High-Temperature Tribological Behavior of Fast-Hot-Pressed NiCr/Cr[sub.3]C[sub.2]-LaF[sub.3] Self-Lubrication Composite

This article details a method for preparing cermet matrix composites via Fast hot pressing (FHP) sintering technology and emphasizes their potential use in extremely high-temperature settings. The material primarily consists of NiCr alloy, Cr[sub.3]C[sub.2], and LaF[sub.3]. An in-depth investigation was conducted on the tribological properties of the specimen by conducting sliding tests against a Si[sub.3]N[sub.4] ball at varying temperatures, including room temperature (RT), 400 °C, 600 °C, and 800 °C. Advanced techniques such as scanning electron microscopy, micro-XRD, and micro-Raman spectroscopy were employed to examine the friction surfaces formed under different frictional temperatures. The findings reveal a uniform composition and high density within the composites. It is noteworthy that as the LaF[sub.3] content increases, the hardness of the ceramic phase diminishes. Conversely, the hardness of the alloy phase augments with the addition of LaF[sub.3], provided that its content remains below 15 wt%. The composite material containing 15 wt% LaF[sub.3] demonstrates superior hardness values, with the ceramic phase reaching HV1412 and the alloy phase achieving HV384. Furthermore, the coefficient of friction of the composite material was evaluated. The coefficient of friction of the composite is between 0.74 and 0.4 and the wear rate is 4.46 × 10[sup.−6]–5.72 × 10[sup.−5] mm[sup.3]N[sup.−1]m[sup.−1] from room temperature to 800 °C. The lubrication behavior at low temperature is mainly attributed to the lubricating effect of LaF[sub.3], and at high temperature it is due to the tribochemical reaction to form LaCrO[sub.3] with good lubricating properties, which plays a synergistic lubricating role with Cr[sub.2]O[sub.3].