Browsing by Author "Van Coller, Marius Cornelius"
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- ItemThe effects of machine parameters on the integrity of WC-Ni coatings deposited onto titanium parts with laser additive manufacturing(Stellenbosch : Stellenbosch University, 2019-04) Van Coller, Marius Cornelius; Oosthuizen, Gert Adriaan; Sacks, Natasha; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.ENGLISH ABSTRACT: Part quality specifications are of the utmost importance within industries that include specialized applications, for instance the medical, aerospace, nautical and mining industries. Attributable to the high costs of specialized parts and the risks involved in operation, such as the loss of human lives and company integrity. Parts are expected to showcase consistent properties throughout their life cycle as catastrophic consequences may ensue if they do not align with industry specifications. The goal of today’s part manufacturers is to extend part lifecycles and mitigate unwanted occurrences like crack formation, deformation or creep in the material. To maintain the highest achievable production rate and most efficient use of resources, consistent material homogeneity of components within stark operating conditions is a crucial pursuit. Titanium and its alloys have become popular contributors within these industries due to their advantageous material properties, e.g. biocompatibility, corrosion resistance and high strength. This said, titanium has poor tribological properties, which restricts its range of applications in environments where friction and wear is prevalent. Titanium’s high temperature wear and oxidation resistance is poor and to solve these inefficiencies, surface treatments have been applied to titanium and its alloys. These modifications largely incorporate the use of hardened coatings, like carbide composites, and employ laser beam technologies for application because of its high energy density, coherence and good directionality. Little research exists on the application of laser additive manufacturing technologies for production of carbide coated parts. In the pursuit to improve the current supply chain capabilities for carbide strengthening and refurbishment, this study investigated the feasibility of depositing tungsten carbide onto titanium parts using laser melting technology. Nickel was employed for the binder material in the cermet as an alternative to cobalt, which is conventionally used for additive manufacturing of hardened carbides. The research study was aimed at designing an experiment to determine which machine parameters result in the optimal adhesion characteristics between titanium alloy Ti-6Al-4V and tungsten carbide in a 10% nickel binder (WC-Ni). The machine parameters evaluated were the laser power, scanning speed and hatch spacing. The experimentation consisted of both a single-track screening experiment and single layer depositions. From the screening, suitable hatch spacings and a process window for scanning speed and laser power was deduced. These results were incorporated into further experimentation that evaluated layered depositions by varying the three parameters under study. The parameter combinations were tailored to maintain a consistent volumetric energy density range between 28.85 J/mm3 and 88.33 J/mm3 to test the individual effects of input parameters at a constant energy input. The evaluated responses were: 1) the surface quality of coatings, 2) penetration and diffusion of the deposition into the substrate, and 3) the consistency of coating material at the substrate interface. Optimal quality coatings yielded between 20wt.% and 40wt.% tungsten carbide at layer surfaces, while maintaining a layer thickness between 30μm and 60μm; diffusion depths of up to 50μm were also achieved. Higher energy densities resulted in deeper penetration and good diffusion of the coating into the substrate but lacked sufficient presence of the coating material at the substrate surface. It was concluded that higher laser powers and high hatch spacings combined with intermediate scan speeds produced the most desirable coatings. This corresponded to depositions in the energy density range of 28 J/mm3 and 58 J/mm3. Furthermore, the validity of the volumetric energy density equation as a predictive metric in laser additive manufacturing was addressed, as significant differences in layer quality were achievable by varying parameter values at identical energy densities.