Ultrahigh Aspect Ratio TiB Nanowhisker-Reinforced Titanium Matrix Composites as Lightweight and Low-Cost Replacements for Superalloys

Abstract

With the increase in demand for high speed and efficient transport, there is a growing call for lightweight materials with high specific properties. Titanium matrix composites (TMCs) are one material of growing interest, whose properties make them a competitive replacement for many superalloys used in the aerospace industry. However, high cost, poor ductility, and the lack of a reliable manufacturing process have limited their application. In this study, we demonstrate the fabrication of high-performance titanium matrix composites reinforced with a network of high aspect ratio TiB nanowhiskers to overcome these challenges. A unique combination of fine BN nanopowder and a low-cost sintering method was employed. Ultralong, 40–50 μm TiB nanowhiskers with an aspect ratio of 500 have been produced from the in situ reaction between Ti and BN during slow heating/cooling, with temperatures at and below 1100 °C. As-sintered composites reached a hardness of 8.52 GPa, a reduced Young’s modulus of 152 GPa, and a yield strength of 1236.5 MPa, a 250% increase when compared to pure titanium as measured by nanoindentation. The improved mechanical properties were attributed to the ultrahigh aspect ratio of TiB, the low titanium grain size, and the near continuous network of TiB reinforcement. Slow heating/cooling allows for control of TiB formation to achieve the maximum aspect ratio as well as complete conversion of BN to TiB. In addition, the TiB network in the grain boundary acted to restrict Ti grain growth during manufacturing and improve the overall TMC properties. The proposed manufacturing method has great potential for the low-cost production of high performance TMCs.