Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed f...Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed fusion(LPBF)using recycled powders were investigated.Re-melted powder surfaces,satellite particles,and deformed powders were found in the recycled powders,combined with a high-oxygencontent surface layer.The increasing oxygen content led to the formation of high-density oxide inclusions;moreover,printing-induced cracks widely occurred and mainly formed along the grain boundaries in the as-built LPBF nickel-based superalloys fabricated using recycled powders.A little change in the Si or Mn content did not increase the hot cracking susceptibility(HCS)of the printed parts.The changing aspect ratio and the surface damage of the recycled powders might contribute to increasing the crack density.Moreover,the configuration of cracks in the as-built parts led to anisotropic mechanical properties,mainly resulting in extremely low ductility vertical to the building direction,and the cracks mainly propagated along the cellular boundary owing to the existence of a brittle precipitation phase.展开更多
The surface microstructure and the surface segregation of FGH 95 nickel-basedsuperalloy powders prepared through plasma rotating electrode processing (PREP) have beeninvestigated by using SEM and AES. The results indi...The surface microstructure and the surface segregation of FGH 95 nickel-basedsuperalloy powders prepared through plasma rotating electrode processing (PREP) have beeninvestigated by using SEM and AES. The results indicate that the surface microstructure of powderschanges from dendrite into cellular stricture as the particle size of powders decrease, and thepredominant precipitates solidified on the particle surfaces were identified as MC' type carbidesenriched with Nb and Ti. It was also indicated that along with the depth of particle surfaces, thesegregation layer of S, C and O elements are thick, and that of Ti, Cr elements are thin for largesire powders while they are in reverse for median size particles.展开更多
The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results th...The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results that show improved resistance to sulfidation by niobium. Research results from a current program on the role of niobium in the Russian powder metallurgy alloy EP741NP are presented. Future research plans on the role of niobium in superalloys are also discussed.展开更多
The hot deformation behaviors of FGH98 nickel-based powder superalloy were experimentally investigated and theoretically analyzed by Arrhenius models and machine learning(ML).Hot compression tests were conducted with ...The hot deformation behaviors of FGH98 nickel-based powder superalloy were experimentally investigated and theoretically analyzed by Arrhenius models and machine learning(ML).Hot compression tests were conducted with a Gleeble-3800 thermo-mechanical simulation machine on the FGH98 superalloy at strain rates of 0.001–1 s–1 and temperatures of 1025–1175℃.The peak stresses under different deformation conditions were analyzed via the Sellars model and an ML-inspired Gaussian process regression(GPR)model.The prediction of the GPR model outperformed that from the Sellars model.In addition,the stress-strain responses were predicted by the GPR model and tested by experimentally measured stress-strain curves.The results indicate that the developed GPR model has great power with wide generalization capability in the prediction of hot deformation behaviors of FGH98 superalloy,as evidenced by the R2 value higher than 0.99 on the test dataset.展开更多
In this article,a grinding force model,which is on the basis of cutting process of single abrasive grains combined with the method of theoretical derivation and empirical formula by analyzing the formation mechanism o...In this article,a grinding force model,which is on the basis of cutting process of single abrasive grains combined with the method of theoretical derivation and empirical formula by analyzing the formation mechanism of grinding force,was established.Three key factors have been taken into accounts in this model,such as the contact friction force between abrasive grains and materials,the plastic deformation of material in the process of abrasive plowing,and the shear strain effect of material during the process of cutting chips formation.The model was finally validated by the orthogonal grinding experiment of powder metallurgy nickel-based superalloy FGH96 by using the electroplated CBN abrasive wheel.Grinding force values of prediction and experiment were in good consistency.The errors of tangential grinding force and normal grinding force were 9.8%and 13.6%,respectively.The contributions of sliding force,plowing force and chip formation force were also analyzed.In addition,the tangential forces of sliding,plowing and chip formation are 14%,19%and 11%of the normal forces on average,respectively.The pro-posed grinding forcemodel is not only in favor of optimizing the grinding parameters and improving grinding efficiency,but also contributes to study some other grinding subjects(e.g.abrasive wheel wear,grinding heat,residual stress).展开更多
In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels we...In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels were comparatively analyzed during creep feed grinding.The infuences of the grinding parameters(abrasive wheel speed,workpiece infeed speed,and depth of cut)on the grinding force,grinding temperature,surface roughness,surface morphology,tool wear,and grinding ratio were analyzed comprehensively.The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels.This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material.Moreover,both the BA and MA abrasive wheeIs exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion.Finally,an analytical model for prediction of the grinding ratio was established by combining the tool wear volume,grinding force,and grinding length.The acceptable errors between the predicted and experimental grinding ratios(ranging from 0.6 to 1.8)were 7.56%and 6.31%for the BA and MA abrasive wheels,respectively.This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel,and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.展开更多
Two cooling schemes (continuous cooling and interrupted cooling tests) were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling...Two cooling schemes (continuous cooling and interrupted cooling tests) were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling γ precipitation and the development of γ precipitates during cooling process were involved in this study. The ultimate tensile strength (ErrS) of the specimens in various cooling circumstances was tested. The experiential equations were obtained between the average sizes of secondary and tertiary γ precipitates, the strength, and cooling rate. The results show that they are inversely correlated with the cooling rate as well as the grain boundary changes from serrated to straight, the shape of secondary γ precipitates changes from irregular cuboidal to spherical, while the formed tertiary γ precipitates are always spherical. The interrupted cooling tests show that the average size of secondary γ precipitates increases as a linear function of interrupt temperature for a fixed cooling rate of 24℃/min. The strength first decreases and then increases against interrupt temperature, which is fundamentally caused by the multistage nucleation of γ precipitates during cooling process.展开更多
With a strain rate range of 0.01–10 s^(−1) and a deformation temperature range of 1110–1200℃,the isothermal compression test was performed on one powder metallurgy superalloy which is macroscopic segregation free.U...With a strain rate range of 0.01–10 s^(−1) and a deformation temperature range of 1110–1200℃,the isothermal compression test was performed on one powder metallurgy superalloy which is macroscopic segregation free.Using electron backscatter diffraction,the effect of strain rate and deformation temperature on grain shape and grain size of superalloys during thermal deformation was studied.The results established that exquisite and equiaxed dynamic recrystallization(DRX)grains are procured at supernal deformation temperature and high strain rate because of the high dislocation density.At the same time,the interaction between high DRX nucleation rate and low grain growth rate at high strain rate is favorable in making finer DRX grains.The equivalent medial grain size expanded with lowering strain rate and elevating proof temperature.Moreover,the grain shape was researched by the effective method of aspect ratio.Most aspect ratio of original grains is 0.61,and the aspect ratio has important implications for DRX and grain growth process.The average aspect ratio increases slightly when deformation temperature rises from 1110 to 1140℃,while the average aspect ratio increases memorably as the deformation temperature is higher than 1140℃.展开更多
The conventional fabrication process for single-crystal nickel-based superalloy materials is directional solidifica-tion,which is classified as casting.With the rapid development of additive manufacturing(AM)technolog...The conventional fabrication process for single-crystal nickel-based superalloy materials is directional solidifica-tion,which is classified as casting.With the rapid development of additive manufacturing(AM)technologies,a novel process for fabricating single-crystal superalloys has become possible.This article reviews recent research on the AM of single-crystal nickel-based superalloys.Laser AM technologies,particularly directed energy deposition,are mainly used to repair single-crystal materials.Electron beam powder bed fusion is an innovative method for the direct fabrication of single-crystal materials.Accordingly,the mechanisms of single-crystal formation during AM are analyzed to elucidate the potential of this process route.Furthermore,this article discusses the challenges faced by AM for single-crystal fabrication,and provides perspectives on the trends of future developments.展开更多
Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because o...Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.展开更多
Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality ...Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.展开更多
The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overc...The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overcome this problem,the AM of metal matrix composites(MMCs)is a highly suitable solution because the properties of MMC can be tailored using various reinforcements.Therefore,extensive research has been conducted on the AM of MMCs;however,the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process.This study introduces an easily synthesizable core-shell composite powder,which was fabricated by a recently developed process called the SMART process.The core-shell powder has a novel morphology,consisting of a metal core and composite shell,distinguishing it from the powders used in conventional AM approaches.Inconel 625/TiCp composites were fabricated using the core-shell composite powder,with various fractions of TiCp up to 10 vol.%.Compared to additive-manufactured Inconel 625,the additive-manufactured MMCs showed enhanced strength with significantly fewer defects.The results of this study may accelerate the application of MMC fabricated by AM,which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.展开更多
Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties...Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts.In this study,efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment(SHT)and Hot Isostatic Pressing(HIP)on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion(PBF-EB)process.The effects of SHT and HIP on porosity,microstructure,texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X.Post-fabrication HIP treatment led to a significant reduction in the porosity content,whereas no notable difference in porosity was observed between SHT and as-built parts.There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong<100>crystallographic texture.Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.展开更多
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFB 0702300)the National Natural Science Foundation of China(No.51871028)the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-003B2).
文摘Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed fusion(LPBF)using recycled powders were investigated.Re-melted powder surfaces,satellite particles,and deformed powders were found in the recycled powders,combined with a high-oxygencontent surface layer.The increasing oxygen content led to the formation of high-density oxide inclusions;moreover,printing-induced cracks widely occurred and mainly formed along the grain boundaries in the as-built LPBF nickel-based superalloys fabricated using recycled powders.A little change in the Si or Mn content did not increase the hot cracking susceptibility(HCS)of the printed parts.The changing aspect ratio and the surface damage of the recycled powders might contribute to increasing the crack density.Moreover,the configuration of cracks in the as-built parts led to anisotropic mechanical properties,mainly resulting in extremely low ductility vertical to the building direction,and the cracks mainly propagated along the cellular boundary owing to the existence of a brittle precipitation phase.
基金This work is financially supported by The National Defence Committee of ChineseTechnology(No.95-YJ-20)
文摘The surface microstructure and the surface segregation of FGH 95 nickel-basedsuperalloy powders prepared through plasma rotating electrode processing (PREP) have beeninvestigated by using SEM and AES. The results indicate that the surface microstructure of powderschanges from dendrite into cellular stricture as the particle size of powders decrease, and thepredominant precipitates solidified on the particle surfaces were identified as MC' type carbidesenriched with Nb and Ti. It was also indicated that along with the depth of particle surfaces, thesegregation layer of S, C and O elements are thick, and that of Ti, Cr elements are thin for largesire powders while they are in reverse for median size particles.
文摘The role of niobium in nickel-based superalloys is reviewed. The importance of niobium as a strengthener is discussed. New developments in nickel-based superalloys are also briefly mentioned, including some results that show improved resistance to sulfidation by niobium. Research results from a current program on the role of niobium in the Russian powder metallurgy alloy EP741NP are presented. Future research plans on the role of niobium in superalloys are also discussed.
基金supported by the National Natural Science Foundation of China(No.91860115)the Science,Technology,and Innovation Commission of Shenzhen Municipality(No.JSGG20210802093205015).
文摘The hot deformation behaviors of FGH98 nickel-based powder superalloy were experimentally investigated and theoretically analyzed by Arrhenius models and machine learning(ML).Hot compression tests were conducted with a Gleeble-3800 thermo-mechanical simulation machine on the FGH98 superalloy at strain rates of 0.001–1 s–1 and temperatures of 1025–1175℃.The peak stresses under different deformation conditions were analyzed via the Sellars model and an ML-inspired Gaussian process regression(GPR)model.The prediction of the GPR model outperformed that from the Sellars model.In addition,the stress-strain responses were predicted by the GPR model and tested by experimentally measured stress-strain curves.The results indicate that the developed GPR model has great power with wide generalization capability in the prediction of hot deformation behaviors of FGH98 superalloy,as evidenced by the R2 value higher than 0.99 on the test dataset.
基金financial support for this work by the National Natural Science Foundation of China(Nos.51775275,51921003 and 51905363)the Funding for Outstanding Doctoral Dissertation in NUAA of China(No.BCXJ19-06)+1 种基金the Natural Science Foundation of Jiangsu Province of China(No.BK20190940)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(No.19KJB460008)。
文摘In this article,a grinding force model,which is on the basis of cutting process of single abrasive grains combined with the method of theoretical derivation and empirical formula by analyzing the formation mechanism of grinding force,was established.Three key factors have been taken into accounts in this model,such as the contact friction force between abrasive grains and materials,the plastic deformation of material in the process of abrasive plowing,and the shear strain effect of material during the process of cutting chips formation.The model was finally validated by the orthogonal grinding experiment of powder metallurgy nickel-based superalloy FGH96 by using the electroplated CBN abrasive wheel.Grinding force values of prediction and experiment were in good consistency.The errors of tangential grinding force and normal grinding force were 9.8%and 13.6%,respectively.The contributions of sliding force,plowing force and chip formation force were also analyzed.In addition,the tangential forces of sliding,plowing and chip formation are 14%,19%and 11%of the normal forces on average,respectively.The pro-posed grinding forcemodel is not only in favor of optimizing the grinding parameters and improving grinding efficiency,but also contributes to study some other grinding subjects(e.g.abrasive wheel wear,grinding heat,residual stress).
基金supported by the National Natural Science Foundation of China(Grant Nos.51775275 and 51921003)National Major Science and Technology Project(Grant No.2017-Ⅶ-0002-0095)+2 种基金Funding for Outstanding Doctoral Dissertation in NUAA(Grant No.BCXJ19-06)the Six Talents Summit Project in Jiangsu Province(Grant No.JXQC-002)Fundamental Research Funds for the Central Universities(Grant No.NP2018110).
文摘In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels were comparatively analyzed during creep feed grinding.The infuences of the grinding parameters(abrasive wheel speed,workpiece infeed speed,and depth of cut)on the grinding force,grinding temperature,surface roughness,surface morphology,tool wear,and grinding ratio were analyzed comprehensively.The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels.This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material.Moreover,both the BA and MA abrasive wheeIs exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion.Finally,an analytical model for prediction of the grinding ratio was established by combining the tool wear volume,grinding force,and grinding length.The acceptable errors between the predicted and experimental grinding ratios(ranging from 0.6 to 1.8)were 7.56%and 6.31%for the BA and MA abrasive wheels,respectively.This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel,and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.
文摘Two cooling schemes (continuous cooling and interrupted cooling tests) were applied to investigate the cooling γ precipitation behavior in powder metallurgy superalloy FGH4096. The effect of cooling rate on cooling γ precipitation and the development of γ precipitates during cooling process were involved in this study. The ultimate tensile strength (ErrS) of the specimens in various cooling circumstances was tested. The experiential equations were obtained between the average sizes of secondary and tertiary γ precipitates, the strength, and cooling rate. The results show that they are inversely correlated with the cooling rate as well as the grain boundary changes from serrated to straight, the shape of secondary γ precipitates changes from irregular cuboidal to spherical, while the formed tertiary γ precipitates are always spherical. The interrupted cooling tests show that the average size of secondary γ precipitates increases as a linear function of interrupt temperature for a fixed cooling rate of 24℃/min. The strength first decreases and then increases against interrupt temperature, which is fundamentally caused by the multistage nucleation of γ precipitates during cooling process.
基金This work received financial support of the National Natural Science Foundation of China(Grant No.51805308)the China Postdoctoral Science Foundation(Grant No.2018M631189)+1 种基金the Natural Science Foundation of Shaanxi Province(No.2019JQ-303)the Wenzhou Municipal Science and Technology Foundation(No.G20180032).
文摘With a strain rate range of 0.01–10 s^(−1) and a deformation temperature range of 1110–1200℃,the isothermal compression test was performed on one powder metallurgy superalloy which is macroscopic segregation free.Using electron backscatter diffraction,the effect of strain rate and deformation temperature on grain shape and grain size of superalloys during thermal deformation was studied.The results established that exquisite and equiaxed dynamic recrystallization(DRX)grains are procured at supernal deformation temperature and high strain rate because of the high dislocation density.At the same time,the interaction between high DRX nucleation rate and low grain growth rate at high strain rate is favorable in making finer DRX grains.The equivalent medial grain size expanded with lowering strain rate and elevating proof temperature.Moreover,the grain shape was researched by the effective method of aspect ratio.Most aspect ratio of original grains is 0.61,and the aspect ratio has important implications for DRX and grain growth process.The average aspect ratio increases slightly when deformation temperature rises from 1110 to 1140℃,while the average aspect ratio increases memorably as the deformation temperature is higher than 1140℃.
基金supported by National Key R&D Program of China(Grant No.2017YFB1103300).
文摘The conventional fabrication process for single-crystal nickel-based superalloy materials is directional solidifica-tion,which is classified as casting.With the rapid development of additive manufacturing(AM)technologies,a novel process for fabricating single-crystal superalloys has become possible.This article reviews recent research on the AM of single-crystal nickel-based superalloys.Laser AM technologies,particularly directed energy deposition,are mainly used to repair single-crystal materials.Electron beam powder bed fusion is an innovative method for the direct fabrication of single-crystal materials.Accordingly,the mechanisms of single-crystal formation during AM are analyzed to elucidate the potential of this process route.Furthermore,this article discusses the challenges faced by AM for single-crystal fabrication,and provides perspectives on the trends of future developments.
基金National Natural Science Foundation of China(Grant Nos.52201040,52275333)China Postdoctoral Science Foundation(Grant No.2021M701291)+2 种基金AVIC Manufacturing Technology Institute of China(Grant No.KZ571801)Hubei Provincial Department of Science and Technology 2020 Provincial Key R&D Plan of China(Grant No.2020BAB049)Wuhan Science and Technology Project of China(Grant No.2020010602012037).
文摘Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.
基金financially supported by National Natural Science Foundation of China(No.91860131 and No.52074157)National Key Research and Development Program of China(No.2017YFB0702901)+1 种基金Shenzhen Science and Technology Innovation Commission under the Projects(No.JCYJ20170817111811303,No.KQTD20170328154443162 and ZDSYS201703031748354)joint Ph.D.program between SUSTech and UoB(No.FEFE/GAS1792)。
文摘Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046%porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.Therefore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.
基金supported by the National Research Foundation of Korea(NRF,Nos.NRF-2021R1A2C2014025,NRF-2022R1A5A1030054,and NRF-2022M3H4A1A02076759)grants funded by the Ministry of Science and ICT.
文摘The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overcome this problem,the AM of metal matrix composites(MMCs)is a highly suitable solution because the properties of MMC can be tailored using various reinforcements.Therefore,extensive research has been conducted on the AM of MMCs;however,the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process.This study introduces an easily synthesizable core-shell composite powder,which was fabricated by a recently developed process called the SMART process.The core-shell powder has a novel morphology,consisting of a metal core and composite shell,distinguishing it from the powders used in conventional AM approaches.Inconel 625/TiCp composites were fabricated using the core-shell composite powder,with various fractions of TiCp up to 10 vol.%.Compared to additive-manufactured Inconel 625,the additive-manufactured MMCs showed enhanced strength with significantly fewer defects.The results of this study may accelerate the application of MMC fabricated by AM,which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.
文摘Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts.In this study,efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment(SHT)and Hot Isostatic Pressing(HIP)on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion(PBF-EB)process.The effects of SHT and HIP on porosity,microstructure,texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X.Post-fabrication HIP treatment led to a significant reduction in the porosity content,whereas no notable difference in porosity was observed between SHT and as-built parts.There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong<100>crystallographic texture.Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.