EROSION BEHAVIOR OF THERMALLY TREATED PYROPHYLLITE COATED WITH TITANIUM CARBIDE

The rock mineral pyrophyllite (Al2O3.4SiO(2).H2O) is an easily machined material. After heat treatment at 1200 degrees C, the pyrophyllite was changed to a mullite based ceramic. Chemical vapor deposition (CVD) was used to apply titanium carbide coating to the thermally treated pyrophyllite substrate. The erosion behavior of the uncoated and coated ceramic was investigated experimentally by exposing it to a silica solid particle-laden flow at velocities from 150 to 250 m s(-1) and temperatures from ambient to 650 degrees C in a specially designed erosion wind tunnel. The results show the effects of velocity, temperature and impact angle on the erosion rate. The cumulative effects of the impacting particle mass on sample weight loss and erosion rate were also investigated. The results reveal that the erosion rate is proportional to the particle velocity to the power n, where for coated samples the exponent n is 4.94 and for the uncoated substrate 1.83. The erosion rate of the coated substrate with titanium carbide specimens decreases significantly with increasing temperature from ambient to 450 degrees C, while this effect is weaker for the uncoated substrate. Both coated and uncoated ceramic materials exhibit maximum erosion rate at a 90 degrees impingement angle which indicates their brittle nature. In addition, the eroded surface was then examined by scanning electron microscopy. This study demonstrates that the tested CVD titanium carbide coating provides excellent protection for the thermally treated pyrophyllite in the particulate flow environment when exposed to high temperature. Pyrophyllite is widely used as an anvil supporting material and as the pressure transmitting medium for applications at very high pressures and temperatures.