Microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact annealing under ambient air and vacuum conditions |
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| Affiliation: | 1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, PR China;2. Key Laboratory on Deep Geo-drilling Technology of the Ministry of Land and Resources, China University of Geosciences (Beijing), Beijing 100083, PR China;1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, PR China;2. Key Laboratory on Deep Geo-drilling Technology of the Ministry of Land and Resources, China University of Geosciences (Beijing), Beijing 100083, PR China;3. Nano Structural Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China;1. Centre for High Resolution TEM, Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa;2. DST/NRF Centre of Excellence in Strong Materials at School of Chemical Engineering and Metallurgy, University of the Witwatersrand, Johannesburg, South Africa;1. Element Six UK Ltd, Global Innovation Centre, OX11 0QR, Harwell Oxford, UK;2. University College Dublin, School of Mechanical & Materials Engineering, Dublin, Ireland;1. School of Mechanical and Materials Engineering, University College Dublin, Ireland;2. School of Physics, University College Dublin, Ireland;3. Department of Mechanical Engineering, Imperial College London, UK |
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| Abstract: | The microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact (PDC) were studied in ambient air and vacuum at the temperature up to 1000 °C. The microstructures and compositions of the annealed PDC were characterized by white light interferometer, X-ray diffractometry (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The results showed that no visible change in the morphologies of surface of PCD layers (PDC surfaces) was observed at 200 °C both in ambient air and vacuum. After annealing at 500 °C, numbers of spalling pits appeared on the PDC surface, and the stress-induced spall mechanism was the dominant thermal damage mechanism in ambient air and vacuum. With the temperature up to 800 °C, the annealed PDC surface in ambient air was seriously damaged with a mixed thermal damage mechanism such as graphitization, oxidation and stress-induced micro-cracks. Whereas, the thermal damage mechanism in vacuum was nearly the same as that at 500 °C. At 900 °C, only a dendritic phase of Co3O4 was contained on the annealed PDC surface due to extensive graphitization and oxidation in ambient air. When it comes to vacuum environment, many cracks were observed on the PDC surface and some fine diamond grains near the cracks spalled, which demonstrated that the thermal damage mechanisms consisted of stress-induced crack and spall mechanisms caused by the different thermal expansion coefficients between the diamond and Co phase. Compared with that at 900 °C, the degree of thermal damage reduced at 1000 °C in vacuum because of the diffusion of unevenly distributed Co. |
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