M. Tech. Metallurgical Engineering / Martensitic stainless steel (MSS) metal matrix composite coatings that can
accommodate most applications were developed using TiC and stellite 6 as
reinforcement powders and Nd: YAG solid state laser for surface alloying. The
alloyed surfaces were characterized by means of optical microscopy (OM),
scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). The
microstructures of the alloyed zones show even distribution and super saturation
of titanium carbide and other complex carbides of chromium (Cr23C6), niobium
(Nb6C5), and iron (Fe7C3) in the matrix of the MSS
A significant increase in the hardness was achieved by the addition of stellite 6,
although with cracks in the alloyed layer. The cracks formation was due to high
heat build-up during the laser alloying process. As a result of the addition of TiC
powder in the form of premixed ratio, the heat build-up in the work-piece was
minimized. This is due to the high absorptance of laser irradiation by the TiC
powder. The alloyed zone of the premixed ratio was free from cracks with
microhardness increase of more than 150% of that of the substrate. Multiple tracks
of 50% and 75% overlap were fabricated. Three-body abrasive wear study of the
overlapped coatings revealed the wear mechanism of the laser coatings to be
adhesion, mild abrasive and less degree of deformation showing less plastic
ploughing and cutting compared to the as-received. The wear mechanism of the
as-received is adhesion, severe abrasive and plastic deformation, showing distinct
grooves and damaged spots in the form of craters. The wear resistance of the
MMC obtained by alloying with the TiC powder was significantly improved with the
75% overlap, about 90% better than the native material.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:tut/oai:encore.tut.ac.za:d1000185 |
| Date | January 2012 |
| Creators | Adebiyi, Damilola Isaac. |
| Contributors | Fedotova, T,, Popoola, Abimbola Patricia Idowu. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format |
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