The influences of NO3- concentration and AC density on corrosion resistance of FeCoNi high entropy alloy in simulated saline-alkali soil solution were studied via a series of measurements. Related results imply that the anticorrosion property of the HEA is significantly improved with the increase in NO3- concentration, particularly at high concentration of 0.1 mol/L, and the passive film covering the HEA becomes dense, intact and uniform. NO3- as a protective barrier is absorbed on the film surface, significantly inhibiting the pitting corrosion of the HEA. As AC density rises, the HEA surface status evolves from passivation to activated state, presenting a serious overall corrosion feature. The AC application facilitates the damage of passivation film grown on the HEA, resulting in a rapid increase in the number of flaws, which remarkedly decreases its resistance capacity against corrosion. Furthermore, under the combined influence of the two factors, the adverse effect of AC interference is obviously larger than the positive impact of NO3- on the corrosion resistance of the HEA at i(AC) of 50 A/m(2), causing plentiful defects within the passive film and severe corrosion of FeCoNi HEA.

The relevance between microstructure and anti-corrosion performance of FeCoNi HEA prepared with different cooling methods was studied in simulated Golmud salinized soil solution. The results reveal that the corrosion rate reduces with increasing cooling rate, and the water-cooling HEA has the best anti-corrosion performance, followed by the air-cooling and furnace-cooled samples, which mainly depends on the grain size and the protectiveness of passivation film. An increase in grain size weakens the micro-galvanic corrosion effect between the grain boundary and the internal grain. Moreover, compact and uniform passive film markedly improves the anti-corrosion performance of water-cooled HEA. Combined with electrochemical tests, the water-cooling HEA exhibits the lowest sensitivity of metastable and stable pitting, as well as its surface passive film possesses excellent self-repairing ability. In addition, the HEA substrate occurs the preferential dissolution of Ni element.

In order to overcome the obstacles of poor wear resistance and complex preparation process of the traditional tillage soil-engaging parts, this study presents a powder laying-feeding multi-material additive manufacturing method based on selective laser melting (SLM), to fabricate the heterogeneous material tillage parts with 316 L stainless steel (316 L) as the part-body and high entropy alloys (HEAs)-diamond composites as the part-blade. The microstructures including SLM forming quality, interfacial bonding of heterogeneous material, graphitization of diamond and interfacial behavior of diamond/HEAs matrix are systematically investigated. The results indicate that, adopting medium laser energy density 79.4 J/mm(3) of the composites during same-layer deposition, the overlapping area of 316 L/composites exhibits metallurgical bonding with high relative density of the composites section. Only slight graphitization of diamond happens and similar to 2 mu m width diffusion zone forms between diamond and HEAs matrix, without harmful carbide formation. Moreover, compared with commercial 65Mn steel, the wear resistance (wear mass loss rate) and corrosion resistance (corrosion current density) of HEAs-diamond composites have been decreased by 28 times and 230 times, respectively. The hetero-material 316L-composites exhibits good interfacial bonding strength of 432.3 MPa with elongation of 11.2 %. This study not only results in a novel solution of tillage wear-resisting parts, but also provides a multi-material additive manufacturing technology for metallic heterogeneous components.

Most of the current studies rely on simulated brine corrosion environments and lack long-term investigations into concrete corrosion damage evolution under actual corrosive conditions. In this paper, high-performance concrete (HPC) with various mix ratios is designed in the context of the Qinghai Salt Lake region in China, and the evolution of corrosion damage of HPC with different water-binder ratios (W/B) and different fly ash (FA) admixtures under long-term field exposure conditions is obtained by testing the ultrasonic velocity and strengths of the HPC in the field exposure of the HPC in the Qinghai Salt Lake region. The results show that the corrosion resistance of HPC is related to its water-binder ratio and mineral admixture type and dosage under the exposure of 8 years in Qinghai Salt Lake area. HPC with a fly ash dosage of 15-35% and silica fume dosage of 10% exhibits better corrosion resistance when the water-binder ratio (W/B) is between 0.24 and 0.38. The dependence relationship between the corrosion resistance coefficient of HPC and the relative dynamic elastic modulus (Erd) and 28 d standard maintenance strength was also established. The Erd of HPC with a corrosion resistance coefficient of 0.80 or above was 0.73-0.93, not 0.60, which provides an important experimental basis for determining the corrosion damage index of HPC in the high-saline brine environment of the salt lake.

The effect of polyphenylene sulfide binder content on the properties of injection molding polyphenylene sulfide/NdFeB magnets were investigated. The maximum filling amount of NdFeB magnetic powder was 87.6 wt.-%, and the mixing process and subsequent injection molding of the polyphenylene sulfide/NdFeB were in good condition. The melt mass-flow rate of the polyphenylene sulfide/NdFeB granular materials reached 121.7 g/10 min, the compressive strength of the polyphenylene sulfide/NdFeB magnet was 92.18 MPa, and its maximum magnetic energy product reached 5.59 MGOe. The structure and morphology characteristics of polyphenylene sulfide/NdFeB magnets were investigated using scanning electron microscopy and atomic force microscopy. The corrosion behavior of polyphenylene sulfide/NdFeB magnets was also studied using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results indicated that the injection molding process facilitated the uniform coating of polyphenylene sulfide particles on NdFeB powder, which directly enhanced the corrosion resistance of polyphenylene sulfide/NdFeB magnets. With an increase in polyphenylene sulfide content, the surface of polyphenylene sulfide/NdFeB magnets became more uniform. The corrosion current density of 13 wt.-% polyphenylene sulfide/NdFeB magnet was approximately one order of magnitude lower than that of 9 wt.-% polyphenylene sulfide/NdFeB magnet, indicating an improved corrosion resistance of polyphenylene sulfide/NdFeB magnet.

The paper systematically studied the effect of AC density on corrosion resistance of FeCoNi HEA in simulated Golmud soil solution. The results imply that the applied iAC seriously decreases the anticorrosion property of the HEA. In particular, under high AC density, the active state is presented and the corrosion characteristic changes from slightly local pitting to uneven overall corrosion with massive large-sized corrosion pits. Moreover, after imposed AC of 100 A/m2, the honeycomb holes are produced within passive film, which suggests that AC severely damages the film integrity, and reduces the protection and stability of the film. This phenomenon is due to the reason that as iAC rises, more generated hydrogen ions/atoms and Cl- are absorbed on the defect regions of passive film, significantly promoting the film dissolution, and facilitating the pitting initiation and development.