Optimization of functionally graded polycrystalline diamond compact based on residual stress: Numerical simulation and experimental verification

Polycrystalline diamond compact (PDC) is composed of a polycrystalline diamond layer with a tungsten carbide substrate, which is commonly used on drill bits. PDC bits are widely used in geological and petroleum drilling. There are frequently issues with failure, such as chipping of teeth during drilling, attributed to the residual stress within the PDC. Residual stresses arise from the difference in material properties between the polycrystalline diamond layer and the tungsten carbide substrate after sintering and cooling. To address the residual stresses inside the PDC, this research work optimized the design of a PDC with a functionally graded structure is reported in this paper. The effect of gradient structural parameters on the residual stresses of the PDC is analyzed using the finite element method. The results show that as the thickness of the gradient structural layer increases, the maximum residual tensile stress gradually decreases and stabilizes. Since the total thickness of the gradient structural layer is fixed, increasing the layer number (decreasing the thickness of the single layer) cannot reduce the maximum tensile stress, but it can minimize the sudden change of axial stress across the interface, thus resulting in less interface cracking. The optimum gradient structure design parameters are obtained and the optimal graded PDC is prepared via fused deposition modeling and sintering technology, resulting in a 62% reduction in maximum shear stress, a 70% decrease in maximum axial stress, and a 40% drop in maximum radial stress compared to conventional PDC. The accuracy of the finite element calculations is demonstrated by the Raman spectroscopy results. This work will provide a reliable guide for the design of functional graded structure PDCs and lay the foundation for their preparation and application.