A spectroscopic study of Fe phases in cemented carbides

Mosse, Ibwanga Sav
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Tungsten carbide (WC) is characterized by its high strength, toughness, hardness, its high resistance to wear and can also be employed at high temperatures. It is used mainly in the form of cemented tungsten carbides which are produced by combining grains of tungsten carbide into a binder matrix element, for example cobalt (Co). Tungsten carbide is commonly used in industrial machinery as cutting tools and abrasives. The primary aim of this project is to investigate the effects of iron (Fe) as an alternative/additional binder in a tungsten carbide system. Therefore, two samples WC-10wt%Co-6wt%TiC and WC-10wt%Co-6wt%TiC-20wt%Fe alloys were prepared by milling and followed by sintering. Several studies have been undertaken in this project to ascertain the effect of Fe on the structural, electronic, magnetic and physical properties of the as-milled and as-sintered samples. A number of different experimental methods were applied to give such information. Transmission Mössbauer spectroscopy and conversion electron Mössbauer spectroscopy were employed as the main techniques to determine the charge states of Fe, Fe phases and other complex phases in the WC-10wt%Co-6wt%TiC-20wt%Fe alloy from the hyperfine interaction parameters. In addition, applied Vickers hardness test, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and strain analysis were utilized as complementary characterization techniques. The Vickers hardness value of 1358±70 HV was measured for the WC-Co-TiC sample whilst a lower value of 820±41 HV was found for the WC-Co-TiC-Fe sample. The microstructure analysis (SEM/EDS) confirmed the presence of WC in the matrix, and Co, Ti, and Fe as the binder elements. XRD results show the formation of the FeCo alloy in the as-milled powder and as-sintered samples. The strain analysis was performed on the as-milled powder, and the as-sintered samples by adopting the method used in accordance with the Topas description, defined in the Topas manual. The WC-Co-TiC sample showed that the tungsten carbide phase appears to have little strain whilst the titanium carbide phase appeared to have no strain. In the WC-Co-TiC-Fe sample, all phases show no strain. The Mössbauer spectrum at room temperature acquired from transmission Mössbauer spectroscopy was fitted with one sextet S1 attributed to -Fe. Best fits to the data obtained from conversion electron Mössbauer spectroscopy required four spectral components: two sextets S1 and S2 assigned to FeCo, one doublet D1 assigned to FeWC and one single SL1 assigned to FeTi alloy.
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the academic requirements for the Degree of Master of Science. March 2016.
Mosse, Ibwanga Sav (2016) A spectroscopic study of Fe phases in cemented carbides, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/21670>