Enhancement in Mechanical Properties of TiAl Alloys by In-Situ Precipitation of Hybrid TiB2-Ti2AlN

Abstract:

TiAl alloy was mixed with BN nanoplates and then sintered at 1300 °C through spark plasma sintering technique, and the hybrid TiB₂-Ti₂AlN/TiAl composites were in-situ prepared. The microstructural evolution and mechanical properties at room temperature of TiAl composites were investigated. Results show that a fully lamellar microstructure can be achieved in the TiAl composites with BN nanoplates of lower content, whereas a transformation to the nearly lamellar microstructure can be observed under higher BN nanoplate content conditions. The microstructure of TiAl composites is significantly refined due to the even distribution of in-situ prepared TiB₂-Ti₂AlN particles at the lamellar colony boundaries. Notably, a continuous core-shell structure of TiB₂-Ti₂AlN particles is formed at the lamellar grain boundary after adding 0.5wt% BN nanoplates. The results of compression and friction wear at room temperature show that the hardness and compressive strength of TiAl composites are greatly improved with the increase in BN nanoplate content from 0wt% to 1wt%. Meanwhile, the average coefficient of friction decreases from 0.59 to 0.47, and the wear rate decreases by 29.9%. These remarkable mechanical properties are mainly attributed to the strengthening effects of the in-situ formation of TiB₂-Ti₂AlN particles, refined microstructure, and core-shell structure.