Tribological properties of FeCoCrNiAlBx high-entropy alloys coating prepared by laser cladding

FeCoCrNiAlBx(x=0, 0.25, 0.50, 0.75) coatings were prepared by laser cladding to study the effects of boron on the structure and properties of high-entropy alloys coatings.The microstructure, microhardness, and wear resistance properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, metallographic micro-hardness test, and friction-wear test, respec-tively, and the mechanism of the wear behavior was also analyzed.The results showed that the high-entropy alloys consisted of BCC phase and eutectic structure, which contained FCC phase and M2 B. With boron addition, the content of BCC phase increased while that of eutectic structure decreased. The wear resistance of the high-entropy coatings was considerably improved with increasing addition of boron, and accordingly, the FeCoCrNiAlB0.75 coating showed the best wear resistance.     

Plasticity performance of Al0.5 CoCrCuFeNi high-entropy alloys under nanoindentation

The statistical and dynamic behaviors of the displacement-load curves of a high-entropy alloy,Al_(0.5)CoCrCuFeNi,were analyzed for the nanoindentation performed at two temperatures.Critical behavior of serrations at room temperature and chaotic flows at 200°C were detected.These results are attributed to the interaction among a large number of slip bands.For the nanoindentation at room temperature,recurrent partial events between slip bands introduce a hierarchy of length scales,leading to a critical state.For the nanoindentation at 200°C,there is no spatial interference between two slip bands,which is corresponding to the evolution of separated trajectory of chaotic behavior.     

FeCoCrNiMo high-entropy alloys prepared by powder metallurgy processing for diamond tool applications

High-entropy alloys (HEAs) show good mechanical properties like high strength, hardness and wear resistance, and this makes them attractive for application in diamond tools. However, there are severe obstacles to improving the mechanical properties of normal diamond tools with metal-matrix alloys. Here, we report the formation of FeCoCrNiMo HEAs by powder metallurgy processing, starting from a gas-atomised powder followed by mechanical milling and consolidation by spark plasma sintering. Our results show that FeCoCrNiMo HEAs with pure FCC phase can be obtained by this method. Specimens with higher hardness can be obtained at higher temperatures and low pressures, while specimens with higher bending strength are formed at lower temperatures and pressures. FeCoCrNiMo HEAs have remarkably higher hardness and better wear behaviour than metal-matrices commonly in used diamond tools, which indicates that a new type of diamond tool with superior properties can be realised from HEAs.

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.     

Microstructures and properties of CoCrCuFeNiMox high-entropy alloys fabricated by mechanical alloying and spark plasma sintering

CoCrCuFeNiMox (x values in molar ratio, x?=?0, 0.2, 0.4 and 0.8) high-entropy alloys were prepared by mechanical alloying and spark plasma sintering method. The effects of Mo addition on microstructure and mechanical properties were investigated. The X-ray diffraction (XRD) result showed that the addition of Mo into CoCrCuFeNi high-entropy alloy (HEA) changed the original phase constitution from FCC to FCC?+?σ?+?μ and the peak intensity of (1 1 1) shifted to the left and decreased steadily. The field emission scanning electron microscope confirmed that the Cu-rich second FCC phase disappeared and the σ phase with a tetragonal structure expanded as the Mo content was increased. Additionally, a high density of dimple-like features were seen in CoCrCuFeNi HEA while typical quasi-cleavage facets could be observed from the fracture surfaces of the HEAs with the addition of Mo. The Mo0.8 alloy showed a good wear resistant and appropriate strength with fracture strain 22.70%, fraction coefficient 0.65, hardness 530?HV and compressive strength 1448?MPa.

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.     

Influence of Cr removal on the microstructure and mechanical behaviour of a high-entropy Al0.8Ti0.2CoNiFeCr alloy fabricated by powder metallurgy

We report a systematic study on the influence of Cr removal on the microstructure and mechanical behaviour of an ultra-fine grained (UFG) high-entropy alloy (HEA), Al_0.8Ti_0.2CoNiFeCr, fabricated via spark plasma sintering (SPS) of mechanically alloyed (MA’ed) powders from constituent elemental powders. The MA’ed Al_0.8Ti_0.2CoNiFeCr powders consist principally of a BCC phase (～85 vol.-%) with a small amount of FCC phase (～15 vol.-%), whereas the MA’ed Al_0.8Ti_0.2CoNiFe powders present similar phases to those in the MA’ed Al_0.8Ti_0.2CoNiFeCr powders. Interestingly, the SPS processed UFG Al_0.8Ti_0.2CoNiFeCr alloy contains mostly an FCC phase (～78 vol.-%) and some BCC phase (～22 vol.-%); in contrast, the SPS processed UFG Al_0.8Ti_0.2CoNiFe alloy consists of a slightly enriched BCC phase (～53 vol.-%) and an FCC phase (～47 vol.-%). In addition, the SPS processed Al_0.8Ti_0.2CoNiFe alloy exhibits slightly higher yield strength, compressive strength and hardness but lower plasticity than those of the SPS processed Al_0.8Ti_0.2CoNiFeCr alloy.

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.     

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...     

Processing and characterisation of nano crystalline AlCoCrCuFeTix high-entropy alloy

In this work multi-component equiatomic and non-equiatomic AlCoCrCuFeTi_x hexanary high-entropy alloys (HEA) was synthesised through mechanical alloying. The prepared powder was sintered via spark plasma sintering. Influence of alloying element variation in the multi-component system was studied in terms of phase formation and crystal structure by using Thermo-Calc and X-ray diffraction characterization technique (XRD). Particle morphology and chemical analysis studies were carried out through scanning electron microscopy along with Electron Dispersive X-ray Spectroscopy. The crystal structure and nano crystallinity of the hexanary system were recognised using transmission electron microscope (TEM and Selected Area Electron Diffraction [SAED]) while the formation of a solid solution was also studied and discussed. From the XRD and TEM characterisation of 20?h in, milled powders and sintered samples, it was confirmed that the developed HEA system forms a single solid solution BCC phase. The sintered alloy exhibits 97% relative density and an average hardness of 590?VHN.

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.     

Phase diagrams of permanent magnet alloys: Binary rare earth alloy systems

Thermodynamic optimization of the binary rare earth alloy(Cee La, Cee Pr, Cee Nd and Lae Nd) systems was performed in this work through the CALPHAD method based on the critical evaluation of all available phase diagram and thermodynamic data reported in the literature. During the thermodynamic modeling, the solution phases including liquid, bcc, fcc and dhcp, were treated as the substitutional solution model. Thermodynamic parameters of the stable phases in the Cee La, Cee Pr, Cee Nd and Lae Nd binary systems are obtained finally and would be used directly to develop the thermodynamic database of the multi-component Nde Fee B-based alloys, which is indispensable for designing alloy compositions and processes of Nde Fee B permanent magnets with highly abundant rare earth metals.     

A comparison study of hydrogen storage performances of SmMg11Ni alloys prepared by melt spinning and ball milling

The melt spinning(MS) and ball milling(BM) technologies are thought to be efficient to prepare nanostructured Mg and Mg-based alloys for improving their hydrogen storage performances. In this paper, two technologies, viz. melt spinning and ball milling, were employed to fabricate the SmMg_(11)Ni alloy. The structure and hydrogen storage performance of these two kinds of alloys were researched in detail. The results reveal that the as-spun and milled alloys both contain nanocrystalline and amorphous structures. By means of the measurement of PCT curves, the thermodynamic parameters of the alloys prepared by MS and BM are ΔN_(Ms)(des) = 82.51 kJ/mol and ΔH_(BM)(des) = 81.68 kJ/mol, respectively, viz.ΔH_(MS)(des) ΔH_(BM)(des). The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun one. The as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one. As to the as-milled and spun alloys, the onset hydrogen desorption temperatures are557.6 and 565.3 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property than the as-spun one. On the basis of time that required by desorbing hydrogen of 3 wt% H_2, the as-milled alloy needs 1488.574,390 and 192 s corresponding to hydrogen desorption temperatures 593,613,633 and 653 K, while the as-spun alloy needs 3600,1020,778 and 306 s corresponding to the same temperatures. The dehydrogenation activation energies of the as-milled and spun alloys are 100.31 and105.56 kJ/mol, respectively, the difference of which is responsible for the much faster dehydriding rate of the as-milled alloy.     

Effect of Al82.8Cu17Fe0.2 alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo₅₊χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_82.8Cu₁₇Fe_0.2alloy into SmCo₅ matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm₂(Co,M)₇ cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)₅ grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo₅-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo₅-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.     

混合实验法在W-Ni-Cu合金组分设计中的应用

采用极端顶点设计法设计W-Ni-Cu合金组分,将组分自变量与相对应的性能因变量(相对密度、显微硬度、抗弯强度)进行回归分析和规划求解,同时采用冷压烧结法制备不同组分的W-Ni-Cu合金,测定合金的密度、显微硬度和力学性能,研究组分对合金性能的影响。结果表明:回归方程复相关系数R~2=1,方程精确度高;合金性能随组分变化而呈规律变化;当Ni含量与Cu含量(均为质量分数)分别为3%和5%时,合金的综合力学性能最佳:相对密度为94.295%、显微硬度286.55、抗弯强度931.51 MPa。W-Ni-Cu合金的相对密度计算值与实验结果的误差为-0.45%~0.06%,显微硬度计算值与实验结果的误差为-8.48%~4.46%,抗弯强度计算值与实验结果的误差为-5.19%~4.15%。误差很小,说明混合实验和极端顶点设计法能优化W-Ni-Cu合金组分,并可靠预测合金性能。     

测定镁合金中高含量硅的钼蓝光度法研究

研究了镁合金中高含量硅 (质量分数为 0.2 %～ 2.0 % )测定的各种影响因素 ,对原国家标准分析方法 (测定范围 :0 .0 0 5 %～ 0 .15 % )中不符合测定高含量硅的各种条件 (称样量、饱和溴水加入量、氟化物的用量等 )进行了重新试验 ,最后拟定了镁合金中高含量硅的分析方法。经对镁合金标样进行分析 ,证明该方法精密度和准确度均较高 ,相对标准偏差在0.77%～ 2.2 6%之间 ,其平均值与其他实验室的定值结果基本一致     

Modelling of heat flow and interdendritic crack formation in twin-roll strip casting of aluminium alloys

Preliminary mathematical analyses of different interdendritic cracks associated with variation of heat transfer and generation of interdendritic strain in horizontal twin-roll strip casting have been investigated. A 1-D transient finite difference model of heat flow, dendritic solidification and interdendritic thermo-metallurgical strain has been developed. The model contains two cracking criteria to predict qualitatively and quantitatively the tendency of interdendritic crack formation during dendritic solidification of pure aluminium and 6022 aluminium alloy. The model predictions are compared to available analytical methods and previous measurements. This is to verify and calibrate the model where good and reasonable agreements are obtained, respectively. The variations of heat transfer modes during different contact cooling zones and their effects on the generation of interdendritic thermo-metallurgical strain at the surface and central strip locations have been analysed. The model predictions point out that the different contact cooling zones of strip surface and surroundings control the stages of interdendritic crack formation in different mushy regions. The mechanism of interdendritic crack formation in twin-roll strip casting process with previous and present cracking criteria have been explained and discussed. These discussions show the importance of selection of mathematical treatment to predict the stages of interdendritic crack formation.     

Magnetic and microwave absorbing properties of Ce-Co-based alloy powders driven with lanthanum content

The composites of Ce-Co-based alloys doped with La content were fabricated via a vacuum arc melting method.The influences of La addition on microstructure,electromagnetic parameters,magnetic property and microwave absorbing property were measured by the corresponding equipment.The morphology characteristics manifest that all samples display sheet structure,and the average particle size of alloy powders increases with increasing La content The saturation magnetization(M_S) decreases with increasing La addition as a whole.The minimum reflection loss(RL) of La_(0.4)Ce_(1.6)Co_(17) alloy powder about-42.29 dB can be obtained about-42.29 dB at 7.84 GHz with the matching thickness of 1.8 mm,and the corresponding effective bandwidth can achieve about 2.24 GHz.In addition,the minimum RL frequency moves towards a lower frequency region as the La content increases.The minimum RL of La_(0.3)Ce_(1.7)Co_(17)alloy powder is less than-20 dB ranging from 1.2 to 2.4 mm in the whole 4-16 GHz.The maximum bandwidth can reach about 4.88 GHz at the given thickness of 1.2 mm.In general,these all indicate that the La addition is beneficial to improving the microwave absorbing performance in both effective bandwidth and absorption intensity.     

Cohesive energy, properties, and formation energy of transition metal alloys

The cohesive energy of transition metals and its contributions related to the s-and d-electrons are calculated. The correlation of interatomic bonding strength, molar volume, and compressibility of transition metals with cohesion energy and corresponding contributions to it is shown. It is demonstrated that the s-electrons play an important part in the cohesion of transition metals. The main contributions to the formation energy of disordered alloys of copper with transition metals are calculated using the tight-binding approach. The results obtained are in qualitative agreement with experimental data on the thermodynamic properties of Cu-3d-metal systems. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 37–54, 2008.     

TiAl基合金热包覆锻造过程中温降的数值分析

通过传热模型和数值计算,研究直径60mm、长100mm的粉末冶金TiAl基合金坯料锻造时的温降规律,对比分析裸锻和热包覆锻造坯料的温降特征。计算与实验结果表明,裸锻坯料温降高达600℃,且内部存在较大的温度梯度,易使锻造坯失效和导致坯料组织的不均匀分布;而热包覆锻造温降仅30℃,远低于裸锻,坯料内部温度场分布较均匀,对锻造过程非常有利,易获得均匀、细小的锻后微观组织。粉末冶金TiAl基合金锻造过程中的温降数值分析为TiAl基合金在热加工过程中的温降控制提供了理论依据。     

添加钴对W-Ni-Fe高密度合金性能的影响

在原料粉末中加入微量的Co元素,用粉末冶金液相烧结法制备了W-Ni-Fe高密度合金;采用金相显微镜、SEM等仪器对合金组织和杂质分布进行了分析。研究结果表明:添加钴元素后,增强了基体相对钨颗粒的润湿性,使钨颗粒表面更加圆滑,更加有利于塑性变形;提高了合金的钨颗粒与基体相之间的界面结合强度,从而提高了合金的强度和延伸率。     

Effect of wheel speed on phase formation and magnetic properties of (Nd0.4La0.6)-Fe-B melt-spun ribbons

The effect of wheel speed on phase formation and magnetic properties of (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 and (Nd_0.4La_0.6)_13.4Fe_79.9B_6.7 ribbons prepared by melt-spinning method was investigated experimentally. Based on X-ray diffraction results, all melt-spun ribbons consist of the main phase with the tetragonal 2:14:1 type structure and the minor α-Fe phase. Magnetic measurements show the maximum magnetic energy product ((BH)_max) and the remanence (M_r) increases firstly and then decreases with the increase of wheel speed, while the coercivity (H_ci) increases, resulting from the variation of the average volume fraction of the α-Fe phase and the average grain size in the melt-spun ribbons. Using Henkel plots, the interaction between the 2:14:1 phase and the α-Fe phase in the melt-spun ribbons was analyzed and the intergranular exchange coupling is manifested. Optimal magnetic properties of H_ci = 7.27 kOe, M_r = 90.94 emu/g and (BH)_max = 12.10 MGOe are achieved in the (Nd_0.4La_0.6)₁₅Fe_77.5B_7.5 ribbon with the wheel speed of 26 m/s. It indicates that magnetic properties of Nd-Fe-B melt-spun ribbons with highly abundant rare earth element La can be improved by optimizing alloy composition and preparation process.     

机械合金化在Fe-Si合金制备中的应用

机械合金化是一种新的材料制备方法, 近年来在功能材料的制备中得到了广泛的应用. 该文简要回顾了机械合金化的发展历史, 阐述了机械合金化的原理及反应机制, 介绍了机械合金化技术在过饱和固溶体、非晶、纳米晶及金属间化合物等领域的应用状况. 指出机械合金化过程的热力学和动力学研究及合金相结构、性能与球磨工艺条件之间的规律是今后研究的重点, 后续处理工艺的改进是产品实现从实验室向工业应用转变的重要保证.     

汽车用粉末冶金钛合金零件的开发与应用

粉末冶金钛合金具有优良的综合性能,逐步在汽车工业中得到了广泛的应用。简要介绍了 粉末冶金钛合金在汽车零部件中的应用,并对其发展前途加以展望。