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Self-piercing riveting (SPR) has been used to join similar and dissimilar materials for vehicle body application. In order to understand the failure mechanism and develop a method to estimate the shear strength of SPR similar and dissimilar materials, finite element modeling was conducted in this study. In the modeling, the contact conditions between the rivet and the workpieces were taken into account to establish the failure criteria of SPR of steel and aluminum sheets. It was found that the failure procedure of riveted dissimilar materials was different from that of riveted similar materials. Furthermore, the experiments were conducted to validate the modeling results. It was shown that the shear strength and failure mode of SPR joints were in agreement with the modeling results. These results suggested that the model could be used to estimate the shear strength of SPR joints. The factors influencing the failure mode and shear strength of SPR joints were discussed in detail. For rivet pull-out mode, the rivet open angle at the upper sheet, friction coefficient between the rivet and sheet, and the yield strength of the substrate were the key factors. For sheet tearing mode, failure occurred at the weaker sheet and the shear strengths mainly depended on the sheet gage and strength grade of the weaker sheet. [ABSTRACT FROM AUTHOR]

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]

The effect of Si on the microstructure and properties of hypereutectic high-chromium cast iron was investigated. The results show that Si is only solid-dissolved in the matrix, and the content of Si is higher in the matrix near the edge of the primary carbide. As the Si content increased from 0.5 to 2.6%, the primary carbides in hypereutectic high-chromium cast iron were significantly refined, and the refining mechanism was verified by first-principles calculations. The increase of silicon content also leads to the increase of carbide volume fraction from 52.4 to 63.9%, the decrease of austenite volume fraction from 45.8 to 2.0%, and the matrix structure gradually transforms from γ-Fe to α-Fe. After hypereutectic high-chromium cast iron was quenched at 1050 °C, a large amount of secondary carbides were precipitated in the matrix and the precipitation of secondary carbides decreased significantly with the increase of silicon content. After quenching at 1050 °C, the hardness of hypereutectic high-chromium cast iron increased significantly, but the hardness of high-silicon (1.9Si and 2.6Si) samples did not change significantly. Increasing the quenching temperature and prolonging the holding time can significantly improve the hardness of high-silicon samples. The increase of silicon content can significantly improve the wear resistance of hypereutectic high-chromium cast iron. When the silicon content exceeds 1.9%, the wear resistance decreases. [ABSTRACT FROM AUTHOR]

In order to solve the problems of low hardness and poor wear resistance of titanium alloy, laser cladding technology was used to prepare NiCrBSi coatings with different amounts of B4C on the surface of Ti-6Al-4V alloy. The effects of B4C content on the microstructure evolution, hardness, fracture toughness, and wear resistance of NiCrBSi coatings were investigated. The results showed that with an increase of B4C addition, the size and number of ceramic phases TiB2, TiC, and CrB in the coating increased, and the ceramic phases were dispersed in the coating. The average microhardness of the coating with 9 wt.% B4C addition was the highest, reaching 1250.3 HV0.2, which is 15% higher than that of the coating without B4C addition. After adding B4C, the fracture toughness of the coating increased. When the addition of B4C was 3 wt.%, the fracture toughness of the coating was the highest, reaching 1.42 MPa m1/2, which is 178.4% higher than that of the coating without B4C. With the increase of the addition of B4C, the wear loss of the coating decreased and the wear resistance increased. [ABSTRACT FROM AUTHOR]

The carbide precipitation behavior of 35 wt%Cr–4 wt%C (35Cr–4C) Hypereutectic High Chromium Cast Iron (HHCCI) during heat treatment was investigated by means of scanning electron microscope and transmission electron microscope, and the effect of rare earth magnesium (RE-Mg) modification on the microstructure evolution and wear resistance of 35Cr–4C cast iron was also studied. The as-cast structure of 35Cr–4C HHCCI is mainly composed of primary carbides, eutectic carbides and austenite matrix. After quenching, there are secondary carbides M7C3 and M23C6 precipitation in the martensite matrix. After tempering, more secondary carbides will be formed and the main precipitate phase is M23C6. After heat treatment of RE-Mg modified HHCCI, more secondary carbides are precipitated, and the distribution in the matrix is more uniform, and the wear resistance is higher than that of unmodified HHCCI. [ABSTRACT FROM AUTHOR]

The effects of different partitioning temperatures and time on the microstructure and properties of Mn-Si-Cr alloy steel were investigated. The results showed that with the increase in the partitioning temperature or the extension of the partitioning time, the martensite arrangement in the Mn-Si-Cr alloy steel became irregular, and the boundary was gradually blurred; the austenite mainly existed in the form of thin film, and the austenite content increased at first and then decreased gradually. When the partitioning temperature was too high or the partitioning time was too long, all led to the decomposition of austenite into low-carbon bainite and carbides. With the increase in the temperature, the hardness of the samples decreased gradually, the wear weight loss increased gradually, and the impact toughness increased linearly. With the extension of the partitioning time, the hardness of the sample gradually decreased. When the partitioning time is 5-10min, the hardness decreases greatly. When the partitioning temperature was 350 °C and the partitioning time was 60s, the test steel can have hardness, impact toughness, and wear resistance and has good comprehensive mechanical properties. [ABSTRACT FROM AUTHOR]

The zirconium alloy cladding tube and end plug used for nuclear fuel rods are usually joined by pressure resistance welding. And the service performance of the fuel rod cladding is directly influenced by the welded joint. In order to understand the forming process deeply, an axisymmetric electro-thermal–mechanical process finite element model was established in this paper. The current density distribution, temperature field evolution, and joint forming process during pressure resistance welding were all simulated by this model. It was shown that due to the contact resistance, a concentrated heat flow was rapidly generated on the tube-plug contact surface caused by welding current. A heat conduction was established on both sides of the welding surface. The high-temperature region on the side of the cladding tube was larger than the end plug. The metal of the tube extruded to both inside and outside of the joint under the coupled loading of heat and pressure. The location of the highest instant temperature on the welding surface moved from the inside to the outside of the joint. The highest temperature was 1568 °C, not reaching the melting point of zirconium alloy. The joining area and the highest temperature increased with welding current increasing, the welding time had little effect on them. Based on the numerical model, two structural design schemes to improve the joint forming quality were proposed. They were expected to provide a guide line for the joint design. [ABSTRACT FROM AUTHOR]

A dense Cu-10Sn alloy bulk specimen was obtained by optimizing the laser powder bed fusion (L-PBF) processing, and the relative density of the specimen reached 99.7%. The grain morphology was mainly the columnar dendrite and inter-dendritic phases generated along the solidification direction. Tensile testing and detailed microstructural characterization were carried out on specimens in the as-built and heat-treated condition. Under the quasi-static tensile condition, the yield strength (σ0.2), ultimate tensile strength (UTS), and the elongation of the as-built Cu-10Sn specimen were 392 MPa, 749 MPa and 29%, respectively. After the solution treatment at 800 °C for 4 h, and aging treatment at 400 °C for 2 hours, the microstructure of the specimen transformed from the columnar grain to equiaxed grain, the dislocation density decrease, and numerous annealing twins were observed in the heat-treated state. Therefore, the quasi-static tensile yield strength (σ0.2) of the specimen was reduced to 245 MPa. However, the UTS and the elongation were increased to 840 MPa and 56%, respectively, due to the interaction between annealing twins and equiaxed grain. [ABSTRACT FROM AUTHOR]

In this study, a Hastelloy X alloy single track was manufactured by means of selective laser melting. The transient temperature field and cooling rate characteristics of single tracks in the manufacturing process were simulated using the ABAQUS software. The cross-comprehensive effects of the scanning speed and power of the selective laser melting process on the surface morphology, geometric characteristics, wetting and spreadability of single tracks were analyzed. The results indicated that the transient peak temperature and average cooling rate decreased with the increase in scanning speed, but increased with the increase in laser power. At the same time, the height and width of the single track gradually increased in conjunction with the laser power and decreased with increased scanning speed. A two-factor variance analysis indicated that the contribution rates of laser power and scanning speed to the geometric size of the single tracks were 89.02% and 10.25%, respectively. Therefore, optimization of the laser's power control exerts a higher process effect on single track formation quality. [ABSTRACT FROM AUTHOR]