Boron Nitride Nanotube-Reinforced Titanium Composite with Controlled Interfacial Reactions by Spark Plasma Sintering

Herein, boron nitride nanotube (BNNT)-reinforced Ti alloy composites with 1 wt% BNNT (3 vol%) are successfully fabricated by spark plasma sintering (SPS). This study addresses two challenges affecting the performance of BNNT-metal matrix composites: i) the dispersion of high-surface-energy BNNTs by an ultrasonic-assisted technique and ii) the control of reactions at the metal/nanotube interface. High-energy ultrasonic vibrations were effective in the dispersion of entangled BNNTs, and sintering at low (750 degrees C and 555 MPa) and high (950 degrees C and 60 MPa) temperature regimes resulted in relative densities of 97% and 99%. Reducing sintering temperatures by up to 35% compared to those used in conventional sintering is effective in minimizing brittle interfacial products. Also, the composites sintered at high-temperatures/low-pressure benefit from the rapid densification (10 min) achieved in the SPS process limiting the extent of reactions (TiB2, TiB). Compressive properties show composites sintered at low and high temperatures exhibit increases of 46% and 50% in yield strength, respectively, as compared to the Ti alloy. Strain hardening exponents of 0.8 and 0.5 characterize the capabilities of the composites to arrest plasticity in the presence of BNNTs, reaction phases, and twin boundaries pinning dislocations. This study unravels the potential of a low-temperature/high-pressure processing window for Ti-BNNT composites.