Journal of Materials Engineering and Performance最新文献

The study explores the impact of detonation frequency (3 and 6 Hz) on the temperature-dependent linear reciprocating wear behavior of Ni-20%Cr coatings deposited by detonation spraying on a nickel-based superalloy (IN718). Dry sliding experiments were carried out at both ambient (25 °C) and high (420 °C) temperatures, using an alumina (Al₂O₃) ball as the counter material and different loads (5, 10, and 20 N). HV_0.2 microhardness indentations were used to test material hardness variations attributed to heat exposure. X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy with energy-dispersive spectroscopy (FESEM with EDS) were used to investigate the wear characteristics and mechanisms. Furthermore, surface roughness and profiles of worn surfaces (including track depth, breadth, and wear volume) enabled the calculation of wear rates using confocal optical 3D profilometry. The results showed the 6 Hz Ni-20%Cr coating showed better wear resistance than the 3 Hz coating. However, a higher wear rate and low friction coefficient at 420 °C were observed due to partial oxide particles, which were insufficient to restrict direct ball-to-metal contact. The research delves into wear maps, tribolayer formation, wear mechanisms, and sub-mechanisms.

Zr alloy with laser-melted Cr coatings exhibits excellent resistance to high-temperature oxidation and are widely used in the nuclear industry. To examine the impact of adding Al on the high-temperature oxidation performance, corrosion, and wear resistance of the coatings, Cr-xAl coatings with varying Al contents were applied to the pure Zr surface using laser cladding. Research results show that laser cladding coatings reveal good interdiffusion between the coatings and the substrate. The hardness and thickness of the coatings increase with the increase in Al content, but the quality of the coatings decreases with the increase of Al elements. A comparison of the high-temperature oxidation weight gain curve and morphology of different samples at 800–1100 °C shows that the oxidation weight gain of Cr-xAl coatings is about half of that of the uncoated substrate, exhibiting excellent high-temperature oxidation resistance. Conclusions drawn from friction morphology and volume loss indicate that the wear volume of Cr and Cr₉₀Al₁₀ coatings is approximately 1/5 of the substrate, demonstrating significantly improved wear resistance compared to the substrate.

Friction stir processing (FSP) is an energy-efficient technique that modifies surfaces and has been used to generate surface metal matrix composites (SMMCs). The AA7075-T6-based two different composites were fabricated in this study by reinforcing multi-walled carbon nanotubes, i.e., SMMC1 and silicon carbide, i.e., SMMC2, through FSP. The matrix material, i.e., AA7075 alloy, is widely used in aerospace and automotive industries due to its good strength/weight ratio. Three-pass FSP with tool speeds of 730 rpm and 65 mm/min was used to develop SMMCs with 7% volume of the reinforcement particles (RPs). Uniform dispersion of the RPs was confirmed through electron probe microanalysis. To investigate the microstructure of the composites and base material, electron backscatter diffraction was employed. To compare the effect of RPs, the SMMCs were examined for mechanical properties, i.e., microhardness, Charpy impact, and tensile strength, and tribological properties. Further, the wear tracks were analyzed for wear mechanism using scanning electron microscopy, and energy-dispersive x-ray analysis revealed the main particles on the tracks. Fractography of the Charpy and tensile specimens provided fracture mechanism. Both the composites outperformed the base metal in terms of mechanical properties and resistance to wear. Regarding the measured attributes, SMMC1 was better than SMMC2 with tensile strength of 629 MPa, impact energy of 25 J, hardness of 160 HV and wear weight loss of 10.2 mg.

The compressive mechanical properties of the 93W-4.9Ni-2.1Fe heavy alloy were investigated across a wide range of strain rates (1.0 × 10⁻³-5.0 × 10³/s) using a mechanical test system (MTS810) and a Split Hopkinson Pressure Bar. The microstructure of the axial cross section of the specimens was subsequently analyzed using scanning electron microscopy, energy-dispersive X-ray spectrometry, and electron backscatter diffraction. The results revealed that under dynamic loading, the yield strength of the 93W-4.9Ni-2.1Fe heavy alloy showed increased strain rate sensitivity compared to quasi-static conditions. With increasing strain rate, the circle equivalent diameter of tungsten grains in the alloy continued to decrease, indicating a growing dominance in bearing the load and contributing to the deformation resistance. However, the work hardening capacity was reduced due to thermal softening effects under dynamic loading. Interface debonding between the tungsten grains and the matrix was observed after loading, and cracks initiated from weaker regions within the matrix, subsequently growing and intersecting. This study provides a theoretical basis for a comprehensive understanding of the high strain rate sensitivity and microstructural evolution of the 93W-4.9Ni-2.1Fe heavy alloy across a broad range of strain rates.

The development of next-generation high-strength steels is crucial for the automotive industry, necessitating advanced joining techniques. This study investigates the joining of STRENX 700 CR and DP 800 steels using resistance spot welding (RSW) with specialized fixtures. Unlike conventional methods, a regional pre-heating treatment was applied exclusively to the heat-affected zone (HAZ) prior to welding. Comparative analyses were performed between pre-heated and non-pre-heated welded joints. The welded joints underwent microstructural analysis, as well as non-destructive and destructive testing. Results revealed that pre-heating led to an expansion of the HAZ and a reduction in hardness. Additionally, there were significant improvements in mechanical properties, including increases in tensile-shear strength, cross-tension strength, and fatigue strength. These findings demonstrate the effectiveness of regional pre-heating in optimizing the mechanical performance of RSW joints, offering valuable insights for the automotive industry's welding applications.

In the present paper, duplex stainless steel was utilized as an insert for welding high manganese steel frog to high-carbon steel rail under three flash welding processes. The effect of the number of flashes and upsetting force on mechanical performance and microstructure of the welded joints was studied. The results showed that the impact energy of the inserts after welding experienced a significant reduction in the 524-6 (with the number of flashes reduced to 6) and 772-8 (with the upsetting force increased to 772 kN) welded joints compared to the 524-8 welded joint (with an upsetting force of 524 kN and 8 flashes). The other mechanical performances of the welded joints under the three states did not differ significantly. No cracks were observed in the transition regions between the high manganese steel and the insert in any of the three welded joints. Nevertheless, notable micro-voids were present in the 524-6 welded joint. The ferrite in the insert of the 524-6 joint was distributed in a horizontal streamline and continuous strip shape. Conversely, in the 524-8 and 772-8 welded joints, the ferrite was distributed in an arch bridge shape. However, the arch amplitude of the ferrite bridge in the insert of the 772-8 welded joint was larger, and the center of the insert was contained a greater number of ferrites. Furthermore, the severe stress concentration in the middle of the insert of the 524-6 and 772-8 welded joints, coupled with the large amount of ferrite in the middle of the insert of the 772-8 welded joint, were the primary reasons for the diminished impact energy of the insert for these two joints.

This study investigates the spheroidization behavior of the O phase in Ti₂AlNb alloy during high temperature deformation through a designed high-throughput experimental approach. The results of the high-throughput deformation experiments indicate that temperature, strain, and strain rate influence the spheroidization behavior of the O phase. Specifically, an increase in temperature and strain promotes the spheroidization of the O phase, while the strain rate exhibits the opposite effect. Moreover, the spheroidization mechanisms of this alloy during high-temperature deformation can be identified and primarily involve grain boundary separation mechanism, terminal dissolution mechanism, continuous dynamic recrystallization mechanism, edge spheroidization mechanism, and shear spheroidization mechanism. Furthermore, the analysis of experimental results reveals that the different morphologies of the spheroidized O phase have varying effects on the microscale mechanical response. In the region of large-sized high-density spheroidized O phase, the influence of back stress may extend to the entire B2 phase, thereby enhancing the B2 phase and subjecting the O phase and B2 phase to similar strains. Therefore, a small quantity of O phase is affected by the forward stress. Conversely, in the region of small-sized low-density spheroidized O phase, a small quantity of B2 phase is affected by the back stress, and the majority of the O phase is affected by forward stress. Eventually, the interaction mechanism between O phase and B2 phase during high-temperature deformation is explored for the first time through theoretical analysis.

In this process, the magnetic field pressure forces the driver to deform radially inward; sequentially, the D9 steel tube gets accelerated and forced to impact the SS316 end plug, causing a joint between the two. Experiments and metallurgical characterization were conducted by changing the working length of the field shapers and end plug shape at different voltages. The effect of change in end plug geometry, change in voltage, and change in field shaper working length was studied. The results were compared based on the values of the welded length, wavelength and crest height for the joined samples. The metallurgical characterization was performed using optical microscopy, the scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS). The micro-hardness test of the joined samples was also performed. To test whether the gap between the joint was present or not, helium leak tests were performed. For the confirmation of the strain hardening, hardness tests were performed near the joint interface.

A multi-factor gray model of hardness and modulus about the content of Ti, Fe, Ni and Cu metal powder in the inner layer of bimetal composite pipe was established, and the proportion of each component was optimized by genetic algorithm. The inner layer with a certain thickness was prepared by high frequency induction heating and powder spraying technology, its hardness and modulus were tested, and compared with the theoretical calculation value, the erosion wear test was carried out. The results indicate that the prepared inner layer is in an amorphous state, exhibiting high hardness and toughness. The gray model can accurately establish the relationship between the hardness and modulus of the inner layer with the component content, and the average error is not exceeding 2%. The inner layer prepared with the optimized raw material ratio demonstrates high erosion wear resistance at different impact angles and temperatures, the damage type is micro-cutting. Compared with the base pipe, the erosion rate is reduced by at least 27%.