Acta Metallurgica Sinica-English Letters最新文献

In this study, the effects of ultrasonic coaxial assisted TIG welding (U-TIG) on the formation, microstructure, and mechanical properties of TC4 titanium alloy welded joints were investigated. The results indicated that at optimal ultrasonic power and welding current settings, remarkable improvements of welded joint were observed. Specifically, the weld depth-to-width ratio increased by 267% compared to conventional TIG welding, reaching 0.22. Furthermore, the microhardness of the welded seam increased by 53%, reaching 550.1 HV, while the tensile strength of the welded joint rose to 1197.7 MPa, representing a 12.2% enhancement. The compressing effect of ultrasound concentrates the energy of the arc, thereby improving the penetration depth of the welded seam. In addition, ultrasonic cavitation plays a crucial role in refining the grain structure of the weld seam, consequently enhancing its strength.

As a representative of the third generation advanced high-strength steels (AHSSs), medium Mn steels (MMS) have broad development prospects in the field of automobile manufacturing. MMS with typical austenite reversion treatment have a soft duplex microstructure, i.e. ferrite + austenite, presenting a high ductility but a low yield strength. Here we show that a flash heating and cooling after austenite reversion treatment can replace the ferrite with strong martensite, which greatly enhances the yield strength of a 0.25C-4Mn steel by about 461–886 MPa. By adjusting the reversion temperature before the flash treatment, the C and Mn concentrations of reverted austenite can be altered, which determine the fraction of reverted austenite surviving the flash treatment. In addition, the mechanical stability of final retained austenite is also linked to the reversion temperature, resulting different work hardening behaviors due to transformation induced plasticity (TRIP) effect. By tweaking the reversion temperature before the flash treatment, an optimized combination of strength and ductility can be achieved. The micromechanical differences caused by the replacement of the matrix are also investigated via in-situ digital image correlation method.

It is extremely difficult to strengthen bulk aluminum (Al) by twins, due to its high stacking fault energy under standard loading conditions. In this study, a simple yet effective solution was proposed for introducing twins to strengthen bulk Al. The method involves the addition of nanoparticles with high volume fraction combined with the tailoring of sintering temperature toward the melting point of Al during hot pressing. Sintering temperature plays an important role in forming twins in bulk Al containing high content nanoparticles. The twin content increases with increasing sintering temperature in the range of 590–640 °C. At sintering temperature of 640 °C, the twin content reaches 17%, enabling the significant improvement in the yield strength of the bulk Al from 251 to 400 MPa, compared with the sample with few or no twins. The twin strengthening may serve as a major strengthening mechanism for bulk Al, and its strengthening contribution is comparable to the dominant Orowan strengthening resulting from the added nanoparticles.

To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys, ATI 718Plus alloys with varying Al contents (1, 3, and 5 wt%) were fabricated using the laser additive manufacturing and the effects of Al content on the microstructure and mechanical properties were systematically analyzed. The experimental and CALPHAD simulation results show that with the increase in Al addition, the freezing range of the alloys was lowered, but this has a paradoxical effect on the susceptibility of the alloy to hot-tearing and solid-state cracking. The addition of Al increased the γ′ and Laves phase volume fractions and suppressed the precipitation of the η phase. Simultaneously improving γ/γ′ lattice misfits effectively promoted the transformation of γ′ phase from spherical to cubic. The precipitation of NiAl phase in the 5 wt% Al-added alloy was determined, the formation mechanism of NiAl phase was analyzed, and the solidification sequence of the precipitated phase in the alloy was summarized. In addition, with the increase in Al addition, the microhardness of the alloy increased gradually, the tensile strength increased at first and then decreased, but the plasticity deteriorated seriously. The insights gained from this study offer valuable theoretical guidance for the strategic compositional design of additively manufactured Ni-based superalloys destined for deployment under extreme conditions.

L1₂ phase-strengthened Fe–Co–Ni-based high-entropy alloys (HEAs) have attracted considerable attention due to their excellent mechanical properties. Improving the properties of HEAs through conventional experimental methods is costly. Therefore, a new method is needed to predict the properties of alloys quickly and accurately. In this study, a comprehensive prediction model for L1₂ phase-strengthened Fe–Co–Ni-based HEAs was developed. The existence of the L1₂ phase in the HEAs was first predicted. A link was then established between the microstructure (L1₂ phase volume fraction) and properties (hardness) of HEAs, and comprehensive prediction was performed. Finally, two mutually exclusive properties (strength and plasticity) of HEAs were coupled and co-optimized. The Shapley additive explained algorithm was also used to interpret the contribution of each model feature to the comprehensive properties of HEAs. The vast compositional and process search space of HEAs was progressively screened in three stages by applying different prediction models. Finally, four HEAs were screened from hundreds of thousands of possible candidate groups, and the prediction results were verified by experiments. In this work, L1₂ phase-strengthened Fe–Co–Ni-based HEAs with high strength and plasticity were successfully designed. The new method presented herein has a great cost advantage over traditional experimental methods. It is also expected to be applied in the design of HEAs with various excellent properties or to explore the potential factors affecting the microstructure/properties of alloys.

AlCoCrFeNi_2.1-xNi₃Al (x = 0, 5.0, 7.5, and 10 wt%, denoted as Ni₃Al0, Ni₃Al5.0, Ni₃Al7.5, and Ni₃Al10) eutectic high-entropy alloy (EHEA) matrix composites were fabricated by mechanical alloying and spark plasma sintering methods. The effects of Ni₃Al content on the microstructures, mechanical and wear properties of AlCoCrFeNi_2.1 EHEA were investigated. The results indicate that the AlCoCrFeNi_2.1-xNi₃Al composites present cellular grid morphologies composing of FCC/Ll₂ and B2 phases, and a small amount of Al₂O₃ and Cr₇C₃ phases. The addition of Ni₃Al significantly enhanced the compressive yield strength, compressive fracture strength, compressive strain and wear properties of the AlCoCrFeNi_2.1 composites. In particular, the Ni₃Al10 composite exhibits excellent comprehensive mechanical properties. The compressive yield strength, compressive fracture strength and compressive strain of the Ni₃Al10 composite, are 1845 MPa, 2301 MPa and 10.1%, respectively. The friction coefficient, wear width and depth, and mass loss of the Ni₃Al10 composite were 0.40, 0.9 mm, 20.5 mm, 0.016 g, respectively. Moreover, the wear mechanism of the Ni₃Al10 composite is major abrasive wear with a small amount of adhesive wear.

The refined explicit finite element scheme considering various strengthening mechanisms and damage modes is proposed for simulation of deformation processes and mechanical properties of carbon nanotube (CNT)-reinforced bimodal-grained aluminum matrix nanocomposites. Firstly, the detailed microstructure model is established by constructing the geometry models of CNTs and grain boundaries, which automatically incorporates grain refinement strengthening and load transfer effect. Secondly, a finite element formulation based on the conventional theory of mechanical-based strain gradient plasticity is developed. Furthermore, the deformation and fracture modes for the nanocomposites with various contents and distributions of coarse grains (CGs) are explored based on the scheme. The results indicate that ductility of the composites first increases and then decreases as the content of CGs rises. Moreover, the dispersed distribution exhibits better ductility than concentrated one. Additionally, grain boundaries proved to be the weakest component within the micromodel. A series of interesting phenomena have been observed and discussed upon the refined simulation scheme. This work contributes to the design and further development of CNT/Al nanocomposites, and the proposed scheme can be extended to various bimodal metal composites.

Nano-zinc oxides (ZnO) demonstrate remarkable antibacterial properties. To further enhance the corrosion resistance and antibacterial efficiency of magnesium alloy micro-arc oxidation (MAO) coatings, this study investigates the preparation of ZnO-containing micro-arc oxidation coatings with dual functionality by incorporating nano-ZnO into MAO electrolyte. The influence of varying ZnO concentrations on the microstructure, corrosion resistance, and antibacterial properties of the coating was examined through microstructure analysis, immersion tests, electrochemical experiments, and antibacterial assays. The findings revealed that the addition of nano-ZnO significantly enhanced the corrosion resistance of the MAO-coated alloy. Specifically, when the ZnO concentration in the electrolyte was 5 g/L, the corrosion rate was more than ten times lower compared to the MAO coatings without ZnO. Moreover, the antibacterial efficacy of ZnO + MAO coating, prepared with a ZnO concentration of 5 g/L, surpassed 95% after 24 h of co-culturing with Staphylococcus aureus (S. aureus). The nano-ZnO + MAO-coated alloy exhibited exceptional degradation resistance, corrosion resistance, and antibacterial effectiveness.

In the present study, Ti–Zr–Cu–Ni amorphous filler metal was used to braze MgAl₂O₄ ceramic and Ti–6Al–4V (TC4) at 875, 900, 925, 950, 975 and 1000 °C for 10 min. The effects of brazing temperature on interfacial microstructure and mechanical properties of the joints were analyzed. The results showed that typical microstructure of the TC4/MgAl₂O₄ joint was solid solution (SS) α-Ti, acicular α-Ti + (Ti, Zr)₂(Ni, Cu) layer, metallic glasses and TiO. With the increase in brazing temperature, (Ti, Zr)₂(Ni, Cu) layer gradually dispersed at bonding interface, a continuous layer of TiO appears near MgAl₂O₄ ceramic. With the increase in brazing temperature, the hard and brittle (Ti, Zr)₂(Ni, Cu) layer gradually dispersed, resulting in the maximum shear strength of 39.5 MPa. The high-resolution TEM revealed the presence of amorphous structure, which is composed of Ti, Zr, Cu, Ni and Al. The values of δ and ΔH_mix are calculated to be about 8% and −39.82 kJ/mol for the amorphous phase.

Iron-based metal matrix composites (IMMCs) have attracted significant research attention due to their high specific stiffness and strength, making them potentially suitable for various engineering applications. Microstructural design, including the selection of reinforcement and matrix phases, the reinforcement volume fraction, and the interface issues are essential factors determining the engineering performance of IMMCs. A variety of fabrication methods have been developed to manufacture IMMCs in recent years. This paper reviews the recent advances and development of IMMCs with particular focus on microstructure design, fabrication methods, and their engineering performance. The microstructure design issues of IMMC are firstly discussed, including the reinforcement and matrix phase selection criteria, interface geometry and characteristics, and the bonding mechanism. The fabrication methods, including liquid state, solid state, and gas-mixing processing are comprehensively reviewed and compared. The engineering performance of IMMCs in terms of elastic modulus, hardness and wear resistance, tensile and fracture behavior is reviewed. Finally, the current challenges of the IMMCs are highlighted, followed by the discussion and outlook of the future research directions of IMMCs.