Microstructure and mechanical properties of novel TiAl alloys tailored via phase and precipitate morphology

Research and development of alloys based on the intermetallic gamma-TiAl phase is experiencing a renewed interest since powder metallurgical approaches provide new near-net-shape processing options. In this work, the manufacturing via spark plasma sintering was facilitated, a straightforward manufacturing technique to consolidate gas atomized pre-alloyed TiAl powder for microstructural and mechanical evaluation. Two alloys, the so-called BMBF3 alloy (Ti-47.4Al-5.6Nb-0.4W, in at.%) and the BMBF2 alloy (Ti-48.6Al-4.1Nb-0.7W-0.4Si-0.5C-0.1B, in at.%) were microstructurally designed via a heat treatment into a mechanically balanced nearly lamellar gamma microstructure, i.e. gamma appears in globular and lamellar morphology, as well as a creep resistant fully lamellar one. The latter exhibits high creep strength up to 850 degrees C, especially due to the formation of p-Ti3AlC carbides. A heat treatment study upon this fully lamellar microstructure of the C-containing alloy links carbide formation and growth kinetics to the mechanical response of the microstructure. Thus, a stabilization heat treatment at 800 degrees C leads to the formation of finest carbides which are homogeneously distributed and increase the strength of the microstructure due to lower dislocation mobility. The two investigated alloys can be addressed as either a ductile TiAl alloy employable up to 750 degrees C (BMBF3), while the BMBF2 alloy is considered useable up to 850 degrees C.