Formation of Ti2AlC0.5N0.5 solid solutions by combustion synthesis of Al4C3-containing samples in nitrogen

Preparation of the solid solution Ti2AlC0.5N0.5 from the powder compacts composed of Ti, Al4C3, 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:Al4C3: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 N2 during the SHS process, which resulted in the higher reaction exothermicity for the sample containing Al than that adopting AlN. The solid solution Ti2AlC0.5N0.5 was identified as the dominant phase in the final products from the Ti–Al4C3–Al powder compacts. However, the increase of nitrogen pressure adversely affected the evolution of Ti2AlC0.5N0.5, 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 Ti2AlC0.5N0.5 was deteriorated due to weak exothermicity and deficiency of TiAl. In addition, the products synthesized from the Ti–Al4C3–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 Ti2AlC0.5N0.5 through combustion synthesis involving gaseous nitrogen.

Research highlights▶ Ti2AlC0.5N0.5 is synthesized from the Ti–Al4C3–Al sample by combustion in nitrogen. ▶ The degree of formation of Ti2AlC0.5N0.5 depends on nitrogen pressure. ▶ The use of AlN in place of Al is not favorable for the formation of Ti2AlC0.5N0.5. ▶ The increase of nitrogen pressure increases the combustion temperature and velocity.