Preparation of Mullite-TiC-TiN Materials by a Plasma Spark Method and Their Properties

The phase composition of synthesized TiC and TiN, microstructure, relative density, open porosity, linear shrinkage, elasticity modulus, Vickers hardness, ultimate strength in compression, and linear dependence of elasticity modulus and ultimate strength in compression of mullite-TiC-TiN-specimens with a different ratio of TiC and TiN sintered by a plasma-arc method in the range 1200 - 1600A degrees C with a compaction load of 30 MPa, are studied. Synthesized powders have intense crystallization of TiC and TiN. Sintered specimens with a different ratio of TiC and TiN demonstrate intense mullitization in the range 1200 - 1600A degrees C. Specimens with a TiC/TiN ratio of 50/50, 70/30, and 90/10 mol.% demonstrate a gradual increase in TiC from 1200 - 1400A degrees C compared with a more intense increase in TiC from 1400 to 1600A degrees C. An increase in TiC concentration and a reduction in TiN content in powder mixtures sintered at 1500A degrees C facilitates formation of a uniform density sintered microstructure with presence of small pores. Specimens in the ratios TiC/TiN of 50/50 and 70/30 mol.% point to a more intense increase in relative density and linear shrinkage; a reduction in open porosity and an increase in elasticity modulus, Vickers hardness, and ultimate strength in compression. This leads to an increase in specimen crack formation resistance in the presence of microcracks with a relatively rectilinear propagation trajectory (composition M50TiC50TiN), and absence of microcracks (composition M70TiC30TiN) around an indenter impression, with the greatest linear dependence of elasticity modulus and ultimate strength in compression in the range 1200 - 1600A degrees C.