Room temperature mechanical properties and tribology of NICRALC and Stellite casting alloys

Abstract

Abstract NICRALC is a family of intermetallic compound-based casting alloys proposed as an economic alternative for abrasion and erosion-resistant cobalt alloys, mainly under more elevated temperature conditions. NICRALC microstructures contain hard chromium carbides dispersed in a continuous Ni–Al–Cr γ′ (L12) ordered intermetallic matrix. In this work, cast NICRALC alloys with different carbon contents, different carbide types and morphological features were compared with one spray-formed NICRALC alloy and one Co-based alloy similar to commercial Stellite 6 ® alloy, with regard to their mechanical and wear behaviour at room temperature. Mechanical properties were evaluated in terms of uniaxial testing in compression, hardness and fracture toughness; wear properties were evaluated in dry-sand–rubber-wheel tests at room temperature and in block-on-ring lubricated sliding tests at 100 °C temperature. The alloys were characterized by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and instrumented micro hardness (commonly called nanoindentation). The worn surfaces and fracture path were analyzed by SEM. Results indicated that the mechanical properties, such as yield stress, fracture toughness and hardness, of NICRALC alloys were dependent upon the carbon content. However, their wear behaviour could not be directly related to hardness and yield stress, but varied depending on the type and distribution of carbides. Among the compositions tested eutectic and near eutectic NICRALC alloys demonstrated wear resistance under abrasion and sliding wear similar to those obtained with Stellite alloy. The alloys with lower fracture toughness showed the higher volume loss as under sliding as under abrasion wear tests in despite its higher hardness and higher yield strength.