ANALYSIS OF GRAIN-GROWTH IN A 2-PHASE GAMMA-TITANIUM ALUMINIDE ALLOY

Microstructure evolution during annealing of a wrought near-gamma tita nium aluminide alloy, Ti-45.5Al-2Nb-2Cr (at. pct), in the temperature range 1200 degrees C to 1320 degrees C was investigated. The mean grai n size of the alpha phase as well as the volume fraction and size of t he gamma particles were evaluated as a function of annealing temperatu re and time. Isothermal annealing at temperatures above the alpha tran sus, T alpha = 1300 degrees C, led to rapid grain growth of the alpha phase, the kinetics of which could be described by a simple power-law type expression with a grain growth exponent p = 2.3. Alpha grain grow th was significantly retarded during annealing at subtransus temperatu res (1200 degrees C < T less than or equal to 1300 degrees C) by the p inning influence of gamma-phase particles. Limiting grain size values predicted by computer simulation models applicable for high-volume fra ctions of precipitates/particles were in good agreement with experimen tal findings. The kinetics of alpha grain growth in the presence of ga mma particles were analyzed, and the results showed that a grain growt h exponent of p approximate to 2.6 could satisfactorily account for th e experimental results.