Amorphous phase formation rules in high-entropy alloys

There have been many interesting studies on high-entropy alloys（HEAs）, also known as multi-component（MC） alloys（MCAs）, in recent years. MC metallic-glasses（MGs） have shown the potential to express the advantages of MCAs and MGs in tandem. Amorphous phase formation rules are a crucial issue in the HEA and MCA field. For equal or near-equal atomic ratio alloys, mixed-entropy among the elements has a significant effect on the phase formation. This paper focuses on HEA amorphous phase formation rules. In the first two sections, the recent progress in amorphous phase formation in HEAs and MCAs is reviewed, including the effective factors and correlative parameters related to amorphous phase formation. In the third section, novel MCMGs including high-entropy（HE） bulk-metallic-glass（HE-BMG） and MCMG films developed in recent decades are summarized, and the giant-magnetic-impedance（GMI） effect of MC amorphous fibers is discussed.

Phase,microstructure and compressive properties of refractory high-entropy alloys CrHfNbTaTi and CrHfMoTaTi

New refractory high-entropy alloys,CrHfNbTaTi and CrHfMoTaTi,derived from the well-known HfNbTaTiZr alloy through principal element substitution were prepared using vacuum arc melting.The phase components,microstructures,and compressive properties of the alloys in the as-cast state were investigated.Results showed that both alloys were composed of BCC and cubic Laves phases.In terms of mechanical properties,the yield strength increased remarkably from 926 MPa for HfNbTaTiZr to 1258 MPa for CrHfNbTaTi,whereas a promising plastic strain of around 15.0%was retained in CrHfNbTaTi.The morphology and composition of the network-shaped interdendritic regions were closely related to the improved mechanical properties due to elemental substitution.Dendrites were surrounded by an incompact interdendritic shell after Mo incorporation,which deteriorated yield strength and accelerated brittleness.

A binder phase of TiO based cermets

A binder phase of TiO based cermets, a kind of imitated gold materials, was developed by adding active element Si to Fe-Cr alloy, and the related mechanisms were studied. The wettability, matching in thermodynamics and interracial strength were investigated by the high temperature sessile drop method and element area scanning. The linear expansion coefficients of the materials were measured using TAH100 thermal analyzer. The results show that the wettability of Fe-Cr alloy on TiO are small, with a wetting angle about 90°. After adding some Si in Fe-Cr alloy, its wetting angle can be decreased to about 25°, the interracial reactions can be prevented effectively and high interface binding can be formed. Fe-25% Cr-1.5% Si matches the thermal expansion coefficient of TiO, so it is a kind of relatively perfect binder for TiO based cermets imitated gold.

Effect of Si on 1Cr18Ni11Nb/TiO interface and investigation of TiO based cermet binder phase

The effect of trace amount of active element Si on the wetting and interface characteristics of 1Cr18Ni11Nb/TiO was investigated. Based on the results, a new binder phase for TiO based cermets imitated gold materials was developed, and the related mechanisms were studied. The results indicated that there was small wet-ability of the 1Cr18Ni11Nb alloy on TiO, and the interface binding strength of 1Cr18Ni11Nb/TiO was low. 1.5%Si in 1Cr18Ni11Nb could not only make the alloy wet TiO, but also lead to mutual dissolving near the interface, forming high interface binding strength and matching with the thermal expansion coefficient of TiO.

The effect of binder phase content on WC-AlCoCrFeNiTi_(0.2) high entropy cemented carbides microstructure and mechanical properties

Thiswork aims to explore WC-G201 high entropy cemented carbides properties fabricated by spark plasma sintering with AlCoCrFeNiTi_(0.2)and WC as binder phase and hard phase respectively.AlCoCrFeNiTi_(0.2)powder and WC powder were mixed at the mass ratio of 5:95,10:90 and 15:85 respectively,and then via SPS at 1300℃for 5min.The results show that the binder phase has good wettability to WC,and with the increase of binder phase content,the hardness of the alloy decreases gradually,fracture toughness increases first and then decreases,the maximum value is 7.88 MPa m1/2.It is estimated that the comprehensive mechanical property of cemented carbides is the best when the binder content is between 5wt%and 10wt%.

WC-Ni基硬质合金的基础研究进展

WC-Ni基硬质合金可应用在磁性材料成形模具和核主泵机械密封关键部件等极端工况领域。由于材料体系的本征特性,WC-Ni基硬质合金的高性能化和质量稳定性控制一直面临挑战。两相区碳窗口、固液转变温度、液相烧结过程中的润湿行为,以及合金组元在黏结相中的固溶特性,是硬质复合材料成分及其制备工艺设计的关键参数。本文以制备工艺体系最完善的WC-Co基硬质合金为参比对象,从上述4个方面对WC-Ni基硬质合金的本征特性及其研究进展进行综述,旨在强化对WC-Ni基硬质合金本征特性的理解,为高性能WC-Ni基硬质合金新材料高效开发提供参考。

高熵硬质合金WC-AlCo_(0.4)CrFeNi_(2.7)的制备及表征

以气雾化法制备的AlCo_(0.4)CrFeNi_(2.7)高熵合金粉末和碳化钨(WC)分别作为粘结相和硬质相,采用放电等离子烧结制备高熵硬质合金,研究了粘结相含量和烧结温度对硬质合金的微观结构和力学性能的影响。结果表明,粘结相占比为10%(质量分数)经1300℃烧结的高熵硬质合金具有最佳力学性能,硬度和断裂韧性分别为1575HV_(30)、9.2 MPa·m^(1/2)。相对于粘结相含量对合金性能的影响,烧结温度的影响效果更显著;两者分别通过影响WC晶粒大小、相对密度以及有害的脆性金属间化合物的生成来影响高熵硬质合金的力学性能。

生物基树脂改性沥青流变特性评价及体系融合行为

受石油资源储量和供应的限制,将生物质材料引入石油沥青已经成为一个热门话题。本研究以麦草秸秆液化产物为原材料合成三种生物基树脂(BPF、BPU和BPF-PU),并将其用于生物沥青的制备,旨在探究生物基树脂对沥青流变特性的影响及二者之间的交互作用。首先,通过频率扫描和多重应力蠕变恢复试验分析了树脂对沥青胶结料黏弹特性和高温抗车辙性能的影响;其次,借助流变学理论对树脂-沥青体系的相态结构进行了分析;最后,从荧光显微结构和官能团分布特征的角度探究了二者之间的融合行为。结果表明,BPF和BPF-PU能够增加沥青中的弹性成分,提升其高温抗车辙性能,而BPU则会强化沥青的黏性响应;三种树脂能够较为均匀地分散到基质沥青中,并与其形成稳定的相态结构,这可能是因为树脂与基质沥青之间形成了醚键(C-O-C)。本研究有助于为农作物秸秆的增值转化和生物沥青的开发提供新的思路,但在生物沥青性能的全面评价方面需要进一步研究。

激光线能量密度对75W-FeCoNiCr合金微观组织及力学性能的影响

利用FeCoNiCr高熵合金为黏结相,并采用激光定向能量沉积(L-DED)方法制备新型75W-FeCoNiCr合金,研究激光线能量密度对合金相组成、相对密度、微观组织及力学性能的影响。研究结果表明,在线能量密度为157.14~325.00 J/mm时,不同线能量密度下的合金相组成没有明显变化,均由BCC-W相、TCP金属间化合物析出相Co_(7)W_(6)相和FCC-FeCoNiCr黏结相组成。随着线能量密度的增大,成分过冷度增加,析出相长大速率加快,其形态由板状/胞状向树枝晶状转变,并且粒径从1μm增加到8μm左右。随着线能量密度的升高,合金的致密度、显微硬度和压缩强度均呈现先升高后降低的趋势。当线能量密度为166.67 J/mm时,析出相主要为均匀胞状结构,此时,合金的致密度、显微硬度和压缩强度均达最高值,分别为98.4%、656 MPa和2261 MPa。

A novel immiscible high entropy alloy strengthened via L1_(2)-nanoprecipitate

The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.

硬质合金中Co相强化的研究现状与展望

WC-Co硬质合金因其优异的性能而应用在各个领域。但因硬质合金中的Co黏结相的相缺陷限制了其使用,例如低硬度、低耐磨性、高温稳定性差等。由此对于Co相强化的研究从未间断,本文旨在系统地整合各种Co相强化研究工作,总结Co相通过传统的物理冶金强化(第二相强化、相界强化和固溶强化)和颗粒增强后的微观组织特征及力学性能,对比Co相采用不同增强方式后的硬质合金硬度和断裂韧度所能达到的范围,建立成分-微观组织-性能之间的联系,归纳各种强化方式所带来的优势和缺陷。为强化Co相的研究和工业生产提供参考依据,选择合适成分配比和后处理工艺,设计性能指标和使用寿命符合工况需要的硬质合金。

Structure and properties of FeCoNiCrCu_(0.5)Al_x high-entropy alloy

Effects of Al content and heat treatment on the structure,hardness and electrochemical properties of FeCoNiCrCu0.5Alx high-entropy alloys were investigated.The phase structure of as-cast alloys evolves from FCC phase to BCC phase with the increase of Al content.The stable phase of FeCoNiCrCu0.5Alx high-entropy alloys will transform from FCC phase to FCC＋BCC duplex phases when x value increases from 0.5 to 1.5.The hardness of BCC phase is higher than that of FCC phase,and the corrosion resistance of BCC phase is better than FCC phase in chlorine ion and acid medium.High hardness and good corrosion resistance can be obtained in as-cast FeCoNiCrCu0.5Al1.0 alloy.

以高熵合金为黏结相的金属陶瓷研究进展

近20年,许多研究者针对以高熵合金为黏结相的金属陶瓷开展了大量的研究,取得了许多有益的成果。本文系统综述了用作金属陶瓷黏结相的高熵合金制备方式,以及高熵合金黏结相金属陶瓷烧结制备技术,评价了烧结温度、烧结时间、碳含量、黏结相成分、黏结相含量等工艺参数对高熵合金黏结相金属陶瓷微观结构、力学性能、抗氧化性能和耐腐蚀性能的影响,可为高熵合金黏结相金属陶瓷的研究提供参考。

WC-Co梯度硬质合金的研究现状

梯度硬质合金(Gradient Cemented Carbides)基于其特殊的结构或成分梯度变化,在不同的位置具备不同的性能,使整体具有优异的综合力学性能。介绍了粘结相梯度硬质合金、表面贫立方相梯度硬质合金、表面富立方相硬质合金和多层梯度结构硬质合金等基本制备原理、组织结构特点和性能优势,指出了梯度硬质合金的发展趋势。

机加工用硬质合金刀具材料粘结相的相变

由于机加工用硬质合金刀具材料中粘结相存在面心立方和密排六方这两种不同的相结构,而不同的相结构其力学性能差异较大,因此,为优化刀具综合力学性能和服役寿命,通过制备不同钴含量的梯度硬质合金,对制备后的梯度硬质合金不同钴含量的位置进行残余应力测量和粘结相EBSD检测方法分析粘结相相变的条件。研究结果表明:在高残余应力的区域,粘结相主要以面心立方的形式存在;而在低应力的区域,粘结相主要以密排六方的形式存在。

Displacive transformation as pathway to prevent micro-cracks induced by thermal stress in additively manufactured strong and ductile high-entropy alloys

The micro-cracking behaviors of two high-entropy alloys(HEAs) of the FeMnCoCrNi family prepared by selective laser melting were systematically studied. Residual stresses were also analyzed by X-ray diffraction technique. Results show that the equiatomic FeMnCoCrNi HEAs with a relatively stable single-phase face-centered cubic(FCC) structure suffered from micro-cracking with residual tensile stress after laser melting. In contrast, the metastable non-equiatomic Fe MnCoCr HEAs with reduced stacking fault energy are free of micro-cracks with residual compressive stress at various volumetric energy densities(VEDs). The displacive transformation from the FCC matrix to the hexagonal close-packed(HCP) phase during cooling prevents the micro-cracking via consuming thermal stress related internal energy. Further, the displacive transformation during tensile deformation contributes to the higher strength and ductility of the metastable dual-phase HEA compared to that of the stable single-phase HEA. These findings provide useful guidance for the design of strong, ductile, and crack-free alloys for additive manufacturing by tuning phase stability.

Alloying behavior and characterization of(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy alloy(HEA)powders fabricated by mechanical alloying were studied.The CoCrFeNiMn)_(90)Al_(10) powders have duplex solid-solution structures.In contrast,nanocrystalline HfNi_(3) anchoring in amorphous structures is found in the(CoCrFeNiMn)_(90)Hf_(10) powders.The(CoCrFeNiMn)_(90)Al_(10) powders show better ferromagnetic behaviors,mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases.Combined with our previous work,the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed.It is found that,compared with the as-cast HEA reported previously,the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader.Moreover,the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.

Microstructure and mechanical properties of a low activation cast WTaHfTiZr refractory high-entropy alloy

In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal,mechanical and physical properties,a novel refractory highentropy alloy,WTaHfTiZr was proposed.The constituent elements were selected in consideration of low activation,high melting point and high thermostability.The alloys were prepared by arc melting.The as-cast alloy shows a dendrite microstructure with two disordered BCC phases,which caused by the preferential nucleation of W and Ta with much higher melting points during solidification.It exhibits a high compressive yield strength of 1,900 MPa and fracture strain of 8.1% at room temperature,and its yield strengths are up to 612 MPa at 700 ℃ and 203 MPa at 1,000 ℃,respectively.The high strengths are attributed mainly to solid solution strengthening and second phase strengthening.This alloy shows great promise as one of the next-generation nuclear fusion reactor materials.

Phase thermal stability and mechanical properties analyses of(Cr,Fe,V)–(Ta,W)multiple-based elemental system using a compositional gradient film

High-entropy alloys(HEAs)generally possess complex component combinations and abnormal properties.The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents.The development of compositionally complex materials such as HEAs requires high-throughput experimental methods,which involves preparing many samples in a short time.Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of(Cr,Fe,V)-(Ta,W).First,we deposited the compositional gradient film by co-sputtering.Second,the mechanical properties and thermal stability of the(Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x(x=13-82)multiplebased-elemental(MBE)alloys were investigated.After the deposited wafer was annealed at 600℃for 0.5 h,the initial amorphous phase was transformed into a body-centered cubic(bcc)structure phase when x=33.Oxides were observed on the film surface when x was 72 and 82.Finally,the highest hardness of as-deposited films was found when x=18,and the maximum hardness of annealed films was found when x=33.

Effects of annealing at 800 and 1000℃ on phase precipitates and hardness of Al_(7)Cr_(20)Fe_(x)Ni_(73)−x alloys

The effects of Fe content on the microstructure,phase constituents and microhardness of the as-cast,800℃or 1000℃-annealed Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=13−66)alloys were investigated.Not all these alloys are composed of the single FCC phase.The BCC and B2 phases are found.It is confirmed that the BCC phase in the Al7Cr20Fe66Ni7 alloy is transformed from the FCC phase at about 900℃ during cooling.While in the 800℃-annealed Al7Cr20Fe60Ni13 alloy,the FCC phase is stable and the hardness decreases.After annealing at 1000℃,for the precipitation of the B2 particles,the Al content in the FCC phase decreases,which results in decreasing of the alloy hardness.Moreover,after annealing at 800℃,a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix,which increases the hardness of the Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=41−49)alloys.These results will help to the composition design and processing design of the Al−Cr−Fe−Ni based high-entropy alloys.