Hongwei Zhang

Yield strength and work hardening are two critical mechanical properties of metallic structural materials. However, increasing yield strength through conventional strengthening mechanisms often restricts further dislocation multiplications and interactions, which significantly reduces work hardening and poses a challenge to achieving an optimal balance between these properties in material design. Here, an innovative approach to simultaneously enhance both yield strength and work hardening in a heterostructured, nanoprecipitation‐strengthened alloy is reported. This alloy exhibits an exceptional combination of a yield strength exceeding 1.5 GPa and an ultrahigh work hardening rate of 6 GPa, resulting in an extremely high tensile strength of 2.2 GPa and a uniform ductility of 20%. The ultrahigh yield strength primarily stems from nanoprecipitates and ultrafine grains, while the exceptional work hardening mainly originates from hetero‐interface‐mediated twinning. The hetero‐deformation between the coarse‐grained and ultrafine‐grained regions results in dislocation pile‐ups and strain gradients near the interfaces, which provides the ultrahigh stress necessary to activate mechanical twinning, thereby substantially improving the work hardening and plastic deformation stability of the alloy. The hetero‐interface architecting strategy can potentially be applied to numerous other alloys, paving the way for designing novel materials with unprecedented mechanical properties for technological applications.

In order to meet the demand for high wear-resistant Co-based material used in fields such as aerospace, energy, medical, etc., this study attempts to improve the comprehensive performance of this material by adding some reinforced phases and adjusting the sintering temperature. Results indicate the pure Co–Cr–W alloy is composed of γ-Co, M₂₉C, and M₆C (Ni₃W₃C), and the Co–Cr–W matrix composites are composed of γ-Co, M₂₉C, M₆C (Co₂W₄C), M₂₃C₆, and WC. With increasing the hot-pressing sintering temperature, the element diffusion in the material becomes sufficient, and the microstructure of Co–Cr–W alloy and composites materials becomes denser. When the sintering temperature is over 1150 °C, the bending strength and the toughness of the Co–Cr–W matrix composites are higher than that of the pure Co–Cr–W alloys. The added reinforced phases help the composites to gain a multi-scale strengthening effect, which makes the composites have a more comprehensive performance. Our results emphasize the importance of added reinforced phases and help to optimize the preparing process in preparing the Co–Cr–W alloys.

The combination of additive manufacturing and conventional metal forming processes provides the possibility for improvements of forming efficiency and flexibility. Substrate preheating is an implementable technique to improve the interface adhesion properties of the hybrid forming method. The present experiment investigates the adhesion of additive manufactured 316 L steel on P20 and 1045 steel substrates under two substrate temperatures, and the geometrical characterization, interfacial microstructure and mechanical property of the hybrid specimens were compared. As a result, it was found that the ratio of deposition height to the width was reduced and the width was increased under substrate preheating. Tensile results show that the ultimate strength of 1045 and 316 L hybrid specimens was obviously increased, while the properties of hybrid specimens P20 and 316 L were similar, under different substrate temperature conditions. For the hybrid specimens with the metallurgically bonding characteristic, the tensile properties can reach the level of 316 L depositioned specimens fabricated by laser metal deposition (LMD). Furthermore, substrate preheating had little effect on the microstructure of the laser metal deposition zone, and significant influence on the microstructure of the heat affected zone, which was reflected in the difference of the hardness distribution.