Study Of NiAl-Based Porous Composites Prepared By SHS

Ni-Al, Fe-Al intermetallic compounds possess high strength, high temperature resistance, good electrical conductivity and excellent thermal conductivity property; porous material made from above intermetallic compounds have been considered as the most promise high temperature structural materials between high temperature alloys and ceramics.some difficulties existed in studying the reaction process and the mechanism of Ni-Al, Fe-Al intermetallic compounds duing to numerous phases and complicated preparation process of intermetallic compounds. It is meaningful to study the reaction process of Ni-Al, Fe-Al intermetallic compounds and the effects of various process parameters for improving the controllability of product performance and expand application fields.In this paper, Ni,Al and Fe powders were used as raw materials, intermetallic compounds was formed by in-situ reaction of Ni-Al and Fe-Al under conditions of heating. Adiabatic temperatures of Ni-Al, Fe-Al intermetallic compounds were calculated. The influences of the reactant ratio (1:1,2:1,3:1) to phases of products were studied. According to DTA and the phase composition of reaction products at different temperatures, the reaction process was analysed, as well as the influence of technological parameters to reaction process.The influences of the reactant ratio to phase composition of products in Ni-Al and Fe-Al systems were approximately same. When the ratio (at.%) of Ni and Al was 1:1, reaction products were pure NiAl phase that was lamellar microstructure with different orientations. When the ratio of Ni and Al was 2:1, reaction products were consist of NiAl and Ni3Al that the morphology was acerose NisAl distributing in dark NiAl matrix. However the reaction products were simple Ni3Al phase which was irregular shape massive texture with fuzzy interfaces at the ratio of 3:1. When the ratio (at.%) of Fe and Al was 1:1, reaction products were pure FeAl phase. When 2:1, FeAl and Fe3Al phases. When 3:1, Fe3Al phase. The microstructure of sintering products of Fe-Al system was apparently different at these three different ratios. It was showed that with increasing the Fe content, the size of particle become finer and more uniform. The combination among particles was becoming more intensive, and pores was becoming much less. The degree of densification was improved.The reaction process of Ni-Al system and FeAl system are similar:One endothermic peak and two exothermic peaks were detected in the process. Firstly, the reactions were initiated by the formation of intermediate phase and trigger an exothermic peak. With the reaction progressing, Al particles began to melt and an endothermic peak appeared. At last, intermediate phases react with the remaining Ni and Fe, forming the final product and trigger the second exothermic peak.Heating rate, Particle size and green density play an important role on the propagation rate of SHS. The smaller the size of Al particles, the more beneficial the solid state diffusion and the generation of liquid phase. At the same time, it can also promote the reaction. The increase of heating rate could make up the heat loss during reaction process. Besides, it could also increase superheat degree of SHS and accelerate the reaction. The higher green density, the more dense the combination among particles. In addition, it was good for mass and heat transfer which would improve reaction rate. Green density also affects the reaction model. If the green density was sufficiently high, the model of reaction could transform Self Propagating into thermal explosion model...