Pressureless sintering and characterization of titanium diboride with binding alloy

In this study, TiB2 reinforced Ni and Fe alloy matrix composites were obtained through pressureless sintering at relatively low temperature. TiB2 is a high temperature ceramic with high hardness and corrosion resistance. It is difficult to sinter TiB2 in plain form due to its bond character and low diffusion coefficient. Thus, sintering requires high temperatures of over 1800 oC. Sintering temperature can be reduced by introducing metal binders. Ni, Fe and their alloys are known to be fruitful additives in liquid phase sintering of TiB2. In the present study, composites containing 10, 17.5 and 25 vol.% TiB2 particles and Ni, Fe alloy matrix were prepared by pressureless sintering at 1375 oC in argon atmosphere. 10 % Ni addition was found to be insufficient at this temperature to provide a continuous matrix. In the obtained composites, green relative density values were about 65-70 % and the sintered relative density values were mostly about 88-90%. Maximum microhardness and bending strength values were attained in 25% Ni matrix composite with values of 1556±115HV0.2 and 279 MPa, respectively. Utilization of PEG or warm compaction was not found to be effective in enhancing density or microhardness. TiB2 particles were in 6-10 micrometer range. In some experiments, ball milling of the starting powders was employed in a WC-Co medium. In the composites obtained from milled powders, the mechanical properties were found to be similar to others, however TiB2 particles were finer, in 2-4 micrometer range. In SEM and EDS analyses, composites were seen to contain some WC particles, due to the milling medium. The properties of the composites having Fe, Fe+Ni ve Fe+Ni+Co matrices were inferior to those of Ni matrix composites.