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(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.Theβ-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 theα″andβphases.Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate(63GPa)was lower than that of the recrystallized substrate(74GPa).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.

Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys

High-entropy alloys can be compelling raw materials for semi-solid applications.In the present study,the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi(x=0,1,2,3)alloys was investigated.Arc-melted samples were cross-rolled at room temperature and then isothermally treated at 1175℃in the semi-solid state for 300 s.Microstructural characterization showed that the alloys containing Cu were formed by two fcc phases.Notably,the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich phase.During solidification,this phase,which is the last to form,nucleates and epitaxially grows on the Cu-lean phase.All the studied CoCrCuFeNi alloys exhibited the same melting behavior.The Cu-rich phase melts at approximately 1120℃,whereas the Culean phase melts at approximately 1350℃,providing a suitable processing temperature range of more than 200℃.The semi-solid microstructures were considerably refined and globular regardless of the alloy composition,being suitable for semi-solid processing.Furthermore,each fcc phase exhibited roughly the same composition under the different processing conditions.The Cu content in the Cu-lean phase was approximately 10 at.%,while Co,Cr,Fe,and Ni were in an approximately equiatomic ratio.Meanwhile,the Cu content was between 80 at.%and 86 at.%in the Cu-rich phase.The isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature(1300℃)only caused the globules to coarsen.In conclusion,this work showed that these alloys can be potential candidates for semi-solid processing.