MICROSTRUCTURE, THERMO-PHYSICAL, MECHANICAL AND WEAR PROPERTIES OF IN-SITU FORMED BORON CARBIDE - ZIRCONIUM DIBORIDE COMPOSITE

Microstructure, thermos-physical, mechanical and wear properties of in-situ formed B₄C-ZrB₂ composite were investigated. Coefficient of thermal expansion, thermal diffusivity and electrical resistivity of the composite were measured at different temperatures up to 1000°C in inert atmosphere. Flexural strength was measured up to 900°C in air. Friction and wear properties have been studied at different loads under reciprocative sliding, using a counter body (ball) of cemented tungsten carbide (WC-Co) at ambient conditions. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) confirmed the formation of ZrB₂ as the reaction product in the composite. Electrical resistivity was measured as 3.02 × 10^-4 Ω·m at 1000°C. Thermal conductivity measured at temperatures between 25°C and 1000°C was in the range of 8 to 10 W·(m-K)^-1. Flexural strength of the composite decreased with increase in temperature and reached a value of 92 MPa at 900°C. The average value of coefficient of friction (COF) was measured as 0.15 at 20 N load and 10 Hz frequency. Increase of load from 5 N to 20 N resulted in decrease in COF from 0.24 to 0.15 at 10 Hz frequency. Specific wear rate data observed was of the order of 10^-5 mm³·(N-m)^-1. Both abrasive and tribo-chemical reaction wear mechanisms were observed on the worn surface of flat and counter body materials. At higher loads (≥ 10 N) a tribo-chemical reaction wear mechanism was dominant.