Investigation and processing of 3D-polycrystalline diamond material

• Main Author: Ngwenya, Sibusiso Hope
• Format: Others
• Language: en
• Published: 2015
• Online Access: http://hdl.handle.net/10539/17715

The purpose of this work was to manufacture three dimensionally-structured polycrystalline diamond materials (3D PCD) with the aim of improving the resistance to wear of the polycrystalline diamond by crack deflection toughening induced by residual stresses. A further aim was to correlate the measured property with the microstructure of the material, to better understand how 3D PCD material concepts might be employed to improve material performance in application. To achieve this, samples were made with composite spherical bilayer granules of grade 2 (mean grain size approximately 2 µm) and grade 22 (mean grain size approximately of 22 µm) diamond powder. The granules had a core/rim structure with the core comprising of grade 22 and the rim of grade 2 fabricated by granulation technique. The average volume fraction of the core versus the rim was 0.51. These granules were compacted and sintered on a 13 wt% cobalt tungsten carbide substrate under high pressure and high temperature (HPHT) conditions by a liquid infiltration and sintering process. Samples were then characterized by X-ray Diffraction, Scanning Electron Microscopy and Energy dispersive X-ray Spectroscopy. The fracture toughness of the material was measured, as well as its wear resistance by turning test methods. The fracture toughness of the resulting material was measured to be 7.02±0.61, with an improved wear resistance and better wear scar morphology when compared to samples made with only 2 µm diamond powders. Evidence of crack deflection was found without any loss of abrasion resistance. The crack deflection was caused by the presence of residual stresses generated within the matrix and the dispersed phase, courtesy of the difference in thermal properties of the granule constituents. Samples made this way showed an improvement in wear resistance.