High-throughput Preparation Based On In-situ Alloying Of Heterogeneous Powders

With the advent of digitalization and smart manufacturing,high-throughput experiments,one of the three pillars of the Materials Genome Project,have attracted widespread attention from researchers for their high efficiency in materials development.In this thesis,we propose the idea of high throughput preparation technology based on in situ alloying of heterogeneous powder,design a special equipment system for laser in situ alloying of heterogeneous powder,and conduct research and analysis on the optimization of in situ alloying process and scanning strategy,high throughput preparation of samples,evolution of microstructure and mechanical properties,etc.The main research contents and results are as follows:(1)Taking Fe-Ni alloy as an example,the elemental diffusion of in-situ alloying under different working conditions was analyzed from the perspective of diffusion kinetics.The calculation results show that the elemental diffusion efficiency of the in situ alloyed samples can be significantly improved by reducing the alloy powder particle size,increasing the laser power,decreasing the laser scanning speed,adopting the scanning strategy of laser remelting or increasing the subsequent high-temperature heat treatment to achieve the composition homogenization,which proves the feasibility of the technical route of in situ alloying of heterogeneous powder from the perspective of diffusion kinetics.(2)A special equipment for in-situ alloying of heterogeneous powders was developed,integrating a quantitative powder pick-up module,an automatic powder mixing module,a four-channel printing module and a supporting multi-material printing control software.The equipment can be loaded with up to four different powder materials,and can perform powder mixing in any ratio,and can automatically prepare more than 200 alloy samples of different compositions in a single run,providing an equipment basis for high-throughput preparation research of alloy blocks.(3)The in-situ alloying process was studied,and 48 sets of samples with different processes were prepared,and the forming process window of the samples was obtained,and the denseness of the samples reached 99.05% by the laser power290 W and scanning speed 500mm/s process.The in-situ alloyed samples with uniform and dense composition were obtained by using a laser power of 200 W and a scanning speed of 700mm/s,supplemented by two laser remelting processes,with a γ-monophase structure,a tensile strength of 722 MPa,an elongation of 44.5% and good corrosion resistance.(4)A study on the high-throughput preparation of Fe Cr Ni alloy composition system was carried out,and 80 samples of different compositions were prepared at one time.The composition deviation of the samples was basically within ±1%,the composition uniformity was >98%,and the molding quality and in-situ alloying of the samples were good.The microstructure of the samples gradually changed from equiaxed crystals to columnar crystals or equiaxed crystals + columnar crystals as the alloy content increased,and the microhardness of the samples gradually converged and increased,reaching the highest value of 319 HV at 12Cr6 Ni.The formation mechanism of the four typical microstructures was analyzed from the viewpoint of non-equilibrium solidification of the melt pool and the influence of cyclic heat.The results of the mechanical properties tests showed that 12Cr6 Ni has a tensile strength of 918 MPa,a yield strength of 884 MPa,and an elongation of 17%,with excellent overall performance.The results show that the heat treatment can regulate the extreme non-equilibrium solidification organization of the printed state to a state closer to that of the samples prepared by traditional means such as vacuum melting,and thus obtain similar properties,which can help to expand the application of in-situ alloying high throughput preparation technology.The special equipment system for laser in-situ alloying of heterogeneous powders and the theory of in-situ alloying high-throughput preparation technology can be used to systematically study the mapping relationship between material composition and properties,establish a database of material composition-structureproperties,and provide an efficient solution for the optimization and design of new high-performance alloys.