High-entropy alloys are at the forefront of metal materials. They are used as alternative materials for the production of high-temperature turbine blades, high-temperature molds, hard coatings on cutting tools and even fourth-generation nuclear reactor components. However, everyone lacks a comprehensive understanding of HEA3D printing. In order to solve this problem, researchers from Singapore University of Technology and Design (SUTD), Nanyang Technological University (NTU), Huazhong University of Science and Technology and Hunan University collaborated to provide a detailed overview of the latest results of HEA 3-D printing. The research was published in "Advanced Materials".
3D printing, more formally known as additive manufacturing (AM), is an emerging technology that provides great flexibility for the design and manufacture of complex and/or custom parts through a layer-by-layer strategy, which has revolutionized Sexual manufacturing.
High-entropy alloy (HEA), as an emerging frontier technology in the field of metal materials, has high mixed configuration entropy, which tends to be based on simple lower surface face-centered cubic (FCC), body-centered cubic (BCC), or matrix center Cube to stabilize the solid solution. Hexagonal close packed (HCP) structure. Generally, the definition of HEA is based on composition or entropy. For the composition-based definition, HEA consists of five or more main elements, each with a concentration of between 5 and 35 atomic percent (at%). The constituent elements of HEAs can be selected from transition metals, alkaline earth metals, alkaline metals, metalloids and non-metals, of which cobalt, chromium, copper, iron, manganese, nickel, hafnium, tantalum, titanium, molybdenum, niobium, vanadium, Zirconium, tungsten, zinc, aluminum, silicon and boron. By screening the appropriate combination of its constituent elements and adjusting their proportions, HEAs can exhibit significant mechanical properties at high temperatures, excellent strength, ductility and fracture toughness at low temperatures, as well as superparamagnetism, superconductivity and excellent Radiation resistance. Therefore, they are considered as replacements for high temperature turbine blades, high temperature molds, hard coatings on cutting tools, etc.
Compared with the traditional manufacturing process, DED and PBF have greater hopes for the development of HEA products. The focused high-energy beams in DED and PBF melt the powder into an almost dense product. At the same time, the ultra-fast cooling rates of DED and PBF help prevent the formation of unwanted intermetallic compounds and the diffusion of constituent elements and lead to the refinement of the microstructure of HEA products. However, rapid curing can cause large temperature gradients, which can cause residual stress and cracks in printed products. Therefore, the constituent elements that are not sensitive to cracks and strong enough to offset the residual stress can mainly be considered for the composition design of HEA powder to improve its printability. Both DED and PBF can utilize HEA pre-alloyed powder developed by gas atomization, water atomization or mechanical alloying to achieve uniformity of printed products. In addition, DED can use elemental powders to print HEA products through in-situ alloying, thereby bypassing the lengthy process of developing HEA powders.
In recent years, atomization has been identified as a technology for developing pre-alloyed powders for DED and PBF. It uses high pressure from gas, water, plasma or rotating force to break up a stream of molten metal into droplets, which then solidify to form spherical powder particles. It has been reported that gas atomization and water atomization have been used to develop printable HEA powders.
Gas atomization is currently the most widely accepted method for producing fine metal spherical powders for 3D printing.
Mechanical alloying is a high-energy ball milling process used to develop fine metal powders for 3D printing. This is one of the most promising techniques to produce a uniform microstructure of HEA powder particles with improved solid solubility.
Due to the unique advantages of 3D printing technology in printing products with design freedom and geometric complexity, the 3D printing of HEAs has attracted more and more attention from academia and industry. DED and PBF processes have been widely used to print HEA products. In these processes, the focused high-energy beam interacts with the powder to form a molten pool, where rapid melting and solidification occur. Rapid curing helps avoid element segregation that normally occurs at linear defects (more precisely, dislocations) or surface defects (stacking faults, grain boundaries, phase boundaries, etc.), and prevents the formation of brittle intermetallic compounds, which improves The performance of mechanical performance products.
Regarding service quality and durability, the mechanical properties of the final product are the most important to determine whether it can replace 3D printing with conventional manufacturing processes.
Microhardness of 3D printed HEA products.
Comparison and summary of tensile yield strength and elongation of 3D printed HEA products
The novel characteristics of HEA, such as extremely high specific strength, excellent mechanical properties at high temperature, extremely low ductility and fracture toughness at low temperature, superparamagnetic and superconductivity, are used for aerospace, transportation, energy, electronics, biological Various applications of medicine and mold paved the way. HEA can be used as hydrogen storage materials, anti-radiation materials, diffusion barriers for electronic products, precision resistors, electromagnetic shielding materials, thermal spraying, hard, low-friction and biomedical coatings, adhesives, and soft magnetic and thermoelectric materials.
DED has also been successfully used to print prototypes of blades using CoCrFeMnNi HEA powder (as shown in the figure below). Other applications in the aerospace industry can be valve mechanisms for aero engines, compressor blades, combustion chambers, exhaust nozzles and gas turbines, among which The printed HEA products can combine their advantages, namely high strength to weight ratio, good oxidation resistance, fatigue resistance, heat resistance, high temperature strength, light weight, wear resistance and creep resistance.