Investigating the effect of nickel particle size and green density on the properties of NiAl-TiB2-TiC composite produced by combustion synthesis

In this study, the effect of nickel particle size and green density on the formed phases, ignition time, and porosity distribution in NiAl-TiB2-TiC composite produced by combustion synthesis method was investigated. For this purpose, reactive powders were weighed and mixed to form a mixture of Ni + Al + x (3Ti + B4C). The green mixture was compressed in the form of a cylinder. The samples were synthesized using an induction furnace which the sample with a constant heating rate. The reaction was ignited in a quartz tube under a flow of argon gas. The microstructure of the products was examined using Scanning Electron Microscopy (SEM), and the phases were determined using X-ray diffraction (XRD). The amount of open, closed and total porosity was measured using Archimedes method, and the distribution of porosity was analyzed by using image analysis software. The results showed that by decreasing the average particle size of nickel from 87µm to 3µm, due to increase in contact surfaces, there was a decrease in ignition time of the samples, and more intensive reactions were encountered. Using finer nickel resulted in a ca. 10% decrease in the porosity of products. The minimum ignition time was obtained at green density of 85%. Increase in the relative density of green sample reduced the amount of secondary open pores; the porosity of the samples with a relative density of 65% and 95% was 58.8% and 26.9% after synthesis, respectively.