Synthesis and characterization of metal carbides for nanoindentation tip applications

Instrumented indentation experiments at elevated temperatures require careful attention to a myriad of experimental details. Not the least of these is the choice of the indenter tip material. Traditional room-temperature indenters, e.g., diamond and sapphire, can break down, react, and wear excessively at elevated temperatures. In this work, rf-induction heating float-zone and high-temperature solution single-crystal growth techniques have been used to prepare a suite of bulk refractory carbide specimens (i.e., ZrC, VC0.86, NbC, TiC0.95, WC). These potential indenter tip materials were subsequently characterized using nanoindentation testing techniques to determine their single-crystal elastic modulus, hardness, and fracture toughness in order to evaluate their potential for use as elevated-temperature nanoindentation tips. Additionally, subject carbide crystal characteristics were compared to those of single-crystal sapphire and polycrystalline WC-Co. The cumulative results show that single-crystal WC is a promising candidate for indenter tip material based on a combination of its high elastic modulus, hardness, and resistance to cracking—in addition to being crystallographically favorable for fabrication in the frequently used three-sided pyramidal indenter tip geometries.