Phase transformation induced expansion for residual stress relief in laser additive manufacturing metal matrix diamond composites

While laser powder bed fusion (LPBF) has emerged as a transformative approach for fabricating geometrically intricate metal matrix-diamond composites, the interfacial integrity of these components is critically undermined by residual stress originating from rapid thermal cycling and severe thermal expansion mismatch between diamond reinforcements and metallic binders. Existing mitigation strategies—including process parameter optimization, ductile phase incorporation, and graded CTE transition layers—fail to eliminate interfacial microcracks due to inherent limitations in thermal strain compensation. Herein, we propose a phase-transformation-driven stress-relief strategy by engineering a W/Co bilayer coating on diamond particles within a CuSn10 matrix. The tungsten interlayer ensures interfacial integrity through carbide bonding and thermal buffering, while the cobalt overlayer exploits HCP→FCC phase transformation during LPBF thermal cycling to generate compensatory volumetric expansion, effectively counteracting thermal contraction-induced residual stress. The W-Co coated diamond/CuSn10 composite achieved a bending strength of 159 MPa (90 % higher than Ti-Cu coated counterparts) and a friction coefficient of 0.25, with complete suppression of interfacial cracking under cyclic wear. Multiscale characterization revealed that Co-induced twinning and dynamic recrystallization synergistically enhanced interfacial toughness, while molecular dynamics simulations quantitatively validated the stress-neutralization mechanism through lattice mismatch analysis. This work establishes a transformative "expansion-compensation" paradigm for residual stress regulation in MMCs, advancing the design of crack-resistant diamond composites for high-stress additive manufacturing applications.