffusion of Al,Ti,and Nb,increases the undercooling,and limits the growth of precipitates.Consequently,the sizes of MC carbides,eutectic(γ+γ′),and primaryγ′significantly decrease,but the area fraction of eutectic(γ+γ′)linerly increases as the cooling rate rises.Thus moderate cooling rate(such as 30℃·min^(-1))should be selected during the solidification process of GH4975 alloy.展开更多
The insufficient absolute strength of Mg-Li alloys severely restricts their aerospace applications.To address this limitation,a dual-phase Mg-Li alloy with enhanced strength was fabricated through rapid solidification...The insufficient absolute strength of Mg-Li alloys severely restricts their aerospace applications.To address this limitation,a dual-phase Mg-Li alloy with enhanced strength was fabricated through rapid solidification combined with hot-press sintering and extrusion.The optimized alloy exhibited yield and ultimate tensile strengths of 283 MPa and 306 MPa under quasi-static loading,respectively,while retaining a uniform elongation of 6%.Multiscale microstructural characterization via XRD,SEM-EBSD,and TEM revealed that rapid solidification induced remarkable grain refinement and precipitate redistribution.Subsequent thermomechanical processing achieved full dynamic recrystallization with refined grains.Crucially,the rapid solidification kinetics notably altered Al partitioning,favoring solid solution in magnesium phase over precipitation in lithium phase.These microstructural modifications activate synergistic strengthening mechanisms:1)Hall-Petch hardening from grain refinement,2)dispersion strengthening via nano-precipitates,3)dislocation strengthening from substructures,and 4)solid solution effects from Al supersaturation.This work establishes a microstructure design paradigm for high-performance Mg-Li alloys through coupled rapid solidification and thermomechanical processing.展开更多
Rapid industrialization in China has caused significant environmental challenges,particularly heavy metal pollution from mine tailings.Toxic heavy metals such as lead(Pb),cadmium(Cd),and mercury(Hg)are released during...Rapid industrialization in China has caused significant environmental challenges,particularly heavy metal pollution from mine tailings.Toxic heavy metals such as lead(Pb),cadmium(Cd),and mercury(Hg)are released during the processing of mining wastewater and leaching of mine tailings.Owing to their excellent physicochemical properties,cementitious materials are widely used for the solidification/stabilization of heavy metals,immobilizing heavy metals via two distinct mechanisms.Physically,their favorable characteristics,including high mechanical strength,low porosity,and durable matrix,create effective barriers.Chemically,the alkaline environment facilitates the precipitation of metal hydroxides/carbonates.Conversely,hydration products(calcium silicate hydrate gels and ettringite)contribute to immobilization through adsorption and physical encapsulation.This study systematically investigated the migration mechanisms of heavy metal contaminants in mine tailings;further,it elucidated the multifaceted immobilization pathways of cementitious materials,which involve synergistic adsorption,precipitation,and encapsulation by hydration products combined with homocrystalline substitution.A comprehensive analysis indicated that cementitious materials significantly reduced the mobility and bioavailability of heavy metals.Nonetheless,their long-term stability and potential environmental impact require further investigation.This study aims to provide theoretical support for environmental management and sustainable resource utilization,and to explore the broader application potential of cementitious technology for heavy metal stabilization,thereby establishing a theoretical foundation for future research on heavy metals in low-cement solidified/stabilized tailings.展开更多
The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation...The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation of Ti-containing inclusions,enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel.Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content;samples with 0.06,0.12,and 0.36 wt.%Ti exhibited equiaxed ratios of 18%,24%,and 41%,respectively.Three primary inclusion types—TiN,Al_(2)O_(3)-TiN,and TiO_(x)-TiN—were identified at the cores of equiaxed dendrites,with nucleation core sizes predominantly ranging from 0.5 to 8μm.Among the tested samples,the 0.36 wt.%Ti addition produced the highest nucleation core density.Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K(0.06 wt.%Ti)to 10.8 K(0.36 wt.%Ti),accelerating solidification front instability and thus enhancing heterogeneous nucleation.Additionally,higher Ti content increased the divergence angle between adjacent columnar dendrites,further promoting the columnar-to-equiaxed transition(CET).展开更多
One of the major challenges in the application of microbially induced carbonate precipitation(MICP)is achieving"bacteria freedom",as it necessitates a substantial volume of bacterial solutions.Nevertheless,b...One of the major challenges in the application of microbially induced carbonate precipitation(MICP)is achieving"bacteria freedom",as it necessitates a substantial volume of bacterial solutions.Nevertheless,both insitu bacterial cultivation and transportation of bacterial solutions have proven to be inefficient.In this study,we suggested the utilization of bacteria in the form of dry powder,enabling easy on-site activation and achieving a relatively high urease activity.We conducted MICP curing experiments on gold mine tailings(GMT)using steel slag(SS)as an additive.The results showed that the average unconfined compressive strength(UCS)values of the tailings treated with MICP and MICP+SS reached 0.51 and 0.71 MPa,respectively.In addition,the average leaching reduction rates of Cu,Pb,Cr,Zn,and T-CN in GMT after MICP treatment reached 98.54%,100%,70.94%,59.25%,and 98.02%,respectively,and the average reduction rates after MICP+SS treatment reached 98.77%,100%,88.03%,72.59%,and 98.63%,respectively.SEM,XRD,FT-IR analyses,and ultra-deep field microscopy results confirmed that the MICP treatment produced calcite-based calcium carbonate that filled the inter-tailing pores and cemented them together,and the hydration mechanism was the main reason for the increased curing efficiency of SS.Our research findings demonstrate that bacterial powder can efficiently achieve the objectives of heavy metal removal and tailing solidification.This approach can substantially de-crease the expenses associated with bacterial cultivation and solution transportation,thereby playing a crucial role in advancing the practical implementation of MICP.展开更多
Conventional low-carbon concrete design approaches have often overlooked carbonation durability and the progressive loss of cover caused by surface scaling,both of which can increase the long-term risk of reinforcemen...Conventional low-carbon concrete design approaches have often overlooked carbonation durability and the progressive loss of cover caused by surface scaling,both of which can increase the long-term risk of reinforcement corrosion.To address these limitations,this study proposes an improved design framework for low-carbon slag concrete that simultaneously incorporates carbonation durability and cover scaling effects into the mix proportioning process.Based on experimental data,a linear predictive model was developed to estimate the 28-day compressive strength of slag concrete,achieving a correlation coefficient of R=0.87711 and a root mean square error(RMSE)of 7.55 MPa.The mechanism-based equation exhibits strong physical interpretability,as each parameter corresponds to a clear physical process,satisfying the requirements of design codes for physical significance.By integrating the strength and carbon-emission models,the carbon-emission efficiency was further analyzed.Across all water–binder ratios(0.3,0.4,0.5),CO_(2) emissions per unit strength decreased steadily with increasing slag content,indicating that carbon efficiency is primarily governed by slag replacement rather than the water/binder ratio.Four design cases,all with a design strength of 30 MPa,were then evaluated to illustrate the combined effects of carbonation and scaling.In Case 1,without considering carbonation durability,the carbonation depth after 50 years exceeded the 25 mm cover,leading to potential corrosion.In Case 2,when carbonation durability was considered,the required actual strength increased to 31.28 MPa.When mild cover scaling of 3 mm was introduced(Case 3),the required strength rose to 34.59 MPa,and under severe scaling of 10 mm(Case 4),it increased to 45.73 MPa.These results indicate that intensified scaling demands higher strength and lower water/binder ratios to maintain durability.Overall,the proposed framework quantitatively balances strength,durability,and embodied carbon,supporting sustainable low-carbon concrete design.展开更多
This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge ...This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge of slag,as well as the proper functioning of gasification equipment.The experimental approach involves the utilization of various techniques,namely ash fusion temperature(AFT)tests,X-ray fluorescence spectroscopy,X-ray diffraction(XRD),scanning electron microscopy(SEM),differential thermal analysis(DSC),and K-value semiquantitative analysis.The results obtained from ash fusion temperature(AFT)tests indicate that the coarse slag exhibits a relatively higher flow temperature compared to the decarburized coarse slag.XRD analysis reveals the presence of diffraction peaks corresponding to Fe and Fe3Si when residue carbon is present in the slag.In contrast,no such peaks are observed in the decarburized coarse slag subjected to the same temperature and cooling mode.This implying that the carbothermal reaction affects the slag's crystallization behavior,consequently influencing the flow temperature in the presence of residual carbon.SEM analysis illustrates that the spheroidization phenomenon is obvious when there is residual carbon in the coarse slag,but there is no spheroidization phenomenon in the decarburized coarse slag.This shows that the surface tension of slag is affected by the presence of residual carbon.Furthermore,DSC results confirm the crystallization transformation and mineral decomposition of the slag at high temperatures.For both carbon-containing slag and decarburized coarse slag,the content of crystals obtained under quenching condition is obviously lower than that under natural cooling condition.展开更多
Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,...Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,little attention has been paid to the influence of humic substances on the EICP.Humic substances cover most of the surface soil across the world land with vegetation,which varies according to the density of vegetation and climate.To understand the compatibility of this technique to distinct problematic soils,it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme.Therefore,this study aims to investigate the effects of humic acid(HA),one type of humic substance,on the soil solidification through EICP.For this purpose,HA was added to natural soil with varying addition amounts(0%,1%,2%,4%,8%,16%)in soil column solidification tests.The results found that the cementation effectiveness was enhanced by a small amount of HA addition(<4%),while an addition up to 8%greatly inhibited the formation of calcium carbonate.At the same time,soil samples were buffered by HA in a weak acidic condition,thus preventing the emission of undesirable by-product ammonia in the ureolysis process.Therefore,this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.展开更多
In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail...In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.展开更多
The effect of carbon ranging from 0.014 to 0.071 wt.%on the solidification and microstructure of a Ni-based superalloy with high Al and Ti contents was studied.The results show that the increase in carbon addition sig...The effect of carbon ranging from 0.014 to 0.071 wt.%on the solidification and microstructure of a Ni-based superalloy with high Al and Ti contents was studied.The results show that the increase in carbon addition significantly increases the size and volume fraction of MC carbides and promotes the change of their morphology from blocky to elongated shape.However,the carbon addition obviously decreases the size and volume fraction of eutectic(γ+γ′)and reducesηphase and borides formation.The change in carbide characteristics is mainly because of the increasing carbide-forming element and carbides precipitation temperature with the increase in carbon which favors the growth of them along the interdendritic liquid film.MC carbides are formed at an earlier solidification stage than the eutectic(γ+γ′).The increased carbide formation consumes more Ti,which delays and reduces the eutectic(γ+γ′)precipitation.The delay of eutectic(γ+γ′)precipitation leads to a deeper undercooling,which significantly decreases the critical Ti concentration for its precipitation.This,in turn,lowers Ti/Al ratio in residual liquids ahead of the eutectic(γ+γ′)and hence reducesηformation subsequently.B and Zr are slightly enriched in the carbides,which are considered during discussing how carbon influences the eutectic(γ+γ′)precipitation.展开更多
Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from...Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from faceted to script-like with increasing cooling rate. Varying the carbon content from 40X10-6 to 320X10-6, the morphology of carbides changes from blocky, rod-like into script-like. Scanning electron microscopy observation of deep-etched samples indicates that these carbides evolve from octahedral to dendritic and then into welldeveloped dendrites accordingly in a three-dimensional manner. The morphology evolution is discussed from the viewpoint of the preferential growth orientation of fcc crystals and the carbide growth rate during directional solidification.展开更多
The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich...The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as het- erogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti2O3 is an effective inoculant for δ-ferrite during solidification in low carbon steel.展开更多
Microbial-induced carbonate precipitation(MICP)is a relatively innovative and environmentally-friendly soil reinforcement technology,primarily used on sand,but its application in loess has rarely been studied.This pap...Microbial-induced carbonate precipitation(MICP)is a relatively innovative and environmentally-friendly soil reinforcement technology,primarily used on sand,but its application in loess has rarely been studied.This paper explores the viability of the MICP technique for improving the engineering properties of typical loess.Sporosarcina pasteurii was used to trigger carbonate precipitation.Factors such as reaction temperature,p H of the media,and the inoculation ratio were adopted to determine the optimum conditions.Different concentrations of Sporosarcina pasteurii and cementation reagent were selected for combination to treat the loess samples with a selfdesigned vacuum test device.The unconfined compressive strength and calcium carbonate content of the treated samples were tested and Scanning Electron Microscopy(SEM)was carried out to evaluate the improving effect.The results showed that the optimum conditions are reaction temperature of 30℃,p H of the media of 9,a higher inoculation ratio can produce higher enzyme activity and monomer enzyme activity.The engineering properties of the MICP-treated loess are significantly improved.The obtained unconfined compressive strength increases nearly 4 times when the OD600 is 1.5 and cementation reagent concentration is 1 mol/L.The test results of calcium carbonate content are consistent with unconfined compressive strength.Finally,the microstructure of loess samples was quantitatively analyzed by Pore(Particle)and cracks analysis system(PCAS).It was showed that MICP has a great influence on the surface porosity,followed by the pore fractal dimension and the probability entropy,but has little influence on the pore average form factor.展开更多
The Mg-3%Al melt was inoculated by carbon with different holding time.The effect of holding time on grain refining efficiency was evaluated.The solidification characteristics of the carbon-inoculated Mg-3%Al melt with...The Mg-3%Al melt was inoculated by carbon with different holding time.The effect of holding time on grain refining efficiency was evaluated.The solidification characteristics of the carbon-inoculated Mg-3%Al melt with different holding time were assessed by computer-aided cooling curve analysis.The results showed that Mg-3%Al alloy could be effectively refined by carbon inoculation.Slight fading phenomenon occurred with increasing the holding time to 60 min.Carbon inoculation could significantly influence the shape of cooling curves of Mg-3%Al melt.The nucleation starting and minimum temperatures increased.The recalescence undercooling and duration decreased to almost zero after carbon inoculation.The grain refining efficiency of carbon inoculation could be assessed by the shape of the cooling curve and solidification characteristic parameters including nucleation starting and minimum temperatures,recalescence undercooling and duration.展开更多
We examined the enhancing effects of different dosages of product of Centrifugation of Bacterial Liquid(product of CBL)on the performance of slag-fGD gypsum-cement-bentonite-sludge system using MICP technology.We anal...We examined the enhancing effects of different dosages of product of Centrifugation of Bacterial Liquid(product of CBL)on the performance of slag-fGD gypsum-cement-bentonite-sludge system using MICP technology.We analyzed the multifaceted performance of the solidified sludge from macroscopic and microscopic perspectives.The experimental results reveal that the increase in product of CBL dosage results in positive impacts on the solidified sludge,including higher side compressive strength,lower leachate heavy metal concentration,and improved crack repair rates.At a 0.4%product of CBL doping concentration,the strength of the solidified sludge is enhanced by 26.6%at 3 d,61.2%at 7 d,and 13.9%at 28 d when compared to the unmodified solidified sludge.After 28 days,the concentrations of Zn and Cu ions reduce by 58%and 18%,respectively,and the crack repair rate is 58.4%.These results demonstrate that the increase in heavy metal concentration in the leachate leads to an increase in the strength of the solidified sludge.The strengthening procedure heavily relies on the mineralisation reaction of Bacillus pasteurii,which produces a substantial amount of CaCO_(3)to cement the particles and fill the pores initially.The modified solidifying sludge exhibits a self-repairing effect and an enhanced multifaceted performance as a result of oxygen being restored after crack formation and reactivation of Bacillus pasteurii.Such conditions facilitate the body's recovery.展开更多
Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon stee...Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon steel droplets (cooled in silicone oil) with different C contents by drop tube processing were observed.The volumes of droplets were set to be 2 mm×2 mm×2 mm (TM) and 5 mm×5 mm×5 mm (FM).For most samples,the microstructures are nearly the same from the surface to the center region.The microstructures of the FM samples with higher C content are much finer than those of the TM samples,which is the opposite of the situation with the lower C content samples.The distribution of C along the diameter of each sample was detected.The segregation of C was observed in TM samples with higher C contents while not in FM samples.This is regarded as relating to recalescence and the diffusion of C atoms during the solidification process.展开更多
In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The ...In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).展开更多
This paper investigated the use of magnesium phosphate cement (MPC) for solidifying sludge with different humic acid (HA) content (ranging from 0 to 4.5%) and explored the solidification mechanism. Fluidity, setting t...This paper investigated the use of magnesium phosphate cement (MPC) for solidifying sludge with different humic acid (HA) content (ranging from 0 to 4.5%) and explored the solidification mechanism. Fluidity, setting time, unconfined compressive strength (UCS), the strength formation mechanism, and the spontaneous imbibition process of solidified sludge (SS) were studied. The results indicate that MPC can be used as a low-alkalinity curing agent. As the HA content increases, fluidity and setting time also increase, while hydration temperature and strength decrease. Additionally, the failure mode of SS transitions from brittleness to ductility. The strength of SS is composed of the cementation strength provided by MPC hydration products, matric suction, osmotic suction, and the structural strength of the sludge. MPC reduces the structural strength caused by the shrinkage of pure sludge under the action of matric suction, but the incorporation of MPC significantly improved the strength when the sludge is eroded by water. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the sludge and MPC can form a dense solid body, forming various hydration products, and synergistically improve the mechanical properties of the sludge.展开更多
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.202503021211112)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘A deep-undercooling rapid-solidification technique combining cyclic superheating and molten glass purification was employed to successfully prepare Cu60Ni40 and Cu65Ni35 alloys at various undercooling levels.Furthermore,through precise compositional regulation by adjusting the Cu content and introducing Co,the Cu60Ni35Co5 alloy was obtained.The morphological evolution of the solidification front and the variation in solidification rate with undercooling were systematically investigated.By combining metallographic analysis,the BCT model,electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM),the microstructural evolution and grain refinement mechanisms of the undercooled alloys were revealed.This work aims to establish the intrinsic relationship among undercooling,solidification behavior,and microstructure,thereby provides both experimental and theoretical foundations for a deeper understanding of the deep undercooling solidification mechanism and microstructural control.
文摘The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investigated.For this purpose,the Mg-0.6Si,Mg-1.34Si,and Mg-3Si(wt%)alloys were considered as hypoeutectic,eutectic,and hypereutectic alloys,respectively.By decreasing the geometrical modulus of the solidifying section(increasing cooling rate),remarkable grain refinement,refining the dendrite arm spacing(DAS),and modification of Mg_(2)Si particles were achieved.Moreover,the grain size was refined via Si addition in the hypoeutectic range,while coarsening of grain size at high Si concentrations was observed.The results of shear punch testing and hardness measurements demonstrated that the ultimate shear strength(USS)and hardness increased by increasing the cooling rate during solidification.Moreover,Si addition generally improved hardness,while the highest USS level was achieved for the eutectic alloy due to the fine grain size and strengthening effect of the eutectic constituent.However,regarding the hypereutectic Mg-3Si alloy that exhibited high hardness,the shear properties were inferior due to the detrimental effect of the primary Mg_(2)Si particles.Finally,the results were discussed with consideration of the relationship between strength and hardness,for which the critical effect of Si was clarified.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52474362,52174317 and 51904146)the General Project Funded by Liaoning Province Education Department(Grant No.JYTMS20230943)。
文摘The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC carbides and eutectic(γ+γ′)formation,differential thermal analysis(DTA)was utilized to investigate the effect of cooing rate(10-90℃·min^(-1))on solidification behavior and micro-segregation of GH4975 alloy.According to the thermodynamic calculation and distribution characteristics of precipitates,the MC carbides can act as nucleation sites forγdendrites,but the nucleation ofγdendrites becomes less dependent on the MC carbide primers at higher cooling rates.As theγdendrites grow,the elements including Ti and Nb gradually accumulate in the residual liquid and leads to the formation of more MC carbides near the interdendritic region.Finally,the solidification is terminated with the formation of eutectic(γ+γ′).With an increase in cooling rate,the liquidus temperature rises,but the solidus temperature decreases,and thus the solidification range is obviously enlarged.The dendritic structure is significantly refined by the increase of cooling rate.The secondary dendrite arm spacing,λ_(2),as a function of cooling rate,T,can be expressed asλ_(2)=216.78T^(-0.42).Moreover,the increasing cooling rate weakens the back diffusion of Al,Ti,and Nb,increases the undercooling,and limits the growth of precipitates.Consequently,the sizes of MC carbides,eutectic(γ+γ′),and primaryγ′significantly decrease,but the area fraction of eutectic(γ+γ′)linerly increases as the cooling rate rises.Thus moderate cooling rate(such as 30℃·min^(-1))should be selected during the solidification process of GH4975 alloy.
基金supported by The National Natural Science Foundation of China(Grant No.62204197)the Key R&D and Transformation Plan of Science and Technology Department of Qinghai Province(Grant No.2022-GX-156)Xi'an Association for Science and Technology(Grant No.959202313058).
文摘The insufficient absolute strength of Mg-Li alloys severely restricts their aerospace applications.To address this limitation,a dual-phase Mg-Li alloy with enhanced strength was fabricated through rapid solidification combined with hot-press sintering and extrusion.The optimized alloy exhibited yield and ultimate tensile strengths of 283 MPa and 306 MPa under quasi-static loading,respectively,while retaining a uniform elongation of 6%.Multiscale microstructural characterization via XRD,SEM-EBSD,and TEM revealed that rapid solidification induced remarkable grain refinement and precipitate redistribution.Subsequent thermomechanical processing achieved full dynamic recrystallization with refined grains.Crucially,the rapid solidification kinetics notably altered Al partitioning,favoring solid solution in magnesium phase over precipitation in lithium phase.These microstructural modifications activate synergistic strengthening mechanisms:1)Hall-Petch hardening from grain refinement,2)dispersion strengthening via nano-precipitates,3)dislocation strengthening from substructures,and 4)solid solution effects from Al supersaturation.This work establishes a microstructure design paradigm for high-performance Mg-Li alloys through coupled rapid solidification and thermomechanical processing.
基金supported by the National Natural Science Foundation of China(No.52374121)the Henan Province Science and Technology Research and Development Joint Fund,China(No.235200810016)the National Key Research and Development Program,China(No.2023YFC2907203).
文摘Rapid industrialization in China has caused significant environmental challenges,particularly heavy metal pollution from mine tailings.Toxic heavy metals such as lead(Pb),cadmium(Cd),and mercury(Hg)are released during the processing of mining wastewater and leaching of mine tailings.Owing to their excellent physicochemical properties,cementitious materials are widely used for the solidification/stabilization of heavy metals,immobilizing heavy metals via two distinct mechanisms.Physically,their favorable characteristics,including high mechanical strength,low porosity,and durable matrix,create effective barriers.Chemically,the alkaline environment facilitates the precipitation of metal hydroxides/carbonates.Conversely,hydration products(calcium silicate hydrate gels and ettringite)contribute to immobilization through adsorption and physical encapsulation.This study systematically investigated the migration mechanisms of heavy metal contaminants in mine tailings;further,it elucidated the multifaceted immobilization pathways of cementitious materials,which involve synergistic adsorption,precipitation,and encapsulation by hydration products combined with homocrystalline substitution.A comprehensive analysis indicated that cementitious materials significantly reduced the mobility and bioavailability of heavy metals.Nonetheless,their long-term stability and potential environmental impact require further investigation.This study aims to provide theoretical support for environmental management and sustainable resource utilization,and to explore the broader application potential of cementitious technology for heavy metal stabilization,thereby establishing a theoretical foundation for future research on heavy metals in low-cement solidified/stabilized tailings.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3700602)the Jiaxing Key Research and Development Program(Grant No.2022BZ10010).
文摘The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification.Titanium(Ti)additions successfully induced the formation of Ti-containing inclusions,enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel.Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content;samples with 0.06,0.12,and 0.36 wt.%Ti exhibited equiaxed ratios of 18%,24%,and 41%,respectively.Three primary inclusion types—TiN,Al_(2)O_(3)-TiN,and TiO_(x)-TiN—were identified at the cores of equiaxed dendrites,with nucleation core sizes predominantly ranging from 0.5 to 8μm.Among the tested samples,the 0.36 wt.%Ti addition produced the highest nucleation core density.Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K(0.06 wt.%Ti)to 10.8 K(0.36 wt.%Ti),accelerating solidification front instability and thus enhancing heterogeneous nucleation.Additionally,higher Ti content increased the divergence angle between adjacent columnar dendrites,further promoting the columnar-to-equiaxed transition(CET).
基金supported by the Ordos City Science and Technology Major Project(2021ZD14-16)the National Key Research and Development Program(2018YFC1802904)the Discipline Signature Achievements of the Shanghai Polytechnic University(A10GY23G004-14).
文摘One of the major challenges in the application of microbially induced carbonate precipitation(MICP)is achieving"bacteria freedom",as it necessitates a substantial volume of bacterial solutions.Nevertheless,both insitu bacterial cultivation and transportation of bacterial solutions have proven to be inefficient.In this study,we suggested the utilization of bacteria in the form of dry powder,enabling easy on-site activation and achieving a relatively high urease activity.We conducted MICP curing experiments on gold mine tailings(GMT)using steel slag(SS)as an additive.The results showed that the average unconfined compressive strength(UCS)values of the tailings treated with MICP and MICP+SS reached 0.51 and 0.71 MPa,respectively.In addition,the average leaching reduction rates of Cu,Pb,Cr,Zn,and T-CN in GMT after MICP treatment reached 98.54%,100%,70.94%,59.25%,and 98.02%,respectively,and the average reduction rates after MICP+SS treatment reached 98.77%,100%,88.03%,72.59%,and 98.63%,respectively.SEM,XRD,FT-IR analyses,and ultra-deep field microscopy results confirmed that the MICP treatment produced calcite-based calcium carbonate that filled the inter-tailing pores and cemented them together,and the hydration mechanism was the main reason for the increased curing efficiency of SS.Our research findings demonstrate that bacterial powder can efficiently achieve the objectives of heavy metal removal and tailing solidification.This approach can substantially de-crease the expenses associated with bacterial cultivation and solution transportation,thereby playing a crucial role in advancing the practical implementation of MICP.
基金supported by the National Natural Science Foundation of China(No.52463034)supported by the Korea Institute of Energy Technology Evaluation and Planning funded by the Ministry of Trade,Industry and Energy(No.2025-02314098)of the Republic of Koreasupported by the Regional Innovation System&Education(RISE)program through the Gangwon RISE Center,funded by the Ministry of Education(MOE)and the Gangwon State(G.S.),Republic of Korea(2025-RISE-10-002).
文摘Conventional low-carbon concrete design approaches have often overlooked carbonation durability and the progressive loss of cover caused by surface scaling,both of which can increase the long-term risk of reinforcement corrosion.To address these limitations,this study proposes an improved design framework for low-carbon slag concrete that simultaneously incorporates carbonation durability and cover scaling effects into the mix proportioning process.Based on experimental data,a linear predictive model was developed to estimate the 28-day compressive strength of slag concrete,achieving a correlation coefficient of R=0.87711 and a root mean square error(RMSE)of 7.55 MPa.The mechanism-based equation exhibits strong physical interpretability,as each parameter corresponds to a clear physical process,satisfying the requirements of design codes for physical significance.By integrating the strength and carbon-emission models,the carbon-emission efficiency was further analyzed.Across all water–binder ratios(0.3,0.4,0.5),CO_(2) emissions per unit strength decreased steadily with increasing slag content,indicating that carbon efficiency is primarily governed by slag replacement rather than the water/binder ratio.Four design cases,all with a design strength of 30 MPa,were then evaluated to illustrate the combined effects of carbonation and scaling.In Case 1,without considering carbonation durability,the carbonation depth after 50 years exceeded the 25 mm cover,leading to potential corrosion.In Case 2,when carbonation durability was considered,the required actual strength increased to 31.28 MPa.When mild cover scaling of 3 mm was introduced(Case 3),the required strength rose to 34.59 MPa,and under severe scaling of 10 mm(Case 4),it increased to 45.73 MPa.These results indicate that intensified scaling demands higher strength and lower water/binder ratios to maintain durability.Overall,the proposed framework quantitatively balances strength,durability,and embodied carbon,supporting sustainable low-carbon concrete design.
基金supported by“the Fundamental Research Funds for the Central Universities”,North Minzu University(2022XYZHG07).
文摘This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge of slag,as well as the proper functioning of gasification equipment.The experimental approach involves the utilization of various techniques,namely ash fusion temperature(AFT)tests,X-ray fluorescence spectroscopy,X-ray diffraction(XRD),scanning electron microscopy(SEM),differential thermal analysis(DSC),and K-value semiquantitative analysis.The results obtained from ash fusion temperature(AFT)tests indicate that the coarse slag exhibits a relatively higher flow temperature compared to the decarburized coarse slag.XRD analysis reveals the presence of diffraction peaks corresponding to Fe and Fe3Si when residue carbon is present in the slag.In contrast,no such peaks are observed in the decarburized coarse slag subjected to the same temperature and cooling mode.This implying that the carbothermal reaction affects the slag's crystallization behavior,consequently influencing the flow temperature in the presence of residual carbon.SEM analysis illustrates that the spheroidization phenomenon is obvious when there is residual carbon in the coarse slag,but there is no spheroidization phenomenon in the decarburized coarse slag.This shows that the surface tension of slag is affected by the presence of residual carbon.Furthermore,DSC results confirm the crystallization transformation and mineral decomposition of the slag at high temperatures.For both carbon-containing slag and decarburized coarse slag,the content of crystals obtained under quenching condition is obviously lower than that under natural cooling condition.
基金JST SPRING,Grant Number JPMJSP2119Japan Society for the Promotion of Science(JSPS)KAKENHI Grant Number JP22H01581。
文摘Enzyme induced carbonate precipitation(EICP)is a promising technique in the field of biocementation due to its efficiency and controllability.Although many studies have proved its reliability in different environment,little attention has been paid to the influence of humic substances on the EICP.Humic substances cover most of the surface soil across the world land with vegetation,which varies according to the density of vegetation and climate.To understand the compatibility of this technique to distinct problematic soils,it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme.Therefore,this study aims to investigate the effects of humic acid(HA),one type of humic substance,on the soil solidification through EICP.For this purpose,HA was added to natural soil with varying addition amounts(0%,1%,2%,4%,8%,16%)in soil column solidification tests.The results found that the cementation effectiveness was enhanced by a small amount of HA addition(<4%),while an addition up to 8%greatly inhibited the formation of calcium carbonate.At the same time,soil samples were buffered by HA in a weak acidic condition,thus preventing the emission of undesirable by-product ammonia in the ureolysis process.Therefore,this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.
基金This work was supported by the Major State Basic Research Development Program of China(973 Program)under the contract number of 2004CB619108the National Natural Science Foundation of China(No.50574018)the NECT-04-0278 Project of the Ministry of Education of China.
文摘In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.
基金This work was supported by National Natural Science Foundation of China(Nos.51904146 and U1960203)the Doctor Start-up Fund of Liaoning Province(Grant No.2019-BS-125).
文摘The effect of carbon ranging from 0.014 to 0.071 wt.%on the solidification and microstructure of a Ni-based superalloy with high Al and Ti contents was studied.The results show that the increase in carbon addition significantly increases the size and volume fraction of MC carbides and promotes the change of their morphology from blocky to elongated shape.However,the carbon addition obviously decreases the size and volume fraction of eutectic(γ+γ′)and reducesηphase and borides formation.The change in carbide characteristics is mainly because of the increasing carbide-forming element and carbides precipitation temperature with the increase in carbon which favors the growth of them along the interdendritic liquid film.MC carbides are formed at an earlier solidification stage than the eutectic(γ+γ′).The increased carbide formation consumes more Ti,which delays and reduces the eutectic(γ+γ′)precipitation.The delay of eutectic(γ+γ′)precipitation leads to a deeper undercooling,which significantly decreases the critical Ti concentration for its precipitation.This,in turn,lowers Ti/Al ratio in residual liquids ahead of the eutectic(γ+γ′)and hence reducesηformation subsequently.B and Zr are slightly enriched in the carbides,which are considered during discussing how carbon influences the eutectic(γ+γ′)precipitation.
基金supported by the National Basic Research Program of China (Grant No. 2010CB631201)the National Natural Science Foundation of China (Grant No. 51201164)
文摘Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from faceted to script-like with increasing cooling rate. Varying the carbon content from 40X10-6 to 320X10-6, the morphology of carbides changes from blocky, rod-like into script-like. Scanning electron microscopy observation of deep-etched samples indicates that these carbides evolve from octahedral to dendritic and then into welldeveloped dendrites accordingly in a three-dimensional manner. The morphology evolution is discussed from the viewpoint of the preferential growth orientation of fcc crystals and the carbide growth rate during directional solidification.
文摘The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as het- erogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti2O3 is an effective inoculant for δ-ferrite during solidification in low carbon steel.
基金the financial support from Shaanxi Natural Science Basic Research Project(Grant no.2020JM-483)the National Natural Science Foundation of China(NSFC)(Grant no.51408464)funded by the China Scholarship Council。
文摘Microbial-induced carbonate precipitation(MICP)is a relatively innovative and environmentally-friendly soil reinforcement technology,primarily used on sand,but its application in loess has rarely been studied.This paper explores the viability of the MICP technique for improving the engineering properties of typical loess.Sporosarcina pasteurii was used to trigger carbonate precipitation.Factors such as reaction temperature,p H of the media,and the inoculation ratio were adopted to determine the optimum conditions.Different concentrations of Sporosarcina pasteurii and cementation reagent were selected for combination to treat the loess samples with a selfdesigned vacuum test device.The unconfined compressive strength and calcium carbonate content of the treated samples were tested and Scanning Electron Microscopy(SEM)was carried out to evaluate the improving effect.The results showed that the optimum conditions are reaction temperature of 30℃,p H of the media of 9,a higher inoculation ratio can produce higher enzyme activity and monomer enzyme activity.The engineering properties of the MICP-treated loess are significantly improved.The obtained unconfined compressive strength increases nearly 4 times when the OD600 is 1.5 and cementation reagent concentration is 1 mol/L.The test results of calcium carbonate content are consistent with unconfined compressive strength.Finally,the microstructure of loess samples was quantitatively analyzed by Pore(Particle)and cracks analysis system(PCAS).It was showed that MICP has a great influence on the surface porosity,followed by the pore fractal dimension and the probability entropy,but has little influence on the pore average form factor.
基金Project(51574127)supported by the National Natural Science Foundation of ChinaProject(2014A030313221)supported by the Natural Science Foundation of Guangdong Province,China
文摘The Mg-3%Al melt was inoculated by carbon with different holding time.The effect of holding time on grain refining efficiency was evaluated.The solidification characteristics of the carbon-inoculated Mg-3%Al melt with different holding time were assessed by computer-aided cooling curve analysis.The results showed that Mg-3%Al alloy could be effectively refined by carbon inoculation.Slight fading phenomenon occurred with increasing the holding time to 60 min.Carbon inoculation could significantly influence the shape of cooling curves of Mg-3%Al melt.The nucleation starting and minimum temperatures increased.The recalescence undercooling and duration decreased to almost zero after carbon inoculation.The grain refining efficiency of carbon inoculation could be assessed by the shape of the cooling curve and solidification characteristic parameters including nucleation starting and minimum temperatures,recalescence undercooling and duration.
基金Funded by the National Nature Science Foundation of China(Nos.51978439,52278269,52278268,and 52108238)the Tianjin Outstanding Young Scholars Science Fund Project(No.22JCJQJC00020)the State Key Laboratory of Green Building Materials Open Foundation(No.2021GBM08)。
文摘We examined the enhancing effects of different dosages of product of Centrifugation of Bacterial Liquid(product of CBL)on the performance of slag-fGD gypsum-cement-bentonite-sludge system using MICP technology.We analyzed the multifaceted performance of the solidified sludge from macroscopic and microscopic perspectives.The experimental results reveal that the increase in product of CBL dosage results in positive impacts on the solidified sludge,including higher side compressive strength,lower leachate heavy metal concentration,and improved crack repair rates.At a 0.4%product of CBL doping concentration,the strength of the solidified sludge is enhanced by 26.6%at 3 d,61.2%at 7 d,and 13.9%at 28 d when compared to the unmodified solidified sludge.After 28 days,the concentrations of Zn and Cu ions reduce by 58%and 18%,respectively,and the crack repair rate is 58.4%.These results demonstrate that the increase in heavy metal concentration in the leachate leads to an increase in the strength of the solidified sludge.The strengthening procedure heavily relies on the mineralisation reaction of Bacillus pasteurii,which produces a substantial amount of CaCO_(3)to cement the particles and fill the pores initially.The modified solidifying sludge exhibits a self-repairing effect and an enhanced multifaceted performance as a result of oxygen being restored after crack formation and reactivation of Bacillus pasteurii.Such conditions facilitate the body's recovery.
基金financially supported by the National Natural Science Foundation of China,Project No.51074210
文摘Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon steel droplets (cooled in silicone oil) with different C contents by drop tube processing were observed.The volumes of droplets were set to be 2 mm×2 mm×2 mm (TM) and 5 mm×5 mm×5 mm (FM).For most samples,the microstructures are nearly the same from the surface to the center region.The microstructures of the FM samples with higher C content are much finer than those of the TM samples,which is the opposite of the situation with the lower C content samples.The distribution of C along the diameter of each sample was detected.The segregation of C was observed in TM samples with higher C contents while not in FM samples.This is regarded as relating to recalescence and the diffusion of C atoms during the solidification process.
基金support of the Research Project Supported by Shanxi Scholarship Council of China(2022-040)"Chunhui Plan"Collaborative Research Project by the Ministry of Education of China(HZKY20220507)+2 种基金National Natural Science Foundation of China(52104338)Applied Fundamental Research Programs of Shanxi Province(202303021221036)Shandong Postdoctoral Science Foundation(SDCX-ZG-202303027,SDBX2023054).
文摘In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).
基金This research work was financially supported by the National Natural Science Foundation of China(Grant No.51972209).
文摘This paper investigated the use of magnesium phosphate cement (MPC) for solidifying sludge with different humic acid (HA) content (ranging from 0 to 4.5%) and explored the solidification mechanism. Fluidity, setting time, unconfined compressive strength (UCS), the strength formation mechanism, and the spontaneous imbibition process of solidified sludge (SS) were studied. The results indicate that MPC can be used as a low-alkalinity curing agent. As the HA content increases, fluidity and setting time also increase, while hydration temperature and strength decrease. Additionally, the failure mode of SS transitions from brittleness to ductility. The strength of SS is composed of the cementation strength provided by MPC hydration products, matric suction, osmotic suction, and the structural strength of the sludge. MPC reduces the structural strength caused by the shrinkage of pure sludge under the action of matric suction, but the incorporation of MPC significantly improved the strength when the sludge is eroded by water. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the sludge and MPC can form a dense solid body, forming various hydration products, and synergistically improve the mechanical properties of the sludge.
