Orientation Dependence of the Micro-Pillar Compression Strength in an Electron Beam Melted Ti-6Al-4V Alloy

An α/β two-phase Ti-6Al-4V alloy was fabricated by electron beam melting to obtain a basketweave structure.The orientation dependence of the mechanical properties of Ti-6Al-4 V alloy was studied by micro-pillar compression and post-mortem transmission electron microscopy analysis.The results indicate that different grains have different mechanical responses,and the possible attributions were discussed.Besides the orientation effect,due to the limited volumes of micropillars,the size of the a phases,dispersion of the β phases,and the presence of the free dislocation path also affect the mechanical properties of the micropillars to a large extent.Although no direct link was discovered between the mechanical properties and the parent β orientations,this work provided a promising method to further study the anisotropic mechanical behavior in Ti-6Al-4V alloy.

Multiple α sub-variants and anisotropic mechanical properties of an additively-manufactured Ti-6Al-4V alloy

Additive manu facturing(AM)is a promising material processing method which gains significant momentum in the aerospace and biomedical industries.However,the anisotropy in the mechanical properties of additively-manufactured materials is still poorly understood.This study was aimed at elucidating crystallographic feature-anisotropy-mechanical property relationship for a Ti-6Al-4V alloy manufactured via selective electron beam melting(SEBM).Abundantαlamellae with six variants were present inside the columnar prior-βgrains with a<100>fiber texture duringβ→αphase transformation.The sixαvariants followed the Burgers orientation relationship of{110}_(β)//{0001}_(α)and<1-11>_(β)//<11-20>_(α).Multiple sub-variants in eachαvariant were observed for the first time.The anisotropy in the mechanical properties was mainly related to the relative amount of sixαvariants.While the horizontally-oriented samples had a lower yield strength,they exhibited a higher ductility and longer fatigue life than the vertically-oriented samples.Cyclic softening occurred at higher strain amplitudes,and cyclic stabilization sustained at lower strain amplitudes.Fatigue crack mainly initiated from the specimen surface at lower strain amplitudes,while multiple crack initiation tended to occur at higher strain amplitudes.Crack propagation was characterized by fatigue striations along with some secondary cracks.