Structural investigation of substoichiometry and solid solution effects in Ti2Al(Cx,N1-x)y compounds

The milling, cold compaction and thermal annealing (4 h-1400 degrees C-Ar flow) of Ti, TiC, Al and AlN powders were used to produce Ti2Al(CxN(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(2)A/CxN(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 Ti2AlCxN(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. (C) 2012 Elsevier Ltd. All rights reserved.