Isothermal and continuous cooling decomposition of alpha and beta phases in gamma titanium aluminides

摘要

The last decade led to significant engineering advances and component demonstrations for gamma-alloy products. The variety of alloy chemistries and process variations available for these products results in a spectrum of microstructures and property variation for the alloys. However, the quantitative aspects of solid-state reactions and microstructural evolution kinetics, as well as the influences of alloy composition upon these, are relatively unstudied. This manuscript succinctly describes the isothermal and continuous-cooling transformations for gamma alloys across a range of compositions from binary, and ternary bases to complex multicomponent chemistries of commercial interest. Time-temperatrue-transformation curves are compared, and the effects of Al concentration and selected alloying additions are highlighted. Both beta-phase forming elements (Cr, Mo & W) and boron in the alloys are examined as grain-size controlling agents. When the alloy contains such agents, the transformation kinetics may be significantly altered relative to other gamma alloys, thus changing the thermal process path and affecting the perfection of lamellar microstructures.