No abstract

The wear resistance of high-value copper components used in the metal casting, automotive, aerospace and electrical equipment industries can be improved by applying nickel (Ni)-based coatings through laser cladding. A high-power diode laser array providing continuous power levels up to 10 kilowatts with beam-shaping optics providing a rectangular focal region of various dimensions was used to deposit Ni-based alloy coatings with controlled thickness ranging from 0.3 mm to 1.6 mm in a single pass on copper (Cu) substrates. Slotted powder feeding plates with various discrete widths delivered uniform streams of powdered metal particles entrained in a carrier gas, matching the selected focal spot dimensions. To enhance laser beam coupling with the substrate and to avoid defects such as cracks, delamination and porosity, Cu substrates were preheated to a temperature of 300°C. The effect of heat input on microstructure of the cladding and extent of the heat-affected zone (HAZ) was evaluated using optical microscopy and scanning electron microscopy. Excessive heat input with longer interaction time increased dilution, porosity and expanded HAZ that significantly reduced the hardness of both the clad and the Cu substrates. Average microhardness of the Ni-C-B-Si-W alloy coating was 572 HV, which was almost 7 times greater than the hardness of the Cu substrate (84 HV). IntroductionCopper (Cu) and its alloys are widely used in metal casting, marine, automotive and electrical equipment industries due to a combination of very high conductivity (both thermal and electrical) and good corrosion resistance. However, these materials are not good candidates for applications involving casting and rolling that demand both high wear resistance and good thermal conductivity, because of their low hardness and poor tribological properties. In order to enhance the wear resistance of Cu-based material in such applications, it is common practice to coat nickel (Ni)-based high performance materials using various techniques such as chemical plating, electro-plating, plasma transferred arc (PTA), thermal spray and laser cladding (LC). Among these techniques, both PTA and LC are capable of producing a metallurgical bond between the substrate and coating. It is reported [1] that PTA can produce thicker metal deposits with lower production costs than LC. However, the development of cost-effective, high-power direct diode laser-based cladding capable of producing deposition rates up to 30 lb/hr now makes LC competitive with PTA. Furthermore, LC with a high-power direct diode laser offers controlled heat input with increased throughput (via large-area cladding) and good wall-plug efficiency resulting in overall cost reduction when fabricating high-performance coatings.Cu-based alloys are generally excellent reflectors and poor absorbers of visible and near-infrared light, which is typically not favorable for laser processing. The variation of the room-temperature optical absorption with wavelength for Cu and Ni is shown in Figure 1. A sharp drop in...