Materials

Inconel 617 (IN617) is a promising structural material for advanced nuclear systems such as heat pipe-cooled reactors, but its fundamental defect evolution under neutron irradiation remains poorly understood. This study employs classical molecular dynamics simulations to investigate the atomic-scale irradiation damage mechanisms in a representative Ni–Cr–Co ternary model of IN617 under successive displacement cascades. The results reveal a near-linear accumulation of Frenkel pairs with dose, with the count increasing by a factor of approximately 24 from the first to the 75th cascade. A critical finding is the stark asymmetry in defect kinetics: interstitials rapidly coalesce into large clusters (with 88.4% of interstitials found in clusters of ≥ 2 atoms after 75 cascades), while vacancies remain predominantly isolated (constituting 68.8% of all vacancy defects). This disparity directly governs microstructural evolution, as interstitial cluster growth drives dislocation loop nucleation, leading to a linear rise in dislocation density to a saturated value of approximately 4.5 × 10⁻⁴ Å⁻². The saturated dislocation structure subsequently undergoes continuous reorganization through reactions between partial dislocations. These insights demonstrate that irradiation hardening in IN617 under simulated conditions is governed primarily by interstitial-type defect clustering, providing a crucial mechanistic basis for assessing its performance in radiation environments.

The simultaneous enhancement of hardness and toughness in WC-Co cemented carbides remains a critical and persistent challenge for advanced cutting-tool applications, where conventional materials often suffer from inherent property trade-offs. In this study, a novel composite ceramic material—WC-(TiZrHfNbTa) (C, N) high-entropy carbonitride (HECN)-Co composite—was successfully fabricated via dry ball milling and spark plasma sintering (SPS) at 1300 °C following 90 h of ball milling. By incorporating varying amounts of HECN (0–15%, mass fraction, same below), the microstructure and mechanical properties of the composites were systematically tailored. The results demonstrate that the addition of HECN effectively refines the WC grains and increases the material density, leading to a pronounced improvement in hardness. Notably, the composite with 10% HECN (WC-10%HECN-9Co) exhibits an optimal balance of hardness and fracture toughness, achieving a Vickers hardness of 2375 ± 25 HV30 and a fracture toughness of 12.9 ± 1.1 MPa·m^1/2. In contrast, excessive HECN addition (15 wt.%) induces excessive grain refinement, which significantly impairs toughness. Our study demonstrates that the introduction of (TiZrHfNbTa) (C, N) HECN as a reinforcing phase offers a viable and effective strategy for designing cemented carbides with an exceptional hardness–toughness synergy, showing great promise for demanding cutting applications such as high-speed machining and the processing of hard-to-cut materials.

This study evaluated the residual mechanical properties of concrete in which Ordinary Portland Cement (OPC) was partially replaced with non-calcined Hwangto (NHT). Specimens were prepared with two water-to-binder (W/B) ratios (0.41 and 0.33) and three NHT replacement levels (0%, 15%, and 30%). The specimens were exposed to elevated temperatures of 20, 100, 200, 300, 500, and 700 °C at a heating rate of 1 °C/min. The results indicated that while the initial compressive strength at room temperature decreased with increasing NHT content, the residual mechanical performance at high temperatures significantly improved. Notably, temporary strength recovery was observed in the 200–300 °C range due to the internal autoclaving effect. At 700 °C, the NHTC (non-calcined Hwangto concrete)-30 series exhibited the highest thermal stability, retaining 28.2% of its initial compressive strength, whereas the Plain (OPC Concrete) and NHTC-15 series retained only 23.6% and 22.4%, respectively. Regarding energy absorption, the dissipated energy varied with the W/B ratio. In the W/B 41 series, the NHTC-30 specimen demonstrated superior ductility and energy dissipation capacity at 700 °C, outperforming the Plain specimen. This enhanced post-peak performance is attributed to the thermal activation of kaolinite into metakaolin, which preserves microstructural integrity by mitigating the severe degradation of hydration products and inhibiting crack propagation. These findings suggest that incorporating NHT effectively enhances the fire resistance and residual structural integrity of concrete, particularly in normal-strength matrices.