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This study investigated four cooling methods for CuCrFeMnNi high-entropy alloy, namely, furnace cooling, air cooling, oil cooling, and water cooling (designated as FC, AC, OC, and WC, respectively), following a 12 h treatment at 800 °C. Results indicate that all four cooled alloys consisted of two FCC solid-solution phases (FCC1 and FCC2) and ρ phases. However, the FC alloy primarily contained FCC2 as the main phase and FCC1 as the secondary phase. The other three cooling methods yielded alloys with FCC2 as the primary phase and FCC1 as the secondary phase. With an increase in cooling rate, the content of the FCC1 phase gradually increased, that of the ρ phase initially decreased and then increased, and that of the FCC2 phase gradually decreased. The microstructure of the CuCrFeMnNi high-entropy alloy under the four cooling methods consisted of gray-black dendrites rich in Cr-Fe and white dendrites rich in Cu. Black ρ-phase particles predominated the dendrite region. As the cooling rate increased, the white interdendritic regions shrank, and the gray-black interdendritic regions expanded. The FC alloy exhibited the lowest microhardness at approximately 202.6 HV. As the cooling rate increased, the microhardness of the alloy progressively increased. The microhardness of the WC alloy was the highest, at approximately 355 HV. The strengthening mechanisms for all the alloys were primarily solid-solution strengthening and second-phase precipitation strengthening. [ABSTRACT FROM AUTHOR]

The effects of ultrasonic-aided quenching (USQ) on the microstructure and corrosion properties of 35CrMoV steel in a simulated seawater environment (wt % (NaCl) = 3.5) were studied. The corrosion properties of the steel were studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to characterize the microstructure and corrosion products. Combined with the EIS equivalent circuit, the corrosion mechanism was investigated. The results show that the microstructure of the USQ specimen is small martensite and that there was no residual ferrite compared with an un-ultrasonic-aided quenching (UUSQ) sample. It was also found that the corrosion products of USQ sample are less than the UUSQ sample, and the corrosion cracks are lighter and thinner than that of the UUSQ sample, which indicates that the corrosion resistance of 35CrMoV in a seawater environment has been obviously improved. [ABSTRACT FROM AUTHOR]

Hot compression tests were performed with strain rates (0.01–10 s−1) and temperatures (850–1150 °C). The power law relationship between the critical stress and critical strain and Zener–Hollomon parameters was determined by θ-σ curves. Microstructure was investigated by electron backscattered diffraction. The results showed that the flow behavior and microstructure of 35CrMo steel was affected by ultrasonic-assisted casting. The activation energy of non-ultrasonic and ultrasonic-assisted 35CrMo steel were 410 ± 9.9 and 386 ± 9.4 kJ/mol, respectively, and the activation energy of ultrasonic-assisted specimens was reduced by 6%. In addition, the ultrasonic-assisted treatment refines the grains to some extent and makes the softening process of ultrasonic-assisted samples progress faster, which promoted the development of dynamic recrystallization and the production of Σ3 boundaries. The discontinuous dynamic recrystallization was the main DRX nucleation mechanism of the 35CrMo steel. [ABSTRACT FROM AUTHOR]

The effect of deep cryogenic treatment on microstructure and wear resistance of LC3530 Fe-based powder laser cladding coating was investigated in this paper. The cladding coating was subjected to deep cryogenic treatment for the different holding times of 3, 6, 9, 12, and 24 h, followed by tempering at room temperature. Microstructure of the cladding coating was observed by optical microscope (OM) and the microhardness was measured by the Vickers-hardness tester. The wear was tested by ball and flat surface grinding testing conducted on the material surface comprehensive performance tester. The wear scars were analyzed using a non-contact optical surface profiler and scanning electron microscope (SEM). The results showed the grain size of cladding coating after 12 h of deep cryogenic treatment was significantly reduced by 36.50% compared to the non-cryogenically treated cladding coating, and the microhardness value increased by approximately 34%. According to the wear coefficient calculated by the Archard model, the wear resistance improved about five times and the wear mechanism was micro-ploughing. The deep cryogenic treatment could enhance the wear resistance of the cladding coating by forming a wear resistant alloy compound and higher surface microhardness. [ABSTRACT FROM AUTHOR]

Hot deformation experiments of as-cast 35CrMoV steel, with strain rates of 0.01 s−1 and 10 s−1, deformation temperatures of 850, 950, and 1050 °C, and an extreme deformation reaching 50%, were carried out using a Gleeble-3810 thermal simulator. Electrochemical corrosion experiments were conducted on the deformed specimens. The microstructure was observed by optical microscope (OM), and the corrosion morphology and corrosion products of the specimens were investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), confocal laser scanning microscopy (CLSM), and X-ray diffraction (XRD) techniques. The results show that the grain size increased gradually with an increase in the deformation temperature at the same strain rate, whereas the corrosion resistance deteriorated. At the same deformation temperature, the grain size becomes smaller as the strain rate increases, which enhances the corrosion resistance. This is mainly attributed to the fine grains, which can form more grain boundaries, increase the grain boundary area, and accelerate the formation of the inner rust layer at the beginning of corrosion. Moreover, fine grains can also refine the rust particles and enhance the bonding strength between the inner rust layer and the matrix. The denseness and stability of the inner rust layer increases as the corrosion process progresses, thereby improving corrosion resistance. [ABSTRACT FROM AUTHOR]

Wear resistance of metallic materials can be effectively improved by the deep cryogenic treatment. In this study, different deep cryogenic treatment conditions were considered, with different soaking durations between quenching and tempering. The main objective is investigating the effects of deep cryogenic treatment and exploring the relationship between the mechanical properties and the microstructure of GB 35CrMoV steel. Hardness and relative wear ratios of samples were evaluated by the Vickers-hardness test and the pin-on-disk wear test, respectively. Worn surface was characterized by a non-contact optical surface profiler. Microstructures were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD). Significant improvements in hardness and wear resistance are observed for higher cryogenic soaking times; the root mean square deviation (RMS) parameter (Sq) was employed to evaluate the effect of deep cryogenic treatment on the worn surface roughness; the improvements were ascribed to the precipitated carbides. The mechanism can be interpreted not only as the promoted effect of deep cryogenic treatment in the decomposition kinetics of martensite, but also as the acceleration on the Ostwald ripening process. [ABSTRACT FROM AUTHOR]