查看更多>>摘要：The new developed γ/γ'Co-Al-Nb-base alloys show great potentials as high-temperature materials.However,finding appro-priate compositions to improve performance of alloys still poses a great challenge to the development of Co-Al-Nb-base alloys.Motivated by the lack of alloying effects on fundamental properties of critical γ'phase,we systematically performed a theoretical investigation on the effect of alloying elements TM(TM:Ti,V,Cr,Zr,Mo,Ta,W,Re,and Ru)on phase sta-bilities and mechanical properties of Ll2-type γ'(Co,Ni)3(Al,Nb).By analyzing the stability of γ'phase with respect to its competitive B2 and D019 phases,the results shown that Ti,V,and Cr enhance the Ll2 stability and widen the Ll2-D019 energy barrier,in which V yields the maximum influence.The analysis of electronic structure indicated that the alternation of valence electrons at fermi level would be the atomic origin for doping TM in γ'phase.The calculated results of mechanical properties shown that V and Cr are expected to be optimal dopant for enhancing the strength and the ductility of γ'phase.The addition of Ta is also beneficial for enhancing the strength at the slight expense of ductility of γ'phase.By drawing the mechanical maps,the preferred composition range for the phases with desired properties is roughly demarcated in theory for the multi-addition of V/Cr and V/Ta in γ'phase.The findings would be useful for optimizing the performance of novelγ/γ'Co-Al-Nb-base superalloys.
查看更多>>摘要：The corrosion behavior of the pre-oxidized GH4169 alloy was studied after 20 h of exposure under a solid NaCl deposit film in a wet O2 environment at 600 ℃ by mass-gain measurements,X-ray diffraction,scanning electron microscopy,transmis-sion electron microscopy methods.The results indicate that the pre-oxidized GH4169 alloy undergoes serious corrosion in the corrosive condition.The preformed Cr2O3 layer is gradually destroyed by deposit NaCl,and the inner Nb2O5 layer beneath the complete outer Cr2O3 layer also reacts with NaCl to form NaNbO3.The electrochemical test results testified the existence of electrochemical reactions during this corrosion process.The corrosion behavior of pre-oxidized GH4169 under a solid NaCl deposit film in a wet O2 environment at 600 ℃ has been discussed in detail.
查看更多>>摘要：Alternating shear stress is a critical factor in the accumulation of damage during rolling contact fatigue,severely limiting the service life of bearings.However,the specific mechanisms responsible for the cyclic shear fatigue damage in bearing steel have not been fully understood.Here the mechanical response and microstructural evolution of a model GGr15 bearing steel under cyclic shear loading are investigated through the implementation of molecular dynamics simulations.The samples undergo 30 cycles under three different loading conditions with strains of 6.2％,9.2％,and 12.2％,respectively.The findings indicate that severe cyclic shear deformation results in early cyclic softening and significant accumulation of plastic dam-age in the bearing steel.Besides,samples subjected to higher strain-controlled loading exhibit higher plastic strain energy and shorter fatigue life.Additionally,strain localization is identified as the predominant damage mechanism in cyclic shear fatigue of the bearing steel,which accumulates and ultimately results in fatigue failure.Furthermore,simulation results also revealed the microstructural reasons for the strain localization(e.g.,BCC phase transformation into FCC and HCP phase),which well explained the formation of white etching areas.This study provides fresh atomic-scale insights into the mecha-nisms of cyclic shear fatigue damage in bearing steels.
查看更多>>摘要：Different amounts of Fe(0.005,0.01,0.03,0.05,and 0.07 wt％)were added to SAC305 to study the shear behavior damage of Fe-doped SAC solder joints under thermal loading(170 ℃,holding time of 0,250,500,and 750 h).The results show that during isothermal aging at 170 ℃,the average shear force of all solder joints decreases with increasing aging time,while the average fracture energy first increases and then decreases,reaching a maximum at 500 h.Minor Fe doping could both increase shear forces and related fracture energy,with the optimum Fe doping amount being 0.03 wt％within the entire aging range.This is because the doping Fe reduces the undercooling of the SAC305 alloy,resulting in the microstructure refining of solder joints.This in turn causes the microstructure changing from network structure(SAC305 joint:eutectic network+β-Sn)to a single matrix structure(0.03Fe-doped SAC305 joint:β-Sn matrix+small compound particles).Specifi-cally,Fe atoms can replace some Cu in Cu6Sn5(both inside the solder joint and at the interface),and then form(Cu,Fe)6Sn5 compounds,resulting in an increase in the elastic modulus and nanohardness of the compounds.Moreover,the growth of Cu6Sn5 and Cu3Sn intermetallic compounds(IMC)layer are inhibited by Fe doping even after the aging time prolonging,and Fe aggregates near the interface compound to form FeSn2.This study is of great significance for controlling the growth of interfacial compounds,stabilizing the microstructures,and providing strengthening strategy for solder joint alloy design.
万方数据
维普