Effect of thermal residual stress on the impact failure of PDC in application

Abstract

In the application of polycrystalline diamond compact (PDC) bits, more than 90 % of PDC cutters premature failure is directly or indirectly caused by excessive impact. During the different impact failures, the thermal residual stress plays a different role. In this study, PDC specimens—designated S1, S2, and S3—were fabricated using intial diamond powders of varying grain sizes (12 μm, 15 μm, and 18 μm, respectively) and a YG16 tungsten carbide substrate at 1500 °C and 7 GPa. A new method was selected by understanding the deformation of different sections of the PDC blanks after sintering to observe and calculate the thermal residual stress at the interface. The result shows that S2 exhibits the lowest thermal residual stress (0.26 GPa), representing a reduction of 73 % and 56 % compared to S1 (0.92 GPa) and S3 (0.59 GPa), respectively. To further evaluate the effects of thermal residual stress, impact tests simulating drilling conditions were conducted. The test result shows that the thermal residual stress at the interface has little effect on the transverse impact resistance, but has a significant effect on the longitudinal impact resistance of PDC. Additionally, the distribution of cobalt (Co) within the PCD and the state of transition layers between PCD and substrate also reflects the magnitude of thermal residual stress. The microstructure shows initial crack formation tends to occur at the interface and then propagate along the gradient lines of residual stress concentration.