CONDUCTIVE TIB2–ALN–BN-BASED COMPOSITE SHS CERAMICS

Abstract

The paper studies the microstructure, phase composition, and electrical conductivity of TiB2–AlN–BN-based composite ceramics obtained by self-propagating high-temperature synthesis (SHS). Electrical resistivity dependence on temperature was measured in the range Т = 300÷1300 K in a vacuum of 2·10–3 Pa using a standard 4-point DC technique. It is found that higher TiB2 content in the initial composition (from 60 to 80 wt.%) and lower Al content (from 20 to 40 wt.%) results in increased TiN and BN content in synthesis products, and decreased TiB2 and AlN content as a result of TiB2 reaction with nitrogen. Lower Al content in the initial mixture leads to lower AlN content in synthesis products. According to the results obtained, electrical resistivity curves are inconsistent during the «heating–cooling» cycle for all ceramic compositions due to changes in the contact zone of conducting phases in the temperature range Т = 800÷1200 К. Three specific temperature ranges were identified: (I) 300 to 800 K when ρ values increase monotonically with increasing temperature, while heating and cooling ρ(Т) curves coincide completely; (II) Т = 800÷1200 К when electrical resistivity behavior varies – its values strongly depend on the sample heat treatment mode; (III) Т > 1200 К, when coincidence of heating-cooling curves is observed.