Effects of laser surface melting on crystallographic texture, microstructure, elastic modulus and hardness of Ti-30Nb-4Sn alloy

The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties. The objective of this study was to determine the effects of cold rolling, recrystallization and laser surface melting (LSM) on the microstructure and mechanical properties of a biphase (alpha"+beta) Ti-30Nb-4Sn alloy. X-ray diffraction (XRD) texture analysis of the cold-rolled substrate revealed the [302](alpha")//ND texture component, while analysis of the recrystallized substrate showed the [302](alpha")//ND and [110](alpha")//ND components. The beta-phase texture could not be directly measured by XRD, but the presence of the [111](beta)//ND texture component was successfully predicted by considering the orientation relationship between the alpha" and beta phases. Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate (63 GPa) was lower than that of the recrystallized substrate (74 GPa). Based on the available literature and the results presented here, it is suggested that this difference is caused by the introduction of crystal defects during cold deformation. The combined nanoindentation/EBSD analysis showed that the nanoindentation results are not affected by crystal orientation. LSM of the deformed alloy produced changes in hardness, elastic modulus and crystallographic texture similar to those produced by recrystallization heat treatment, creating a stiffness gradient between surface and substrate.