Yanhui Wang’s research while affiliated with Hebei University of Engineering and other places

In order to address the shortcomings of the traditional bidirectional RRT* algorithm, such as its high degree of randomness, low search efficiency, and the many inflection points in the planned path, we institute improvements in the following directions. Firstly, to address the problem of the high degree of randomness in the process of random tree expansion, the expansion direction of the random tree growing at the starting point is constrained by the improved artificial potential field method; thus, the random tree grows towards the target point. Secondly, the random tree sampling point grown at the target point is biased to the random number sampling point grown at the starting point. Finally, the path planned by the improved bidirectional RRT* algorithm is optimized by extracting key points. Simulation experiments show that compared with the traditional A*, the traditional RRT, and the traditional bidirectional RRT*, the improved bidirectional RRT* algorithm has a shorter path length, higher path-planning efficiency, and fewer inflection points. The optimized path is segmented using the dynamic window method according to the key points. The path planned by the fusion algorithm in a complex environment is smoother and allows for excellent avoidance of temporary obstacles.

In this study, novel multiple gradient structures with various distributions of austenite/martensite phase, grain sizes, and dislocation densities were fabricated in medium-Mn steel by using torsion treatment, and the corresponding tensile properties and deformation mechanisms were investigated. The results showed that the yield strength and the total elongation of the multiple-gradient-structured samples increased by 27% and 25%, respectively, compared with their homogeneous counterparts. A distinct phase transformation behavior was observed in the present gradient medium-Mn steel. That is, the strain-induced martensitic transformation was promoted in the center during the entire tensile deformation process; however, it was suppressed at the surface during the initial deformation stage and then significantly triggered during the remaining deformation process. Moreover, active strain partitioning at the macroscale and microscale occurred during plastic deformation, which led to a higher hetero-deformation induced (HDI) stress in the multiple-gradient samples. A combination of a strong and persistent transformation-induced plasticity effect, active HDI strengthening and HDI hardening, and dislocation strengthening contributed to the superior strength–ductility synergy of the gradient-structured medium-Mn steel.

The effect of tempering at 200 °C for 20 min on the mechanical properties of a cold‐rolled and intercritical annealed medium Mn steel was investigated in this study. This effect was mainly dependent on the original annealing condition. For the sample annealed at relatively low temperature (660 °C), the austenite stability of this sample was further improved significantly after tempering. Thus, transformation‐induced plasticity effect was severely inhibited during deformation, which led to the decrease in properties of the sample. By contrast, for the sample possessing suitable austenite fraction (∽30%) and heterostructure, that is, the sample annealed at 680 °C for 10 min, the simultaneously increased strength and ductility were significantly intrigued by tempering treatment. EPMA and 3DAP results revealed that C concentration in austenite was increased due to the C repartition during tempering, which led to the persistent TRIP effect in a broad strain range during tensile deformation. In addition, the heterogeneous‐deformation‐induced stress of the heterostructured sample was found to be obviously intensified by tempering treatment. Thus, an excellent strength plastic synergistic effect with a product of ultimate tensile strength and total elongation of approximately 70 GPa·% was obtained in the tempered sample. This article is protected by copyright. All rights reserved.

The deformation mechanisms of a novel medium Mn steel (Fe–0.14C–7.8Mn–1.65Al–0.11Zr, wt%) were investigated through mixed multiphase preservation-intercritical annealing route. A heterogeneous duplex microstructure consisting of plate-like and equiaxed austenite and ferrite with multiple morphologies and multiscale and Mn inhomogeneous distribution was obtained after intercritical annealing at 680 °C for 10 min. The heterostructured sample exhibited excellent strength–ductility synergy with a yield strength of 1022 MPa, an ultimate tensile strength of 1280 MPa, and a total elongation of 53%. Comparative analysis revealed that hetero-deformation-induced (HDI) stress was generated during tensile deformation. This stress was primarily responsible for the superhigh yield strength of the heterostructured sample. In addition, the HDI stress could initially trigger premature martensitic transformation of austenite in the grain or phase boundary region and delay the martensite transformation of untransformed austenite to a large strain range due to the shielding effect of the formed core–shell structure, which comprised an untransformed core austenite and a shell α'-martensite. Multiple strengthening and ductility-enhancing mechanisms involving transformation-induced plasticity effect, twin-induced plasticity effect, HDI synergistic hardening, and dislocation strengthening occurred sequentially during deformation, leading to the extraordinary strength–ductility combination of the heterostructured medium Mn steel.

Gradient structures (GS) with various grain size distributions are successfully architectured in a commercial low-alloying steel by using the pre-torsion and thermal annealing routes, and the corresponding mechanical properties and hetero-deformation induced (HDI) strengthening and work-hardening are investigated. Results demonstrate that an optimal grain size distribution from ~5.0 ± 2.8 μm at the surface to 11.1 ± 4.5 μm at the center leads to the maximum HDI strengthening of ~325 MPa. The HDI work-hardening intensifies continuously with the decreased average grain size of the GS due to the formation of abundant geometrical necessary dislocations (GNDs) whose density decreases abnormally from the fine-grain surface to the coarse-grain core caused mainly by the interactions between the short-range GNDs and long-range GNDs. Thanks to the HDI strengthening and work-hardening, the yield strength increases with a reduction of uniform ductility approximately following the linear inverse rule, in stark contrast to the banana-shaped strength-ductility trade-off of monolithic materials, and an exceptional strength-ductility synergy is achieved.