The growth in the use and wear of Ti-based alloy components in mining and offshore explorations has led to a search for techniques to re-engineer such components for reuse. The most desirable method of restoring/protecting the component surfaces is by hard-facing to enhance longevity in service. Laser cladding is one of the viable techniques to achieve a thick coating on such components which involves the addition of reinforcing particulates to improve surface properties such as hardness, wear and erosion resistance amongst others. A fundamental study and understanding of the resultant microstructure-property of the laser clad, hard-facing composite becomes necessary. In this study, laser cladding of Ti-6Al-4V wire with Spherotene particulate reinforcement and laser cladding of modified pre-blend of Ti-6Al-4V and TiB_2 powder were undertaken. The resulting physical and microstructural characteristics, hardness, and performance characteristics of laser clad composites were investigated. Samples from the as-deposited laser clad composites were characterised using optical microscopy, scanning electron microscopy (with chemical microanalysis) and X-ray diffraction. Performance characteristics were examined via erosion testing of the laser clad Ti-6Al-4V/Spherotene using plain and abrasive water jetting, and tensile testing of the laser clad Ti-6Al-4V/TiB_2 composite. The results showed that a crack and pore free clad containing as high as 76 wt.% Spherotene in the Ti matrix was achieved at an energy density of 150 J.mm^-2, 275 mm/min traverse speed, 700 mm/min wire feed rate and 30 g/min powder feed rate. The microstructure of the laser clad Ti-6Al-4V/Spherotene is characterised by nano-sized precipitates of reaction products (W and TiC) uniformly distributed in a beta-Ti solid solution matrix. Matrix hardness is enhanced by the presence of the reaction products in the Ti ranging between 410-620 kgf.mm^-2. Moreover, the modication made to the 90 wt.% Ti-6Al-4V/10 wt.% TiB2 feedstock by attaching the TiB2 to Ti-6Al-4V allowed uniform distribution of reinforcing element in the deposited composite. The composite microstructure on solidication is characterised by TiB eutectic needle-like features uniformly distributed in a Ti-rich primary phase. The hardness of the composite ranged between 440-480 gf.mm^-2. Tensile tests showed that the mean elastic modulus of Ti-6Al-4V/TiB_2 composite is 145 GPa, which is a 27% improvement when compared to that of Ti-6Al-4V. Erosion test indicated that the Ti-6Al-4V/Spherotene composite offered as high as 13 and 8 times resistance of that of Ti-6Al-4V when subjected to PWJ and AWJ impacts respectively.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:632487 |
| Date | January 2014 |
| Creators | Farayibi, Peter Kayode |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/14268/ |
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