Characterization of Ti4AlN3

Bulk samples of Ti(4)AIN(3) were fabricated by reactive hot isostatic press ing (hipping) of TiH2, AIN, and TiN powders at 1275 degrees C for 24 hours under 70 MPa. Further annealing at 1325 degrees C for 168 hours under Ar re sulted in dense, predominantly single-phase samples, with <1 vol pct of TiN as a secondary phase. This ternary nitride, with a grain size of approxima te to 20 mu m on average, is relatively soft (Vickers hardness 2.5 GPa), li ghtweight (4.6 g/cm(3)), and machinable. Its Young's and shear moduli are 3 10 and 127 GPa, respectively. The compressive and flexural strengths at roo m temperature are 475 and 350 MPa, respectively. At 1000 degrees C, the def ormation is plastic, with a maximum compressive stress of approximate to 45 0 MPa. Ti4AlN3 thermal shocks gradually, whereby the largest strength loss (50 pct) is seen at a Delta T of 1000 degrees C. Further increases in quenc h 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 approximate to 0.4 mm defect, reduce s the flexural strength by only approximate to 12 pct. The thermal-expansio n coefficient in the 25 degrees C to 1100 degrees C temperature range is 9. 7+/-0.2 x 10(-6) degrees C-1. The room-temperature electrical conductivity is 0.5 x 10(6) (Omega . m)(-1). The resistivity increases linearly with inc reasing temperature. Ti4AlN3 is stable up to 1500 degrees C in Ar, but deco mposes in air to form TiN at approximate to 1400 degrees C.