Investigations on diffusion behaviors in Ti-rich Ti-Nb-Zr-Cr system: Experimental measurement and CALPHAD modeling

Accurate diffusivities are essential for the design and production of biomedical alloys with excellent properties. In the present work, ternary and quaternary interdiffusion behaviors in Ti-rich Ti-Nb-Cr, Ti-Zr-Cr and Ti-Nb-Zr-Cr systems at 1273 K were experimentally investigated via the diffusion couple technique. Ternary interdiffusivities of bcc Ti-Nb-Cr alloys were then determined using the Matano-Kirkaldy method. Subsequently, on the basis of the presently obtained interdiffusivities together with the diffusivity and mobility parameters of Ti-Nb-Zr-Cr sub-binary and sub-ternary systems and the thermodynamic descriptions for bcc Ti-Nb-Zr-Cr system, the atomic mobilities of Ti,Nb, Zr and Cr in bcc Ti-Nb-Zr-Cr alloys were assessed by means of CALPHAD (CALculation of PHAse Diagrams) method. Moreover, the comprehensive comparisons between the experimental diffusion properties of bcc Ti-Nb-Cr, Ti-Zr-Cr and Ti-Nb-Zr-Cr systems (i.e., interdiffusivities, composition profiles, interdiffusion fluxes and diffusion paths) and the calculated/model-predicted data due to the present atomic mobilities were conducted in order to verify the reliability of the mobilities. The present atomic mobilities for bcc Ti-Nb-Zr-Cr system can provide the accurate ternary and quaternary interdiffusivity matrices over a wide composition range.