Journal of Materials Engineering and Performance最新文献

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%.

This study investigated the synergistic effects of Ti and Cr alloying elements on the microstructure, mechanical and wear properties of Cu-Zn manganese brasses. The simultaneous addition of Ni and Pb elements decreases the size of silicides and thus increases the yield strength of brass. The addition of Ti on the basis of Ni and Pb increases the content of silicides, and the generation of massive small-sized silicides increases the hardness and the wear resistance of brass. Cr element has refining effect on the size of silicides, and the smallest-sized and most uniformly distributed silicides induce the largest ultimate tensile strength and elongation. However, the simultaneous addition of Cr and Ti elements causes the agglomeration of silicides, and this results in poor ductility and wear resistance of brass.

Despite inherent chemical and physical stability of stainless steel, the significantly lower productivity of energy compared to energy usage still necessitates research in harsh environments that demand high material performance under challenging condition. This study explores the formation and characterization of mechanical properties, corrosion, and heat-transfer behaviors for thermal oxide layers on SS304 through various heat treatment conditions. The heat treatment at low temperature (500 °C) formed thin oxide layers with few tens of nanometers (S-500), delivering to superior mechanical properties, measured by nanoindenter. However, the thin layers of S-500 show rapid corrosion behaviors in NaCl solution, investigated by linear sweep voltammetry polarization curves. In contrast, the thick oxide layers of S-700 with the thickness of 2.5-3.5 µm grown at high temperature (above 600 °C) showed low mechanical properties but superior corrosion resistance. The difference between heat treatment conditions derive to diverse oxide compositions from SS304 substrate, particularly, Cr₂O₃ at 700 °C. The Cr₂O₃ provided high corrosion resistance, but it reduced thermal conductivity due to its intrinsic properties.

In this study, Mg was removed from an A332 molten alloy using mixtures of mineral zeolites enriched with 1, 2, and 3 wt.% of amorphous silica nanoparticles (SiO_2NP) to obtain an A380 aluminum alloy. Mineral zeolite with 3 wt.% SiO_2NP was found to be the most efficient mixture, removing Mg from an initial content of 2 wt.% to a final content of 0.046 wt.% 70 min after injection. The results indicated that a decrease in the Mg content, followed by thermal aging treatment (T6) at 150 °C for 10 h, resulted in a reduction of the volumetric fraction percentage (V_f%) of needle-like β-Al₅FeSi intermetallics from 1.123 to 0.181. Similarly, T6 treatment modified the lamellar Si-eutectic to cell-eutectics, as revealed by microstructure analysis. Consequently, the mechanical properties of the alloy, such as fracture strength (σ_f), yield-stress (σ_o), and strain (ε), were improved. The microstructural modification postulated in this study can enhance the contact stiffness under load cycles of 100 Hz at 400 mN, owing to the high storage elastic modulus of 57 GPa, estimated by dynamic mechanical analysis nanoindentation.

Abaca fibers were alkaline boiling treated with sodium hydroxide aqueous solution combined with impregnating in aluminum dihydrogen phosphate solution to improve the thermal shock resistance and reinforce shells for investment casting. The microstructure and thermal shock resistance of the treated fibers were analyzed, and their influence on the properties of reinforced shells was investigated. It is found that the hemicellulose and lignin at the surfaces of the fibers undergoing alkaline boiling were removed. A dense protective film was formed on the boiled fibers surfaces through impregnating in a solution of 15.0 wt.% aluminum dihydrogen phosphate. Moreover, the results demonstrated that the weight loss of the boiled-impregnated fibers reduces by 44.61%, compared to the raw fibers, indicating significantly improving the thermal shock resistance. Furthermore, the high-temperature strength of specimens reinforced with boiled-impregnated fibers of 1.29 wt.% reached a peak of 20.11 MPa, increasing by 68.12% compared to the unreinforced. And the alkaline boiled-immersed fibers reinforced shell occurred at elevated temperature a low deformation underweight of only 0.49%. Especially, the impregnated fibers with thermal shock resistance not only ensured good permeability of reinforced shells, but also enhanced the high-temperature cracking resistance capacity. This fully demonstrates the effectiveness of impregnating treatment in improving thermal shock resistance of fibers, and it is very promising to be applied in practical shell-making.

Graphical Abstract

Electronic devices such as smart portable devices, drones and electric vehicles are in the process of rapid performance development, which puts higher demands on the thermal conductivity and density of thermal interface materials. These fields hope that under the premise of improving the thermal conductivity of thermal interface materials, the density can be kept unchanged or even reduced, so as to avoid the substantial increase in equipment quality caused by the use of more thermal interface materials. In this context, hexagonal boron nitride was used in conjunction with spherical alumina, and the hexagonal boron nitride was oriented in the through-plane direction through the traditional preparation process of a silicone rubber-based TIMs combined with clever post-processing. When the filling amount of hexagonal boron nitride is 7.2 wt.%, the composite has a through-plane thermal conductivity of 3.257 W m^-1 K^-1 and a specific gravity of 2.45 which is 86.1% of the traditional thermal interface material (DQL-TP300). At the same time, samples with hexagonal boron nitride oriented exhibited better performance of compression rate, breaking elongation and tensile strength. It provides a feasible solution for preparing the silicone rubber-based thermal interface materials with high thermal conductivity, low density and low cost.

The hot deformation behavior, microstructure evolution and dynamic recrystallization mechanism of the newly designed 15Cr-30Ni-Fe heat-resistant alloy were studied. The flow curves of the alloy exhibit obvious dynamic recrystallization characteristics of a single stress peak, and the increase in Al/Ti ratio enhances the deformation resistance of the alloy during hot working. The constitutive equation corrected by strain compensation was established. The processing map of the alloy was constructed based on the dynamic material model, and the accuracy of the processing map was confirmed by checking the evolution of the microstructure. With the increase in Al/Ti ratio, the optimum hot working window of the alloys at a strain of 0.9 is broadened from 1050-1150 °C/0.01-0.1 s⁻¹ to 1015-1150 °C/0.01-0.57 s⁻¹. The strain-induced precipitation of nano-sized Laves phase, (Ti,Nb)C and γ'-Ni₃(Ti, Al, Nb) pinning the movement of dislocations and grain boundaries in the alloy with a high Al/Ti ratio hinders the growth of DRX grains. The dynamic recrystallization mechanism in 15Cr-30Ni-Fe heat-resistant alloy is mainly discontinuous dynamic recrystallization (DDRX) with grain boundary bulge, supplemented by continuous dynamic recrystallization (CDRX) with sub-grain nucleation.

In response to the presence of joint defects and occurrence of softening in aluminum alloys resulting from resistance spot welding (RSW), heat treatment pulse has been used to improve welded joints. The effects of applying a heat treatment current on the microstructure, mechanical properties, precipitated phase, and fracture characteristic of the resistance spot welding joints were studied. The microstructures of the welded joints were analyzed by optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Moreover, the mechanical properties of the welded joints were analyzed by tensile and microhardness tests. The results showed that the heat treatment pulse increased the uniformity of the element distributions and grain sizes of the welded joints and eliminated the intergranular crack in the columnar crystal zones of these joints. Compared with the single pulse, the mechanical properties of the welded joint improved by applying a heat treatment pulse. The tensile shear force of the welded joint increased by 11.2% after applying an appropriate heat treatment current. The hardness of the joints decreased slightly, the toughness increased, and the fracture modes changed from ductile-brittle fracture to ductile fracture. This method improved the easy softening of the joint during aluminum alloy RSW and avoided the formation of defects.