Theses and Dissertations (Mechanical Engineering)

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Browsing Theses and Dissertations (Mechanical Engineering) by Author "Machio, C., Dr."

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    Impact of equal channel angular pressing operational parameters on the mechanical properties of characterized Titanium-Based powders
    (Vaal University of Technology, 2020-03) Nhlapo, Mirriam; Machio, C., Dr.; Masu, L., Prof.
    The powder metallurgy technique Equal Channel Angular Pressing is a severe plastic deformation method. Where desired microstructure and texture can be developed by applying temperature, changing the orientation of the billet through a number of successive passes. It has been extensively researched as a tool for processing solid metal, where it has been shown to provide components with ultra-fine grains that impart superior mechanical properties. The ECAP of titanium-based powder has the potential to greatly aid the cheaper production of titanium-based components. The main objective of this study was to investigate the fundamental interaction between titanium powder characteristics and ECAP process parameters to establish a one on one relationship between powder characteristics, ECAP process parameters and the mechanical properties of the green compacts. Six different titanium powders were used in this study to determine major powder characteristics such as particle size distribution, morphology, density, flowability and chemical composition. The powder was compacted using ECAP technique to produce billets which are also called green compacts. The green compacts were produced based on selective ECAP parameters which were considered effective. Thereafter the green compacts were analysed to check any improvement on mechanical and physical properties. The particle size distribution test results obtained agreed with the supplier’s particle sizes. Four of the powder’s compositions were found to be cohesive, the other two powders, one was freeflowing, the other one flowability could not be measured, due to large particle size distribution. The test results revealed that the morphology for all the powders was irregular with some powders showing angularity, others were dendritic. The tests revealed that the interstitial elements were within the required limits for all the compositions. After the ECAP process, it was found that particle size distribution alone has some effect on the mechanical properties of components. But the morphology, density, flowability and chemical composition, have major effect on mechanical properties of ECAP samples. The relative density was measured after ECAP process, the free-flowing and cohesive powders yielded a relative density of 90% and above, after ECAP first and second pass. The microhardness of the new ECAP billets was found to match that of steels and wrought iron. It was found that application of temperature, backpressure and great number of passes improved the mechanical and physical properties of the billets.