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The effects of silicon alloying and heat treatment on the microstructure and properties of Fe-35Cr-4C-xSi (x = 0.5, 1.2, 19, 2.6) hypereutectic high-chromium cast iron (HHCCI) were explored through first-principles calculations and phase diagram calculations combined with XRD, SEM, TEM and other methods. With the increase of Si content, the matrix structure of HHCCI transforms from martensite to ferrite. The phase diagram analysis reveals that higher silicon content results in elevated austenite transformation initiation temperatures, reduced austenite phase areas, and expanded ferrite phase regions. Additionally, the study calculates the diffusion activation energy of C atoms within silicon-bearing and silicon-free HHCCI matrices, providing valuable insights into the role of silicon in promoting the transformation of the HHCCI matrix into ferrite. Notably, silicon facilitates the diffusion of C atoms into the silicon-bearing HHCCI matrix, thereby preventing complete austenitization. After ultra-high-temperature heat treatment, the matrix structure of high-silicon HHCCI (1.9 wt.% Si) can be transformed from ferrite to martensite. With the increase of Si content, the corrosive wear resistance of HHCCI increases first and then decreases. The 1.9Si HHCCI after ultra-high-temperature heat treatment exhibits the best corrosive wear resistance in both acidic and alkaline corrosive wear environments, and the silicon-bearing HHCCI is more resistant to alkaline corrosive wear. This study reveals promising applications of silicon-bearing HHCCI in industries such as hydraulics and coal mining, particularly as a material for making slurry pumps. Notably, in comparison with previous work by our research group, this study delves deeper into the mechanisms underlying the structural and performance changes of silicon-bearing HHCCI due to heat treatment and silicon content variation. [ABSTRACT FROM AUTHOR]

The excellent hardness and wear resistance of AlCoCrFeNiMo0.8–TiC composite coating benefit from various strengthening mechanisms, including fine grain strengthening, dislocation strengthening, load transfer strengthening, solid solution strengthening, and precipitation strengthening. To analyze their contributions in the strength and hardness, an accurate prediction model is essential. In this work, a prediction model for the hardness increment was established based on some key elastic constants calculated by the first-principles. Subsequently, the contributions of strengthening mechanisms were quantitatively evaluated by the developed prediction model. It was found that the Young's modulus and shear modulus for B2 phase were 179.65 GPa and 67.36 GPa, respectively, and those of σ phase were 354.08 GPa and 139.19 GPa, respectively. The precipitation strengthening was the predominant mechanism in the composite coating, with a strength contribution of 736.4 MPa and a hardness contribution of 225.2 HV, which accounted for 76.2% of the contribution values. The prediction model has high accuracy, which is evidenced by the small relative error (9.1%) between the total theoretical hardness contribution (295.2 HV) and the Vickers hardness tested by nanoindentation (322.1 HV). The AlCoCrFeNiMo0.8–TiC composite coating has various strengthening mechanisms. To quantitatively analyze these contributions on the hardness, a prediction model is established based on the elastic moduli obtained by the first-principles calculations. [ABSTRACT FROM AUTHOR]

This work aims to elucidate the microstructure characteristics of each phase in carbidic austempered ductile iron and the nucleation and growth of acicular ferrite in an austempering temperature range of 250–450 °C. The research results showed that the carbides (Fe, Cr)3C obtained by the eutectic reaction had high indentation hardness and indentation modulus, and the interface between acicular ferrite and eutectic carbides belonged to incoherent boundary. Since the nucleation driving force of acicular ferrite increased with an increase in temperature difference (ΔT), the size of acicular ferrite gradually decreased with the decrease in isothermal temperature. When the austempering temperature was above 400 °C, acicular ferrite preferentially nucleated around the graphite nodules and inside grains. However, acicular ferrite preferentially nucleated around the graphite nodules and the eutectic carbides at temperature below 400 °C. Additionally, a fine twin structure had been found inside some acicular ferrite after austempering at a low temperature (250 °C). [ABSTRACT FROM AUTHOR]