Preparation of Nb5Si3 intermetallic and Nb5Si3/Nb composite by self-propagating high-temperature synthesis

Production of niobium silicide Nb5Si3 and composite Nb5Si3/Nb was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts in this study. Effects of sample green density, preheating temperature, and initial stoichiometry on the combustion characteristics, as well as on the composition of final products were studied. Experimental evidence indicates the self-sustained combustion front propagating in a spinning mode. Moreover, phase transformation continues during the cooling of the burned sample, leading to the emergence of an afterglow on the compact. As the sample density and preheating temperature increased, the combustion temperature was found to increase and the flame-front velocity was correspondingly enhanced. XRD analysis shows that the nature of end products is significantly influenced by the starting stoichiometry of sample compacts. It was found that the compact with an initial composition of Nb:Si = 5:3 yielded predominantly α-Nb5Si3, whereas the sample made up of Nb:Si = 3:2 produced largely β-Nb5Si3. Based upon the data measured from the samples of Nb:Si = 5:3, an activation energy of 259.2 kJ/mol was deduced for the formation of Nb5Si3 by SHS. In the synthesis of the Nb5Si3/Nb composite, the increase of elemental Nb content in the final composition lowered the combustion temperature and thereby reduced the flame-front velocity. The Nb5Si3/Nb composites with a concentration of Nb ranging from 5 to 15 mol.% were directly produced by SHS in this study. XRD analysis of the Nb5Si3/Nb composite identifies the formation of Nb5Si3 dominated by the α form, along with the existence of elemental Nb.