摘要
难熔高熵合金(RHEAs)是一类以Nb, Mo, W, Ta等难熔元素为主元的高熵合金(HEAs),具有简单的相结构和优异的高温综合力学性能,在航空航天、核能和石油等领域具有广阔的应用前景。由于RHEAs室温脆性难加工的特点,传统的工艺方法在制备RHEAs时存在制造过程复杂、周期长、材料利用率低、成本高等诸多问题,极大地限制了RHEAs的发展和应用。激光增材制造(LAM)技术因其能实现复杂零件的直接自由成形,而逐渐成为制备RHEAs的一条重要途径,为RHEAs的研发和应用带来了新的契机。对近年来激光增材制造RHEAs的研究现状进行了综述,介绍了激光增材制造RHEAs的成形特性,分析了RHEAs打印件的相组成和显微组织特征,总结了打印件的显微硬度、压缩强度以及耐磨、耐腐蚀和抗高温氧化性能。最后归纳出目前激光增材制造RHEAs的现存问题,并对其未来的发展趋势进行了展望。
Refractory high entropy alloys(RHEAs),a branch of high entropy alloy with refractory elements such as Nb,Mo,W and Ta as the principal elements,have simple and stable phase structure,excellent high temperature comprehensive mechanical properties,thus have a broad application prospect in aerospace,nuclear reactor,petrochemical and other high temperature service requiring fields.RHEAs are difficult to process at room temperature due to their hard and brittle nature.The traditional technologies have problems in the fabrication of RHEAs,such as complex manufacturing process,long process cycle,low material utilization rate and high cost,which seriously restrict the development and application of RHEAs.Recently,laser additive manufacturing(LAM)technology is gradually becoming an important method to manufacture RHEAs due to its ability to achieve direct free forming of complex metal parts with high laser energy density,which brings new opportunities for the development and application of RHEAs.Based on this,this paper reviewed the current research stats of LAMed RHEAs in recent years,introduces the forming characteristics of LAMed RHEAs,analyzed and summarized the microstructure and mechanical properties of LAMed RHEAs.Furthermore,the current challenges and future development trends of LAMed RHEAs were also pointed out and prospected.In RHEAs system,the melting point of the refractory elements was generally above 1600℃,and higher energy input was needed to achieve the full melting of the alloy powders.However,RHEAs tended to have large melting and boiling point differences between its constituent elements,with some elements having melting points even higher than the boiling points of others.As a result,the evaporation of low melting point elements was inevitable when achieving the complete melting of all elemental powders during LAM process.In addition,cracking was also a common problem in LAMed RHEAs due to the hard and brittle nature of RHEAs.At present,the remelting strategy was an effective way to solve the problems of insufficient melting of refractory elements and reduce burning loss of low melting point elements.Also,through adjusting the alloy composition and optimizing the forming process parameters,the cracking problems could also be effectively alleviated.However,it was still a big challenge to realize the breakthrough of forming quality and size of LAMed RHEAs.The main elements such as W,Mo,Nb,Ta and V of RHEAs were all body centered cubic(bcc)structure,and most of the elements were mixed in equal or near molar fractions in the current study.Therefore,LAMed RHEAs usually had bcc single-phase structure,which was similar to those manufactured by other reported processes.However,due to the high temperature gradient and rapid solidification during LAM process,the microstructure of LAMed RHEAs was much finer than that of traditional arc melting technology.In addition,although the rapid solidification avoids the macro-segregation,micro-segregation was still occurred in LAMed RHEAs because of the non-equilibrium solidification.For example,in MoNbTaWV alloy fabricated by laser selective melting(SLM),V element was severely segregated in the inter-dendritic region,and W and Ta were mainly concentrated in the dendritic core region.The microstructure of RHEAs was related to the composition and fraction of the elements.Therefore,high throughput in situ alloying based on laser melting deposition(LMD)technology had a significant effect on rapid screening of RHEAs.Through the high-throughput design of LAM,gradient materials of any composition with various microstructure could be obtained.In terms of properties,LAMed RHEAs had excellent mechanical properties in microhardness and compression strength.Most of LAMed RHEAs reached the hardness of HV 800 and the compression strength of 1000 MPa.For high temperature strength,some LAMed RHEAs could maintain a yield strength over 500 MPa at 1000℃,which was much better than traditional nickel-based superalloys.Besides,LAMed RHEAs also showed excellent potential in functional properties,such as corrosion and high temperature oxidation resistance.In summary,researchers had made considerable progress in the process optimization,microstructure and mechanical properties control of LAMed RHEAs,but there were still some problems to be further solved in the future.Firstly,new RHEAs system suitable for LAM should be further developed to break away from the high cracking tendency and low forming ability of RHEAs in traditional systems.Secondly,it was necessary to further improve and optimize LAM process of RHEAs.In-depth understanding of the synthesis principle and forming process,such as the action mechanism between the laser and powder,the evolution law of molten pool,the formation mechanism of metallurgical defects to achieve accurate control of the forming quality of LAMed RHEAs.Furthermore,the high-temperature service properties of LAMed RHEAs needed to be further explored.As a new generation of high temperature alloys,RHEAs were potentially applied in the fields of aerospace,military equipment,nuclear energy and chemical industry with high requirements on thermal part components.Therefore,further understanding and optimizing the high temperature service properties of LAMed RHEAs would be the focus of future research.
作者
张文军
伊浩
曹华军
黄健康
Zhang Wenjun;Yi Hao;Cao Huajun;Huang Jiankang(College of Mechanical and Vehicle Engineering,Chongqing University,Chongqing 400030,China;State Key Laboratory of Mechanical Transmission,Chongqing University,Chongqing 400044,China;State Key Labo-ratory of Advanced Processing and Recycling of Non-Ferrous Metals,Lanzhou University of Technology,Lanzhou 730050,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2023年第5期601-617,共17页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(52005059)
装备预研教育部联合基金项目(8091B032107)
中国博士后科学基金项目(2022T150771)资助。
