Effects of carbon addition on the microstructure and mechanical property of in-situ reinforced TiAl matrix composite powders produced by plasma rotating electrode process

To investigate effects of carbon addition on microstructural characteristics of rapidly solidified TiAl alloys, Ti-43Al-6Nb-xC (x = 0,0.5,1.0 at.%) powders are produced by plasma rotating electrode process (PREP). Due to the greater viscosity of composite melts with carbides than those without carbides, the average sizes of carbon containing TiAl powders are much larger than theoretical average diameters. In addition, phase compositions of carbon-free TiAl powders usually consist of alpha phase and beta phase, while alpha phase is predominant in carbon containing TiAl powders due to alpha-phase stabilizer. beta ->alpha phase transformation during the rapid solidification and Burgers relationships {110}(beta)||(0001)(alpha) and <111>(beta)||(11-20)(alpha) are illustrated in TiAl powders. Three types of microscopic structures are unfolded in TiAl composite powders: smooth structures, dendrite structures and equiaxed structures, which stem from various cooling rates. With carbon contents rising to 1.0 at.%, the average grain size in TiAl powders with the particle size range of 100 similar to 150 mu m is refined from 24.31 +/- 0.38 mu m to 11.32 +/- 0.36 mu m, moreover, the distribution ranges of particle sizes vary dramatically. Additionally, the micro-hardness of TiAl powders gradually upgrades as carbon contents ascend. The maximum micro-hardness of TiAl composite powders with 1.0 at.% carbon addition touches at 758.7 +/- 15.4HV. Solid solution strengthening, refinement strengthening and second-phase strengthening are main sources for the ascent of micro-hardness.

Automated summary

In this study, TiAl alloy powders with different carbon contents were produced by plasma rotating electrode process (PREP) and the effects of carbon addition on microstructural characteristics were investigated. The results show that carbon-containing TiAl powders have larger particle sizes and alpha phase is the predominant phase. Different cooling rates result in smooth, dendrite, and equiaxed microstructures in TiAl powders. With increasing carbon content, the average grain size of TiAl powders becomes smaller and the micro-hardness gradually increases.