Microstructure characterization and mechanical properties of TiAl-based alloys prepared by mechanical milling and spark plasma sintering

摘要

High Nb containing TiAl alloy powders with or without mechanical milling were consolidated by spark plasma sintering (SPS) technique. The effects of SPS temperature and mechanical-milling treatment on phase constitution and microstructure were studied, and the mechanical properties at room temperature were tested. The phases in the as-atomized powder are composed of major alpha(2) phases, a few gamma phases and a trace of beta phases. After milling, the diffraction peaks for alpha(2) phase are obviously broadened, and the intensities of diffraction peaks for both gamma phase and beta phase are decreased. Similar phase constitution including a large quantity of gamma phases and a few alpha(2) phases are exhibited in the alloys sintered by either as-atomized powder or as-milled powder. At a sintering temperature of 1200 degrees C, the microstructure of the alloy sintered by using as-atomized powder consists of inhomogeneous gamma and alpha(2) phases as well as a few alpha(2)/gamma lamellar colonies. By contrast, the densities increase and the microstructures are apparently refined for the alloys sintered by using as-milled powder. Fully dense alloys with uniformly distributed gamma and alpha(2) grains can be obtained at extending milling time or increasing rotating speed. The nucleation of gamma phase during SPS of the powders is dependent on recrystallization. The heterogeneity of deformation should be responsible for the formation of heterogeneous gamma grains in the alloys sintered by using as-atomized powder. The heterogeneous grain size for the alloys sintered by using as-milled powders is mainly derived from the inhomogeneous nucleation of gamma phase and the uneven distribution of alpha(2) grains. Good mechanical property accompanied by a fine grain size and a dense microstructure can be achieved by optimizing the process parameters. (C) 2017 Elsevier Inc. All rights reserved.