Cobalt removal and pore filling in polycrystalline diamond layer of polycrystalline diamond compact

Abstract

Metal binders’ cobalt plays a significant role in the sintering process of polycrystalline diamond compact (PDC), which not only can reduce synthesis temperature and pressure but increase impact ductility of PDC. However, the abundant metal binder cobalt leads to thermal degradation of the PDC and destroys its mechanical properties in oil and gas drilling at elevated temperatures. We removed cobalt by using a solution mixed H₂O₂ with H₂SO₄, diluting it by cold water in the process. Since removed cobalt produced holes leading to structural damage, the holes on the surface of the PDC were then filled with suitable HFCVD parameters, and the results were analysed using characterization methods including SEM, EDS, and XRD. With an acid concentration of 10%, the amount of the metal cobalt in the PDC is minimal and depth of cobalt removal up to 70 μm, and this method of removing cobalt increases efficiency and reduces the use of acid, making it eco-friendly. The diamond holes are efficiently filled by the HFCVD technique, resulting in a reduction in surface porosity from 6.701% to 1.756% and a pore filling rate of up to 81.63%, as well as a flatter and denser surface compared to the pre-processed substrate.

Keywords:

• Polycrystalline diamond compact
• Caro’s acid
• remove cobalt
• diamond hole filling
• porosity

Author contributions

Fuming Deng: Supervision, Conceptualisation, Funding acquisition; Donglin Cao: Writing- Original draft preparation, Visualisation, Project administration; Qingyuan Cai: Validation; Lei Zhang: Data curation; Miao Gu: Investigation; Xiaotian Xing, Investigation; Tiantian Huang: Investigation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under Grant (U20A20238); the Yue Qi Distinguished Scholar Project of China University of Mining & Technology (Beijing) (2019JCB04).