Particle coarsening behavior of α-β titanium alloys

A systematic study was undertaken to develop particle coarsening relationships in terms of time, temperature, and volume percents of phases and to determine the rate-controlling mechanisms for the coarsening of α-β Ti-Mn and Ti-V alloys. This investigation is confined to equiaxed-type α+ β microstructures. For a given alloy anc te nperature, the coarsening of particles refers to the growth of particles under essentially constant volume percents of the component phases. The coarsening exponents increased from 0 24 to 0.29 and from 0.28 to 0.32 for Ti-V and Ti-Mn systems, respectively, when the temperature was increased from 973 to 1073 K. In addition, it was found that the activation energy chances as the temperature is increased from 973 to 1108 K for the Ti-Mn system. Based on these results, it is suggested that the rate-controlling mechanism for particle coarsening changes from mixed (bulk + grain-boundary) diffusion control toward bulk diffusion control when the temperature is increased from 973 to 1108 K for the Ti-Mn system. Similarly, for the Ti-V system, it is suggested that the rate-controlling mechanism changes from grain-boundary diffusion control toward mixed diffusion control when the temperature is increased from 973 to 1073 K. These results clearly indicate that the rate-controlling mechanism depends on temperture as well as the diffusivities of the alloying elements. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.