Microstructure and Mechanical Properties of Nb-Al-N and Nb-Si-B Powder Compacts Produced by Spark Plasma Sintering

Abstract

ABSTRACTNb-Al-N and Nb-Si-B powder compacts were prepared by spark plasma sintering, and their microstructure, mechanical properties and oxidation behavior were investigated. Adding nitrogen was easily done by blending or mechanically alloying Nb and AIN powders and then sintering them. The addition of nitrogen caused the formation of Nb2N in all the Nb-Al-N compacts and Nb2N and Nb3Al2N in compacts with high aluminum and nitrogen contents. The highest room-temperature hardness and the highest yield stress at 1473K were observed for compacts consisting of Nb2N and Nb3Al2N and those consisting of Nb2N and Nb2Al, respectively. Nb-Si-B compacts were prepared from elemental powders. Two or three of NbB2, Nb5Si3, Nb5Si3B2 and NbSi2 phases were identified as constituent phases of Nb-Si-B compacts depending on composition unless a large amount of silicon is consumed by forming SiO2. Contributions of NbB2, NbSi3 and Nb5Si3B2 phases to room-temperaturehardness and yield stress at 1973K were much larger than those of NbSi2. However, the oxidation resistance of Nb-Si-B compacts increased with increasing the volume fraction of NbSi2.The oxidation resistance of NbSi3B2 was better than that of NbSi3, but was not as good as that of NbSi2.