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

摘要

Microstructure, thermos-physical, mechanical and wear properties of in-situ formed B4C-ZrB2 composite were investigated. Coefficient of thermal expansion, thermal diffirsivity and electrical resistivity of the composite were measured at different temperatures up to 1000 degrees C in inert atmosphere. Flexural strength was measured up to 900 degrees 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 ZrBz as the reaction product in the composite. Electrical resistivity was measured as 3.02 x 10(-4) Omega.m at 1000 degrees C. Thermal conductivity measured at temperatures between 25 degrees C and 1000 degrees 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 degrees 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) mm(3).(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.