Micro-abrasive wear resistance of heat-treated electroless nickel‑phosphorus coatings deposited on copper‑beryllium alloy C17200

Abstract

Copper‑beryllium alloys are widely used to manufacture thermoplastics injection molds due to their high thermal conductivity. Even though these alloys admit precipitation hardening at temperatures between 250 and 400 °C, they still call for surface coatings to enhance their abrasion resistance. However, application of these coatings can generate over-aging under specific deposition temperature ranges. This phenomenon causes a loss of substrate mechanical properties, making some industrial applications unfeasible, for example: construction of core pins with high slenderness ratio, and cores and cavities injection mold with narrow closure regions. This work proposes a solution to increase abrasive wear resistance of copper‑beryllium alloy C17200 through an electroless nickel‑phosphorus (NiP) coating. Temperature used in heat treatment of the coating was lower than substrate aging temperature. In this work, the heat treatment was carried out at 200 °C for 24 h. Hardness of coating and substrate was evaluated by measuring the cross-sectional microhardness profile after heat treatment. Microstructure, chemical composition, and crystallinity of coating and substrate were characterized using scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GD-OES), and X-ray diffraction (XRD), respectively. Wear behavior of coating-substrate systems was evaluated by micro-abrasive wear tests optical profilometry and SEM. NiP coating combined with heat treatment increased the surface hardness from 340 HV for uncoated alloy to an average of 997 HV for coated and heat treated alloy while maintaining substrate hardness. The application of this coating reduced the wear coefficient in the order of 3.03 × 10−6 to 2.04 × 10−6 (mm3 N−1 m−1). All the conditions analyzed, showed a mixed micro-abrasive wear mechanism with rolling and grooving wear characteristics.