Influence of calculated purity of boron powder on TiB₂-Cu composites

TiB₂-Cu composites were fabricated by self-propagating high-temperature synthesis (SHS). The effects of four kinds of calculated purities of boron powder: 90%, 92%, 95% and 100%, on the relative density, phase composition, microstructure, bending strength and fracture toughness of TiB₂-Cu composites were studied. The results show that the combination property of TiB₂-Cu composites is the best when the calculated purity of boron powder is 92%, it is not the actual purity of boron powder, which is 90%. Based on the principle that the boron powder and its oxygen impurity reacted to form volatile B₂O₃, two reasons from analysis can be obtained: the lower the calculation purity of boron powder is, the higher the actual contents of boron and its impurity are. Higher impurity content can bring higher porosity. On the other hand, a little titanium dissolves into copper matrix at high temperature with the result that titanium is consumed and boron is residual. It is considered that the calculation purity of boron powder should exceed its actual purity. Considering the combination effects of two reasons, the calculated purity of boron, 92%, is the best one.