Enhancing the fracture toughness and hardness of sapphire by high-temperature rolling

Although the hardness of sapphire is very high, in some applications, for example, working as panels in mobile phones and watches as well as optical windows in various military optical sensors, it still suffers from the destruction of being scratched and marked as well as mechanical failure by fracture. Here we reported that the technique of high-temperature rolling we developed recently could be exploited to sapphire to enhance its hardness and fracture toughness. After rolling at 1200 degrees C, Vickers' hardness and fracture toughness of sapphire increase by 4%-6% and 13%-27%, respectively. The enhancement of fracture toughness was explained by the residual compressive stress layer that was introduced in sapphire during rolling. The improvement of hardness was thought to be related to the hardening effect of dislocations. This work provides a new strategy for the mechanical property enhancement of sapphire in further applications. (A) Physical image of the rolling equipment (The red single and double arrows represent the motion form of the loading head and the sample stage, respectively.) and sapphire plate after high-temperature rolling at 1200 degrees C. The treated zone is circled by red dash line, and the untreated region is outside of the dash line; (B) Vickers' hardness and (C) fracture toughness of sapphire in the untreated and treated regions. image