A systematic study on residual stress of functionally graded PDC fabricated by powder-layering: Simulation and experimental verification

Polycrystalline diamond compact (PDC), a high-performance composite material, is synthesized by sintering high-purity diamond powder onto a WC-Co cemented carbide substrate under HTHP conditions. It exhibits exceptional performance in applications such as petroleum drilling and geological exploration. However, significant residual stresses develop within PDC during the cooling stage following synthesis, which are recognized as a primary source of PDC failure. This paper investigates gradient-structured PDC from the perspective of optimizing residual stress, combining numerical simulation with experiments. Numerical simulations were conducted to analyze the residual stress in gradient-structured polycrystalline diamond compact and the influence of gradient layer thickness on residual stress, establishing the optimal total thickness for sample fabrication. Results demonstrate that gradient-structured PDC significantly reduces residual stress magnitude and improves its distribution compared to conventional PDC, and the thicker the gradient layer, the more significant the improvement. Gradient-structured PDC samples were fabricated via the powder layer-spreading method. Through scanning electron microscopy, it was shown that the gradient layers exhibited a gradual transition morphology with good sintering between layers. EDS results confirmed the successful fabrication of the designed gradient structure, showing good agreement between the actual and intended elemental distributions. The residual stress of gradient-structured PDC was measured using laser Raman spectroscopy, and the results were consistent with the simulation. The side of the gradient layer, PCD/gradient-layer interface and WC/gradient-layer interface are all under compressive stress, indicating significant residual stress modification.