Jian Han

Shape memory alloys (SMAs) are widely applied in various fields due to their superior shape memory effect (SME) and superelasticity. However, most SMAs show unsatisfactory shape memory performance in a high-temperature environment due to their low phase transition temperatures. As a result, elevating the phase transition temperature of SMAs is essential. Among all kinds of SMAs, Ti-V-Al-based shape memory alloys have prominent advantages, including high phase transition temperatures and lightweight. In this study, a novel Ti-10V-10Al high-temperature lightweight shape memory alloy (HTSMA) was fabricated using a selective laser melting (SLM) method. The investigation results indicate that the Ti-10V-10Al has superior tensile properties, with a tensile strength of 1107.4 MPa and an elongation of 9.3%, exceeding many reported Ti-based SMAs. More importantly, the alloy achieves a shape recovery rate of 98% at a 5% pre-strain, indicating its excellent shape memory effect. This research provides a new insight for designing a high-performance SLM Ti-V-Al HTSMAs.

Shape memory alloys (SMAs) are widely applied in various fields due to their superior shape memory effect (SME) and superelasticity. However, most SMAs show unsatisfactory shape memory performance in a high-temperature environment due to their low phase transition temperatures. As a result, elevating the phase transition temperature of SMAs is essential. Among all kinds of SMAs, Ti-V-Al-based shape memory alloys have prominent advantages, including high phase transition temperatures and lightweight. In this study, a novel Ti-10V-10Al high-temperature lightweight shape memory alloy (HTSMA) was fabricated using a selective laser melting (SLM) method. The investigation results indicate that the Ti-10V-10Al has superior tensile properties, with a tensile strength of 1107.4 MPa and an elongation of 9.3%, exceeding many reported Ti-based SMAs. More importantly, the alloy achieves a shape recovery rate of 98% at a 5% pre-strain, indicating its excellent shape memory effect. This research provides a new insight for designing a high-performance SLM Ti-V-Al HTSMAs.

Ti-Ni-Fe shape memory alloy offers advantages including low phase transformation temperature and favorable mechanical properties. In this study, Ti-Ni-Fe shape memory alloy was fabricated for the first time by double-wire arc additive manufacturing (D-WAAM) using Ni50.7Ti49.3 and pure Fe welding wires as feedstock. A systematic investigation was conducted on microstructural evolution and mechanical properties. The results indicated that the as-deposited alloy was composed of B2-NiTi as the matrix, Ti2Ni and α-Ti precipitates. The alloy exhibited average tensile strength of 1026 MPa and a fracture strain of 13%. Cyclic tensile tests revealed that the alloy achieved a high reversible strain of 4.87% and a low residual strain of 1.37%, indicating excellent superelasticity. The microhardness along the deposition direction exhibited a gradient distribution: approximately 200 HV0.2 at the bottom region, 325 HV0.2 in the middle region, and microhardness decreased from 425 HV0.2 to 325 HV0.2 at the top region.

With the advancement of welding technology, the demand for 70S-6 welding wire steel has steadily increased in industries such as construction, automotive, pressure vessels, and line pipe manufacturing. To optimize the production process of the target material, this study utilized the finite-element software ABAQUS to numerically simulate the multi-pass finish rolling process of 70S-6 welding wire steel. The study investigates the effects of the key rolling parameters—pass distribution (8/10/12 passes), finish rolling temperature (860/880/900 °C), and rolling speed (0.5 Vp/1.0 Vp/1.5 Vp, here Vp denotes the reference industrial rolling speed) on the rolling force, temperature field, and equivalent stress/strain during finish rolling. The results show that the increased number of passes homogenizes deformation, reduces local stress concentration and enhances mechanical properties. Specifically, 12 passes reduce the peak rolling force from 250,972 N to 208,124 N, significantly enhancing stress and temperature uniformity across the section. Increasing the finish rolling temperature lowers the pass-averaged flow stress and attenuates rolling-force fluctuations. At 880 °C, the simulated core–surface temperature gradient is minimal (50 °C), whereas at 900 °C the gradient increases (80 °C) but the rolling-force histories exhibit a lower peak level and smaller low-frequency oscillations; thus 880 °C is preferable when through-thickness thermal uniformity is targeted, while 900 °C is more suitable when a smoother load response is required. Increasing the finish rolling speed from 0.5 Vp to 1.5 Vp reduces the peak rolling force from 233,165 N to 183,665 N and significantly damps low-frequency load oscillations. However, it concurrently intensifies stress localization at the outer-surface tracking points P3/P4, which are in direct contact with the rolls, where the local equivalent stress approaches 523 MPa, even though the overall strain distribution along the bar length becomes more uniform. Overall, the optimal processing window is identified as a 12-pass schedule, a finish rolling temperature of 880–900 °C, and a rolling speed of 1.0–1.5 Vp, which can improve both rolling quality and temperature and stress and strain uniformity.

This study investigates the forming process (stamping) of bipolar plates which have applied a novel ultra-thin (0.1 mm) super ferritic stainless steel, i.e., SUS470, whose chromium is sufficiently high for corrosion resistance. A three-dimensional finite element model of the stamping process was developed using the commercial software ABAQUS version 2022. The model incorporated optimized die parameters obtained through Central Composite Design (CCD). This model was used to analyze the effects of key forming parameters, including stamping speed and friction coefficient, on the distribution of stress, strain, and thickness reduction during the stamping process. The finite element modeling (FEM) results disclose that the inner corner of the flow channel is a critical defect-prone region, exhibiting stress concentration, uneven strain distribution, and severe thinning. The optimal forming quality can be achieved at a stamping speed of 100 mm/s and a friction coefficient of 0.185 among all varied options. Further, a comparative study of single-stage, conventional two-stage, and optimized two-stage stamping strategies based on previous investigation demonstrates that the optimized two-stage stamping process can effectively alleviate stress and strain concentrations at the corners, significantly reduce thinning problems, and enhance the uniformity and stability during stamping. In summary, this study provides theoretical support for the design of the forming process (stamping) of high-performance super ferritic stainless steel bipolar plates, which is beneficial to subsequent practical engineering application.