A single-phase CoNiV medium-entropy alloy with excellent processability, high toughness, corrosion resistance and hydrogen embrittlement resistance, not only has a tensile strength of 1GPa at an elongation greater than 90%, but also has excellent corrosion resistance and hydrogen resistance brittleness. This is attributed to the single effect of single-phase solid solution of fcc structure, stacking fault energy and solid solution elements. The related results open the way to design alloys with good mechanical properties under high environmental stability.
Machines, infrastructure, power plants, and structural components around people all require materials with high strength and damage tolerance, but in hydrogen-containing, acidic, or mixed environments, the mechanical properties of the materials gradually decline due to hydrogen embrittlement and corrosion , Seriously affecting the service life of components. The advanced materials (such as stainless steel, nickel-based alloys, titanium alloys, etc.) that have been applied at this stage can enhance the corrosion resistance to a certain extent through composition adjustment and other measures, but further increase in the strength of the alloy will reduce the corrosion resistance. This is because changes in the microstructure increase the strength while causing a potential difference, which is prone to electrochemical corrosion; hydrogen will accumulate inside the precipitated phase, the interface and other areas, resulting in material failure. Therefore, it is very important to explore both mechanical properties and corrosion resistance in acidic environments in the presence of hydrogen.
Recently, the team of Professor Li Xiaogang and Professor Luo Hong of Beijing University of Science and Technology, Dierk Raabe of Mapu Institute and others proposed an isoatomic CoNiV medium entropy alloy (MEA), which has no obvious hydrogen embrittlement in the environment of 300K hydrogen and has good The mechanical properties have good corrosion resistance in an acid environment. The alloy has good strength, plasticity, corrosion resistance and hydrogen embrittlement. Related papers were published in Nature Communications with the title "A strong and ductile medium-entropy alloy resists hydrogen embrittlement and corrosion". This is one of the few research papers reported by the journal in recent years on corrosion-resistant metal materials.
Paper link:
https://www.nature.com/articles/s41467-020-16791-8
In this study, an isoatomic CoNiV medium-entropy alloy was prepared by vacuum induction melting and drop casting. It was homogenized at 1200℃×24h in an argon atmosphere, the cold rolling reduction rate was 75%, and recrystallization was performed at 950℃×1h under argon. After annealing, the final alloy has a single fcc structure with a grain size of about 10.5 μm and a random crystal texture.
The study found that the diffusivity of hydrogen in MEA is lower than that in pure V, which is related to the addition of a large amount of Ni and Co. On the one hand, a single fcc solid solution is formed, and the hydrogen diffusivity is low; on the other hand, a dense The surface barrier film hinders the release rate of hydrogen on the surface. Stacking fault energy (SFE) also plays an important role in strain hardening. It will affect the splitting of the crystal lattice into partial crystal lattices, thereby reducing dislocation cross-slip and leading to dislocation reaction products. The yield strength of MEA is about 600MPa, the tensile strength is about 1GPa, and the elongation is over 90%.
The study found that MEA formed a stable barrier film during the electrochemical corrosion process. The dissolved concentration of Co and Ni ions in MEA (~0.9, ~1.1μg/L) is much lower than the ion concentration of their respective pure metals under the same conditions (~2×107, ~300μg/L), but the V ion concentration Slightly higher. It shows that the barrier film on MEA can prevent Ni and Co from dissolving from the substrate. The addition of V increases the stability of the barrier film, which ultimately leads to the improvement of the corrosion resistance of MEA.
In summary, the isoatomic CoNiVMEA proposed in this paper not only has a high ultimate tensile strength of 1 GPa at an elongation greater than 90%, but also has excellent corrosion resistance at a strain rate of 300K and 10^-4/s And hydrogen embrittlement. This high comprehensive performance is caused by the combined action of the single fcc structure of single-phase solid solution, stacking fault energy and solid solution elements. This study opens the way to design alloys with good mechanical properties under high environmental stability.