Mechanical properties and deformation mechanisms of martensitic Ti6Al4V alloy processed by laser powder bed fusion and water quenching

Martensitic Ti6Al4V samples were fabricated by laser powder bed fusion additive manufacturing, water quenching of wrought and the additively manufactured Ti6Al4V samples respectively, their microstructural characteristics, tensile properties and deformation behaviours have been investigated in this study. These samples showed differences in grain orientations, size of the prior beta grains, thickness of the martensite (alpha') laths, the lattice strain and presence of the beta phase between the alpha' laths. A relationship between the yield strength and the thickness of alpha' laths and lattice strain has been developed. The significant difference in the ductility in terms of the total strain at fracture among the martensitic Ti6Al4V samples processed by the different routes has been observed and investigated. The additively manufactured Ti6Al4V showed the highest post-uniform plastic deformation (deformation after necking) with rapid reduction of stress, its failure mode was dominated by the inter-alpha' quasi-cleavage and intra-alpha' ductile fractures. The water quenched-wrought Ti6Al4V displayed the negligible post-uniform plastic deformation, the inter-prior beta cleavage fracture was its dominant failure mode. The water quenched-additively manufactured Ti6Al4V produced the highest yield strength and medium post-uniform plastic deformation, during which the reduction of stress was much slower, its failure mode was dominated by the inter-alpha' quasi-cleavage fracture. Plastic deformation was mainly taken by the sliding between alpha' laths, however, grain reorientation and slip in alpha' with the different scales in the martensitic Ti6Al4V processed by the different routes were also observed with the evidence of the changes in the relative intensities and shift of 2 theta angles for the diffraction peaks in X-ray diffraction (XRD) spectra in the fractured samples compared to the as-processed samples.

Automated summary

Martensitic Ti6Al4V samples fabricated through laser powder bed fusion and water quenching of wrought Ti6Al4V samples exhibit differences in microstructural characteristics, mechanical properties, and deformation behaviors. The relationship between yield strength and microstructural features such as lattice strain and thickness of alpha' laths was investigated. Variations in ductility and failure modes were observed among the samples processed by different routes, with the additively manufactured Ti6Al4V showing the highest post-uniform plastic deformation and the water quenched-wrought Ti6Al4V displaying negligible post-uniform plastic deformation. Dynamic changes in grain orientations and slip mechanisms were also observed in the martensitic Ti6Al4V samples processed by various routes.