Laser surface treatment of materials with presence of carbides at the surface.
Jabbar, Abdul Aleeem B (2012) Laser surface treatment of materials with presence of carbides at the surface. PhD thesis, Dublin City University.
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Some of the studies associated with laser assisted processing including machining, surface treatment applications, and electrochemical response of the selective surfaces were carried out prior to the thesis work by the thesis author. In the light of the previous studies, additional study on laser controlled melting of surfaces is carried out for pre-prepared Haynes 188 and Inconel 718 alloys, and high speed steel workpieces. Metallurgical and morphological changes in the laser treated layer are examined using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and X-ray Diffraction. A carbon film of about 50 thickness and containing 5% TiC particles is formed at the workpiece surface prior to the laser treatment process. The carbon film formed at the surface enhances the absorption of laser irradiation and accommodates uniformly distributed TiC particles. The residual stress formed at the surface of the laser treated workpiece is obtained using X-ray Diffraction technique while indentation tests are carried out to measure microhardness and fracture toughness of the resulting surfaces. It is found that laser treated surfaces of Hayness 188 and Inconel 718 alloys, and high speed steel are free from microcracks and surface asperities. The formation of carbnotride and nitride phases at the surface vicinity of laser treated layer contribute to increased hardness and dense layer formation at the surface. The residual stress formed at the surface of Hayness 188 alloy is on the order of 590 ± 15 MPa, 460± 15 MPa for high speed steel, and 48014 MPa for Inconel 718 alloy. For high speed steels, ε-Fe3N, and ε-Fe3 (N,C) compounds are formed at the laser treated surface which are attributed to the presence of carbon film and high pressure nitrogen assisting gas during the laser processing. The fracture toughness of laser treated surface reduces considerably because of increased hardness and dense layer formed at vicinity of laser treated surface. Partially dissolution of carbide particles takes place at the surface of the Inconel 718 alloy. The formation of fine grains, nitride compounds formed as well as dissolution of Laves phase at the surface region enhance hardness at the surfaces of laser treated Inconel 718 alloy workpiece.
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