EFFECTS OF BORON AND HEAT-TREATMENT ON STRUCTURE OF DUAL-PHASE TI-TIC

An in situ method was developed to fabricate a two-phase mixture of titanium carbide in a titanium matrix by solidification from a titanium-carbon melt. The solidified morphology consisted of three-dimensional TiC dendrites in a titanium matrix. The secondary dendrite arm spacing was found to be influenced by the presence of boron. The structure and microhardness of the components as a function of boron content and heat-treatment procedure were determined. Heat treatment plays a major role in the structure while the effect of boron is minimal. Results from X-ray diffraction analysis indicate that the solidified carbide is very rich in vacancies in the carbon sublattice. Annealing leads to a redistribution of the titanium atoms to occupy some of the vacant carbon sites. This thermal redistribution effect results in a dramatic decrease in the hardness of the carbides. The lattice parameter measurement supports the above structure evolution.