Influence of boron nitride reinforcement to improve high temperature oxidation resistance of titanium.

Influence of boron nitride (BN) addition in commercially pure titanium (Cp-Ti) was characterized for their microstructural variation, hardness and oxidation kinetics. Feedstock powders Cp-Ti with 3 wt.% BN (3BN) and 6 wt.% BN (6BN) were prepared by roller mill followed by additive manufacturing using laser engineered net shaping (LENS™). Rate of oxidation was measured from thermogravimetric analysis (TGA) at 1000°C for 50 h. Average instantaneous parabolic constants (k p ) for Cp-Ti, 3BN and 6BN were 41.2±12.0, 28.6±2.8 and 18.2±9.2 mg2·cm-4·h-1, respectively. Cp-Ti displayed acicular α-Ti microstructure. After TGA, large equiaxed grains along with TiO2 formation at the grain boundaries was observed, which increased the hardness. With BN addition, plate-like TiN and needle-like TiB secondary phases were also observed. Hardness for Cp-Ti, 3BN and 6BN were 256.9, 424.0 and 548.3 HV0.2, respectively. Overall, a small addition of BN was effective in improving the oxidation resistance of Cp-Ti.