Effects of laser surface melting on crystallographic texture, microstructure, elastic modulus and hardness of Ti-30Nb-4Sn alloy
(1. School of Mechanical Engineering, University of Campinas, Rua Mendeleyev, 200, CEP 13083-860, Campinas, SP, Brazil;
2. Instituto de Pesquisas Energéticas e Nucleares, Av. Prof. Lineu Prestes, 2242, CEP 05508-000, S？o Paulo, SP, Brazil;
3. Institut de Tecnologia de Materials, Universitat Politècnica de València, Camino de Vera, s/n, Código Postal 46022, Valencia, Spain;
4. Department of Materials Engineering, Federal University of S？o Carlos, Rodovia Washington Luís, Km 235, CEP 13565-905, S？o Carlos, SP, Brazil)
2. Instituto de Pesquisas Energéticas e Nucleares, Av. Prof. Lineu Prestes, 2242, CEP 05508-000, S？o Paulo, SP, Brazil;
3. Institut de Tecnologia de Materials, Universitat Politècnica de València, Camino de Vera, s/n, Código Postal 46022, Valencia, Spain;
4. Department of Materials Engineering, Federal University of S？o Carlos, Rodovia Washington Luís, Km 235, CEP 13565-905, S？o Carlos, SP, Brazil)
Abstract: 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 (α″+β) Ti-30Nb-4Sn alloy. X-ray diffraction (XRD) texture analysis of the cold-rolled substrate revealed the [302]α″//ND texture component, while analysis of the recrystallized substrate showed the [302]α″//ND and [110]α″//ND components. The β-phase texture could not be directly measured by XRD, but the presence of the [111]β//ND texture component was successfully predicted by considering the orientation relationship between the α″ and β 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.
Key words: titanium alloy; cold rolling; laser surface melting; recrystallization; crystallographic texture; stiffness- graded material