Phase Selection and Processing of High Temperature Intermetallic Alloys.

摘要

A crucial issue in the development of high temperature intermetallic systems for structural applications is the formulation of materials processing strategies in order to achieve controlled microstructures that are designed to provide for the required mechanical performance in elevated temperature aggressive environments. In the research effort at University of Wisconsin-Madison an integrated approach coupling processing with microstructure control as guided by the operative phase equilibria has been used to identify several intermetallic alloys that show promise for further development. The processing efforts have been directed to examining the phase selection, solidification pathways and product phase thermal stability to provide a basis for microstructural development and alloy design. In Ti and Nb base alloy systems such as Ti-Al, TI-Al-Nb, Nb-Cr and Nb-Al the formation of alternate phases has been identified and examined in terms of the operative kinetics and metasable phase equilibria. Powder samples have been examined following atomization and containerless drop tube processing to analyze soldification structure development. Long term microstructural stability is a key issue in particulate consolidation and high temperature application. A detailed study in Ti-Al alloy has demonstrated that the thermal stability of (alpha 2 + gamma) phase structures can be changed by more than 150 C by controlled manipulations of the microstructural morphology. In order to analyze the observed microstructural variations kinetics models have been developed to describe the competitive phase reactions during powder solidification and solid state treatment. (js)