High-performance titanium alloys with good corrosion resistance are expected to be applied in marine environments. In this work, we developed a Ti20W alloy using powder metallurgy and hot extrusion, which combined remarkable mechanical properties and good corrosion resistance. The Ti20W alloys exhibited ultrahigh strength (>1400 MPa) and good ductility (>7%), and the specific yield strength was comparable to the common high-strength Ti alloys. The ultrahigh-strength Ti20W alloys had characteristics of the solid solution of W atoms and the precipitation of fine alpha phases. Compared with Ti6Al4V alloy, the Ti20W alloys showed lower corrosion current density values in 3.5 wt% NaCl solution, which was attributed to the solid solution of W elements and the finer alpha phases. The W oxides, particularly WO3, acted as the barrier to effectively block the penetration of Cl- into the inner oxide layer, thereby enhancing the corrosion resistance. The fine alpha phases could be bridged by the surrounding matrix oxides during the passivation process, which contributed to decreasing the galvanic corrosion between the alpha phases and the matrix, further improving the corrosion resistance.

Recently, the all-d-metal Ni(Co)MnTi based Heusler compounds are found to have a giant magnetocaloric effect (GMCE) near room temperature and manifest different functionalities like multicaloric effects, which can be employed for solid-state refrigeration. However, in comparison to other traditional Heusler compounds, the relatively large thermal hysteresis (Delta Thys) and moderately steep ferromagnetic phase transition provides limi-tations for real applications. Here, we present that fast solidification (suction casting) can sufficiently tailor the GMCE performance by modifying the microstructure. Compared with the arc-melted sample, the magnetic en-tropy change of the suction-casted sample shows a 67% improvement from 18.4 to 29.4 Jkg- 1K-1 for a field change (Delta mu 0H) of 5 T. As the thermal hysteresis has maintained a low Delta Thys value (5.5 K) for the enhanced first-order phase transition, a very competitive reversible magnetic entropy change of 21.8 Jkg- 1K- 1 for Delta mu 0H = 5 T is obtained. Combining high-resolution transmission electron microscopy (HRTEM) and positron annihilation spectroscopy (PAS) results, the difference in lattice defect concentration is found to be responsible for the sig-nificant improvement in GMCE for the suction-cast sample, which suggests that defect engineering can be applied to control the GMCE. Our study reveals that fast solidification can effectively regulate the magnetocaloric properties of all-d-metal NiCoMnTi Heusler compounds without sacrificing Delta Thys.

This work presented a novel net-shape-forming technology to prepare oxide dispersion strengthened (ODS) copper by cold spray additive manufacturing. There were three types of Al2O3 particles in the internal oxidation Cu-Al2O3 raw powders. After cold spraying, two types of nano-sized Al2O3 inside the raw powder were inherited into the deposition, and the micro-sized Al2O3 on the powder surface was crushed to nano-size under severe plastic deformation, which dispersed along the interface of deformed powder due to the plastic flow of Cu caused by adiabatic shearing. The plastic deformation produced by cold spraying was 20% higher than the hot extrusion with extrusion ratio of 11:1, which fully achieves the Al2O3 fragmentation, dispersion distribution and densification of the cold sprayed deposition. Moreover, due to the significant work hardening and grain refinement effect by SPD during cold spraying, Vickers hardness and nanoindentation hardness of the ODS Cu deposition increased to 185.63 HV3 and 2.76 GPa, respectively, which were significantly higher than the raw powders and hot extrusion sample.

The Co40Cr20Ni30Al5Ti5 multi-principal element alloy (MPEA) with heterogeneous grain structure (HGS) and nano L12 precipitates is successfully designed by cold rolling and proper heat treatment. The HGS alloy exhibits excellent corrosion resistance and passivation performance, originated from high-density grain boundaries in fine grains and abundant defects in deformed grains, which encourages surface to form a thicker and more efficient passive layer to inhibit the initial pitting corrosion. This finding indicates that the developed MPEA with HGS can possess an excellent combination of corrosion resistance and mechanical properties, providing highly positive factors for future applications.

The traditional approaches for improving corrosion resistance of alloys typically lead to the sacrifice of mechanical properties because the microstructures needed for improving corrosion resistance often contradict those for high strength. Here we demonstrate that selected laser melting (SLM), a net-shape additive manufacture technique, can maintain good mechanical properties while double the corrosion-resistance of a N-doped CoCrFeNi HEA. The SLM processed sample possesses a heterogeneous microstructure with 3D dislocation cells inside each grain. The SLM-induced 3D dislocation cell structure can provide effective diffusion paths to significantly promote Cr outward segregation, forming a thick protective Cr oxide layer, which renders excellent corrosion resistance. Furthermore, Cr segregation along cell boundaries provides numerous sites for nucleation of oxides, and stabilizes the cell structure for good mechanical properties. The strategy discovered here may also be applied to other HEAs with multiple strengthening mechanisms.

High-entropy alloys (HEAs) are expected to possess various excellent properties due to their vast composition design space and unique core effects. Annealing treatments after cold rolling are widely discussed as an effective means to improve the overall performance of the alloy. Nevertheless, the effect of annealing treatments on the corrosion resistance of cold-deformed alloys is still somewhat controversial. Therefore, cold rolling and annealing at different temperatures are performed on the Co40Cr20Ni30Al5Ti5 high-entropy alloy to investigate the effect of annealing temperature on its corrosion behavior. The annealing temperature range covers all stages of the HEA recovery-recrystallization-grain growth (in 50 °C gradients). The experimental results show that the HEA recrystallization is fundamentally complete at 850 °C and fully austenitized at 1050 °C. The best corrosion resistance performance is observed at 850 °C, with the lowest corrosion current density (ipass) and the lightest pitting in full immersion experiments. In addition, excellent passivation properties, such as the lowest steady-state current density iss and highest passivation film growth rate, are achieved at 850 °C. Further analyses of the growth films also show that the passivation films formed at 850 °C are thicker and uniform, and additionally have the highest Cr2O3 content. Accordingly, the effects of annealing temperature on HEA corrosion resistance and passivation behavior are discussed. The superior corrosion resistance and passivation behavior at 850 °C are attributed to the coupling of grain size and passivation film composition. The current findings might guide the optimized design of future cold-deformed alloys for better corrosion resistance.

The corrosion behaviors of selective laser melted (SLMed) FeCoCrNi multi-principal element alloys (MPEAs) with carbon or nitrogen addition in 0.5 M H2SO4 solution were investigated. Both C and N addition refined the grains and introduced a heterogeneous structure in SLMed FeCoCrNi MPEA, but they had opposite effects on the corrosion behavior. The doped carbon participated as nano-sized carbides in SLMed MPEA, and localized galvanic corrosion occurred, degrading the corrosion resistance. The doped nitrogen was gathered with chromium and formed CrN chemical clusters in SLMed MPEA, and a protective passive film with a higher Cr2O3/Cr(OH)3 ratio formed, which improved corrosion resistance.

Abstract In this study, the microstructure and mechanical properties of a Cu-rich multiple-principal-element alloy with the composition (Cu50Ni20Cr20Mn10)95Al5 (at.%) were investigated. It was found that after 900 °C/1 h annealing process, the as-cast alloy has achieved promising mechanical properties with a yield stress of 510 MPa, an ultimate tensile stress of 820 MPa and tensile elongation of 30 %. These properties are superior to those of traditional nickel–aluminum bronze (NAB) alloys. Moreover, the as-annealed alloy exhibited much better anti-corrosion properties with respect to the NBA alloys. Transmission electron microscopy observations showed that high-number-density nano-scaled L12-type ordered particles have precipitated in the Cu-rich phase after heat treatment and this was regarded as the main mechanism responsible for the enhancement of yield stress.

A novel strategy was developed to fabricate nano-porous silver (NPS) with a three-dimensional bi-continuous open porous structure. A high temperature oxidation (HTO) craft and a strong oxidant-assisted low-temperature oxidation method were used to tune the dealloying of AgXCu(1-X) ribbons. The NPS fabricated from the Ag15Cu85 ribbon by the HTO pretreatment exhibited a ligament size of ∼841 nm after 1 h of dealloying. However, the NPS fabricated from the Ag15Cu85 ribbon by the H2O2 craft exhibited a ligament size of ∼61 nm after 1 h of dealloying. In addition, the NPS fabricated by the strong oxidant-assisted dealloying craft exhibited an ultrahomogeneous ligament pore structure and a higher Tafel slope in regard to its hydrogen evolution reaction.