Characterization of Ti4AIN3

Bulk samples of Ti4AIN3 were fabricated by reactive hot isostatic pressing (hipping) of TiH2, AlN, and TiN powders at 1275 °C for 24 hours under 70 MPa. Further annealing at 1325 °C for 168 hours under Ar resulted in dense, predominantly single-phase samples, with < 1 vol pct of TiN as a secondary phase. This ternary nitride, with a grain size of ≈20 μm on average, is relatively soft (Vickers hardness 2.5 GPa), lightweight (4.6 g/cm3), and machinable. Its Young's and shear moduli are 310 and 127 GPa, respectively. The compressive and flexural strengths at room temperature are 475 and 350 MPa, respectively. At 1000 °C, the deformation is plastic, with a maximum compressive stress of ≈450 MPa. Ti4AlN3 thermal shocks gradually, whereby the largest strength loss (50 pet) is seen at a AT of 1000 °C. Further increases in quench temperature, however, increase the retained strength before it ultimately decreases once again. This material is also damage tolerant; a 100 N-load diamond indentation, which produced an ≈0.4 mm defect, reduces the flexural strength by only ≈12 pet. The thermal-expansion coefficient in the 25 °C to 1100 °C temperature range is 9.7±0.2 × 10-6 °C-1 The room-temperature electrical conductivity is 0.5 × 106 (Ω · m)-1. The resistivity increases linearly with increasing temperature. Ti4AlN3 is stable up to 1500 °C in Ar, but decomposes in air to form TiN at ≈1400 °C.