3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Influence of ruthenium and molybdenum ion implantation on the machining performance of WC-Co straight grade inserts(2019) Mkhaliphi, Thuli GoodnessThe aim of this study was to determine the effect of Ru and Mo ion implantation on the tool life of WC-Co straight grade cutting tool inserts during face milling of AISI H13 tool steel. The cutting tool inserts were implanted at 6 different ion implantation dosages. The acceleration voltage was kept constant for 5 ion implantation dosages at 100 keV and it was then increased to 120 keV for one of the ion implantation dosages. The face milling tests were conducted under unlubricated conditions according to ISO standard 8688-1: 1989. In order to ensure intermittent conditions the radial depth of cut was set at 30% of the cutter diameter. A 5 insert cutter was fully loaded during machining. The non-implanted inserts were used as the baseline for the volume of material to cut. The induced cutting forces of the ion implanted inserts were higher than that of non-implanted inserts due to increased shear area as a result of cutting edge chipping. The estimated heat generated when using ion implanted inserts had a scattered relationship with respect to the non-implanted inserts; this was attributed to the several factors involved in heat generation during machining. Several overlapping failure mechanisms were observed between the non-implanted and ion implanted inserts. The flank wear scar of the ion implanted inserts was smaller than that of non-implanted inserts indicating abrasion resistance from increased micro-hardness resistance. Even though the surface roughness of the machined components using ion implanted inserts was slightly higher than that of non-implanted inserts, it was still within allowable tolerances. Uncoated inserts failed prematurely due to workpiece adhesion that resulted to flaking and excessive chipping on the rake face. The ion implantation dosage of 8E+15 ions/cm2 at 100 keV and 2E+16 ions/cm2 at 120 keV were the best dosages with low wear rate, acceptable surface roughness and heat generation similar to that of non-implanted inserts.Item The Effect of Manganese, Nitrogen and Molybdenum on the Corrosion Resistance of a Low Nickel (<2 wt%) Austenitic Stainless Steel(2007-02-22T11:27:56Z) Muwila, AsimenyeThis dissertation is a study of the effect of manganese, nitrogen and molybdenum on the corrosion behaviour of a low nickel, austenitic stainless steel. The trademarked steel, HerculesTM, has a composition of 10 wt% Mn, 0.05 wt% C, 2 wt% Ni, 0.25 wt% N and 16.5 wt% Cr. Eighteen alloys with a HerculesTM base composition were made with varying manganese, molybdenum and nitrogen contents, to establish the effect of these elements on the corrosion behaviour of the steel, and to determine a composition that would ensure increased corrosion resistance in very corrosive applications. The manganese was varied in three levels (5, 10 and 15 wt%), the molybdenum in three levels (0.5, 1 and 2 wt%) while the nitrogen was varied only in two levels (0.15 and 0.3 wt%). The dissertation details the manufacturing and electrochemical corrosion testing of these alloys. Preliminary tests were done on 50g buttons, and full-scale tests on 5 kg ingots. The buttons had a composition that was not on target, this was however rectified in the making of the ingots. Potentiodynamic tests were done in a 5 wt% sulphuric acid solution and the corrosion rate (mm/y) was determined directly from the scans. From the corrosion test results, it was clear that an increase in manganese decreases the corrosion rate, since the 5 wt% Mn alloys had the highest corrosion rate, whereas the 15 wt% Mn alloys, the lowest. The addition of molybdenum at 5 wt% Mn decreased the corrosion rate such that a trend of decreasing corrosion rate with increasing molybdenum was observed. At 10 and 15 wt% Mn molybdenum again decreased the corrosion rate significantly, but the corrosion rate value remained more or less constant irrespective of the increasing molybdenum content. At nitrogen levels lower than those of HerculesTM (less than 0.25 wt%) there was no change in corrosion rate as nitrogen was increased to levels closer to 0.25 wt%. For nitrogen levels higher than 0.25 wt%, corrosion rates decreased as nitrogen levels were increased further from 0.25 wt% but only at Mo contents lower than 1.5 wt%. The HerculesTM composition was developed for its mechanical properties. Microstructural analyses revealed that the 5 wt% Mn alloys were not fully austenitic and since the 15 wt% Mn alloys behave similarly to the 10 wt% Mn alloys, it was concluded that 10 wt% Mn was optimum for HerculesTM. All the alloys tested had a much lower corrosion rate than HerculesTM. Any addition of molybdenum thus improved the corrosion rate of this alloy. An alloy with a HerculesTM base composition, 10 wt% Mn, 0.15 wt% N and a minimum addition of 0.5 wt% Mo would be a more corrosion resistant version of HerculesTM. Pitting tests were done on the 10 wt% Mn ingots in a 3.56 wt% sodium chloride solution. The results showed that an increase in molybdenum increased the pitting resistance of the ingots. Immersion tests in a 5 wt% sulphuric acid solution at room temeperature on the 10 wt% Mn ingots confirmed that the ingots corroded by means of general corrosion.