Investigation of tribological properties of berrylium-copper alloy used in plastic injection molding

Beryllium-Copper (Be-Cu) 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 protection coatings to improve their wear resistance. However, if these coatings are carried out under specific deposition temperature ranges, it can cause over-aging of these alloys. In this case, it causes a significant loss in the mechanical properties of the Be-Cu alloy used as the substrate material, making it impossible to manufacture some industrial applications such as core pins with high accuracy, and cores and cavities injection mold with narrow closure regions. This work proposes a solution to increase corrosion and wear resistance of Be-Cu alloy through an electroless Nickel-Phosphorus (Ni-P), Nickel-Boron (Ni-B) and Nickel-Phosphorus/Nickel-Bor (Ni-P/ Ni-B) coating. Hardness of coating and substrate was evaluated by measuring the cross-sectional hardness profile. Microstructure and crystallinity of coating and substrate were characterized using optical metal microscopy (OM) and X-ray diffraction (XRD), respectively. Corrosion and wear behavior of coating-substrate systems were evaluated by reciprocating wear tests, electrolytic corrosion tests, surface profilometry and OM. While the Ni-P coating presented a flat surface with a thickness of 12 µm, the Ni-B and Ni-P/Ni-B duplex coatings had a rough and wavy surface appearance with an average thickness of 7-8 µm and 12-13 µm, respectively. By XRD analysis, it was determined that the electroless coatings are composed of a mixture of amorphous and crystalline phases and the electroless duplex coating exhibits a more amorphous structure compared to the single coatings. While the Be-Cu alloy used as the substrate material maintained its hardness, the hardness of the electroless Ni-P coating increased 2.2 times, and the Ni-B and Ni-P/Ni-B duplex coating increased 3.7 times. The application of Ni-B and Ni-P/Ni-B duplex coating increased the wear resistance compared to Ni-P coating under high load (7.5 and 10 N). It has been observed that the corrosion resistance of electroless Ni-P and Ni-B coatings can provide sufficient protection compared to the Be-Cu alloy used as the substrate material.