Control of beta phase in an EPM-processed intermetallic compound based on Ti[sbnd]Al[sbnd]Mn[sbnd]Mo

Abstract

Gamma TiAl alloys have been under considerable research in recent years because of their good specific strength and the high resistance to creep and oxidation at elevated temperatures. Since the first report on their promising high temperature properties the gamma alloys have been continuously improved and their merits are highly valued now. Among the methods to produce the gamma alloys, EPM (Elemental Powder Metallurgy) method drew attention due to its amenability to the cost-effective near-net shape processing. In the EPM method alloying reaction is basically the exothermic reactions between elemental powders. A practical drawback of using this reaction as a sole method of alloying is the Kirkendall pores generated by the difference in the diffusivities of each alloying element. Therefore high temperature deformation process is added to seal the pores and consolidate the alloying reaction. In the previous attempt, the authors used hot extrusion to consolidate the TiAl compound containing Mn and Mo for improved mechanical properties. The Mo addition and the inherent characteristics of EPM, however, raised a question about the presence of {beta} phase that may cause undesirable effect on high temperature mechanical properties. In the present work, the authors attempted to answer this question from the standmore » point of finding a practical control method of {beta} phase and optimizing the microstructure.« less