EFFECT OF MICROSTRUCTURE ON THERMAL STABILITY AND MECHANICAL PROPERTIES OF AN ENGINEERING γ-TIAL BASED ALLOY DURING LONG-TERM EXPOSURE AT 700°C AND 800°C IN AIR

摘要

This paper summarizes a systematic approach to gain a basic knowledge of the possible microstructural modifications, the stability of the phase, and the underlying mechanisms which induce these changes in γ-TiAl based alloys during long-term service operations at elevated temperatures. A γ-TiAl based alloy with the nominal composition of Ti-46.5at.%A1-4at.%(Cr,Nb,Ta,B) has been exposed to air at 700°C and 800°C for up to 10,000 hours. The sheet material exhibits different microstructures prior to static annealing: an equiaxed microstructure which consists of fine grained γ-TiAl phase with a small volume fraction of the α{sub}2-Ti{sub}3Al and β/B2 phase at grain boundaries and triple junctions and a fully lamellar microstructure with fine lamellar spacing. Evolution of type and composition of constitutional phases for both types of microstructure has been recorded as a function of annealing time and temperature. Additionally, in case of fully lamellar material the impact of thermally induced microstructural changes on mechanical properties was investigated.