Microstructural characterization of laser cladding of Cu-30Ni

Cu-Ni alloys are known for their corrosion resistant properties and one of the important applications of these alloys is in marine components. Such components can be subject to wear resulting ultimately in failure. Refurbishment of such worn components, particularly in situ, would provide a cost-effective alternative to complete replacement. One such method proposed for refurbishment of large marine components is laser cladding. The successful application of this technique requires some research to establish the optimum processing parameters to be used for particular combinations of substrate and clad materials. We have been investigating the laser cladding of Cu-30Ni alloy plates with a diode laser in order to establish the microstructure of the clad material and the heat affected zone in the substrate as a function of the process parameters. This paper reports on various microstructural observations of these clads and discusses certain undesired features encountered. In the present study, a diode laser (Nuvonyx–ISL system with max. power 4 kW) was used as the heat source. The laser beam has a rectangular cross section which at the focal length is 12 mm × 0.5 mm. A diode laser was chosen since it has the highest output efficiency (ratio of output power to input power) compared to other laser sources such as CO2 or YAG laser. Commercially available Cu-30Ni alloy was used for both substrate and filler material. The substrate plates were 19 mm thick and wires of 0.89 mm diameter were used for the filler material. Chemical compositions for the cladding material and substrate are shown in Table I. The melting temperature range for the alloy from the phase diagram [4] is 1170–1240 ◦C. Cu-30Ni alloy exhibits complete solid solubility down to around 200 ◦C where the phase separation is kinetically constrained due to the low temperature and rapid heat extraction, consequently a single phase microstructure is expected in these laser cladding studies. The microstructure was evaluated with respect to different process parameters: laser power, laser translation speed, wire feed rate and beam angle (angle between the beam and travel direction over the substrate). The range of these parameters is given in Table II. The microstructures were characterized using optical microscopy, X-ray diffraction and EDS (Energy Dispersive Spectrometer) analysis. No clear relationship between so-