Effects of forming conditions and TiC-TiB2 contents on the microstructures of self-propagating high-temperature synthesized NiAl-TiC-TiB2 composites

Abstract

The NiAl-TiC-TiB2 composites were processed by self-propagating high-temperature synthesis (SHS) method using raw powders of Ni, Al, Ti, B4C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC-TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods: in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl-TiC-TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl-TiC-TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC-TiB2 attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl-TiC-TiB2 composites are different.