Journal of Materials Engineering and Performance最新文献

Understanding the microstructural formation in the wire arc additive manufacturing (WAAM) process is highly important, and it is very challenging to predict the microstructure formation and mechanical properties of the as-deposited samples. The present study investigates the effect of process conditions such as current, travel speed, and gas flow rate on the mechanical and metallurgical properties of SS 316L stainless steel. The microstructure of the as-deposited samples reveals a diffusion zone with columnar dendrites and equiaxed grains in the bottom layers, skeletal δ-ferrite in the middle layers, and coarse dendritic structure in the top layers, respectively. Microstructure development in the samples' vertical direction shows pearlitic-ferritic grains to bainitic lamellae. The maximum and minimum grain sizes at the fusion region are 18 ± 1 µm and 7.56 ± 1 µm. Further, the using design of experiments technique the parameters are optimized for maximum tensile strength and hardness. The results show that travel speed has the highest impact on tensile strength (688 MPa), followed by current and gas flow rate. The main process parameter that affects the hardness (198 HV) is current followed by wire feed rate and gas flow rate. A relation of the strength concerning strain and temperature for various conditions is established using the Johnson–Cook model. The formation of γ-Fe, austenite, MnSi, Fe-Ni, etc., are observed in the x-ray diffraction images of as-deposited samples. The dislocation density varies from 1.745 × 10⁻⁴ to 9.922 × 10⁻⁴ nm⁻², and the microstrain is varying from 2.43 × 10⁻³ to 3.8 × 10⁻³. The fracture surfaces of as-deposited samples show the formation of dimples and river facets.

The development of high-performance photocatalysts is crucial in addressing water environmental pollution using photocatalytic technology. In this study, CPVA/SnS₂ heterojunctions modified with conjugated polyvinyl alcohol were prepared using water-soluble polyvinyl alcohol. The effects of temperature and CPVA loading amount on the chemical composition, morphology, optical and electrochemical properties, and visible-light photocatalytic reduction of aqueous Cr(VI) performance of CPVA/SnS₂ were evaluated. The results showed that the CPVA was uniformly coated on the surface of SnS₂, improving the light absorption range and the effective utilization of photogenerated carriers. All CPVA/SnS₂ heterojunctions exhibited enhanced photocatalytic activity compared to bare SnS₂. The reaction rate for the photocatalytic reduction of Cr(VI) by CPVA/SnS₂-B (0.034 min⁻¹) was 3.46 times higher than that of SnS₂ (0.0098 min⁻¹). The photocatalytic mechanism of S-scheme heterojunction for the photocatalytic reduction of Cr(VI) by CPVA/SnS₂ was proposed based on the trapping experiments and electrochemical results. This study provides a straightforward strategy for the construction of efficient photocatalysts.

To assess the yield strength of gradient-nanostructured (GNS) material by small punch test, an analytical method is proposed in this paper. The constructed theoretical model of GNS material is integrated into the classical circular plate bending theory, and an analytical formula specific to GNS material with different microstructures is derived. In order to mitigate the influence of stress state, the analytical formula is modified. The yield strength obtained by the revised analytical formula is close to the standard tensile test results, with errors falling within permissible range. Additionally, the relationship between elastic modulus and surface microstructure of GNS material is established. Thus, the yield strength of GNS material could be evaluated by the surface grain size without measuring of the surface elastic modulus.

Superduplex stainless steels (SDSSs) have high mechanical and corrosion resistance. Those properties are due to the biphasic microstructure formed by ferrite and austenite in similar proportions. Oil and gas companies use a cold-worked seamless tube manufactured in SDSS in oil country tubular goods applications. However, the understanding of how the cold work influences the dislocation density in each one of the SDSS phases is unclear. In this work, a cold-worked SDSS W-alloyed was investigated. Samples in as-received condition (AR-CW) and solution thermal treated at 1050, 1100, and 1150 °C were analyzed using XRD. Additionally, the AR-CW sample was characterized in TEM. The dislocation density was measured using Williamson & Smallman model, which uses the crystallite size and lattice microstrain as input parameters. Those parameters were calculated using different models: Scherrer; Monshi–Scherrer; and Williamson–Hall. The cold work promotes a smaller crystallite size and a bigger lattice microstrain. The thermal treatment reduces the levels of dislocation density, and the increase in the treatment temperature results in higher dislocation density.

The combined effect of annealing temperature and pre-deformation on the superelastic behaviors of NiTi shape memory alloy wires was investigated by testing two types of samples with 72 and 35% area reduction. It is found that the annealed samples with 72% area reduction exhibited larger martensitic transformation stress, and the annealed samples with 35% area reduction exhibited superior superelastic cycle stability. The stress hysteresis of martensitic transformation for both two types of samples decreased with decreasing annealing temperature. In addition, pre-deformation enhanced the superelastic cycle stability and increased the stress hysteresis of the NiTi wires with 72% area reduction, but it had little effect on the stress hysteresis of the NiTi wires with 35% area reduction.

This paper deals with the experimental research, modeling and parametric-based optimization of the mechanical properties of the friction stir welded AZ80A Mg alloy. A four-factor, five-level-based central composite design matrix was employed to minimize the experimental runs. Adaptive neuro-fuzzy inference system (i.e., ANFIS) was employed to map the relationship amid the parameters of FSW process (namely tool pin geometry, traverse speed, axial force, and rotational speed) and mechanical properties (including yield strength, tensile strength and hardness) of the joints. Later, the formulated ANFIS model was used along with simulated annealing (SA) algorithm determining the optimized parameters of FSW process so as to attain flaw free AZ80A Mg alloy joints. Formulated ANFIS model-SA algorithm anticipated that the friction stir welded AZ80A Mg alloy joints will possess a tensile strength of 240.52 MPa during the single-response optimization scenario and a tensile strength of 240.522 MPa during the multiple-response optimization scenario. Experimental results announced that the FSW process parameter combination of tool rotational speed of 1250 rpm, tool traverse speed of 1.75 mm/sec, axial force of 3 kN and tool possessing a threaded cylindrical pin geometry have contributed for attainment of largest values of mechanical properties during both the single-response and multiple-response optimization scenarios. During the confirmatory experimental work, the flaw free friction stir welded AZ80A Mg alloy joints exhibited a tensile strength of 242.16 MPa and the results of confirmatory experiment revealed that the ANFIS-SA system had exhibited superiority in modeling and optimization of the FSW process during joining of AZ80A Mg alloys.

Short-circuit transfer gas metal arc welding (GMAW) has shown great potential in wire and arc manufacturing (WAAM) of complex components with overhang structures. The difficulties lie in the identification of the short range of process window and remaining a stable process. This paper combines Taguchi's method with grey relational analysis to explore the effects of short-circuit transfer process parameters on multiple bead quality performances including aspect ratio, dilution rate, number of humps, and hardness gradient, followed by multi-objective optimization and experimental validation. The results show that welding voltage has the most significant effect on aspect ratio and dilution rate, while welding speed is the most important factor influencing number of humps and hardness gradient. As welding voltage increases, both aspect ratio and dilution rate keep increasing. With increase in welding speed, the number of humps and hardness gradient are increased. The optimal combination of process parameters for short-circuit transfer robotic GMAW of Q235 steel is a welding current of 80 A, a welding voltage of 22 V, a welding speed of 30 cm min⁻¹, and a travel angle of 60°. The research outcomes provide theoretical basis for the industrial application of short-circuit transfer GMAW for WAAM of overhang structures.

This work investigated the application of the LSV-KOH test to quantify deleterious phases in a UNS S32707 hyper duplex stainless steel (HDSS). HDSS is a metal alloy with excellent corrosion resistance, but it can form deleterious phases (DP) when exposed to high temperatures. These phases can reduce the corrosion resistance and mechanical properties of HDSS by creating chromium-depleted zones in the microstructure. The LSV-KOH test was applied to a UNS S32707 HDSS aged at different temperatures ranging from 700 to 950 °C. The total amount of DP was quantified by quantitative metallography using a scanning electron microscope (SEM). The effect of KOH concentration on the test results was studied and optimized. The optimal KOH concentration found was 6.0 mol L⁻¹. A R² of 0.99 was reached when LSV-KOH response was plotted versus DP%. The LSV-KOH was compared with the DL-EPR test, the results demonstrated that the LSV-KOH test was more sensitive and accurate than the DL-EPR test in detecting and quantifying DP. Further investigation of the specimens’ surfaces after each test demonstrated that LSV-KOH acts directly on deleterious phases, while DL-EPR acts in DP contours. The study demonstrates that the LSV-KOH test has several advantages over the DL-EPR test for evaluating the microstructural transformations of HDSS caused by thermal ageing.

A Ni-Cr alloy powder, designated MB40, with an average size of 30.5 µm, was used as a grain boundary modifier in a recycled neodymium-iron-boron (Nd-Fe-B) matrix to improve the corrosion resistance, coercivity and other properties of the rare-earth sintered magnet. Nd-Fe-B powder with an average grain size of 95.1 µm was obtained by milling. The effects of doping with different amounts of MB40 (0, 0.5 and 1 wt.%) on the properties of the recycled magnet compared with an initial magnet were investigated. X-Ray Diffraction analysis revealed the formation of the Fe₁Nd₁Ni₄ and NiCrFe phases, after sintering, as well as the tetragonal phase Nd₂Fe₁₄B matrix phase in the magnet doped with 1 wt.% of MB40. Scanning Electron Microscopy images coupled with energy-dispersive x-ray spectroscopy demonstrated that in the sample doped with 1 wt.% MB40, Cr-Ni diffuses into the grain boundaries, thus improving the microstructure of the magnet. Electrochemical Impedance Spectroscopy and potentiodynamic polarization were employed for corrosion characterization. The magnet doped with 1wt.% MB40 exhibited the highest corrosion potential (E_corr = − 696 mV), polarization resistance (R_P = 1151.2 Ω·cm²) and a low corrosion rate (V_corr) of 4.34 µm·year^-1 compared to the starting (initial) sample. The optimum characteristics of recycled NdFeB were obtained by blending milled NdFeB powder with 1 wt.% MB40, achieving the best values for product energy (BH_max), coercivity (H_C) and hardness, respectively 48.03 MGOe, 10.8 KOe and 587 HV.

In this paper, the microstructural evolution and tribological behavior of an FeCoNiCr alloy containing Sm fabricated by the Laser Metal Deposition technique were investigated. The study employs x-ray diffraction analysis, energy-dispersive spectroscopy, and friction coefficient measurements to comprehensively investigate the impact of Samarium (Sm) addition on the microstructural evolution and frictional behavior of high-entropy alloys (HEAs). Results reveal that the inclusion of 0.4-0.8 wt.% Sm effectively inhibits the formation of coarse phases at the interface between HEAs and 45 steel substrates, enhancing their bonding strength while inducing the precipitation of secondary phases within the HEA matrix. During frictional processes, distinct characteristics in friction coefficients in the friction pair between HEAs against 304 stainless steel beads and SiC beads are observed. Sm-added HEAs demonstrate relatively stable friction coefficients and different friction behaviors with various Sm content, which can be attributed to changes in friction mechanisms caused by formation of oxide particles as lubricant on the contact surface.