Boron nitride nanotube reinforced titanium metal matrix composites with excellent high-temperature performance

Boron nitride nanotube (BNNT) reinforced titanium (Ti) matrix composites were prepared using the cold press-and-sinter method. In the composite sintered at 800 °C for 1 h, BNNTs were homogeneously distributed in the Ti matrix and restricted the growth of Ti grains. The compressive strength of the as-sintered Ti-4 vol% BNNT composite achieved 985 MPa at room temperature versus 678 MPa without the BNNT reinforcements. The highest compressive strength of 277 MPa at 500 °C was obtained from the Ti-5 vol% BNNT composite. When sintered at 1000 °C, chemical reactions occurred between Ti and BNNTs leading to the formation of the interfacial TiB phase, which serves as a strong binding between BNNTs and the Ti matrix. The reinforcements were attributed by a mixture of BNNTs and TiB after sintering at 1000 °C for 3 h. However, no BNNT was observed in the microstructure after sintering at 1100 °C for 3 h due to complete transformation into TiB whiskers.