Cocrystallization of MAX-Phases in the Ti–Al–C System

  
V.T.Witusiewicz,
 
U.Hecht,
 
B.Hallstedt,
  
A.Dovbenko,
  

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Omeliana Pritsaka str.,3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2015, #07/08
http://www.materials.kiev.ua/article/1977

Abstract

The structure and phase transformations in the Ti–Al–C system were studied by X-ray diffraction, differential thermal analysis, and scanning electron microscopy, including energy-dispersive X-ray spectroscopy and electron back-scatter diffraction on samples obtained by arc melting and annealing at high temperatures. It is shown that the ternary system has a cocrystallization region for both MAX-phases, N and H. The Ti41.5Al38.5C20 samples contain three phases at all experimental temperatures (from 650 to 1660 °C): Ti3AlC2 (N-phase of Ti3SiC2 crystal structure type), Ti2AlC (H, Cr2AlC type), and binary intermetallic TiAl3 (ε, its own crystal structure type). The morphology in the as-cast alloy and annealed samples (at temperatures above and below the solidus temperature, 1660 and 1250 °C, respectively) shows that invariant solidification at 1405 °C (solidus temperature) precedes the univariant simultaneous solidification of N- and H-phases, both MAX-phases separating from the melt.


AL–TI–C SYSTEM, MAX-PHASES, SOLIDUS, TI2ALC, TI3ALC2