Microstructural evolution and hardness of TiAl3 and TiAl2 phases on Ti–45Al–2Nb–2Mn–1B by plasma pack aluminizing

Abstract

The surface of Ti-45Al-2Nb-2Mn-1B (at%) titanium aluminide was aluminized in a so called plasma pack aluminizing by packing the substrate in a mixture of aluminum copper alloy and application of an 18kHz pulsed DC glow discharge plasma in argon gas. The plasma energy provided the necessary heat for melting and mutual diffusion of titanium and aluminum at the surface of titanium aluminide alloy in less than 1h without any further heat treatment. The microstructure and hardness of different phases on the surface of Ti-45Al-2Nb-2Mn-1B alloy were characterized using optical and electron microscopy, X-ray diffraction (XRD), EDX analysis and Vickers microhardness tests.The thickness of the surface layers was up to 300μm. The surface layers consisted mainly of TiAl3 and TiAl2 compounds. These compounds appeared in blocky and round shapes with different micrometer sizes in a matrix of aluminum alloy phase. The hardness of the surface layers was up to 600 HV0.1, which was higher than that of Ti-45Al-2Nb-2Mn-1B substrate (330 HV0.1).