Reactive hot-pressing studies of high density oxide-carbide composite ceramics

Abstract

A number of brittle-brittle composites have been synthesized by reactive hot pressing. By using one inert phase and a phase formed in situ from metal hydride and a solid nonmetal, it was possible to produce microcomposites in which the reacting phase formed a continuous matrix, and isolated the grains of the inert phase. Densification rates for the reactively hot-pressed materials were appreciably higher than for the conventionally hot-pressed materials with the same nominal composition. Composites formed by Al 2O 3TiC, Al 2O 3TiB 2 and B 4CTiB 2 exhibited high Rockwell A hardness. Reactively hot-pressed Al 2O 3TiC composite was tested on inconel 718 and exhibited performance better or equivalent to the commercially available Al 2O 3TiC tool. B 4CTiB 2 tested on titanium 6–4 alloy exhibited higher uniform flank wear at short cutting times than a commercial WC 6% Co cutting tool (Carboloy grade 883). However, it continued cutting to the end of the 3-min test, while the carbide tool was limited to 2 min of cutting due to gross deformation. The volume of the tool material worn showed linear dependence on cutting times at all cutting speeds higher than 200 surface feet per minute (sfm). At those speeds, the dominant wear mechanism appeared to be chemical interaction with the workpiece, while at 200 sfm, microfracturing became more prominent.