Formation of Ti 2AlC 0.5N 0.5 solid solutions by combustion synthesis of Al 4C 3-containing samples in nitrogen

Abstract

Preparation of the solid solution Ti 2AlC 0.5N 0.5 from the powder compacts composed of Ti, Al 4C 3, and Al or AlN was investigated by self-propagating high-temperature synthesis (SHS) under gaseous nitrogen. The molar proportion of three reactant powders was formulated as Ti:Al 4C 3:Al (or AlN) = 2:1/6:1/3. For both types of the samples, the increase of nitrogen pressure from 0.45 to 1.82 MPa augments the combustion temperature and thus accelerates the reaction front. In contrast to the inertness of AlN, Al particles reacted energetically with Ti and N 2 during the SHS process, which resulted in the higher reaction exothermicity for the sample containing Al than that adopting AlN. The solid solution Ti 2AlC 0.5N 0.5 was identified as the dominant phase in the final products from the Ti–Al 4C 3–Al powder compacts. However, the increase of nitrogen pressure adversely affected the evolution of Ti 2AlC 0.5N 0.5, because Ti was over-nitrified and Al also reacted with nitrogen. When AlN was used to replace Al in the reactant compacts, the formation of Ti 2AlC 0.5N 0.5 was deteriorated due to weak exothermicity and deficiency of TiAl. In addition, the products synthesized from the Ti–Al 4C 3–AlN samples under nitrogen of 1.48 and 1.82 MPa were dominated by titanium carbonitride Ti(C,N). This implies that the use of AlN in place of Al is unfavorable for the formation of Ti 2AlC 0.5N 0.5 through combustion synthesis involving gaseous nitrogen.