To investigate the improvement in the fatigue strength of magnesium alloy by peening methods,magnesium alloy AZ31 was treated by submerged laser peening(SLP),cavitation peening(CP),and shot peening(SP),and the fatigue...To investigate the improvement in the fatigue strength of magnesium alloy by peening methods,magnesium alloy AZ31 was treated by submerged laser peening(SLP),cavitation peening(CP),and shot peening(SP),and the fatigue properties were evaluated by a plane bending fatigue test.In the case of SLP,both the impact induced by laser ablation(LA)and that caused by laser cavitation(LC),which developed after LA,were used.In the present study,the fatigue life at a constant bending stress was examined to determine the suitable coverage.It was found that the fatigue strengths at N=10^(7)for the SLP,CP,and SP specimens treated by each optimum condition were 56%,18%,and 16%higher,respectively,than that of the non-peened(NP)specimen,which was 97 MPa.The key factors in the improvement of fatigue strength by peening methods were work hardening and the introduction of compressive residual stress.展开更多
Among the existing series of softer metals,magnesium(Mg)has attracted much attention due to its impressive strength-to-weight ratio.However,due to its ease of deformability,Mg tends to suffer from rapid degradation in...Among the existing series of softer metals,magnesium(Mg)has attracted much attention due to its impressive strength-to-weight ratio.However,due to its ease of deformability,Mg tends to suffer from rapid degradation in a wide variety of abrasive and electrochemical environments.One method of improving its surface properties is through surface modification techniques.Among the existing techniques,laser shock peening(LSP)has been one of the most widely utilized processes due to its surface-hardening-like effects.Despite this understanding,a comprehensive review has yet to exist that encapsulates the strengthening mechanism of LSP for Mg and its influence in degradation environments.This review aims to encapsulate the existing research around the LSP field for Mg.Specifically,an understanding of the surface-strengthening effects in relation to its mechanical,tribological,corrosion,and tribo-corrosion characteristics is elucidated.Additionally,the feasibility of LSP for Mg materials in critical industries is also discussed.Through this work,a novel understanding of LSP for Mg can be understood,which can provide a future direction for research in this field.展开更多
A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in m...A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging(DSA) temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening(LP) which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.展开更多
Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mech...Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties.Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material.This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis.The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening.Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process.Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties.With this study,hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.展开更多
The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening(LP). Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ℃...The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening(LP). Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ℃ for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope (SEM), energy-dispersive spectra (EDS), transmission electron microscope (TEM) and X-ray diffraction technique (XRD), respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing (Fe,Cr)2O3, NiCrO3 and Ni(A1,Cr)2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.展开更多
This paper presents a new technique,termed femtosecond laser shock peening ablation in liquids(fs-LSPAL),which can realize simultaneous crack micro/nanomanufacturing and hierarchical micro/nanolaser ablation,giving ri...This paper presents a new technique,termed femtosecond laser shock peening ablation in liquids(fs-LSPAL),which can realize simultaneous crack micro/nanomanufacturing and hierarchical micro/nanolaser ablation,giving rise to the formation of diverse multiscale hierarchical structures,such as macroporous ratcheted structures and enéchelon microfringes decorated with parabolic nanoripples.Through analysis of surface morphologies,many phenomena have been confirmed to take place during fs-LSPAL,including enéchelon cracks,nanostriation,ripple densification,crack branching,and selective formation of high spatial frequency laser-induced periodic surface structures of 100–200 nm in period.At a high laser power of 700 mW,fs-LSPAL at scanning speeds of 0.2 mm s^-1 and 1 mm s^-1 enables the generation of height-fluctuated and height-homogeneous hierarchical structures,respectively.The height-fluctuated structures can be used to induce‘colony’aggregates of embryonic EB3 stem cells.At 200 mW,fs-LSPAL at 1 mm s^-1 is capable of producing homogeneous tilt macroporous structures with cracked structures interleaved among them,which are the synergistic effects of bubble-induced light refraction/reflection ablation and cracks.As shown in this paper,the conventional laser ablation technique integrated with its self-driven unconventional cracking under extreme conditions expands the horizons of extreme manufacturing and offers more opportunities for complex surface structuring,which can potentially be used for biological applications.展开更多
Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the...Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting(EBM),as a mature AM process,were studied in this work.Microstructure,surface topography,residual stress,and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP treatments.The distribution of porosities in EBM sample was assessed via X-ray computed tomography.The results showed that EBM samples with two LSP treatments possessed a lower porosity value of 0.05%compared to the value of 0.08%for the untreated samples.The strength of EBM samples with two LSP treatments was remarkably raised by 12%as compared with the as-built samples.The grains ofαphase were refined in near-surface layer,and a dramatic increase in the depth and magnitude of compressive residual stress(CRS)was achieved in EBM sample with multiple LSP treatments.The grain refinement ofαphase and CRS with larger depth were responsible for the strength enhancement of EBM samples with two LSP treatments.展开更多
Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP p...Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.展开更多
Laser shot peening forming is a novel technology,which employs residual stress induced by intense laser to shape precisely the plate.In this paper,the aeronautic aluminum alloy LY12CZ was selected as an object to rese...Laser shot peening forming is a novel technology,which employs residual stress induced by intense laser to shape precisely the plate.In this paper,the aeronautic aluminum alloy LY12CZ was selected as an object to research experimentally the magnitude of deformation versus numbers of laser shot peening,and surface quality in laser shot zone was also investigated.The specimen was impacted along its centerline by the high-power,short-duration pulses laser.The experimental results show that the arc height and hardness becomes greater with numbers of shot peening increasing and eventually arrives to saturated state,and sur- face roughness after laser shot peening decreases slightly and dislocation density increases greatly,which indicates that the laser shot peening is a technique combining laser shock processing and metal forming.展开更多
The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness te...The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness tester were employed to characterize the microstructure, composition and hardness of this alloy. The results show that the surface roughness is increased by shot-peening, and the microstructure with fine-grain can be obtained by LR pre-treatment. The pre-treated samples were oxygen-permeated at (810± 10) ℃ for 10 h in atmospheric air. The outer layer consists essentially of TiO2, trace Ti2 N, Ti3Al and Ti3AlN for the SP pre-treatment and thin oxygen solution layer is found in the subsurface layer. As for LR pre-treatment, the outer layer consists mainly of TiO2 and small amounts of TiO, and the inner layer consists of alpha crystals, rich in interstitial atoms. Samples by LR pre-treatment has thicker hardened layer with higher hardness values in comparison with SP pre-treated ones.The boost diffusion of oxygen and hardening mechanisms were discussed based on the experimental results.展开更多
The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction...The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction stress measurement shows that LSP results in prominent increase of surface compressive stress,quasi-symmetrically distributed in the laser peened region.The fatigue life of the alloy 7050 in rivet fastener hole structure is notably improved owing to LSP.The sequence of LSP and fastener hole preparation also influence the fatigue cycle life of the alloy.展开更多
This paper reviews the current status of research and development on laser peening without protective coating(LPPC) in Japan. LPPC is an innovative process since it does not require any surface coating that is formed ...This paper reviews the current status of research and development on laser peening without protective coating(LPPC) in Japan. LPPC is an innovative process since it does not require any surface coating that is formed prior to laser irradiation in conventional laser peening for preventing the surface from melting. Surface residual stress of various metal materials was converted from tensile to compressive by LPPC. High cycle fatigue property was remarkably improved for steels, aluminum alloys and titanium alloys. Accelerating stress corrosion cracking (SCC) tests showed that LPPC completely prevents SCC of sensitized austenitic stainless steels, nickel-based alloys and their weld metals. LPPC has been utilized to combat against SCC in Japanese nuclear power reactors since 1999.展开更多
Laser shot peening (LSP) is a novel technology to impress a compressive residual stress into the surfaces of metals or alloys. This treatment can reduce the rate of fatigue cracking and stress corrosion cracking in st...Laser shot peening (LSP) is a novel technology to impress a compressive residual stress into the surfaces of metals or alloys. This treatment can reduce the rate of fatigue cracking and stress corrosion cracking in structural metals or alloys. In this paper, some preliminary experiments were carried out with Nd:Glass laser of a pulse of 20 ns duration and 1.064 μm wavelength, an energy per pulse of 10 to 60 joules, and specimen was selected LY12CZ. The residual stress along the thickness effected by number of laser shots was taken into account in experiment. The magnitude of compressive residual stress near the surface increases with number of laser shots increasing, while decreases with the depth increasing. The mathematical modeling of laser shock processing was established, and a finite-element analysis method was based on ABAQUSExplicit software. The results of simulation are in agreement with those of the experiments, which indicate that the numerical simulation can play a direction role in laser shot peening.展开更多
基金This work was partly supported by JSPS KAKENHI,Grant Numbers 20H02021 and 22KK0050.
文摘To investigate the improvement in the fatigue strength of magnesium alloy by peening methods,magnesium alloy AZ31 was treated by submerged laser peening(SLP),cavitation peening(CP),and shot peening(SP),and the fatigue properties were evaluated by a plane bending fatigue test.In the case of SLP,both the impact induced by laser ablation(LA)and that caused by laser cavitation(LC),which developed after LA,were used.In the present study,the fatigue life at a constant bending stress was examined to determine the suitable coverage.It was found that the fatigue strengths at N=10^(7)for the SLP,CP,and SP specimens treated by each optimum condition were 56%,18%,and 16%higher,respectively,than that of the non-peened(NP)specimen,which was 97 MPa.The key factors in the improvement of fatigue strength by peening methods were work hardening and the introduction of compressive residual stress.
文摘Among the existing series of softer metals,magnesium(Mg)has attracted much attention due to its impressive strength-to-weight ratio.However,due to its ease of deformability,Mg tends to suffer from rapid degradation in a wide variety of abrasive and electrochemical environments.One method of improving its surface properties is through surface modification techniques.Among the existing techniques,laser shock peening(LSP)has been one of the most widely utilized processes due to its surface-hardening-like effects.Despite this understanding,a comprehensive review has yet to exist that encapsulates the strengthening mechanism of LSP for Mg and its influence in degradation environments.This review aims to encapsulate the existing research around the LSP field for Mg.Specifically,an understanding of the surface-strengthening effects in relation to its mechanical,tribological,corrosion,and tribo-corrosion characteristics is elucidated.Additionally,the feasibility of LSP for Mg materials in critical industries is also discussed.Through this work,a novel understanding of LSP for Mg can be understood,which can provide a future direction for research in this field.
基金Supported by National Natural Science Foundation of China(Grant No.51175236)Research Fund for the Doctoral Program of Higher Education of China(Grant No.20123227110022)+1 种基金Industrial Science and Technology Project of Jiangsu Province,China(Grant No.BE2013097)Jiangsu Provincial Innovation Program of Graduated Student of China(Grant No.1011110008)
文摘A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging(DSA) temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening(LP) which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.
基金This study was co-supported by National Natural Science Foundation of China (51501219), National Key Development Program of China (2016YFB 1192704), NSFC -Liaoning Province United Foundation (U 1608259) and National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2015BAFOBBO 1-01).
基金supported by in part by the National Science Foundation through the awards CAREER #1846478 and STTR #1521188
文摘Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties.Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material.This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis.The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening.Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process.Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties.With this study,hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.
基金The authors thank Professor Yongxiang Hu for the ns-LSP experiment on Mg-3Gd alloy and his useful discussion.The research was supported by the National Key R&D Program of China(2017YFA0303700)the National Natural Science Foundation of China(NSFC)(11574208).
基金Funded by the National Natural Science Foundation of China(No.51175234)the Heights Talent Support Programs in Six Industrial Fields in Jiangsu Province(No.2011-JXQC069)
文摘The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening(LP). Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ℃ for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope (SEM), energy-dispersive spectra (EDS), transmission electron microscope (TEM) and X-ray diffraction technique (XRD), respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing (Fe,Cr)2O3, NiCrO3 and Ni(A1,Cr)2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.
基金the financial support by RIKEN FY2019‘Emerging Collaboration Seed’of‘Collaboration Seed Fund’(Grant No.100948-201901010000-340130)。
文摘This paper presents a new technique,termed femtosecond laser shock peening ablation in liquids(fs-LSPAL),which can realize simultaneous crack micro/nanomanufacturing and hierarchical micro/nanolaser ablation,giving rise to the formation of diverse multiscale hierarchical structures,such as macroporous ratcheted structures and enéchelon microfringes decorated with parabolic nanoripples.Through analysis of surface morphologies,many phenomena have been confirmed to take place during fs-LSPAL,including enéchelon cracks,nanostriation,ripple densification,crack branching,and selective formation of high spatial frequency laser-induced periodic surface structures of 100–200 nm in period.At a high laser power of 700 mW,fs-LSPAL at scanning speeds of 0.2 mm s^-1 and 1 mm s^-1 enables the generation of height-fluctuated and height-homogeneous hierarchical structures,respectively.The height-fluctuated structures can be used to induce‘colony’aggregates of embryonic EB3 stem cells.At 200 mW,fs-LSPAL at 1 mm s^-1 is capable of producing homogeneous tilt macroporous structures with cracked structures interleaved among them,which are the synergistic effects of bubble-induced light refraction/reflection ablation and cracks.As shown in this paper,the conventional laser ablation technique integrated with its self-driven unconventional cracking under extreme conditions expands the horizons of extreme manufacturing and offers more opportunities for complex surface structuring,which can potentially be used for biological applications.
基金financially supported by the Shanghai Science and Technology Committee Innovation Grant(Nos.17JC1400600 and 17JC1400603)the Distinguished Professor Program of Shanghai University of Engineering Science。
文摘Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting(EBM),as a mature AM process,were studied in this work.Microstructure,surface topography,residual stress,and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP treatments.The distribution of porosities in EBM sample was assessed via X-ray computed tomography.The results showed that EBM samples with two LSP treatments possessed a lower porosity value of 0.05%compared to the value of 0.08%for the untreated samples.The strength of EBM samples with two LSP treatments was remarkably raised by 12%as compared with the as-built samples.The grains ofαphase were refined in near-surface layer,and a dramatic increase in the depth and magnitude of compressive residual stress(CRS)was achieved in EBM sample with multiple LSP treatments.The grain refinement ofαphase and CRS with larger depth were responsible for the strength enhancement of EBM samples with two LSP treatments.
基金supported by the National Natural Science Foundation of China (Grants 11002150,11332011,and 11402277)the Basic Research Equipment Project of the Chinese Academy of Sciences (YZ200930) for financia support
文摘Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.
基金Funded by the National Science Foundation of China(Grant No.50475127,50275068)
文摘Laser shot peening forming is a novel technology,which employs residual stress induced by intense laser to shape precisely the plate.In this paper,the aeronautic aluminum alloy LY12CZ was selected as an object to research experimentally the magnitude of deformation versus numbers of laser shot peening,and surface quality in laser shot zone was also investigated.The specimen was impacted along its centerline by the high-power,short-duration pulses laser.The experimental results show that the arc height and hardness becomes greater with numbers of shot peening increasing and eventually arrives to saturated state,and sur- face roughness after laser shot peening decreases slightly and dislocation density increases greatly,which indicates that the laser shot peening is a technique combining laser shock processing and metal forming.
基金Project (50171073) supported by the National Natural Science Foundation of China
文摘The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness tester were employed to characterize the microstructure, composition and hardness of this alloy. The results show that the surface roughness is increased by shot-peening, and the microstructure with fine-grain can be obtained by LR pre-treatment. The pre-treated samples were oxygen-permeated at (810± 10) ℃ for 10 h in atmospheric air. The outer layer consists essentially of TiO2, trace Ti2 N, Ti3Al and Ti3AlN for the SP pre-treatment and thin oxygen solution layer is found in the subsurface layer. As for LR pre-treatment, the outer layer consists mainly of TiO2 and small amounts of TiO, and the inner layer consists of alpha crystals, rich in interstitial atoms. Samples by LR pre-treatment has thicker hardened layer with higher hardness values in comparison with SP pre-treated ones.The boost diffusion of oxygen and hardening mechanisms were discussed based on the experimental results.
文摘The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction stress measurement shows that LSP results in prominent increase of surface compressive stress,quasi-symmetrically distributed in the laser peened region.The fatigue life of the alloy 7050 in rivet fastener hole structure is notably improved owing to LSP.The sequence of LSP and fastener hole preparation also influence the fatigue cycle life of the alloy.
文摘This paper reviews the current status of research and development on laser peening without protective coating(LPPC) in Japan. LPPC is an innovative process since it does not require any surface coating that is formed prior to laser irradiation in conventional laser peening for preventing the surface from melting. Surface residual stress of various metal materials was converted from tensile to compressive by LPPC. High cycle fatigue property was remarkably improved for steels, aluminum alloys and titanium alloys. Accelerating stress corrosion cracking (SCC) tests showed that LPPC completely prevents SCC of sensitized austenitic stainless steels, nickel-based alloys and their weld metals. LPPC has been utilized to combat against SCC in Japanese nuclear power reactors since 1999.
文摘Laser shot peening (LSP) is a novel technology to impress a compressive residual stress into the surfaces of metals or alloys. This treatment can reduce the rate of fatigue cracking and stress corrosion cracking in structural metals or alloys. In this paper, some preliminary experiments were carried out with Nd:Glass laser of a pulse of 20 ns duration and 1.064 μm wavelength, an energy per pulse of 10 to 60 joules, and specimen was selected LY12CZ. The residual stress along the thickness effected by number of laser shots was taken into account in experiment. The magnitude of compressive residual stress near the surface increases with number of laser shots increasing, while decreases with the depth increasing. The mathematical modeling of laser shock processing was established, and a finite-element analysis method was based on ABAQUSExplicit software. The results of simulation are in agreement with those of the experiments, which indicate that the numerical simulation can play a direction role in laser shot peening.