To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the...To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the alloy across different planes were investigated.The anisotropy of SLM-fabricated Ti-6Al-4V alloys was analyzed,and the electron backscatter diffraction technique was used to investigate the influence of different grain types and orientations on the stress-strain distribution at various scales.Results reveal that in room-temperature compression tests at a strain rate of 10^(-3) s^(-1),both the compressive yield strength and microhardness vary along the deposition direction,indicating a certain degree of mechanical property anisotropy.The alloy exhibits a columnar microstructure;along the deposition direction,the grains appear equiaxed,and they have internal hexagonal close-packed(hcp)α/α'martensitic structure.α'phase has a preferential orientation approximately along the<0001>direction.Anisotropy arises from the high aspect ratio of columnar grains,along with the weak texture of the microstructure and low symmetry of the hcp crystal structure.展开更多
The TiB+TiC dual-reinforced B_(4)C/TC4 composite was in-situ fabricated via incorporating 0.5wt%B_(4)C reinforcement during the laser melting deposition process.Different heat treatments of annealing and solid solutio...The TiB+TiC dual-reinforced B_(4)C/TC4 composite was in-situ fabricated via incorporating 0.5wt%B_(4)C reinforcement during the laser melting deposition process.Different heat treatments of annealing and solid solution were used to regulate the microstructure,mechanical properties,and corrosion properties of B_(4)C/TC4 composite.Results show that with the increase in temperature from 500℃to 800°C,partial lamellarα-Ti in the as-deposited sample is gradually transformed into equiaxedα-Ti,accompanied by the disappearance of basketweave microstructure.At 1100°C,a small portion of TiC phase suffers fusion.This composite exhibits the optimal combination of strength and plasticity after annealing at 500℃for 4 h followed by furnace cooling,which is attributed to the stress release effect and the refined basketweave microstructure.However,this composite shows a decline in corrosion resistance after various heat treatments due to grain coarsening and micro-galvanic corrosion.展开更多
To enhance the anti-corrosion performance of TC4 alloy across a wide temperature range for modern aircrafts operating in increasingly harsh environments, the (TiB+TiC) hybrid reinforced TC4 composites were prepared by...To enhance the anti-corrosion performance of TC4 alloy across a wide temperature range for modern aircrafts operating in increasingly harsh environments, the (TiB+TiC) hybrid reinforced TC4 composites were prepared by laser melting deposition (LMD) via the in-situ reaction between B_(4)C reinforcement and molten TC4 alloy. The effect of B_(4)C content (0, 0.5, 1.5, wt%) on the microstructure and room/high-temperature corrosion behaviour of the composites was investigated. Microstructural analysis revealed that the microstructure of the composites was significantly influenced by the B_(4)C content. The composite containing 0.5 wt% B_(4)C exhibited an optimal microstructure characterized by refined grains, equiaxed α-Ti transformed from lath-shaped α-Ti, well-distributed (TiB+TiC) phases with a proper amount and reduced pore/dislocation defects. This composite also demonstrated the best corrosion resistance at both room temperature (25 ℃) and high temperature (800 ℃), which was primarily attributed to its comprehensive advantages including a favorable microstructure, a uniform dispersion of thermally stable (TiB+TiC) phases and a stable passivation film.展开更多
The microstructural evolution and phase transformations during partial remelting of in-situ Mg2Sip/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refi...The microstructural evolution and phase transformations during partial remelting of in-situ Mg2Sip/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refining primary α-Mg grains and Mg2Si particles. After being partially remelted, a semisolid microstructure with small and spheroidal primary α-Mg particles can be obtained. The microstructural evolution during partial remelting can be divided into four stages： the initial rapid coarsening, structural separation, spheroidization and final coarsening, which are essentially caused by the phase transformations of β→α, α＋β→L and α→L, α→L, and α→L and L→α, respectively. The Mg2Si particles have not obvious effect on the general microstructural evolution steps, but can slower the evolution progress and change the coarsening mechanism. During partial remelting, Mg2Si particles first become blunt and then become spheroidal because of melting of their edges and corners, and finally are coarsened owing to Ostwald ripening.展开更多
Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good print...Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality.Despite the slight evaporation of Mn,energy dispersive spectrometer mapping and Xray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic(fcc)phase,indicating successful in-situ alloying.The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.展开更多
A quasi-equiatomic CoCrFeCuNi high-entropy alloy(HEA) with a broad-spectrum antibacterial ability and good mechanical properties has been fabricated by selective laser melting(SLM) and in-situ alloying of a blend of p...A quasi-equiatomic CoCrFeCuNi high-entropy alloy(HEA) with a broad-spectrum antibacterial ability and good mechanical properties has been fabricated by selective laser melting(SLM) and in-situ alloying of a blend of pre-alloyed CoCrFeNi powder and Cu elemental powder.The as-built HEA alloy has a homogeneous distribution of Cu and presents a single FCC phase.Compared with the same HEA fabricated using the traditional ingot metallurgy(IM) process,the HEA alloy fabricated by SLM releases more Cu ions to prevent growth and biofilm formation by gram-negative Escherichia coli and gram-positive Staphylococcus aureus,which enhances the applicability of the HEA alloy in potential applications that requires antibacterial ability.The results of this study confirm the feasibility of combining the antibacterial CoCrFeCuNi HEA alloy and SLM technology in fabricating complex shaped parts or structures with a strong antibacterial ability to be used in medical application or other environments desired for antibacterial ability.展开更多
The selective laser melting （SLM） of Ti-Ni mixed powder with atomic ratio of 1：1 was performed in the present work in order to elaborate shape memory alloy （SMA）. The martensite phase of Ti-Ni alloy can be found ...The selective laser melting （SLM） of Ti-Ni mixed powder with atomic ratio of 1：1 was performed in the present work in order to elaborate shape memory alloy （SMA）. The martensite phase of Ti-Ni alloy can be found by X-ray diffraction （XRD） analysis under temperature field, moreover, the Ti2Ni phase at a high scanning velocity. The crystalline phase images also show that the synthesized Ti-Ni alloy possessed a refined martensite microstructure. In order to evaluate the mechanical properties, the microhardness and porosity were measured. The microhardness is relatively high about 400HVo.2 with champ temperature. Besides, the porosity is quite low due to the excellent laser energy absorptivity and meltability of Ni element. The differential scanning calorimetry （DSC） analysis shows that the transformation temperature from austenite phase to martensite phase is relatively high and stable.展开更多
A controllable in-situ aging treatment of Inconel 718 alloy was successfully developed by governing the types and times of the thermal cycles during selective laser melting(SLM).The sequential precipitation of γ’,co...A controllable in-situ aging treatment of Inconel 718 alloy was successfully developed by governing the types and times of the thermal cycles during selective laser melting(SLM).The sequential precipitation of γ’,composite phase of primary/secondary γ’ coated by a γ " shell,and γ" occurs as the times of vertical thermal cycles increase when laser peak temperature(Tp)is between the precipitation temperature of strengthening phase(Tpre)and liquid temperature(T_L),which causes an increase in microhardness by 40 HV.Also,short-term aging mechanisms on three types of strengthening phases are proposed based on a great number of vacancies in the matrix.展开更多
A key component of future lunar missions is the concept of in-situ resource utilization(ISRU),which involves the use of local resources to support human missions and reduce dependence on Earth-based supplies.This pape...A key component of future lunar missions is the concept of in-situ resource utilization(ISRU),which involves the use of local resources to support human missions and reduce dependence on Earth-based supplies.This paper investigates the thermal processing capability of lunar regolith without the addition of binders,with a focus on large-scale applications for the construction of lunar habitats and infrastructure.The study used a simulant of lunar regolith found on the Schr?dinger Basin in the South Pole region.This regolith simulant consists of20 wt%basalt and 80 wt%anorthosite.Experiments were conducted using a high power CO_(2)laser to sinter and melt the regolith in a 80 mm diameter laser spot to evaluate the effectiveness of direct large area thermal processing.Results indicated that sintering begins at approximately 1180℃and reaches full melt at temperatures above 1360℃.Sintering experiments with this material revealed the formation of dense samples up to 11 mm thick,while melting experiments successfully produced larger samples by overlapping molten layers and additive manufacturing up to 50 mm thick.The energy efficiency of the sintering and melting processes was compared.The melting process was about 10 times more energy efficient than sintering in terms of material consolidation,demonstrating the promising potential of laser melting technologies of anorthosite-rich regolith for the production of structural elements.展开更多
This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualis...This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W.Detailed morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore formation.Lower laser power led to increased pore coverage,whereas a denser structure was observed at higher laser power.This laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the samples.An increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore volume.Lower laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher power.The interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.展开更多
Selective laser melting(SLM)is a cost-effective 3 D metal additive manufacturing(AM)process.However,AM 316 L stainless steel(SS)has different surface and microstructure properties as compared to conventional ones.Bori...Selective laser melting(SLM)is a cost-effective 3 D metal additive manufacturing(AM)process.However,AM 316 L stainless steel(SS)has different surface and microstructure properties as compared to conventional ones.Boriding process is one of the ways to modify and increase the surface properties.The aim of this study is to predict and understand the growth kinetic of iron boride layers on AM 316 L SS.In this study,the growth kinetic mechanism was evaluated for AM 316 L SS.Pack boriding was applied at 850,900 and 950℃,each for 2,4 and 6 h.The thickness of the boride layers ranged from(1.8±0.3)μm to(27.7±2.2)μm.A diffusion model based on error function solutions in Fick’s second law was proposed to quantitatively predict and elucidate the growth rate of FeB and Fe_(2)B phase layers.The activation energy(Q)values for boron diffusion in FeB layer,Fe_(2)B layer,and dual FeB+Fe_(2)B layer were found to be 256.56,161.61 and 209.014 kJ/mol,respectively,which were higher than the conventional 316 L SS.The findings might provide and open new directions and approaches for applications of additively manufactured steels.展开更多
Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co2...Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co28 Cr9 W1.5 Si(wt.%)alloy,fabricated by laser powder bed fusion(LPBF),was comprehensively investigated.During the layer-by-layer featured process,in-situ formation of Si rich,amorphous,nano-oxide inclusions was observed,whose formation is ascribed to the high affinity of Si to oxygen.Meanwhile,distinctive body-centered cubic(BCC)Co5 Cr3 Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear.The precipitates,rarely reported in previous studied Co-Cr alloys,were found to tightly bond with the in-situ oxidization.Furthermore,the morphologies,the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified.The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations,thereby increasing the strength of the alloy.It was understood that when the plastic deformation proceeds,the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate.A quantitative analysis of the strengthening mechanism was also established,in which an additional important contribution to strength(~169 MPa)caused by the effects of in-situ formed oxide inclusions was calculated.展开更多
Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selectiv...Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selective Laser Melting(SLM),known for its high precision,is a promising additive manufacturing technology that has been widely adopted across various industries.Studies have reported that under certain SLM manufacturing conditions and process parameters,the HE resistance of SLM ASS is significantly better than that of conventionally manufactured(CM)ASS,showing great potential for application in high-pressure hydrogen systems.Thus,studying the HE of SLM ASS is crucial for further improving the safety of high-pressure hydrogen systems.This paper provides an overview of the SLM process,reviews the mechanisms of HE and their synergistic effects,and analyzes the HE characteristics of SLM ASS.Additionally,it examines the influence of unique microstructures and SLM process variables on HE of SLM ASS and offers recommendations for future research to enhance the safety of high-pressure hydrogen systems.展开更多
TA15 alloy fabricated by laser melting deposition was investigated at 500℃ under tensile deformation. The damage behavior of microstructure was analyzed by the real time observation of the microstructure evolution, m...TA15 alloy fabricated by laser melting deposition was investigated at 500℃ under tensile deformation. The damage behavior of microstructure was analyzed by the real time observation of the microstructure evolution, microcracks initiation and propagation using in-situ tensile equipment fitted in the SEM chamber. Finally, the mechanism of fracture was discussed. The result showed anisotropic mechanical properties in X-and Z-direction. The existence of columnar β grains and its orientation to the tensile direction were the major factors inducing the anisotropic mechanical properties. As compared to Z-direction specimen, high tensile strength was observed in X-direction specimen due to the resistance in slips propagation provided by the prior-β grain boundaries( β GBs). Accumulation of the cracks at prior β GB caused the shear fracture. In case of Z-direction specimen, parallel orientation of prior β GB and GB α with the tensile direction resulted in a homogeneous deformation. The high reduction of cross section showed the enhanced ductile characteristics at high temperature.展开更多
In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the p...In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the production of parts and larger structures was investigated in detail.With different experimental setups in normal and microgravity,laser spots with diameters from 5 mm to 100 mm were realized to melt the regolith simulant EAC-1A and an 80%/20%mixture of TUBS-T and TUBS-M,which are used as a substitute for the actual lunar soil.In the experiments performed,the critical parameters are the size of the laser spot,the velocity of the laser spot on the surface of the powder bed,the gravity and the wettability of the powder bed by the melt.The stability of the melt pool as a function of these parameters was investigated and it was found that the formation of a stable melt pool is determined by gravity for large melt pool sizes in the range of 50 mm and by surface tension for small melt pool sizes in the range of a few mm.展开更多
Ti-Mo alloys/composites are expected to be the next-generation implant material with low moduli but without toxic/allergic elements.However,synthesis mechanisms of the Ti-Mo biomaterials in Selective Laser Melting(SLM...Ti-Mo alloys/composites are expected to be the next-generation implant material with low moduli but without toxic/allergic elements.However,synthesis mechanisms of the Ti-Mo biomaterials in Selective Laser Melting(SLM)vary according to raw materials and fundamentally influence material performance,due to inhomogeneous chemical compositions and stability.Therefore,this work provides a comparative study on microstructure,mechanical and wear performance,and underlying thermal mechanisms of two promising Ti-Mo biomaterials prepared by SLM but through different synthesis mechanisms to offer scientific understanding for creation of ideal metal implants.They are(i)Ti-7.5 Mo alloys,prepared from a conventional Ti/Mo powder mixture,and(ii)Ti-7.5 Mo-2.4 Ti C composites,in-situ prepared from Ti/Mo_(2)C powder mixture.Results reveal that the in-situ Ti-7.5 Mo-2.4 Ti C composites made from Ti/Mo_(2)C powder mixture by SLM can produce 61.4%moreβphase and extra Ti C precipitates(diameter below 229.6 nm)than the Ti-7.5 Mo alloys.The fine Ti C not only contributes to thinner and shorterβcolumnar grains under a large temperature gradient of 51.2 K/μm but also benefits material performance.The in-situ Ti-7.5 Mo-2.4 Ti C composites produce higher yield strength(980.1±29.8 MPa)and ultimate compressive strength(1561.4±39 MPa)than the Ti-7.5 Mo alloys,increasing by up to 12.1%.However,the fine Ti C with an aspect ratio of 2.71 dominates an unfavourable rise of elastic modulus to 91.9±2 GPa,44.7%higher than the Ti-7.5 Mo alloys,which,nevertheless,is still lower than the modulus of traditional Ti-6 Al-4 V.While,Ti C and its homogeneous distribution benefit wear resistance,decreasing the wear rate of the in-situ Ti-7.5 Mo-2.4 Ti C composites to 6.98×10^(-4)mm^3 N^(-1)m^(-1),which is 36%lower than that of the Ti-7.5 Mo alloys.Therefore,although with higher modulus than the Ti-7.5 Mo alloys,the SLM-fabricated in-situ Ti-7.5 Mo-2.4 Ti C composites can expect to provide good biomedical application potential in cases where combined good strength and wear resistance are required.展开更多
ZGH401 alloy was prepared under varying laser power levels and scanning speeds by the orthogonal test method using selective laser melting(SLM).The effect of different energy densities on microstructure and mechanical...ZGH401 alloy was prepared under varying laser power levels and scanning speeds by the orthogonal test method using selective laser melting(SLM).The effect of different energy densities on microstructure and mechanical properties of the formed alloy was investigated.The microstructure of ZGH401 was analyzed by scanning electron microscope,electron back-scattered diffraction,and electron probe microanalysis.The results show that the defects of the as-built ZGH401 are gradually reduced,the relative density is correspondingly enhanced with increasing the energy density,and the ultimate density can reach 99.6%.An increase in laser power leads to a corresponding rise in hardness of ZGH401,while a faster scanning speed reduces the residual stress in asbuilt ZGH401 samples.In addition,better tensile properties are achieved at room temperature due to more grain boundaries perpendicular to the build direction than parallel to the build direction.The precipitated phases are identified as carbides and Laves phases via chemical composition analysis,with fewer carbides observed at the molten pool boundaries than within the molten pools.展开更多
In this study,non-toxic in-situβphases of reinforced Ti/Zr-based bulk metallic glass matrix composites(BMGCs)of(Ti_(0.65)Zr_(0.35))100-xCux(x=5,10,15 at.%)are fabricated via selective laser melting.The effect of Cu c...In this study,non-toxic in-situβphases of reinforced Ti/Zr-based bulk metallic glass matrix composites(BMGCs)of(Ti_(0.65)Zr_(0.35))100-xCux(x=5,10,15 at.%)are fabricated via selective laser melting.The effect of Cu content on phase formation,microstructure,and mechanical properties is investigated.The average volume fraction and width of theβphase decreases with increasing Cu content,while a more amorphous phase and the(Ti,Zr)_(2)Cu phase forms.In the center zone of the molten pool,theβphase grows in the direction of the temperature gradient,and the amorphous phase distributes among theβphases.This occurs using:sphere morphology(for x=5),a more continuous elongated sphere and network morphology(for x=10),and network morphology(for x=15),respectively.In the edge zone of the molten pool,due to the smaller cooling rate and the existence of a partially molten zone,theβphase becomes coarser,and an amorphous phase forms for more continuous networks.Furthermore,the hardness improves significantly with increasing Cu content.No crack is found for x=5.Although the average volume fraction of theβphase for x=5 is about 90%,the compression yield strength is 1386±64 MPa,reaching to an average level of conventionally fabricated counterparts,due to finer microstructure,and twinning and martensitic transformation of theβphase.展开更多
Preliminary characterization of microstructure and mechanical properties of(TiB+TiC)/TC4 and TiC/Ti60 in-situ titanium matrix composites prepared by laser melting deposition is reported in this paper.The results indic...Preliminary characterization of microstructure and mechanical properties of(TiB+TiC)/TC4 and TiC/Ti60 in-situ titanium matrix composites prepared by laser melting deposition is reported in this paper.The results indicate that in-situ reaction occurred during laser melting deposition of coaxially fed mixed powders from TC4 and B4C with formation of form TiB and TiC reinforcement.For TiC/Ti60 composites,there are some un-melted TiC particles and re-solidified TiC particles appeared as discontinuous chain-like morphology.Reinforcements of TiB and TiC with fraction about 25 vol%were formed with feeding 5 wt%B4C.The morphology of TiB tended to be needle-like and prismatic,while TiC appeared as granular.Small amount of un-reacted B4C with reduced size remained within the composites.A thin skull of reaction product formed around the un-reacted B4C weakened its interface bonding with the titanium alloy matrix,thus resulting in less outstanding properties of the composites.Under 600℃,the ultimate tensile strength of the TiCP(5wt%)/Ti60 composites was 60 MPa higher than that of Ti60 alloy,following with decreased elongation.展开更多
The utilization of metallized pellets in electric arc furnace represents a pivotal strategy for the iron and steel industry to attain a green transformation.However,their low melting rate limits their application,maki...The utilization of metallized pellets in electric arc furnace represents a pivotal strategy for the iron and steel industry to attain a green transformation.However,their low melting rate limits their application,making it essential to understand the melting characteristics of metallized pellet and the factors that influence their melting rate.A model of isolated metallized pellet in slag-iron bath was established and verified by published experimental data.In the molten pool formed by the melting of metallized pellet,the melting process of isolated metallized pellet can be divided into three stages:the frozen shell formation stage,the frozen shell remelting stage,and the metallized pellet parent melting stage.In addition,increasing the preheating temperature of the metallized pellet and the temperature of slag-iron bath,along with reducing size and slag content of metallized pellet,can enhance the melting efficiency.The simulation results indicate that increasing the preheating temperature of the metallized pellet to 1300 K can shorten the melting time by 74.83%;increasing the temperature of slag-iron bath to 1923 K can shorten the melting time by 21.52%;reducing the size of the metallized pellet to 15 mm can shorten the melting time by 41.21%;reducing the slag content of the metallized pellet to 30%can shorten the melting time by 22.79%.展开更多
基金National Natural Science Foundation of China(51504138,51674118,52271177)Hunan Provincial Natural Science Foundation of China(2023JJ50181)Supported by State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(P2024-022)。
文摘To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the alloy across different planes were investigated.The anisotropy of SLM-fabricated Ti-6Al-4V alloys was analyzed,and the electron backscatter diffraction technique was used to investigate the influence of different grain types and orientations on the stress-strain distribution at various scales.Results reveal that in room-temperature compression tests at a strain rate of 10^(-3) s^(-1),both the compressive yield strength and microhardness vary along the deposition direction,indicating a certain degree of mechanical property anisotropy.The alloy exhibits a columnar microstructure;along the deposition direction,the grains appear equiaxed,and they have internal hexagonal close-packed(hcp)α/α'martensitic structure.α'phase has a preferential orientation approximately along the<0001>direction.Anisotropy arises from the high aspect ratio of columnar grains,along with the weak texture of the microstructure and low symmetry of the hcp crystal structure.
基金Tianjin Municipal Natural Science Foundation(23JCYBJC00040)National Natural Science Foundation of China(52175369)。
文摘The TiB+TiC dual-reinforced B_(4)C/TC4 composite was in-situ fabricated via incorporating 0.5wt%B_(4)C reinforcement during the laser melting deposition process.Different heat treatments of annealing and solid solution were used to regulate the microstructure,mechanical properties,and corrosion properties of B_(4)C/TC4 composite.Results show that with the increase in temperature from 500℃to 800°C,partial lamellarα-Ti in the as-deposited sample is gradually transformed into equiaxedα-Ti,accompanied by the disappearance of basketweave microstructure.At 1100°C,a small portion of TiC phase suffers fusion.This composite exhibits the optimal combination of strength and plasticity after annealing at 500℃for 4 h followed by furnace cooling,which is attributed to the stress release effect and the refined basketweave microstructure.However,this composite shows a decline in corrosion resistance after various heat treatments due to grain coarsening and micro-galvanic corrosion.
基金supported by the Tianjin Municipal Natural Science Foundation(No.23JCYBJC00040)the National Nat-ural Science Foundation of China(No.52175369)the Tian-jin Research Innovation Project for Postgraduate Students(No.2022SKY134).
文摘To enhance the anti-corrosion performance of TC4 alloy across a wide temperature range for modern aircrafts operating in increasingly harsh environments, the (TiB+TiC) hybrid reinforced TC4 composites were prepared by laser melting deposition (LMD) via the in-situ reaction between B_(4)C reinforcement and molten TC4 alloy. The effect of B_(4)C content (0, 0.5, 1.5, wt%) on the microstructure and room/high-temperature corrosion behaviour of the composites was investigated. Microstructural analysis revealed that the microstructure of the composites was significantly influenced by the B_(4)C content. The composite containing 0.5 wt% B_(4)C exhibited an optimal microstructure characterized by refined grains, equiaxed α-Ti transformed from lath-shaped α-Ti, well-distributed (TiB+TiC) phases with a proper amount and reduced pore/dislocation defects. This composite also demonstrated the best corrosion resistance at both room temperature (25 ℃) and high temperature (800 ℃), which was primarily attributed to its comprehensive advantages including a favorable microstructure, a uniform dispersion of thermally stable (TiB+TiC) phases and a stable passivation film.
基金Project(G2010CB635106)supported by the National Basic Research Program of ChinaProject(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of ChinaProject supported by the Program for Hongliu Outstanding Talents of Lanzhou University of Technology,China
文摘The microstructural evolution and phase transformations during partial remelting of in-situ Mg2Sip/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refining primary α-Mg grains and Mg2Si particles. After being partially remelted, a semisolid microstructure with small and spheroidal primary α-Mg particles can be obtained. The microstructural evolution during partial remelting can be divided into four stages： the initial rapid coarsening, structural separation, spheroidization and final coarsening, which are essentially caused by the phase transformations of β→α, α＋β→L and α→L, α→L, and α→L and L→α, respectively. The Mg2Si particles have not obvious effect on the general microstructural evolution steps, but can slower the evolution progress and change the coarsening mechanism. During partial remelting, Mg2Si particles first become blunt and then become spheroidal because of melting of their edges and corners, and finally are coarsened owing to Ostwald ripening.
基金supported financially by the Shenzhen ScienceandTechnologyInnovationCommission(Nos.ZDSYS201703031748354 and JCYJ20170817110358927)the Science and Technology Planning Project of Guangdong Province of China(No.2017B090911003)the Natural Science Foundation of Guangdong Province(No.2016A030313756)。
文摘Quasi-equiatomic Co Cr Fe Mn Ni high entropy alloy(HEA)has been in-situ alloyed by selective laser melting(SLM)from a blend of Co Cr Fe Ni pre-alloyed powder and Mn elemental powder.The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality.Despite the slight evaporation of Mn,energy dispersive spectrometer mapping and Xray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic(fcc)phase,indicating successful in-situ alloying.The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.
基金financial support to Deliang Zhang by the “Xing Liao Talent Plan” of the Science and Technology Department of Liaoning Province, China (No. XLYC1802080) is gratefully acknowledgedsupported by grants to Dake Xu from the National Natural Science Foundation of China (Nos. U2006219 and 51871050)the Fundamental Research Funds for the Central Universities (Nos. N180203019 and N2002019)。
文摘A quasi-equiatomic CoCrFeCuNi high-entropy alloy(HEA) with a broad-spectrum antibacterial ability and good mechanical properties has been fabricated by selective laser melting(SLM) and in-situ alloying of a blend of pre-alloyed CoCrFeNi powder and Cu elemental powder.The as-built HEA alloy has a homogeneous distribution of Cu and presents a single FCC phase.Compared with the same HEA fabricated using the traditional ingot metallurgy(IM) process,the HEA alloy fabricated by SLM releases more Cu ions to prevent growth and biofilm formation by gram-negative Escherichia coli and gram-positive Staphylococcus aureus,which enhances the applicability of the HEA alloy in potential applications that requires antibacterial ability.The results of this study confirm the feasibility of combining the antibacterial CoCrFeCuNi HEA alloy and SLM technology in fabricating complex shaped parts or structures with a strong antibacterial ability to be used in medical application or other environments desired for antibacterial ability.
文摘The selective laser melting （SLM） of Ti-Ni mixed powder with atomic ratio of 1：1 was performed in the present work in order to elaborate shape memory alloy （SMA）. The martensite phase of Ti-Ni alloy can be found by X-ray diffraction （XRD） analysis under temperature field, moreover, the Ti2Ni phase at a high scanning velocity. The crystalline phase images also show that the synthesized Ti-Ni alloy possessed a refined martensite microstructure. In order to evaluate the mechanical properties, the microhardness and porosity were measured. The microhardness is relatively high about 400HVo.2 with champ temperature. Besides, the porosity is quite low due to the excellent laser energy absorptivity and meltability of Ni element. The differential scanning calorimetry （DSC） analysis shows that the transformation temperature from austenite phase to martensite phase is relatively high and stable.
基金financially supported by the National Natural Science Foundation of China (No. 50905068)the China Postdoctoral Science Foundation funded projects (Nos. 2017M620317 and 2018T110759)
文摘A controllable in-situ aging treatment of Inconel 718 alloy was successfully developed by governing the types and times of the thermal cycles during selective laser melting(SLM).The sequential precipitation of γ’,composite phase of primary/secondary γ’ coated by a γ " shell,and γ" occurs as the times of vertical thermal cycles increase when laser peak temperature(Tp)is between the precipitation temperature of strengthening phase(Tpre)and liquid temperature(T_L),which causes an increase in microhardness by 40 HV.Also,short-term aging mechanisms on three types of strengthening phases are proposed based on a great number of vacancies in the matrix.
文摘A key component of future lunar missions is the concept of in-situ resource utilization(ISRU),which involves the use of local resources to support human missions and reduce dependence on Earth-based supplies.This paper investigates the thermal processing capability of lunar regolith without the addition of binders,with a focus on large-scale applications for the construction of lunar habitats and infrastructure.The study used a simulant of lunar regolith found on the Schr?dinger Basin in the South Pole region.This regolith simulant consists of20 wt%basalt and 80 wt%anorthosite.Experiments were conducted using a high power CO_(2)laser to sinter and melt the regolith in a 80 mm diameter laser spot to evaluate the effectiveness of direct large area thermal processing.Results indicated that sintering begins at approximately 1180℃and reaches full melt at temperatures above 1360℃.Sintering experiments with this material revealed the formation of dense samples up to 11 mm thick,while melting experiments successfully produced larger samples by overlapping molten layers and additive manufacturing up to 50 mm thick.The energy efficiency of the sintering and melting processes was compared.The melting process was about 10 times more energy efficient than sintering in terms of material consolidation,demonstrating the promising potential of laser melting technologies of anorthosite-rich regolith for the production of structural elements.
基金supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region(152131/18E).
文摘This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W.Detailed morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore formation.Lower laser power led to increased pore coverage,whereas a denser structure was observed at higher laser power.This laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the samples.An increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore volume.Lower laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher power.The interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.
文摘Selective laser melting(SLM)is a cost-effective 3 D metal additive manufacturing(AM)process.However,AM 316 L stainless steel(SS)has different surface and microstructure properties as compared to conventional ones.Boriding process is one of the ways to modify and increase the surface properties.The aim of this study is to predict and understand the growth kinetic of iron boride layers on AM 316 L SS.In this study,the growth kinetic mechanism was evaluated for AM 316 L SS.Pack boriding was applied at 850,900 and 950℃,each for 2,4 and 6 h.The thickness of the boride layers ranged from(1.8±0.3)μm to(27.7±2.2)μm.A diffusion model based on error function solutions in Fick’s second law was proposed to quantitatively predict and elucidate the growth rate of FeB and Fe_(2)B phase layers.The activation energy(Q)values for boron diffusion in FeB layer,Fe_(2)B layer,and dual FeB+Fe_(2)B layer were found to be 256.56,161.61 and 209.014 kJ/mol,respectively,which were higher than the conventional 316 L SS.The findings might provide and open new directions and approaches for applications of additively manufactured steels.
基金supported by Guangdong Academy of Science Fund(No.2020GDASYL-20200101001)Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030006)the National Natural Science Foundation of China(Nos.51871132 and 51701171)。
文摘Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process.In this work,a novel nano-oxides dispersion strengthened Co28 Cr9 W1.5 Si(wt.%)alloy,fabricated by laser powder bed fusion(LPBF),was comprehensively investigated.During the layer-by-layer featured process,in-situ formation of Si rich,amorphous,nano-oxide inclusions was observed,whose formation is ascribed to the high affinity of Si to oxygen.Meanwhile,distinctive body-centered cubic(BCC)Co5 Cr3 Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear.The precipitates,rarely reported in previous studied Co-Cr alloys,were found to tightly bond with the in-situ oxidization.Furthermore,the morphologies,the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified.The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations,thereby increasing the strength of the alloy.It was understood that when the plastic deformation proceeds,the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate.A quantitative analysis of the strengthening mechanism was also established,in which an additional important contribution to strength(~169 MPa)caused by the effects of in-situ formed oxide inclusions was calculated.
基金finncially supported by the National Natural Science Foundation of China(No.52075183)the Guangdong Basic and Applied Research Fundamental(No.2023A1515010692)the Key-Area Research and Development Program of Guangdong Province(Nos.2024B1111080002 and 2020B0404020004).
文摘Austenitic stainless steel(ASS)is a common material used in high-pressure hydrogen systems.Prolonged exposure to high-pressure hydrogen can cause hydrogen embrittlement(HE),raising significant safety concerns.Selective Laser Melting(SLM),known for its high precision,is a promising additive manufacturing technology that has been widely adopted across various industries.Studies have reported that under certain SLM manufacturing conditions and process parameters,the HE resistance of SLM ASS is significantly better than that of conventionally manufactured(CM)ASS,showing great potential for application in high-pressure hydrogen systems.Thus,studying the HE of SLM ASS is crucial for further improving the safety of high-pressure hydrogen systems.This paper provides an overview of the SLM process,reviews the mechanisms of HE and their synergistic effects,and analyzes the HE characteristics of SLM ASS.Additionally,it examines the influence of unique microstructures and SLM process variables on HE of SLM ASS and offers recommendations for future research to enhance the safety of high-pressure hydrogen systems.
基金supported by the Basic Science Center Program for Multiphase Media Evolution in Hypergravity of the National Natural Science Foundation of China(No.51988101)the Beijing Natural Science Foundation,China(No.2202017)。
文摘TA15 alloy fabricated by laser melting deposition was investigated at 500℃ under tensile deformation. The damage behavior of microstructure was analyzed by the real time observation of the microstructure evolution, microcracks initiation and propagation using in-situ tensile equipment fitted in the SEM chamber. Finally, the mechanism of fracture was discussed. The result showed anisotropic mechanical properties in X-and Z-direction. The existence of columnar β grains and its orientation to the tensile direction were the major factors inducing the anisotropic mechanical properties. As compared to Z-direction specimen, high tensile strength was observed in X-direction specimen due to the resistance in slips propagation provided by the prior-β grain boundaries( β GBs). Accumulation of the cracks at prior β GB caused the shear fracture. In case of Z-direction specimen, parallel orientation of prior β GB and GB α with the tensile direction resulted in a homogeneous deformation. The high reduction of cross section showed the enhanced ductile characteristics at high temperature.
基金supported by 40th DLR Parabolic Flight Campaign and within the project"Powder based Additive Manufacturing at reduced Gravitation"(Grant No.FKZ:50WM2068)European Space Agency,OSIP Off-Earth Manufacturing and Construction Campaign(Grant No.4000134280/21/NL/GLC/mk)。
文摘In order to increase the sustainability of future lunar missions,techniques for in-situ resource utilization(ISRU)must be developed.In this context,the local melting of lunar dust(regolith)by laser radiation for the production of parts and larger structures was investigated in detail.With different experimental setups in normal and microgravity,laser spots with diameters from 5 mm to 100 mm were realized to melt the regolith simulant EAC-1A and an 80%/20%mixture of TUBS-T and TUBS-M,which are used as a substitute for the actual lunar soil.In the experiments performed,the critical parameters are the size of the laser spot,the velocity of the laser spot on the surface of the powder bed,the gravity and the wettability of the powder bed by the melt.The stability of the melt pool as a function of these parameters was investigated and it was found that the formation of a stable melt pool is determined by gravity for large melt pool sizes in the range of 50 mm and by surface tension for small melt pool sizes in the range of a few mm.
基金the financial support from the China Scholarship Council(No.201806830109)。
文摘Ti-Mo alloys/composites are expected to be the next-generation implant material with low moduli but without toxic/allergic elements.However,synthesis mechanisms of the Ti-Mo biomaterials in Selective Laser Melting(SLM)vary according to raw materials and fundamentally influence material performance,due to inhomogeneous chemical compositions and stability.Therefore,this work provides a comparative study on microstructure,mechanical and wear performance,and underlying thermal mechanisms of two promising Ti-Mo biomaterials prepared by SLM but through different synthesis mechanisms to offer scientific understanding for creation of ideal metal implants.They are(i)Ti-7.5 Mo alloys,prepared from a conventional Ti/Mo powder mixture,and(ii)Ti-7.5 Mo-2.4 Ti C composites,in-situ prepared from Ti/Mo_(2)C powder mixture.Results reveal that the in-situ Ti-7.5 Mo-2.4 Ti C composites made from Ti/Mo_(2)C powder mixture by SLM can produce 61.4%moreβphase and extra Ti C precipitates(diameter below 229.6 nm)than the Ti-7.5 Mo alloys.The fine Ti C not only contributes to thinner and shorterβcolumnar grains under a large temperature gradient of 51.2 K/μm but also benefits material performance.The in-situ Ti-7.5 Mo-2.4 Ti C composites produce higher yield strength(980.1±29.8 MPa)and ultimate compressive strength(1561.4±39 MPa)than the Ti-7.5 Mo alloys,increasing by up to 12.1%.However,the fine Ti C with an aspect ratio of 2.71 dominates an unfavourable rise of elastic modulus to 91.9±2 GPa,44.7%higher than the Ti-7.5 Mo alloys,which,nevertheless,is still lower than the modulus of traditional Ti-6 Al-4 V.While,Ti C and its homogeneous distribution benefit wear resistance,decreasing the wear rate of the in-situ Ti-7.5 Mo-2.4 Ti C composites to 6.98×10^(-4)mm^3 N^(-1)m^(-1),which is 36%lower than that of the Ti-7.5 Mo alloys.Therefore,although with higher modulus than the Ti-7.5 Mo alloys,the SLM-fabricated in-situ Ti-7.5 Mo-2.4 Ti C composites can expect to provide good biomedical application potential in cases where combined good strength and wear resistance are required.
基金National Defense Science and Technology Project Management Center(2021-JCJQ-JJ-0092)。
文摘ZGH401 alloy was prepared under varying laser power levels and scanning speeds by the orthogonal test method using selective laser melting(SLM).The effect of different energy densities on microstructure and mechanical properties of the formed alloy was investigated.The microstructure of ZGH401 was analyzed by scanning electron microscope,electron back-scattered diffraction,and electron probe microanalysis.The results show that the defects of the as-built ZGH401 are gradually reduced,the relative density is correspondingly enhanced with increasing the energy density,and the ultimate density can reach 99.6%.An increase in laser power leads to a corresponding rise in hardness of ZGH401,while a faster scanning speed reduces the residual stress in asbuilt ZGH401 samples.In addition,better tensile properties are achieved at room temperature due to more grain boundaries perpendicular to the build direction than parallel to the build direction.The precipitated phases are identified as carbides and Laves phases via chemical composition analysis,with fewer carbides observed at the molten pool boundaries than within the molten pools.
基金supported by the National Key Research and Development Plan of China(No.2018YFB0704101)the Fundamental Research Funds for the Central Universities(No.3102019ZX013)the Planning Programme of Shan Xi Province’s Co-Ordination and Innovation Project of Science and Technology(No.2016KTZDCY02-02)。
文摘In this study,non-toxic in-situβphases of reinforced Ti/Zr-based bulk metallic glass matrix composites(BMGCs)of(Ti_(0.65)Zr_(0.35))100-xCux(x=5,10,15 at.%)are fabricated via selective laser melting.The effect of Cu content on phase formation,microstructure,and mechanical properties is investigated.The average volume fraction and width of theβphase decreases with increasing Cu content,while a more amorphous phase and the(Ti,Zr)_(2)Cu phase forms.In the center zone of the molten pool,theβphase grows in the direction of the temperature gradient,and the amorphous phase distributes among theβphases.This occurs using:sphere morphology(for x=5),a more continuous elongated sphere and network morphology(for x=10),and network morphology(for x=15),respectively.In the edge zone of the molten pool,due to the smaller cooling rate and the existence of a partially molten zone,theβphase becomes coarser,and an amorphous phase forms for more continuous networks.Furthermore,the hardness improves significantly with increasing Cu content.No crack is found for x=5.Although the average volume fraction of theβphase for x=5 is about 90%,the compression yield strength is 1386±64 MPa,reaching to an average level of conventionally fabricated counterparts,due to finer microstructure,and twinning and martensitic transformation of theβphase.
基金National Key Basic Research Program(2011CB606305)National Nature Science Foundation of China(50871023)
文摘Preliminary characterization of microstructure and mechanical properties of(TiB+TiC)/TC4 and TiC/Ti60 in-situ titanium matrix composites prepared by laser melting deposition is reported in this paper.The results indicate that in-situ reaction occurred during laser melting deposition of coaxially fed mixed powders from TC4 and B4C with formation of form TiB and TiC reinforcement.For TiC/Ti60 composites,there are some un-melted TiC particles and re-solidified TiC particles appeared as discontinuous chain-like morphology.Reinforcements of TiB and TiC with fraction about 25 vol%were formed with feeding 5 wt%B4C.The morphology of TiB tended to be needle-like and prismatic,while TiC appeared as granular.Small amount of un-reacted B4C with reduced size remained within the composites.A thin skull of reaction product formed around the un-reacted B4C weakened its interface bonding with the titanium alloy matrix,thus resulting in less outstanding properties of the composites.Under 600℃,the ultimate tensile strength of the TiCP(5wt%)/Ti60 composites was 60 MPa higher than that of Ti60 alloy,following with decreased elongation.
基金financially supported by China’s National Key R&D Program(Grant No.2022YFC3901403)China Baowu Low Carbon Metallurgy Innovation Foundation(Grant No.BWLCF202211)+1 种基金Fundamental Research Funds for the Central Universities(Grant No.N2225046)Program of Introducing Talents of Discipline to Universities(Grant No.B21001).
文摘The utilization of metallized pellets in electric arc furnace represents a pivotal strategy for the iron and steel industry to attain a green transformation.However,their low melting rate limits their application,making it essential to understand the melting characteristics of metallized pellet and the factors that influence their melting rate.A model of isolated metallized pellet in slag-iron bath was established and verified by published experimental data.In the molten pool formed by the melting of metallized pellet,the melting process of isolated metallized pellet can be divided into three stages:the frozen shell formation stage,the frozen shell remelting stage,and the metallized pellet parent melting stage.In addition,increasing the preheating temperature of the metallized pellet and the temperature of slag-iron bath,along with reducing size and slag content of metallized pellet,can enhance the melting efficiency.The simulation results indicate that increasing the preheating temperature of the metallized pellet to 1300 K can shorten the melting time by 74.83%;increasing the temperature of slag-iron bath to 1923 K can shorten the melting time by 21.52%;reducing the size of the metallized pellet to 15 mm can shorten the melting time by 41.21%;reducing the slag content of the metallized pellet to 30%can shorten the melting time by 22.79%.
