高熵合金粘结相WC基硬质合金的研究进展

WC基硬质合金因其高硬度、高强度、耐腐蚀的优点广泛应用于切削工具、凿岩工具以及军工等领域。但传统WC基硬质合金无法同时满足高强度和高韧性的要求,从而限制其在部分领域的应用。高熵合金（HEA）是至少五种或更多种等量或大约等量的金属元素形成的合金,其固有的高熵效应可以抑制合金材料中间相的形成,促进形成单一的固溶体,从而具备高硬度、高韧性、抗高温氧化、耐腐蚀性、高耐磨性等优异的性能。研究者用高熵合金代替Co作为WC基硬质合金的粘结相进行深入研究,发现高熵合金作粘结相制备的WC基硬质合金具有较高的硬度、强度和刚度,良好的耐磨性和韧性。文章阐述了WC基硬质合金的概述、特点、分类及用途,介绍了以高熵合金作为粘结相的WC基硬质合金的制备方法以及力学性能,然后对WC基硬质合金的应用和发展进行了总结与展望。     

铸态共晶高熵合金的研究进展

铸态共晶高熵合金在室温下的力学性能受到其化学成分、相组成和微观组织形貌的影响,是选用恰当的共晶高熵合金以适应于复杂服役环境的重要判据.文中通过调研近年来共晶高熵合金的相关文献,概述了共晶高熵合金的研究现状,按化学元素和共晶组织的相组成特点对共晶高熵合金进行了分类,即主要由FCC相+B2/BCC相组成的AlCoCrFeN...     

高熵合金激光选区熔化研究进展

近年来,高熵合金以其多主元成分、独特的组织和许多优异的性能在各个领域引起了极大关注。这种基于"构型熵"设计的新型合金,有望突破传统合金的性能极限,已经成为材料科学发展新的热点和方向之一。传统的电弧熔炼技术限制了高熵合金复杂结构件的制备及其工业化应用,新兴的增材制造技术已成为当前复杂金属构件制备中最具前景的制造方法之一。综述了高熵合金激光选区熔化技术的研究进展,包括工艺、优化和应用等,并对高熵合金未来的工业化应用提出了展望。     

共晶高熵合金的研究进展

高熵合金具有高的混合熵、缓慢的扩散和严重的品格畸变等特性,合金具有简单的组织结构和优异的综合性能,这为开发新型合金体系提供了广阔的发展思路.共晶高熵合金具有流动性好、凝固组织成分相对均匀、铸造缺陷少、组织可调控性等优点,可制备大尺寸高熵合金锭,因此共晶高熵合金的研究促进了高熵合金的工业化发展.概述了共晶高熵合金的国内外...     

选区激光熔化CoCrFeNi-X高熵合金的研究进展

CoCrFeNi高熵合金因其单一稳定的面心立方固溶体结构,具有优异的塑性变形能力和较高的屈服强度,已成为众多追求高韧性制件研究的热门体系之一。同时选区激光熔化技术因其成形尺寸灵活和超快加热冷却速率,具备传统制备方式不可比拟的优势。通过梳理近些年选区激光熔化技术成功制备出的CoCrFeNiX高熵合金体系,首先针对8种不同合金体系的相结构和组织形貌,分析了组织结构对力学性能的影响;其次针对3种采用不同工艺参数制备的CoCrFeNi-X高熵合金成形件,分析制备工艺对成形密度及力学性能的影响;最后就合金成分设计对CoCrFeNi-Alx、CoCrFeNi-Mn两种主流合金体系做了详细研究现状分析。期望对采用选区激光熔化技术制备CoCrFeNi-X体系高熵合金的实验研究和工业应用提供一定的理论指导。     

间隙原子掺杂高熵合金的研究进展

分析了间隙原子C、N、O、B对高熵合金组织和性能的影响;总结了四种间隙原子含量及其产生的固溶强化、晶粒细化、第二相强化作用对高熵合金组织及性能等方面影响,大量的研究表明,在高熵合金体系中掺杂间隙原子不仅可以调控相结构组成（促进/抑制相变,析出第二相颗粒）,还可以改变其形变机制（TWIP、TRIP效应）以实现材料的强韧化.其有效利用既可以拓宽高熵合金的设计思路,也可以有效降低航空材料的制备成本.最后提出了含间隙原子的高强高韧高熵合金组织结构设计研究的新方向：（1）了解不同类型高熵合金的掺杂机理,建立更适合高熵合金体系的固溶强化模型;（2）找出合适的间隙原子及其掺杂量来调节高熵合金微观结构和力学性能.研究设计掺杂不同间隙原子的高熵合金有望揭示不同间隙原子对其相结构、形变机制和力学性能的影响,具有重要的科学及工程实践意义.     

高熵合金耐腐蚀性能研究进展

文章介绍了高熵合金块体材料和高熵合金涂层在常温环境中、高温条件下和一些特殊介质中的腐蚀行为,论述了合金元素、热处理、环境因素及制备工艺对高熵合金耐蚀性的影响,并简要分析了高熵合金耐蚀性研究面临的问题.     

高熵合金复合涂层研究现状及展望

高熵合金涂层能在经济实用的基础上发挥高熵合金的优良综合性能,但其强化方式主要为固溶强化,强化效果有很大局限性,因此有必要在高熵合金涂层中引入硬质颗粒实现复合增强,从而得到性能更加优良的高熵合金复合涂层。综述了制备高熵合金复合涂层的主要技术,如激光熔覆技术、等离子熔覆技术和氩弧熔覆技术,重点介绍了直接添加和原位合成硬质颗粒增强高熵合金复合涂层的研究现状,分析了其组织与结构,并分别从硬度、耐磨性、耐腐蚀性和抗高温氧化性这几个方面论述了硬质颗粒对高熵合金复合涂层性能的影响,最后针对高熵合金复合涂层研究中存在的问题进行了总结和展望。     

含Cu高熵合金的组织结构和力学性能分析

高熵合金（HEAs）是一种由5种或5种以上元素以接近等原子比的方式混合而成的一种新型合金。HEAs的概念为开发具有独特性能的先进材料提供了新的途径,这是传统的基于单一主导元素的微合金化方法无法实现的。由于Cu元素与HEAs中其他元素的混合焓均为正值,因而更容易偏聚形成富Cu的面心立方（fcc）结构。本文主要总结了合金成分、制备方法对含Cu HEAs组织结构的影响规律以及含Cu HEAs的热稳定性。例如Al的添加会使CoCrCuFeNi合金从fcc单相转变为fcc+bcc的双相结构,而Ni含量的增加则会将AlCoCrCuNi的多相组织转变为单相fcc结构。与传统铸造工艺相比,选区激光熔化和喷溅急冷等具有极高的冷却速度,限制了元素的扩散,因而制备而成的AlCoCuFeNi和AlCoCrCuFeNi合金均是bcc结构。组织结构的改变会进一步影响含Cu HEAs力学性能,因而本文也探讨了合金成分、制备工艺和服役温度与力学性能的关系。例如,V的添加可以提高合金的强度,以先进制备方法如选区激光熔化或激光粉末熔融得到的合金具有优于铸造合金的力学性能。     

高熵合金耐磨性能研究进展

磨损是机械失效的一种普遍形式,约占据机械零件失效的80%。摩擦磨损不仅增加了原料和能源的损耗,而且无法保证机械零件的安全可靠性。高熵合金由于其特殊的四大效应,使得它成为近年来有别于传统合金材料领域的研究热点,通过调整高熵合金元素种类及配比、选择合适的制造方法和热处理工艺可以在一定程度上减缓磨损速率、降低磨损量,起到提高耐磨性能的效果。归纳了耐磨高熵合金的类别,讨论了不同元素及配比对块体高熵合金磨损性能的影响,总结了采用不同制造方法、热处理工艺及表面化学改性制备的高熵合金的耐磨性能差异。最后,结合高熵合金在摩擦磨损方面的现状及存在的问题,对未来高熵合金在耐磨金属材料领域的研究进行了展望。     

高熵合金拉伸测试不确定性和力学性能表征

摘要：高熵合金的拉伸力学性能测试不确定性,使现行传统的拉伸(压缩)试验技术,不适合于高熵合金的力学性能测量。金属拉伸力学性能测试不确定性,是拉伸试验弹性变形阶段,张应力改变了被测金属原子水平上的微观结构引起的。在此弹性变形微观理论基础上,提出用“力学性能 拉伸应变速率”曲线,表征高熵合金的原始力学性能,服役力学性能,以及加工变形力学性能。     

Configurational entropy and solute correlation in disordered alloys

A new approach in expressing the excess configurational entropy of a binary alloy phase is reported, which, through economy of formulation and ease of manipulation, offers a convenient and effective alternative to the widely-used regular solution approximation. The key to this development is the direct use of the diffuse intensity α_k (Fourier transform of the pair correlations) to specify the state of clustering or short-range order in an alloy. Detailed attention is given to the formulaS _XS = 1/2k _B〈lnα_k〉 which sets the excess entropy proportional to the mean value of the logarithm of the intensity. As an example of application, a concise analysis for pair correlations and thermodynamic properties at equilibrium is carried out. The result coincides with the spherical model for alloys, a variant of the Ising model resembling the Gaussian model of Clapp and Moss but far exceeding it in accuracy. In this manner the merit of the proposed entropy formulation is established.     

SPS-assisted Synthesis of SICp reinforced high entropy alloys: reactivity of SIC and effects of pre-mechanical alloying and post-annealing treatment

In this work a traditional high entropy alloy (FeCoNiCrAl) was reinforced by uniformly distributed reactive silicon carbide (SiC) particles by a powder metallurgy synthetic route, using as precursors simply mixed powders or mechanically prealloyed ones. The reactive sintering produced a single isomorphic BCC structure. The sample microstructure resulted equiassic, more homogenous in samples based on prealloyed powders. The instability of SiC in the presence of metal precursors resulted in the formation of more stable carbides and silicides, as well as in carbon diffusion in the high entropy alloy matrix and partially unreacted SiC particles. The formation of these newly formed fine precipitates, as well as the presence of residual SiC were useful to increase the hardness of the alloy.     

Development of high strength zirconium alloys

Abstract

Assessment of the effects of various alloying elements and strengthening methods in zirconium alloys has indicated that alloys with adequate strengtl1 for use as pressure tube material at temperatures above 400°C can be developed. Ternary, quaternary and quinary alloys based on zirconium have been prepared and subjected to various thermal and deformation treatments. Their age-hardening behaviour and tensile properties are described and some information on their corrosion resistance and response to fast neutron irradiation at 300° and 450°C is presented. The target of UTS in the range 90–120 kpsi at 450°C can be achieved in alloys having an acceptable thermal neutron capture cross section. Adequate strength combined with the ductility necessary for pressure tube fabrication can be obtained by air cooling selected alloys from temperatures high in the (α + β) range.

Résumé

L'evaluation des effets de divers éléments d'alliage et des méthodes dc durcissement permet de croire que des alliagcs ayant une résistance adéquate peuvent être développés pour des tubes de force utilisés à des températures supérieures à 400°C. Des alliages ternaires, quaternaires et quénaires à base de zirconium ont été préparés et soumis à divers cycles thermiques et cycles de déformation. L'étude a porté sur leur vieillissement et leurs propriétés en traction; quelques observations sur leur tenue en corrosion et en irradiation par des neutrons rapides à 300° et 450°C sont présentées. Il est possible d'atteindre des résistances à la traction de 90 à 120 kpsi a 450°C pour des alliages ayant une faible section de capture des neutrons. Une résistance suffisante jointe à la ductilité nécessaire pour la fabrication des tubes peut être obtenue par refroidissement à l'air de certains alliages à partir d'une température élevée dans le domaine α + β.     

Development of high strength wrought aluminum-base alloys

Work is reported on small-scale laboratory techniques described for development of high strength wrought aluminum alloys and on structure and properties of alloys produced. Alloy screening tests were on splat cooled samples and mechanical property measurements were from cast and rolled thin section cast plates. The highest tensile strengths obtained were in excess of 115,000 psi; highest yield strenghts were in excess of 110,000 psi. Four different alloys tested showed yield strengths in excess of 90,000 psi with elongations in excess of 5 pct.     

Processing of a new high entropy alloy: AlCrFeMoNiTi

This work, a new composition of high-entropy alloys (HEAs) was designed. The composition was carefully tailored with the aim to obtain a solid solution with a BCC crystalline structure to be an alternative binder in cermets. Thus, the composition of the HEA has been designed taking into account various criteria which has fulfilled a metallic binder of a Ti(C,N) cermet:(1) high hardness and oxidation resistance and (2) good wetting behaviour with Ti(C,N) particles because the processing of cermets is by LPS. The design of the alloy has been performed using theoretical calculations of physicochemical properties of the elements involved and the calculation of phase diagram by Thermocalc. The designed alloy has been processed by casting and powder metallurgy (PM) to study the influence of the processing route on the phases formed and on the resulting properties. The powders were produced by gas atomisation and then consolidated by hot pressing.

Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.     

Al-Zn-Mg-based cast alloys having high mechanical properties

The effect of alloying elements and heat treatment on the structure and properties of cast alloys based on the Al-Zn-Mg system and containing more than 9% (Zn + Mg) is analyzed. The optimum chemical composition of an alloy from this system is determined, and the heat-treatment conditions required for improving the mechanical properties of the alloy are found.     

Solid Solution strengthening of high purity niobium alloys

Athermal solid solution strengthening was examined in substitutional Nb(Cb)-Hf, Nb-W, and Nb-Ta alloys deformed at 900 K. Ultrahigh vacuum degassed single crystals were tested in compression. The concentration dependence of the yield stress is nearly linear in Nb-Hf and Nb-W alloys for the range of compositions tested (< 6 at. pct). The rate of hardening with solute addition was the greatest for the Nb-Hf alloys, considerably less for the Nb-W alloys, and the least for the Nb-Ta alloys which exhibited little strengthening. The results indicate that athermal strengthening in these alloys appears to be primarily dependent on the atomic size misfit between solvent and solute atoms and not on the elastic modulus mis-fit. Results on the slip behavior are also presented. J. R. SLINING, formerly Research Assistant, Department of Metal-lurgical Engineering, Michigan Technological University, Houghton, Mich. 49931