Experimental approach to probe into mechanisms of high‐temperature erosion of NbB2‐ZrO2

In the backdrop of potential applications of boride‐based materials in high‐speed supersonic aircrafts, the present investigation probes in comprehending the mechanisms of high‐temperature erosive wear of spark plasma sintered NbB2‐ZrO2 composite. The solid particle erosion experiments were performed at different temperatures starting from room temperature (25°C) to 800°C using Al2O3 particles (50 μm). The air‐erodent particle mixture was impinged toward the target surface at normal impact with a velocity of 50 m/s. The detailed microstructural analysis using HRTEM reveals the generation and accumulation of a large number of dislocations within NbB2 and ZrO2 grains of the eroded surfaces. Such observations indicate the activation of dislocation plasticity during erosion at 800°C. XRD‐based analyses provided residual stress‐based interpretation for the enhancement of erosion resistance at high temperatures. In contrast, substantial material loss via brittle failure, involving the generation and intersection of the lateral/radial cracks, was recorded after room temperature erosion. In case of erosion at 400°C and 800°C, the residual stress relaxes as a consequence of high‐temperature exposure prior to erosion. The accumulation of dislocations near the crater region and shot peening phenomena play a dominant role in decreasing erosion rate with increasing erosion test temperature. Spark plasma sintered NbB2‐ZrO2 pellet (diameter of ~15.5 mm and thickness of ~4 mm), eroded at three different temperatures, such as 25°C, 400°C and 800°C using 50 μm Al2O3 particles. The air‐Al2O3 particle mixture was impinged on the specimen surface at a normal impact with a velocity of 50 m/s and standoff distance of 10 mm. The detailed microstructural analysis using SEM, TEM and HRTEM reveals the generation and accumulation of a large number of dislocations within NbB2 and ZrO2 grains of exposed surface after erosion while, along the grain boundary regions prior to erosion. Such observations indicate the activation of dislocation plasticity during high‐temperature erosion, which help in reducing the material loss at 800°C as compared to low temperature erosion.