Xing-Xing Zhang

Laser Powder Bed Fusion (LPBF) of Inconel 718 induces complex residual stresses that can lead to premature failure. This study investigates the residual stress field of an as-built plate using high-energy synchrotron X-ray diffraction. Cross-verification of peak-fitting algorithms demonstrated that the Pseudo-Voigt function was marginally more accurate, with peak-fitting-related uncertainties in stress calculation remaining below 15.3 MPa. The reconstructed field reveals an anisotropic “core compression, edge tension” pattern, dominated by longitudinal stresses. This pattern is fundamentally driven by the temperature gradient mechanism: constrained thermal expansion during heating induces compressive plastic deformation, which reverses to severe tension during constrained cooling shrinkage. This cycle imparts alternating downward ‘push’ and upward ‘pull’ bending moments at the edges. Ultimately, critical tensile stresses concentrate at lateral edges (reaching 791 MPa), resulting in macroscopic self-equilibration with a compressive core (-355 MPa). These insights can guide the optimization of scanning strategies to mitigate residual-stress-induced failures in additively manufactured components.

This study investigates the impact of preintroduced defects on helium (He) diffusion in reduction-activated ferrite/martensitic steel under He plasma irradiation of 100 eV at room temperature. Defects are introduced via cold deformation before irradiation. Microstructural evolution is characterized using transmission electron microscopy, Doppler broadening spectroscopy, and synchrotron x-ray diffraction. Compared to the undeformed specimen, the 30% deformation@annealed specimen exhibited increased dislocation density and almost no vacancies, showing larger He bubbles and broader affected zones. Dislocations enhance He diffusion toward defect traps, facilitating localized accumulation that enables He self-trapping and bubble nucleation and growth. In contrast, 30% deformation specimens without annealing exhibited high dislocation density and abundant vacancies, demonstrating medium-sized bubbles within narrower zones. The high vacancy concentration effectively traps He atoms, strongly inhibiting their mobility. Concurrently, the dispersion of He among numerous vacancy sites reduces local concentration, suppressing bubble growth. Furthermore, under simultaneous dislocation-enhanced and vacancy-inhibited diffusion conditions, the retarding effect of vacancies dominates the microstructure in only 30% deformation specimens.

Tungsten carbide particles reinforced metal matrix composite (MMC) coatings can significantly improve surface wear resistance owing to their increased surface hardness. However, the presence of macro‐ and micro‐residual stresses in MMC coatings can have detrimental effects, such as reducing service life. In this study, neutron diffraction was used to determine the residual stresses in spherical fused tungsten carbide (sFTC) reinforced Cu matrix composite surface deposits after laser melt injection. We also developed a thermo‐mechanical coupled finite element model to predict residual stresses. Our findings reveal that sFTC/Cu composite deposits produced with a preheating temperature of 400°C have low residual stresses, with a maximum tensile residual stress of 98 MPa in the Cu matrix on the top surface. In contrast, the sFTC/bronze (CuAl10Ni5Fe4) composite deposit exhibits very high residual stresses, with a maximum tensile residual stress in the Cu matrix on the top surface reaching 651 MPa. These results provide a better understanding of the magnitudes and distributions of residual stresses in sFTC‐reinforced Cu matrix composite surface deposits manufactured via laser melt injection.