The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,a...The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,and high-cycle fatigue properties,were studied.The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material.The maximum surface residual compressive stress was−661 MPa,and the compressive-stress-affected depth was greater than 1000μm.The roughness and Vickers micro-hardness increased with the number of shocks,and the maximum hardness-affected depth was about 700μm after three LSP treatments.LSP enhanced the fraction of low-angle grain boundaries,changed the grain preferred orientations,and notably increased the pole density ofαphase on the near surface from 2.41 to 3.46.The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening,while the LSP had a limited effect on the tensile properties.The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20%compared with that of the untreated sample,which was caused by the suppression of the initiation and propagation of fatigue cracks.展开更多
The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composit...The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.展开更多
The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour,in terms of the tensile and fatigue strength,at room temperature and at...The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour,in terms of the tensile and fatigue strength,at room temperature and at 200℃,and to correlate the mechanical performance with its microstructure,in particular with the secondary dendrite arm spacing(SDAS).The mechanical tests carried out on the overaged alloy at 200℃ indicate that the addition of about 1.3 wt.%Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa,respectively,and fatigue strength at about 100 MPa.Compared to the quaternary(Al−Si−Cu−Mg)alloy C355,the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200℃.The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature,while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200℃.展开更多
Co-based superalloys such as FSX-414 have been recently used in gas turbine first stage nozzles. During service, nozzles are exposed to low cycle fatigue, which can lead to cracking of these components. The cracks on ...Co-based superalloys such as FSX-414 have been recently used in gas turbine first stage nozzles. During service, nozzles are exposed to low cycle fatigue, which can lead to cracking of these components. The cracks on these nozzles are usually welded with ttmgsten arc welding （TIG） using Co-based filler metals. In this paper, the effect of TIG on the tensile and low cycle fatigue properties of Co-based superalloy FSX-414 was studied at 950℃. The experimental results show that the yield and ultimate tensile stresses of welded and unwelded specimens are comparable to each other. But toughness of welded specimens is lower than that of unwelded ones. The low cycle fatigue properties of FSX-414 were studied at a strain rate of 3.3×10^-4 s^-1, strain ratio R=-1 （R=emin/emax） and Aet （total strain change） from 0.8% to 2%. In welded specimens, at high strain cycling, the nucleation and growth of cracks occur in the welded zone. But at Aet=0.8%, fracture occurs in the same zones of unwelded specimens. The results show that the total fatigue lives of the welded specimens are shorter than those of unwelded ones. In all of the low cycle fatigue tests, softening phenomena are observed.展开更多
The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has bee...The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has been observed,and the coating shows significant influence on the fatigue behavior.The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction.The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated.Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test.What’s more,inclusion particles were proved to play a crucial role in causing these cracks.展开更多
基金the National Natural Science Foundation of China(No.52205240).
文摘The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,and high-cycle fatigue properties,were studied.The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material.The maximum surface residual compressive stress was−661 MPa,and the compressive-stress-affected depth was greater than 1000μm.The roughness and Vickers micro-hardness increased with the number of shocks,and the maximum hardness-affected depth was about 700μm after three LSP treatments.LSP enhanced the fraction of low-angle grain boundaries,changed the grain preferred orientations,and notably increased the pole density ofαphase on the near surface from 2.41 to 3.46.The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening,while the LSP had a limited effect on the tensile properties.The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20%compared with that of the untreated sample,which was caused by the suppression of the initiation and propagation of fatigue cracks.
文摘The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.
文摘The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour,in terms of the tensile and fatigue strength,at room temperature and at 200℃,and to correlate the mechanical performance with its microstructure,in particular with the secondary dendrite arm spacing(SDAS).The mechanical tests carried out on the overaged alloy at 200℃ indicate that the addition of about 1.3 wt.%Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa,respectively,and fatigue strength at about 100 MPa.Compared to the quaternary(Al−Si−Cu−Mg)alloy C355,the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200℃.The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature,while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200℃.
文摘Co-based superalloys such as FSX-414 have been recently used in gas turbine first stage nozzles. During service, nozzles are exposed to low cycle fatigue, which can lead to cracking of these components. The cracks on these nozzles are usually welded with ttmgsten arc welding （TIG） using Co-based filler metals. In this paper, the effect of TIG on the tensile and low cycle fatigue properties of Co-based superalloy FSX-414 was studied at 950℃. The experimental results show that the yield and ultimate tensile stresses of welded and unwelded specimens are comparable to each other. But toughness of welded specimens is lower than that of unwelded ones. The low cycle fatigue properties of FSX-414 were studied at a strain rate of 3.3×10^-4 s^-1, strain ratio R=-1 （R=emin/emax） and Aet （total strain change） from 0.8% to 2%. In welded specimens, at high strain cycling, the nucleation and growth of cracks occur in the welded zone. But at Aet=0.8%, fracture occurs in the same zones of unwelded specimens. The results show that the total fatigue lives of the welded specimens are shorter than those of unwelded ones. In all of the low cycle fatigue tests, softening phenomena are observed.
基金National Natural Science Foundation of China （No. 51275185, No. 51405171） National Basic Research Program of China （No. 2010CB630802-3）+1 种基金 Graduate Innovation and Entrepreneurship Fund of Huazhong University of Science and Technology （No. 0109070112） Fundamental Research Funds for the Central Universities （No. 0118110621）
文摘The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa.Surface morphology of fractured and non-fractured specimen has been observed,and the coating shows significant influence on the fatigue behavior.The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction.The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated.Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test.What’s more,inclusion particles were proved to play a crucial role in causing these cracks.
