Densification and microstructure of spark plasma sintered TiB۲ ceramics with AlN addition

In this research study, the effects of aluminum nitride (AlN) additive on the densification behavior and microstructure development of titanium diboride (TiB۲) based ceramic matrix composite were investigated. In this way, a monolithic TiB۲ ceramic and a TiB۲-۵ wt% AlN ultrahigh temperature ceramic composite were fabricated by spark plasma sintering (SPS) process at a temperature of ۱۹۰۰ œC for a dwell time of ۷ min under an externally applied pressure of ۴۰ MPa in vacuum conditions. The relative density measurements were carried out using the Archimedes principles for evaluation of bulk density and the rule of mixtures for calculation of theoretical density. Compared to the additive-free monolithic TiB۲ ceramic sample with a relative density of ~۹۶%, the addition of AlN as a sintering aid greatly improved the sinterability of TiB۲ matrix composite and a near fully dense sample with a relative density of ~۱۰۰% were obtained by spark plasma sintering process. The removal of harmful oxide impurities of titania (TiO۲) and boria (B۲O۳) from the surfaces of starting TiB۲ powder particles and the in-situ formation of new phases such as aluminum diboride (AlB۲) and Al۲Ti as an intermetallic compound of aluminum and titanium, not only improved the sinterability of the composite ceramic, but also significantly prevented the extreme growth of TiB۲ grains.

Keywords:

Titanium diboride , Aluminum nitride , Spark plasma sintering , Microstructure , Densification