Time Dependence of AlN Densification by Plasma Sintering

Abstract

Pure and 3wt%-Y₂O₃ doped AlN powder compacts were sintered in an r.f. inductively coupled plasma under reduced pressure. The effects of the r.f. output power and gas pressure on their densification were investigated. AlN powder compacts doped with 3wt%-Y₂O₃ showed rapid densification to the theoretical density, while pure AlN densified only to 68% of the theoretical density under the experimental conditions studied. Time dependence of the densification of 3wt%-Y₂O₃ doped AlN was found to be divided into three stages; (1) rapid densification region occurring during insertion to plasma, (2) plateau region of constant density, (3) re-densification region with evaporation of AlN. Direct measurements of the specimen temperature showed that the densification at the first stage proceeded during rapid heating up to 1800°C, and that the re-densification at the third stage occurred as a result of elevation of the specimen temperature from 1800°C to >2000°C.