Structural investigation of substoichiometry and solid solution effects in Ti 2Al(C x,N 1-x) y compounds

Abstract

The milling, cold compaction and thermal annealing (4h-1400°C-Ar flow) of Ti, TiC, Al and AlN powders were used to produce Ti 2Al(C xN (1-x)) y compounds with x=0, 0.25, 0.5, 0.75, 1 and 0.7≤y≤1. X-ray diffraction analysis, scanning electron microscopy observations combined with microanalysis confirmed the formation of the almost pure Ti 2AlC xN (1-x) carbonitrides for y=1 whereas increasing amounts of titanium aluminides were formed when y decreases. Proportions of the different phases deduced from Rietveld refinements of the X-ray diffractograms indicate that no or very poor substoichiometry in carbon was possible in carbide whereas C and N deficiency can be achieved in nitrides and carbonitrides Ti 2AlC xN (1-x). Electron Energy Loss Spectroscopy investigations confirm that carbonitrides can have at least 20% of vacancies on the C or N site. The a lattice parameter varies linearly with x whereas it is not the case for the c lattice parameter, its values being lower for the carbonitrides. Furthermore, a strong broadening of the carbonitrides' XRD peaks is observed, a phenomenon that can be mainly attributed to C and N concentration gradients inside the samples. © 2012 Elsevier Ltd.