难熔高熵合金激光增材制造的发展:材料性能与制造工艺调控技术(特邀)

Development of Refractory High Entropy Alloys by Laser Additive Manufacturing:Regulating Material Properties and Manufacturing Processes(Invited)

难熔高熵合金具有超越传统合金的优异性能,强度和硬度更高,高温性能和耐蚀性更优异,在航空航天、核工程、武器装备等领域具有广阔的应用前景。难熔高熵合金发展面临着两个难点:常规真空电弧熔炼方法制备的难熔高熵合金存在成分偏析严重、研发周期冗长、材料尺寸受限等难题;难熔高熵合金的硬度很高,难以实现复杂结构的成形和加工。因此,现有的冶金、成形、加工等技术面临挑战。通过激光增材制造实现材料与结构一体化成形是突破现有问题的发展方向,国内外学者在此方面进行了大量探索。本文对难熔高熵合金激光增材制造的发展现状进行了综述与分析,介绍了难熔高熵合金复杂构件从材料到制造的研究进展,阐述了高熵合金的研发途径、增材成形工艺和缺陷调控、难熔高熵合金在不同温度下的力学性能,以及增材制造工艺面临的挑战和取得的进展,最后总结了难熔高熵合金增材制造未来的应用方向和发展趋势。

Significance Refractory high entropy alloy(RHEA)has superior properties such as high strength,high hardness,high temperature resistance and high corrosion resistance,which is expected to become a new material of high-temperature structure.RHEA has huge application prospects in aerospace,nuclear engineering,weapons and other fields.At present,the RHEA prepared by vacuum arc melting technology has some problems,such as large size limitation,difficult formation of complex structure,serious component segregation and long development cycle.RHEA formed by laser additive manufacturing has obvious advantages such as uniform composition,excellent microstructure and properties,integral forming of complex shape,etc.It has application potential in raw material development and high-performance parts preparation,so it has received hot attention in the research field.Progress The primary task of RHEA formed by laser additive manufacturing is defect control.The microstructure defects of RHEA produced by laser additive manufacturing can be divided into cracks and pores.The crack defects can be divided into hot crack and cold crack.The addition of a small number of nanoparticles,process optimization and post-treatment can eliminate the crack defects.Pore defects can be divided into four types:unfused pore,metallurgical pore,micro pore and shrinkage pore.The main control method of pore defects is process optimization.By controlling the defects,the forming of RHEA and its properties are improved greatly.Additive manufacturing of RHEAs is an effective method to develop new alloys quickly.The process parameters of laser additive technology are numerous,strongly coupled and nonlinear.Single-factor experiment,numerical overlap optimization of molten pool and numerical simulation are the rapid optimization strategies for laser additive manufacturing of RHEA.Laser additive manufacturing enables rapid development iterations of RHEA.By mechanical mixing powder or preforming alloy powder,laser additive manufacturing technology can realize the formation of various metal powders by varying component ratios,and realize the rapid screening and performance evaluation of alloy composition.NbMoTaW alloys have very high strength but poor ductility,which can be strengthened and toughened by appropriately adding low melting point ductility elements and reducing brittle elements in the matrix.HfNbTaZr alloy has good plasticity,but the yield strength is generally low,which can be strengthened by adding strengthening elements.Due to the difficulty of controlling the forming crack defects,there are few studies on the tensile properties of RHEA formed by laser additive manufacturing.And more research work is needed,especially major breakthroughs in material mechanism and forming process.Finally,the complex structural parts formed by laser additive manufacturing for RHEA is still in the initial attempt stage.Conclusions and Prospects In this paper,the research on RHEAs formed by laser additive manufacturing is reviewed,and the development approaches,forming process and defect control,and the main research and challenges on mechanical properties of refractory high entropy alloys at multiple temperature stages are summarized.The research progress of complex parts of refractory high entropy alloy is introduced.Finally,the future application and development trend of RHEA formed by additive manufacturing are discussed.The integrated manufacturing of materials and shape is essential for RHEA,and laser additive manufacturing is the development direction of component manufacturing.The progress of materials and processes is the prerequisite for the integral forming of complex components in RHEA formed by laser additive manufacturing.At present,it has the ability to form simple samples,so more in-depth research is needed to accelerate the industrial application process of integrated manufacturing of shape and properties for RHEA in laser additive manufacturing.