Laser cladding of nickel-based alloy coatings on copper substrates

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...

Microstructure and Properties of Ni–Co Composite Cladding Coating on Mould Copper Plate

“…The formation of pores is usually due to the overheating of the molten pool, gas entrapment, surface impurities, etc. [19]. These pores in the coating decrease the service life of a mould copper plate.…”

The potential use of laser cladded functionally graded materials to mitigate degradation in boiler tube heat exchangers for power plant applications: A review

“…Balu et al [72] cladded copper substrate with nickel-based alloy to improve its wear resistance properties. The substrate was preheated at 300 °C to prevent processing defects caused by poor laser beam coupling, which could also be related to avoiding thermal shock.…”

Formation of a joint between deposited and base metals during laser cladding of a nickel-based powder onto a copper-based alloy

“…Balu et al [7] have operated laser cladding with two kinds of Ni-based powder on Cu substrate with and without pre-heating. They observed that the grain size in the HAZ is high distanced from the interface.…”

“…Despite the limited HAZ, laser cladding often induces an area of local chemical dilution between the powder and the substrate. Authors explained that dilution is obtained at the interface when a fusion between the substrate and the coating occur [7][8][9]. This dilution, dependent on the input laser power [10], has to be restricted in order to avoid a large HAZ but seems necessary to ensure good metallurgical bonding.…”

“…Using the same definition of the dilution rate, Luo et al [15] present the same observation during laser cladding of NiCrBSi. Balu et al [7] used the metallurgical method to measure the dilution rate during laser cladding of Ni-based powder on a Cu substrate. They found that a high dilution can lead to a high HAZ.…”