The first Youth Forum on Advanced Alloy Materials in 2024 and the 2nd Youth Editorial Board Exchange Meeting have been successfully concluded.
The conference has a special graduate student forum, including 10 reports of the doctoral student forum and 10 reports of the master's student forum, and the review team composed of the chairman and vice chairman of the graduate student forum will give birth to 1 gold medal and 2 silver awards respectively in the doctoral and master's student forums, and the specific selection results are as follows:
Doctoral Student Forum
Gold
Harbin Institute of Technology, Yang Xiaokang, Ph.D. candidate
Title: Introducing surface defects in γ phases and improving the high-temperature mechanical properties of TiAl alloys
Presentation: The active introduction of different types of defects in γ phases with low formation energies is one of the effective means to improve the mechanical properties of TiAl alloys at room temperature and high temperature. Ta was added to the TiAl alloy to study the defect type, microstructure, mechanical properties at room temperature and high temperature and related mechanisms of the alloy. The results show that four kinds of surface defects are formed in the γ phases between the lamellar clusters after the addition of Ta, including stacked lamination faults (SFs), twin grain boundaries (TB), low-angle grain boundaries (LAGB) and 120° rotating grain boundaries (RB). Ta can promote the generation of SFs by reducing lamination faults. The insertion of the outer SF changes the stacking sequence and generates twins. The continuous generation of SFs leads to the continuous widening of the twins. The substitution of Ta for Al will result in lattice distortion and vacancies. Vacancies are filled by Al atoms to form a blade-shaped dislocation, resulting in LAGB. Substitution also reduces the formation energy of RB, which in turn forms RB. The compressive strength and strain of Ta alloy reach 2606 MPa and 40.6 %, and the tensile strength and elongation of 900°C alloy reach 550.2 MPa and 10.8 %. The blade dislocation at LAGB and the elastic stress field at TB and RB increase the critical slitting stress of the dislocation and hinder the dislocation slip. SFs decompose the dislocation into partial dislocations to consume their energy.
Silver
Jiang Wentao, Ph.D. candidate, Harbin University of Science and Technology
Title: Research on the strengthening and toughening of lightweight refractory high-entropy alloys based on AlNbTiV system
Report content: Refractory high-entropy alloys (RHEAs), as an emerging material, have a wide range of applications in aerospace, wear-resistant and corrosion-resistant materials and other fields. With the increasing standard of living and the rapid development of modern science and technology, high-entropy alloys with excellent high-temperature performance have gradually entered the market. Lightweight is one of the main problems restricting the application of refractory high-entropy alloys, and most of the refractory high-entropy alloys such as NbMoTaW and HfNbTaTiZr still have the problems of high density and low specific strength. Therefore, it is necessary to reduce the density of the alloy while meeting the excellent high-temperature performance.
The microstructure, density and mechanical properties of Al-Nb-Ti-V-Zr alloy with different phases were studied by adjusting the element content, and the strengthening and toughening mechanism of the alloy was discussed, which provided a theoretical basis for the design and application of lightweight refractory high-entropy alloy.
Al and Zr are prone to form intermetallic phases, which change the microstructure of the alloy and have a certain impact on the properties. The increase of Al and Zr content promoted the formation of C14-Laves phase and improved the strength of the alloy, and the improvement of the mechanical properties of the alloy was mainly affected by the two strengthening mechanisms of second phase strengthening and solution strengthening. The appropriate use of low-density elements to control the alloy composition can effectively improve the mechanical properties of refractory high-entropy alloys and reduce the alloy density at the same time. In this study, the compressive yield strength of Al0.8Nb0.5TiV2Zr0.5 alloy can reach 1723 MPa and 1108 MPa at room temperature and 1073 K, respectively, and its specific strengths are 312 and 200 MPa·cm3g-1, respectively.
Ti is mainly enriched in the BCC matrix phase, so the increase of Ti content will lead to the increase of the volume fraction of the BCC matrix phase, which in turn inhibits the formation of the C14-Laves phase. Under the condition of sufficient Ti content, the refractory high-entropy alloy with a single BCC structure was successfully designed and prepared by using the solid solution phase formation criterion and other parameters. The results show that the Al0.5Nb0.5Ti3Zr2Vx alloy exhibits excellent compressive properties, and with the increase of external stress, the alloy does not fracture after yielding at room temperature, resulting in work hardening, and the compressive strain reaches 50%, with a strength of nearly 2.0 GPa. The tensile test results show that the alloy has the highest tensile strength (918 MPa) at a V content of 1.0, while the alloy does not yield and fracture when the V content is 1.5. Microstructure analysis showed that the increase of V concentration (reaching 1.5) promoted the segregation of Al and Zr at grain boundaries, forming a hexagonal nanostructured Al-Zr intermetallic phase that was not compatible with the matrix, and deteriorated the properties of the alloy. When the V content is less, the alloy strength is higher, which is mainly affected by fine-grain strengthening and solution strengthening.
Silver
Daniel Zhang, Ph.D. candidate, Huazhong University of Science and Technology
Title: Numerical Simulation of Formation and Evolution of Solvent Plumes for Directional Solidification of Superalloys
Report content: The directional solidification process of superalloy is very easy to produce freckle defects, which will affect the pass rate of leaf batch production. Freckles are closely related to the formation and evolution of solute plumes. It is difficult to determine the formation mechanism and evolution of solute plume by process test alone. Therefore, numerical simulation is used to study the formation and evolution of the superalloy directional solidification solute plume. The phase field model was used to simulate the morphology evolution and solute distribution of primary dendrites during directional solidification, the lattice Boltzmann model was used to simulate the buoyant-driven solute convection, and the simulation was accelerated by GPU parallel computing technology. Numerical simulations were carried out on the growth process of a single dendrite under natural convection conditions, and the convergence of the model was verified. The formation and evolution of solute plume under critical stability conditions were simulated, and the oscillation of dendrite tip growth rate was found. The simulation results show that with the increase of the pumping speed and temperature gradient, the velocity of solute convection decreases and the solute plume is inhibited. Soluble plumes tend to form at grain boundaries, and solute plumes are more likely to form with larger grain boundary angles.
Master's Student Forum
Gold
Wu Zhenping, Nanchang University, Master Student
Title: Metamorphism and strengthening mechanism of ultra-low micro Sr+Er alloyed high-strength and toughness cast Al-11Si-3Cu alloy
Report content: The mechanical properties of aluminum-silicon-copper alloys need to be improved to meet the growing demand of the manufacturing industry, and alloying technology can often improve the mechanical properties of aluminum-silicon-copper alloys, but the high cost of alloying elements limits the wide application of alloying technology in traditional cast aluminum-silicon-copper alloys. Therefore, it is of great significance to develop cast aluminum-silicon-copper alloys with high strength and toughness through trace alloying elements. This report will introduce a high-strength and toughness cast aluminum-silicon-copper alloy modified by ultra-low micro Sr and Er alloying elements, and analyze its metamorphic mechanism and strengthening mechanism, so as to provide some ideas for the development of low-cost and high-strength aluminum-silicon-copper alloys.
Silver
Lei Haofeng, China Three Gorges University, master's degree candidate
Title: Composition Design and Performance Control of Eutectic High-Entropy Alloys
At present, there are many design methods for eutectic high-entropy alloys, which can be divided into two categories: empirical parameter prediction method and thermodynamic simulation. Similar eutectic high-entropy alloys can be obtained quickly by designing the composition of high-entropy alloys through empirical parameters, but the known components of eutectic high-entropy alloys are required. This has limited the widespread development of eutectic high-entropy alloys. The eutectic high-entropy alloy obtained by thermodynamic simulation method takes a long period and the calculation is complex, so the eutectic high-entropy alloy cannot be obtained easily and effectively. This report proposes an efficient and accurate compositional design method: when the elements solidify, they generally give priority to the formation of compounds according to the enthalpy of mixing with each other, and when the composition of the alloy reaches the eutectic point, the two will form eutectic alloys. Some studies have shown that most of the eutectic high-entropy alloys of duplex can generally be regarded as composed of two different components, the atomic radius and chemical activity of the elements of component A are similar, and the mixing enthalpy between them is close to zero, which is easy to form a simple solid solution, while the elemental mixing enthalpy of component B is very negative, and it is easy to combine with the elements of component A to form intermetallic compounds, such as Co, Cr, Fe and Ni and Nb/ Ta satisfies the requirements of component A and component B respectively, and the new eutectic high-entropy alloy strategy is based on the redistribution of the mixed enthalpy and binary eutectic components of the elements in the two components, so that the eutectic composition can be reached between the elements of component A and component B in the whole alloy system, so as to quickly design eutectic high-entropy alloys. Multivariate synergistic regulation performance: The study shows that eutectic high-entropy alloys can be designed based on the infinite solid solution strategy. According to the binary phase diagram, an infinite solid solution can be formed between any element of Nb-Ta-Mo-W, and Nb-Ta-Mo-W can form a eutectic high-entropy alloy with CoCrFeNi. Based on the infinite solid solution strategy, any combination of the four elements with CoCrFeNi can also form eutectic high-entropy alloys. The synergistic effect of eutectic high-entropy alloys results in finer layers and higher strength. Therefore, by manipulating the system of multiple synergistic elements, we can design more eutectic high-entropy alloys with excellent performance.
Silver
Li Shilong, Huazhong University of Science and Technology, Master Candidate
Title: Research on the Effect of Solution Treatment on the Microstructure and Mechanical Properties of Heat-resistant Aluminum-Silicate Alloy
Report content: For the supereutectic Al-14Si-2Cu-1Ni-0.5Mg-0.5Mn-0.5RE alloy (AS14 alloy for short), the evolution of the microstructure, phase composition and mechanical properties of the supereutectic aluminum alloy under different single-step and double-step solution processes were studied by OM, SEM, EDS, tensile test and other analytical test methods. The results show that with the increase of solution temperature, the edge of the primary crystalline Si in the alloy structure gradually passivates, the eutectic Si gradually melts into nearly spherical or granular form, and the metal compound gradually breaks into small blocks or granules. When the single-step solution temperature is 510°C, the tensile strength at room temperature, tensile strength at high temperature and elongation at room temperature of AS14 alloy are the best. After two-step solution + aging treatment, the size of the Si phase in the alloy structure is smaller, the shape is more regular, and the fragmentation of metal compounds is more obvious. Compared with the single-step solution aging treatment, the tensile strength of AS14 alloy at room temperature and high temperature were slightly improved, which were 364.7MPa and 189.6MPa, respectively.
Congratulations to the above winners
ps: The certificate is on the way, please pay attention to check ~