The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle o...The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle on the fracture surface roughness plays an important role in estimating the damage degree and stability of deep rock mass.In this paper,the variations of fracture surface roughness of granite after different heating and thermal cycles were investigated using the joint roughness coefficient method(JRC),three-dimensional(3D)roughness parameters,and fractal dimension(D),and the mechanism of damage and deterioration of granite were revealed.The experimental results show an increase in the roughness of the granite fracture surface as temperature and cycle number were incremented.The variations of JRC,height parameter,inclination parameter and area parameter with the temperature conformed to the Boltzmann's functional distribution,while the D decreased linearly as the temperature increased.Besides,the anisotropy index(Ip)of the granite fracture surface increased as the temperature increased,and the larger parameter values of roughness characterization at different temperatures were attained mainly in directions of 20°–40°,60°–100°and 140°–160°.The fracture aperture of granite after fracture followed the Gauss distribution and the average aperture increased with increasing temperature,which increased from 0.665 mm at 25℃to 1.058 mm at 800℃.High temperature caused an uneven thermal expansion,water evaporation,and oxidation of minerals within the granite,which promoted the growth and expansion of microfractures,and reduced interparticle bonding strength.In particular,the damage was exacerbated by the expansion and cracking of the quartz phase transition after T>500℃.Thermal cycles contributed to the accumulation of this damage and further weakened the interparticle bonding forces,resulting in a significant increase in the roughness,anisotropy,and aperture of the fracture surface after five cycles.展开更多
This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencin...This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencing thermal cycles,it was found that both microstructures consisted of priorβ,grain boundaryα(GBα),and basketweave structures containingα+βlamellae.Thermal cycles realized the refinement ofαlaths,the coarsening of priorβgrains andβlaths,while the size and morphology of continuously distributed GBαremained unchanged.The residualβcontent was increased after thermal cycles.Compared with the heat-treated sample with nanoscale Ti2Cu formed,short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti2Cu formation.No formation of brittle Ti2Cu means that only grain refinement strengthening and solid-solution strengthening matter.The yield strength increased from 809.9 to 910.85 MPa(12.46%increase).Among them,the main contribution from solid solution strengthening(~51 MPa)was due to the elemental redistribution effect betweenαandβphases caused by thermal cycles through quantitative analysis.The ultimate tensile strength increased from 918.5 to 974.22 MPa(6.1%increase),while fracture elongation increased from 6.78 to 10.66%(57.23%increase).Grain refinement ofαlaths,the promotedα′martensite decomposition,decreased aspect ratio,decreased Schmid factor,and local misorientation change ofαlaths are the main factors in improved ductility.Additionally,although the fracture modes of the samples in the top and middle regions are both brittle-ductile mixed fracture mode,the thermal cycles still contributed to an improvement in tensile ductility.展开更多
The existing researches of stepless capacity regulation system by depressing the suction valve for reciprocation compressor always adopt hypothesis that the compressor valves are open or close instantaneously, the val...The existing researches of stepless capacity regulation system by depressing the suction valve for reciprocation compressor always adopt hypothesis that the compressor valves are open or close instantaneously, the valve dynamic has not been taken account into thermal cycle computation, the influence of capacity regulation system on suction valves dynamic performance and cylinder thermal cycle operation has not been considered. This paper focuses on theoretical and experimental analysis of the valve dynamic and thermal cycle for reciprocating compressor in the situation of stepless capacity regulation. The valve dynamics equation, gas forces for normal and back flow, and the cylinder pressure varying with suction valve unloader moment during compression thermal cycle are discussed. A new valve dynamic model based on L-K real gas state equation for reciprocating compressor is first deduced to reduce the calculation errors induced by the ideal gas state equation. The variations of valve dynamic and cylinder pressure during part of compression stroke are calculated numerically. The calculation results reveal the non-normal thermal cycle and operation condition of compressor in stepless capacity regulation situation. The numerical simulation results of the valve dynamic and thermal cycle parameters are also verified by the stepless capacity regulation experiments in the type of 3L-10/8 reciprocating compressor. The experimental results agree with the numerical simulation results, which show that the theoretical models proposed are effective and high-precision. The proposed theoretical models build the theoretical foundation to design the real stepless capacity regulation system.展开更多
Heat moving source models along with transient heat analysis by finite element method were used to determine weld thermal cycles and isothermal sections obtained from the application of a gas tungsten arc welding bead...Heat moving source models along with transient heat analysis by finite element method were used to determine weld thermal cycles and isothermal sections obtained from the application of a gas tungsten arc welding beads on Inconel 718 plates. Analytical (Rosenthal’s thick plate model) and finite element results show an acceptable approximation with the experimental weld thermal cycles. The isothermal sections determined by numerical simulation show a better approximation with the experimental welding profile for double-ellipse model heat distribution than Gauss model. To analyze the microstructural transformation produced by different cooling rates in the fusion and heat affected zones, Vickers microhardness measurements (profile and mapping representation) were conducted. A hardness decrement for the heat affected zone (~200 HV0.2) and fusion zone (~240 HV0.2) in comparison with base material (~350 HV0.2) was observed. This behavior has been attributed to the heterogeneous solubilization process of the γ″ phase (nickel matrix), which, according to the continuous-cooling-transformation curve, produced the Laves phase,δ and MC transition phases, generating a loss in hardness close to the fusion zone.展开更多
Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensi...Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process.The thermal cycle curves are produced on the strength of the simulation results.Meanwhile,the microstructure characteristics of the welded joint are investigated combined with simulation results.The results show that weld zone,heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure.Moreover,the simulation results are well matched with experiment results.展开更多
The effect of different peak temperature(Tp) and cooling time (t8/5) on microstructure, hardness, impact toughness and fracture morphology in the heat-affected zone (HAZ) of HQ130 steel was studied by using weld therm...The effect of different peak temperature(Tp) and cooling time (t8/5) on microstructure, hardness, impact toughness and fracture morphology in the heat-affected zone (HAZ) of HQ130 steel was studied by using weld thermo-simulation test. Experimental results indicate that the impact toughness and hardness decrease with the decrease of Tpor increase of t8/5 under the condition of a single thermal cycle. There is a brittle zone in the vicinity of Tp= 800℃, where the impact toughness is considerably low. There is a softened zone in the vicinity of Tp=700℃, where the hardness decreases but the toughness increases. In the practical application of multi-layer and multipass welding, the welding heat input should be strictly limited (t8/5≤20s) so as to reduce the softness and brittleness in the HAZ of-HQ130 steel.展开更多
The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied allo...The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6AI-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.展开更多
The effects of thermal cycle parameters on the tensile strength and fracture characteristics of phase transformation diffusion bonding(PTDB) joint of titanium and stainless steel (Ti/SS) were studied in this paper. Wi...The effects of thermal cycle parameters on the tensile strength and fracture characteristics of phase transformation diffusion bonding(PTDB) joint of titanium and stainless steel (Ti/SS) were studied in this paper. With the maximum cyclic temperature of 1 173～1 223 K , the minimum cyclic temperature of 1 073～1 093 K , the heating velocity of 30～50 K/s , the cooling velocity of 15～20 K/s , the cycle numbers of 15～20 and bonding pressure is 13 MPa , the tensile strength of joint is more than 380 MPa , exceeding 80% of that of Ti.展开更多
Cu/Al compound materials,named as copperclad aluminum bus bars,are widely used in heat dissipation of modern engineering.The thermal cycle tests were conducted at 200,250 and 300℃for different cycle times,respectivel...Cu/Al compound materials,named as copperclad aluminum bus bars,are widely used in heat dissipation of modern engineering.The thermal cycle tests were conducted at 200,250 and 300℃for different cycle times,respectively.Effects of thermal cycle temperatures and thermal cycle times on micro structures and mechanical properties of the interface were studied.The results show that the width of bonding layer and bond strength are significantly affected by thermal cycle temperatures and times.Nonetheless,the variety or the quantity of intermediate compounds is scarcely influenced.Al_(2)Cu,Cu_(9) Al_(4)and CuAl were identified on the interface.With the increase in cycle times,grains of the material grew up.However,grains of the interface grew up more apparently than those of Cu and Al.The knowledge may be applied in the establishment of service condition and quality evaluation of material.展开更多
Single thermal cycle simulation tests were carried out for X80 high strength steel pipes from three steel mills by a Gleeble 3500HS thermal simulation test machine,and coincidence degree of the thermal simulation curv...Single thermal cycle simulation tests were carried out for X80 high strength steel pipes from three steel mills by a Gleeble 3500HS thermal simulation test machine,and coincidence degree of the thermal simulation curve with the set curve under heat inputs of 6–30 kJ/cm was observed;The relationship between different heat inputs and microstructure,impact toughness and hardness of steel pipe CGHAZ(coarse grain heat affected zone)was studied by metallographic examination,impact test and hardness test.The results show that with the increase of heat input,original austenite grain size increases gradually,the lath bainite ratio decreases and the granular bainite ratio increases.The impact toughness of C steel pipe is lower than those of A and B steel pipe,and the impact toughness of CGHAZ from the three steel pipes show different trends:for A steel pipe CGHAZ,impact toughness increases first and then decreases,with the highest value of 270–320 J under 20–25 kJ/cm;for B steel pipe CGHAZ,impact toughness decreases slightly;for C steel pipe CGHAZ,impact toughness increases,with the highest value of 260–300 J under 25 kJ/cm.As the heat input increases,the hardness of three X80 steel pipes CGHAZ shows a decreasing trhighend,and C steel pipe has the largest decreasing range.展开更多
The unstable dimensional distortion of LF21 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM. At the same time, distortion mechanism was analyzed f...The unstable dimensional distortion of LF21 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM. At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and microstructure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LF21 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 130 h after welding. The relative elongation of welded specimen is 4.2×10 -5 . After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.展开更多
Based on the chasteal nucleation theory, the kinetic precipitation model of carbon - nitride particles in weld HAZ is proposed. Using the model,welding simulation technology and the quantitative metallo- graphic anal...Based on the chasteal nucleation theory, the kinetic precipitation model of carbon - nitride particles in weld HAZ is proposed. Using the model,welding simulation technology and the quantitative metallo- graphic analysis,the precipitation transformation temperatue (PTT) curve is obtained.The data from the simulated welds are in good apreement with the value that the PTT curves predicated.展开更多
The 10Ni5CrMoV steel examined was a 16 mm thick plate. Specimens measuring 12 mm×12 mm×120 mm were thermally cycled using DM-100A weld simulator with various parameters. The main results are summarized as fo...The 10Ni5CrMoV steel examined was a 16 mm thick plate. Specimens measuring 12 mm×12 mm×120 mm were thermally cycled using DM-100A weld simulator with various parameters. The main results are summarized as follaws. In the coarse-grained austenitized region（ Tm = 1 300℃ ＋ 1300℃ ） ,the microstructure is in good toughness. At the condition of Tm = 1 300℃ ＋ 850℃ and t8/5=43 s, the toughness decreases heavily because M-A constituent and twin martensite appear at the prior aastenite grain boundaries. When Tm= 1300℃ ＋ 850℃ or 1300℃ ＋ 730℃ and t8/5 = 85 s, local brittle zone is formed because of relatively coarse granular bainite.展开更多
The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--...The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--strain curves were compared to those of solder Sn-37Pb. The parameters in Anand model for solder Sn-3.5Ag were fitted based on experimental data and nonlinear fitting method, and its validity was checked by means of experimental data. Furthermore, the Anand model was used in the FEM analysis to evaluate solder joint thermal cycle reliability. The results show that solder Sn-3.5Ag has a better creep resistance than solder Sn-37Pb. The maximum stress is located at the upper right comer of the outmost solder joint from the symmetric center, and thermal fatigue life is predicted to be 3.796 × 10^4 cycles under the calculated conditions.展开更多
Conductivity and oxidation behavior of Fe-16Cr alloy were investigated under long-term stability operation at 750℃and thermal cycles from room temperature to 750℃.The results showed that the area specific resistance...Conductivity and oxidation behavior of Fe-16Cr alloy were investigated under long-term stability operation at 750℃and thermal cycles from room temperature to 750℃.The results showed that the area specific resistance(ASR)of Fe-16Cr alloy increased over time and reached about 56.29 mΩcm~(2)after 40,000 h of long-term stability operation at 750℃by theoretical calculation.The ASR of Fe-16Cr remained about 11 mΩcm~(2)after 52 thermal cycles from room temperature to750℃.The analysis of structure showed that the oxidized phase on the surface of Fe-16Cr was mainly composed of Cr_(2)O_3and Fe Cr_(2)O_(4)spinel phase under long-term stability operation at 750℃.While the Cr_(2)O_(3)phase was mainly observed on the surface of Fe-16Cr alloy after 52 thermal cycles,the oxidation rates of Fe-16Cr alloy were 0.0142μm h~(-1)and 0.06μm cycle~(-1)under long-term stability operation and under thermal cycle,respectively.The property of Fe-16Cr alloy with 2.6 mm thickness met the lifespan requirement of interconnect for solid oxide fuel cell(SOFC)stacks.The Cr element all diff used onto oxidation surface,indicating that it was necessary to spray a coating on the surface to avoid poisoning cell cathode of SOFCs.Two 2-cell stacks were assembled and tested to verify the properties of Fe-16Cr alloy as SOFC interconnect under long-term stability operation and thermal cycle condition.展开更多
Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped laser.The microstructure evolution of the reduced activation steel was investigated using the sca...Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped laser.The microstructure evolution of the reduced activation steel was investigated using the scanning electron microscope,transmission electron microscope and electron backscatter diffraction.The experimental results showed that the grains close to the substrate were smaller than the grains in the upper layers.Compared to those deposited using a Gaussian laser,the samples deposited using a ring-shaped laser showed a more homogeneous microstructure.Furthermore,a finite element analysis(FEA)model was applied to reveal the thermal history during laser melting deposition.The simulation results were well validated with the experimental results.FEA results indicate that the peak temperature increases and the cooling rate decreases,as the layer gets further from the substrate.Additionally,the temperature and the cooling rate resulting from the Gaussian laser model were higher at the midline of the samples and lower around the edges,whereas those of the ring-shaped laser model were consistent with both at the center and around the edges.展开更多
The effect of different peak temperature T_P) and cooling time (t_(8/5)) on hardness,impact toughness and fracture morphology in the heat--affected zone (HAZ) of HQ130steel was studied by using welding thermo--simulat...The effect of different peak temperature T_P) and cooling time (t_(8/5)) on hardness,impact toughness and fracture morphology in the heat--affected zone (HAZ) of HQ130steel was studied by using welding thermo--simulation test. Experimental results showthat the impact toughness and hardness decrease with the decrease of T_P or increase oft_(8/5) under the condition of a single thermal cycle. There is a brittle zone in the vicinityof T_P=800℃, where the impact toughness is considerebly low. There is softened zonein vicinity of T_P=700℃, Where the harkness decreases but the toughness increases. Inthe practical application of multi--layer and multi--pass welding, the welding heat inputshould be strictly limited (t_(8/5)≤20s) so as to reduce the softness and brittleness in theHAZ of HQ130 steel.展开更多
In the twin-roll strip casting process,molten steel solidifies by losing heat through its interface with the casting rollers.The heat extraction along this interface has an effect on the quality of the strips and shou...In the twin-roll strip casting process,molten steel solidifies by losing heat through its interface with the casting rollers.The heat extraction along this interface has an effect on the quality of the strips and should be affected by coating,rolls’material,and cooling water flow rate.It is necessary to understand the effect of these casting parameters on the solidification structure of twin-roll strip casting.A three-dimensional computational domain is set up to simulate the solidification process of molten steel and heat exchange between steel strip/air,coating,rolls,and cooling water in the channel of roll sleeves.The effect of the cooling water intensity and flow intensity of molten steel in the pool on the solidification structures is studied during the thermal cycle of rolls in the twin-roll strip casting.These predicted results are helpful to optimize casting parameters and improve the strip quality in the twin-roll strip casting process.展开更多
The unstable dimensional distortion of LD31 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM(three-coordinate measuring machines). At the same time...The unstable dimensional distortion of LD31 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM(three-coordinate measuring machines). At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and micro structure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LD31 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 200h after welding. The relative elongation of welded specimen is 3.0×10-5; After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.展开更多
Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processi...Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processing of DLD,the deposited steel layer is affected by the subsequent layer depositing.The DLD block shows different microstructure and mechanical properties at the bottom,middle and top of the deposited parts.To date,there are few research works about the effects of inter-layer interval time and laser power on the microstructure evolution and mechanical properties of the deposited layers.In this study,the idle time and laser power layer by layer during DLD of 12CrNi2 steel were controlled to cause the deposited layers to maintain a high cooling rate,while the bottom deposited layer was subjected to a weak tempering effect.Results show that a high proportion of martensite is produced,which improves the strength of the deposited layer.Under the laser scanning strategy of laser power 2,500 W,scanning velocity 5 mm·s^(-1),powder feeding rate 11 g·min^(-1),overlap rate 50%,and a laser power difference of 50 W and a 2 min interval,the tensile strength of the deposited layer of 12CrNi2 steel is in the range of 873-1,022 MPa,and the elongation is in the range of 16.2%-18.9%.This study provides a method to reduce the tempering effect of the subsequent deposition layers on the bottom layers,which can increase the proportion of martensite in the low-alloy high-strength steel,so as to improve the yield strength of the alloy steel.展开更多
基金funding support from the National Natural Science Foundation of China(Grant No.52274082)the Program of Qingjiang Excellent Young Talents,Jiangxi University of Science and Technology(Grant No.JXUSTQJBJ2020003)the Innovation Fund Designated for Graduate Students of Jiangxi Province(Grant No.YC2023-B215).
文摘The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle on the fracture surface roughness plays an important role in estimating the damage degree and stability of deep rock mass.In this paper,the variations of fracture surface roughness of granite after different heating and thermal cycles were investigated using the joint roughness coefficient method(JRC),three-dimensional(3D)roughness parameters,and fractal dimension(D),and the mechanism of damage and deterioration of granite were revealed.The experimental results show an increase in the roughness of the granite fracture surface as temperature and cycle number were incremented.The variations of JRC,height parameter,inclination parameter and area parameter with the temperature conformed to the Boltzmann's functional distribution,while the D decreased linearly as the temperature increased.Besides,the anisotropy index(Ip)of the granite fracture surface increased as the temperature increased,and the larger parameter values of roughness characterization at different temperatures were attained mainly in directions of 20°–40°,60°–100°and 140°–160°.The fracture aperture of granite after fracture followed the Gauss distribution and the average aperture increased with increasing temperature,which increased from 0.665 mm at 25℃to 1.058 mm at 800℃.High temperature caused an uneven thermal expansion,water evaporation,and oxidation of minerals within the granite,which promoted the growth and expansion of microfractures,and reduced interparticle bonding strength.In particular,the damage was exacerbated by the expansion and cracking of the quartz phase transition after T>500℃.Thermal cycles contributed to the accumulation of this damage and further weakened the interparticle bonding forces,resulting in a significant increase in the roughness,anisotropy,and aperture of the fracture surface after five cycles.
基金sponsored by the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact 2021ZX52002222019the Natural Science Foundation of China(NSFC No.U2141216)the Chongqing Technology Innovation and Application Special Program.
文摘This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencing thermal cycles,it was found that both microstructures consisted of priorβ,grain boundaryα(GBα),and basketweave structures containingα+βlamellae.Thermal cycles realized the refinement ofαlaths,the coarsening of priorβgrains andβlaths,while the size and morphology of continuously distributed GBαremained unchanged.The residualβcontent was increased after thermal cycles.Compared with the heat-treated sample with nanoscale Ti2Cu formed,short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti2Cu formation.No formation of brittle Ti2Cu means that only grain refinement strengthening and solid-solution strengthening matter.The yield strength increased from 809.9 to 910.85 MPa(12.46%increase).Among them,the main contribution from solid solution strengthening(~51 MPa)was due to the elemental redistribution effect betweenαandβphases caused by thermal cycles through quantitative analysis.The ultimate tensile strength increased from 918.5 to 974.22 MPa(6.1%increase),while fracture elongation increased from 6.78 to 10.66%(57.23%increase).Grain refinement ofαlaths,the promotedα′martensite decomposition,decreased aspect ratio,decreased Schmid factor,and local misorientation change ofαlaths are the main factors in improved ductility.Additionally,although the fracture modes of the samples in the top and middle regions are both brittle-ductile mixed fracture mode,the thermal cycles still contributed to an improvement in tensile ductility.
基金supported by China National Key Technology R&D Program(Grant No. 2008BAF34B13)China Postdoctoral Science Foundation Funded Project(Grant No. 2011M501363)
文摘The existing researches of stepless capacity regulation system by depressing the suction valve for reciprocation compressor always adopt hypothesis that the compressor valves are open or close instantaneously, the valve dynamic has not been taken account into thermal cycle computation, the influence of capacity regulation system on suction valves dynamic performance and cylinder thermal cycle operation has not been considered. This paper focuses on theoretical and experimental analysis of the valve dynamic and thermal cycle for reciprocating compressor in the situation of stepless capacity regulation. The valve dynamics equation, gas forces for normal and back flow, and the cylinder pressure varying with suction valve unloader moment during compression thermal cycle are discussed. A new valve dynamic model based on L-K real gas state equation for reciprocating compressor is first deduced to reduce the calculation errors induced by the ideal gas state equation. The variations of valve dynamic and cylinder pressure during part of compression stroke are calculated numerically. The calculation results reveal the non-normal thermal cycle and operation condition of compressor in stepless capacity regulation situation. The numerical simulation results of the valve dynamic and thermal cycle parameters are also verified by the stepless capacity regulation experiments in the type of 3L-10/8 reciprocating compressor. The experimental results agree with the numerical simulation results, which show that the theoretical models proposed are effective and high-precision. The proposed theoretical models build the theoretical foundation to design the real stepless capacity regulation system.
基金CONACyT-México for the scholarship providedCONACyT (Project 736)SIP-IPN are also acknowledged for funds given to conduct this research
文摘Heat moving source models along with transient heat analysis by finite element method were used to determine weld thermal cycles and isothermal sections obtained from the application of a gas tungsten arc welding beads on Inconel 718 plates. Analytical (Rosenthal’s thick plate model) and finite element results show an acceptable approximation with the experimental weld thermal cycles. The isothermal sections determined by numerical simulation show a better approximation with the experimental welding profile for double-ellipse model heat distribution than Gauss model. To analyze the microstructural transformation produced by different cooling rates in the fusion and heat affected zones, Vickers microhardness measurements (profile and mapping representation) were conducted. A hardness decrement for the heat affected zone (~200 HV0.2) and fusion zone (~240 HV0.2) in comparison with base material (~350 HV0.2) was observed. This behavior has been attributed to the heterogeneous solubilization process of the γ″ phase (nickel matrix), which, according to the continuous-cooling-transformation curve, produced the Laves phase,δ and MC transition phases, generating a loss in hardness close to the fusion zone.
文摘Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process.The thermal cycle curves are produced on the strength of the simulation results.Meanwhile,the microstructure characteristics of the welded joint are investigated combined with simulation results.The results show that weld zone,heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure.Moreover,the simulation results are well matched with experiment results.
文摘The effect of different peak temperature(Tp) and cooling time (t8/5) on microstructure, hardness, impact toughness and fracture morphology in the heat-affected zone (HAZ) of HQ130 steel was studied by using weld thermo-simulation test. Experimental results indicate that the impact toughness and hardness decrease with the decrease of Tpor increase of t8/5 under the condition of a single thermal cycle. There is a brittle zone in the vicinity of Tp= 800℃, where the impact toughness is considerably low. There is a softened zone in the vicinity of Tp=700℃, where the hardness decreases but the toughness increases. In the practical application of multi-layer and multipass welding, the welding heat input should be strictly limited (t8/5≤20s) so as to reduce the softness and brittleness in the HAZ of-HQ130 steel.
基金supported by Aviation Science Foundation of China(ASFC),No.00G51007.
文摘The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La+Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6AI-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.
文摘The effects of thermal cycle parameters on the tensile strength and fracture characteristics of phase transformation diffusion bonding(PTDB) joint of titanium and stainless steel (Ti/SS) were studied in this paper. With the maximum cyclic temperature of 1 173～1 223 K , the minimum cyclic temperature of 1 073～1 093 K , the heating velocity of 30～50 K/s , the cooling velocity of 15～20 K/s , the cycle numbers of 15～20 and bonding pressure is 13 MPa , the tensile strength of joint is more than 380 MPa , exceeding 80% of that of Ti.
基金financially supported by the National Natural Science Foundation of China(No.51201107)。
文摘Cu/Al compound materials,named as copperclad aluminum bus bars,are widely used in heat dissipation of modern engineering.The thermal cycle tests were conducted at 200,250 and 300℃for different cycle times,respectively.Effects of thermal cycle temperatures and thermal cycle times on micro structures and mechanical properties of the interface were studied.The results show that the width of bonding layer and bond strength are significantly affected by thermal cycle temperatures and times.Nonetheless,the variety or the quantity of intermediate compounds is scarcely influenced.Al_(2)Cu,Cu_(9) Al_(4)and CuAl were identified on the interface.With the increase in cycle times,grains of the material grew up.However,grains of the interface grew up more apparently than those of Cu and Al.The knowledge may be applied in the establishment of service condition and quality evaluation of material.
基金supported by Science and Technology Research Project of Universities of Hebei Province(No.QN201.221)。
文摘Single thermal cycle simulation tests were carried out for X80 high strength steel pipes from three steel mills by a Gleeble 3500HS thermal simulation test machine,and coincidence degree of the thermal simulation curve with the set curve under heat inputs of 6–30 kJ/cm was observed;The relationship between different heat inputs and microstructure,impact toughness and hardness of steel pipe CGHAZ(coarse grain heat affected zone)was studied by metallographic examination,impact test and hardness test.The results show that with the increase of heat input,original austenite grain size increases gradually,the lath bainite ratio decreases and the granular bainite ratio increases.The impact toughness of C steel pipe is lower than those of A and B steel pipe,and the impact toughness of CGHAZ from the three steel pipes show different trends:for A steel pipe CGHAZ,impact toughness increases first and then decreases,with the highest value of 270–320 J under 20–25 kJ/cm;for B steel pipe CGHAZ,impact toughness decreases slightly;for C steel pipe CGHAZ,impact toughness increases,with the highest value of 260–300 J under 25 kJ/cm.As the heat input increases,the hardness of three X80 steel pipes CGHAZ shows a decreasing trhighend,and C steel pipe has the largest decreasing range.
文摘The unstable dimensional distortion of LF21 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM. At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and microstructure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LF21 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 130 h after welding. The relative elongation of welded specimen is 4.2×10 -5 . After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.
文摘Based on the chasteal nucleation theory, the kinetic precipitation model of carbon - nitride particles in weld HAZ is proposed. Using the model,welding simulation technology and the quantitative metallo- graphic analysis,the precipitation transformation temperatue (PTT) curve is obtained.The data from the simulated welds are in good apreement with the value that the PTT curves predicated.
文摘The 10Ni5CrMoV steel examined was a 16 mm thick plate. Specimens measuring 12 mm×12 mm×120 mm were thermally cycled using DM-100A weld simulator with various parameters. The main results are summarized as follaws. In the coarse-grained austenitized region（ Tm = 1 300℃ ＋ 1300℃ ） ,the microstructure is in good toughness. At the condition of Tm = 1 300℃ ＋ 850℃ and t8/5=43 s, the toughness decreases heavily because M-A constituent and twin martensite appear at the prior aastenite grain boundaries. When Tm= 1300℃ ＋ 850℃ or 1300℃ ＋ 730℃ and t8/5 = 85 s, local brittle zone is formed because of relatively coarse granular bainite.
基金Project(50376076) supported by the National Natural Science Foundation of China
文摘The experimental tests of tensile for lead-flee solder Sn-3.5Ag were performed for the general work temperatures range from 11 to 90 ℃ and strain rate range from 5 × 10^-5 to 2 × 10^-2s^-1, and its stress--strain curves were compared to those of solder Sn-37Pb. The parameters in Anand model for solder Sn-3.5Ag were fitted based on experimental data and nonlinear fitting method, and its validity was checked by means of experimental data. Furthermore, the Anand model was used in the FEM analysis to evaluate solder joint thermal cycle reliability. The results show that solder Sn-3.5Ag has a better creep resistance than solder Sn-37Pb. The maximum stress is located at the upper right comer of the outmost solder joint from the symmetric center, and thermal fatigue life is predicted to be 3.796 × 10^4 cycles under the calculated conditions.
基金financially supported by the Key R&D Program from the Ministry of Science and Technology of China(No.2018YFB1502600)the Ningbo Major Special Projects of the Plan“Science and Technology Innovation 2025”(No.2019B10043)+1 种基金the Science and Technology Project of Zhejiang Energy Group Co.,Ltd.(No.znkj-2018-008)the Key Laboratory of Solar Energy Utilization&Energy Saving Technology of Zhejiang Province。
文摘Conductivity and oxidation behavior of Fe-16Cr alloy were investigated under long-term stability operation at 750℃and thermal cycles from room temperature to 750℃.The results showed that the area specific resistance(ASR)of Fe-16Cr alloy increased over time and reached about 56.29 mΩcm~(2)after 40,000 h of long-term stability operation at 750℃by theoretical calculation.The ASR of Fe-16Cr remained about 11 mΩcm~(2)after 52 thermal cycles from room temperature to750℃.The analysis of structure showed that the oxidized phase on the surface of Fe-16Cr was mainly composed of Cr_(2)O_3and Fe Cr_(2)O_(4)spinel phase under long-term stability operation at 750℃.While the Cr_(2)O_(3)phase was mainly observed on the surface of Fe-16Cr alloy after 52 thermal cycles,the oxidation rates of Fe-16Cr alloy were 0.0142μm h~(-1)and 0.06μm cycle~(-1)under long-term stability operation and under thermal cycle,respectively.The property of Fe-16Cr alloy with 2.6 mm thickness met the lifespan requirement of interconnect for solid oxide fuel cell(SOFC)stacks.The Cr element all diff used onto oxidation surface,indicating that it was necessary to spray a coating on the surface to avoid poisoning cell cathode of SOFCs.Two 2-cell stacks were assembled and tested to verify the properties of Fe-16Cr alloy as SOFC interconnect under long-term stability operation and thermal cycle condition.
基金This work was supported financially by the National Key R&D Program of China(Grant No.2018YFB1105801)the National Natural Science Foundation of China(Grant No.51701134).
文摘Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped laser.The microstructure evolution of the reduced activation steel was investigated using the scanning electron microscope,transmission electron microscope and electron backscatter diffraction.The experimental results showed that the grains close to the substrate were smaller than the grains in the upper layers.Compared to those deposited using a Gaussian laser,the samples deposited using a ring-shaped laser showed a more homogeneous microstructure.Furthermore,a finite element analysis(FEA)model was applied to reveal the thermal history during laser melting deposition.The simulation results were well validated with the experimental results.FEA results indicate that the peak temperature increases and the cooling rate decreases,as the layer gets further from the substrate.Additionally,the temperature and the cooling rate resulting from the Gaussian laser model were higher at the midline of the samples and lower around the edges,whereas those of the ring-shaped laser model were consistent with both at the center and around the edges.
文摘The effect of different peak temperature T_P) and cooling time (t_(8/5)) on hardness,impact toughness and fracture morphology in the heat--affected zone (HAZ) of HQ130steel was studied by using welding thermo--simulation test. Experimental results showthat the impact toughness and hardness decrease with the decrease of T_P or increase oft_(8/5) under the condition of a single thermal cycle. There is a brittle zone in the vicinityof T_P=800℃, where the impact toughness is considerebly low. There is softened zonein vicinity of T_P=700℃, Where the harkness decreases but the toughness increases. Inthe practical application of multi--layer and multi--pass welding, the welding heat inputshould be strictly limited (t_(8/5)≤20s) so as to reduce the softness and brittleness in theHAZ of HQ130 steel.
基金supportedby Innovation Program of Shanghai Municipal Education Commission (No.2019-01-07-00-09-E00024).
文摘In the twin-roll strip casting process,molten steel solidifies by losing heat through its interface with the casting rollers.The heat extraction along this interface has an effect on the quality of the strips and should be affected by coating,rolls’material,and cooling water flow rate.It is necessary to understand the effect of these casting parameters on the solidification structure of twin-roll strip casting.A three-dimensional computational domain is set up to simulate the solidification process of molten steel and heat exchange between steel strip/air,coating,rolls,and cooling water in the channel of roll sleeves.The effect of the cooling water intensity and flow intensity of molten steel in the pool on the solidification structures is studied during the thermal cycle of rolls in the twin-roll strip casting.These predicted results are helpful to optimize casting parameters and improve the strip quality in the twin-roll strip casting process.
文摘The unstable dimensional distortion of LD31 aluminum alloy weldments at room temperature and after thermal cycles was studied by use of light interference and CMM(three-coordinate measuring machines). At the same time, distortion mechanism was analyzed from the viewpoint of mechanics and micro structure. Experimental results show that there exists obvious difference of unstable dimensional distortion between LD31 welded specimens under two conditions mentioned above. Under room temperature, dimensional variation of welded specimens will decrease gradually and finally tends to be stable during 200h after welding. The relative elongation of welded specimen is 3.0×10-5; After thermal cycles, distortion of welded specimen is much larger than that at room temperature. After 11 thermal cycles, the dimension will tend to be stable. Dimensional unstable distortion of weldments mainly results from temperature condition, microstructure variation and relaxation of welding residual stress.
基金the National Key Technologies Research and Development Program of China(Grant No.2016YFB1100200)。
文摘Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processing of DLD,the deposited steel layer is affected by the subsequent layer depositing.The DLD block shows different microstructure and mechanical properties at the bottom,middle and top of the deposited parts.To date,there are few research works about the effects of inter-layer interval time and laser power on the microstructure evolution and mechanical properties of the deposited layers.In this study,the idle time and laser power layer by layer during DLD of 12CrNi2 steel were controlled to cause the deposited layers to maintain a high cooling rate,while the bottom deposited layer was subjected to a weak tempering effect.Results show that a high proportion of martensite is produced,which improves the strength of the deposited layer.Under the laser scanning strategy of laser power 2,500 W,scanning velocity 5 mm·s^(-1),powder feeding rate 11 g·min^(-1),overlap rate 50%,and a laser power difference of 50 W and a 2 min interval,the tensile strength of the deposited layer of 12CrNi2 steel is in the range of 873-1,022 MPa,and the elongation is in the range of 16.2%-18.9%.This study provides a method to reduce the tempering effect of the subsequent deposition layers on the bottom layers,which can increase the proportion of martensite in the low-alloy high-strength steel,so as to improve the yield strength of the alloy steel.
