10. Wear Characteristics of LASER Cladded Surface Coating

Laser cladding by a powder injection technique has been widely used in industrial applications such as rapid manufacturing, parts repair, surface coating, and innovative alloy development. The capability to mix two or more types of powders and to control the feed rate of each powder flow makes laser cladding a flexible process for fabricating heterogeneous components or functionally graded materials. This technology also allows the material gradient to be designed at a microstructure level because of small localized fusion and strong mixing motion in the melt pool of laser cladding. Thus materials can be tailored for a flexible functional performance in particular applications. The inherently rapid heating and cooling rates associated with the laser-cladding process enable extended solid solubility in the metastable or non-equilibrium phases of production, offering the possibility of creating new materials with advanced properties. Laser cladding uses the same concept as arc welding methods, except that a laser is used to melt the surface of the substrate and the additional material, which can be in the form of wire, powder or strip. Laser cladding is commonly performed with CO₂, Nd: YAG, and more recently fibre lasers. Laser cladding typically produces clads having low dilution, low porosity and good surface uniformity. This technique produces minimal heat input on the part, which largely eliminates distortion and the need for post-processing, and avoids the loss of alloying elements or hardening of the base material. The clad material experiences a rapid natural quench when cooling down after deposition, which results in a fine-grained microstructure. Among the different surface treatments used to improve the wear resistance of metallic materials, laser cladding is an attractive alternative to conventional techniques due to the intrinsic properties of laser radiation: high input energy, low distortion, avoidance of undesirable phase transformations and minimum dilution between the substrate and the coating. Furthermore, the advantages of laser cladding include great processing flexibility and the possibility of selectively cladding small areas. These advantages not only result in better quality products but also offer significant economic benefits. This chapter describes in details three major aspects of LASER cladding surface coating with respect to wear characteristics. The first subsection will describe different LASER cladding techniques and their effect on surface morphology. And how these surface morphologies are affecting the wear characteristics. The second subsection will provide the details on different aspects of filler metal selection for wear resistance applications. Then, the effect of process parameters on the surface morphology will be discussed thoroughly. The focus will be particularly on the effect of heat input on the wear behaviour of the cladded surface. The overall aim is to cover a broad area of LASER cladding surface coating in terms of wear characteristics and the improvement in wear resistance compared to other techniques.