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.     

Effect of Ni on Microstructure and Mechanical Properties of CrMnFeCoNi High Entropy Alloy

The effect of Ni content on microstructure and mechanical properties of the CrMnFeCoNi high entropy alloy (HEA) has been studied. The Ni content varied from 0 to 20 at% in the composition (CrMnFeMn)_100?xNi_x, where x?=?0, 2.5, 5, 10, 15, and 20 at%. The alloys were synthesized by vacuum arc melting and the microstructure as well as hardness of the as-cast alloys were studied. Alloys with low Ni content (x?≤?2.5%) consists of a two-phase microstructure of dendritic and inter-dendritic regions with fcc (matrix) and tetragonal (sigma) crystal structure, respectively. When the Ni content is 5 at%, two-phase structure with fcc (matrix) and bcc (secondary phase) is observed, with the addition of Mn-rich inclusions that are present in the entire matrix. Alloys with higher Ni content (x?≥?10, at%) exhibit a single phase of fcc structure. Hardness of the HEAs decreases from 320 to 120 Hv with increase in Ni content, and the high hardness of these alloys with low Ni content is due to the mixture of both fcc and hard tetragonal (sigma) phases.

     

等离子合金化AlCoCrCuFe_xMnNi高熵合金涂层的组织与性能

在45#钢基体上采用等离子束合金化法制备AlCoCrCuFe_xMnNi高熵合金涂层。采用SEM,EDS,XRD等研究高熵合金涂层的组织,利用显微硬度计测试涂层的显微硬度分布。结果表明:采用等离子束合金化Al,Co,Cr,Cu,Mn和Ni等摩尔单质金属粉,在等离子束作用下45#钢基材中的Fe元素参与表面合金化,形成了厚度约为1 mm的AlCoCrCuFe_xMnNi七主元高熵合金涂层,涂层主要由BCC结构的枝晶和FCC结构的枝晶间组织组成。另外,还有σ相主要分布在枝晶间,涂层从表面到基材,体系的混合熵呈高熵-中熵-低熵梯度变化。涂层的维氏显微硬度(HV0.2)达到670~400的梯度分布。     

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.     

Overcoming the Strength-Plasticity Trade-Off in a Multi-phase Equiatomic CrCuNiTiV 3d Transition Metal High-Entropy Alloy

The phase components, microstructures, and mechanical properties of a multi-phase equiatomic 3d transition metal high entropy alloy, CrCuNiTiV, were investigated. In the as-cast condition, the alloy was mainly composed of a body-centered cubic (BCC) dendritic phase and a face-centered cubic (FCC) interdendritic phase, with the BCC dendrite uniformly distributed in the FCC matrix. Through annealing, three phases decomposed from the FCC parent phase, and small particles and stripes were derived from the elongated stripes of the as-cast alloy. Outstanding plasticity was acquired with only a small sacrifice in the yield strength after annealing. Specifically, the plasticity increased from 12.7 pct in the as-cast condition to 23.4 pct in the annealed condition while high yield strengths of 965 and 877 MPa were retained in the as-cast and annealed alloys, respectively. Overcoming the strength-plasticity trade-off in the annealed CrCuNiTiV alloy was mainly achieved via the large volume fraction of FCC interdendritic phases, together with the precipitation of one BCC phase and two FCC phases.

     

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...     

淬火温度对80mm调质690MPa级低碳贝氏体高强钢板组织性能的影响

通过金相显微镜、扫描电镜、力学性能测试,研究了830～930℃淬火+650 ℃回火对690 MPa高强钢显微组织和力学性能的影响.结果表明:实验钢经两相区830 ℃淬火+650 ℃回火后的组织为板条状铁素体和回火索氏体,其屈服强度较低为679 MPa.淬火温度在完全奥氏体化相区为890～930℃时,随着淬火温度升高,材...     

Microstructure and Corrosion Properties of AlCoCrFeNi High Entropy Alloy Coatings Deposited on AISI 1045 Steel by the Electrospark Process

Electrospark deposition (ESD) was employed to clad the AlCoCrFeNi high-entropy alloy (HEA) on AISI 1045 carbon steel. The relationship between the microstructure and corrosion properties of the HEA-coated specimens was studied and compared with that of the copper-molded cast HEA material. Two major microstructural differences were found between the cast HEA material and the HEA coatings. First, the cast material comprises both columnar and equiaxed crystals with a columnar-to-equiaxed transition (CET), whereas the HEA coatings consist of an entirely columnar crystal structure. The CET phenomenon was analyzed based on Hunt’s criterion. Second, unlike the cast HEA material, there was no obvious Cr-rich interdendritic segregation and nano-sized precipitate distributed within the dendrites of the HEA coating. With regard to corrosion properties, the corrosion current of the HEA-coated specimen was significantly lower than for the 1045 steel and the cast HEA material. This was attributed to the ESD specimen having a relatively high Cr oxide and Al oxide content at the surface. Moreover, for the ESD specimen, the absence of Cr-rich interdendritic phase and second-phase precipitation resulted in a relatively uniform corrosion attack, which is different from the severe galvanic corrosion attack that occurred in the cast specimen.     

Spray Forming of Bulk Ultrafine-Grained Al-Fe-Cr-Ti

An Al-2.7Fe-1.9Cr-1.8Ti alloy has been spray formed in bulk and the microstructure and properties compared with those of similar alloys produced by casting, powder aomization (PA), and mechanical alloying (MA) routes. In PA and MA routes, a nanoscale metastable icosahedral phase is usually formed and is known to confer high tensile strength. Unlike previous studies of the spray forming of similar Al-based metastable phase containing alloys that were restricted to small billets with high porosity, standard spray forming conditions were used here to produce a ~98 pct dense 19-kg billet that was hot isostatically pressed (“HIPed”), forged, and/or extruded. The microstructure has been investigated at all stages of processing using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and synchrotron X-ray diffraction (XRD) at the Diamond Light Source. Consistent with the relatively low cooling rate in spray forming under standard conditions, the microstructure showed no compelling evidence for the formation of metastable icosahedral phases. Nonetheless, after downstream processing, the spray-formed mechanical properties as a function of temperature were very similar to both PA rapid solidification (RS) materials and those made by MA. These aspects have been rationalized in terms of the typical phases, defects, and residual strains produced in each process route.     

Influence of zirconium addition on the microstructure,thermodynamic stability,thermal stability and mechanical properties of mechanical alloyed spark plasma sintered (MA-SPS) FeCoCrNi high entropy alloy

ABSTRACT

Equiatomic FeCoCrNi (Zr₀) and non-equiatomic FeCoCrNiZr_0.4 (Zr_0.4) high-entropy alloys (HEAs) were synthesised by mechanical alloying and spark plasma sintering. XRD analysis verified the formation of FCC and BCC solid solution phases in both alloys after 30?h of ball milling. While the SPS FeCoCrNi alloy contains both FCC and BCC solid solution phases, the FeCoCrNiZr_0.4 presents an FCC solid solution. The thermodynamic analysis showed that FeCoCrNiZr_0.4 is more stable with respect to the FeCoCrNi alloy. The phase stability of FeCoCrNiZr_0.4 was revealed up to ～800°C. The shear strength and hardness of the FeCoCrNi HEA improved with Zr addition. Failure analysis of the shear punch tested samples revealed a ductile fracture with dimple structure for FeCoCrNi and a brittle fracture with a smooth featureless surface for FeCoCrNiZr_0.4.     

C Si Mn Cr Nb钢双相组织性能的柔性控制

 根据C Si Mn Cr Nb试验钢的双道次变形和分段冷却热模拟试验结果,进行了试验钢控轧控冷试验,分析了工艺参数对试验钢组织和性能的影响,获得了具有不同力学性能的铁素体+马氏体或铁素体+贝氏体双相组织。结果表明,试验钢两段轧制分段冷却后550 ℃卷取获得铁素体+马氏体双相组织,屈服强度415 MPa,抗拉强度710 MPa,伸长率23.0％,屈强比0.59。500 ℃卷取得到铁素体加粒状贝氏体双相组织,与550 ℃卷取相比,屈服强度升高35 MPa,抗拉强度降低45 MPa,伸长率略微降低。     

An Ultra-low Carbon, Thermomechanically Controlled Processed Microalloyed Steel: Microstructure and Mechanical Properties

In the current study, a novel ultra-low carbon, high-molybdenum-bearing microalloyed steel has been thermomechanically processed. Transformation of this steel during continuous cooling has been assessed. Variation in the microstructure and mechanical properties at different finish rolling temperatures has been studied. The average grain size, misorientation of grain boundary, and distribution of ferrite grains have been analyzed by using electron backscatter diffraction. The lower yield strength (251 to 377?MPa) with moderate tensile strength (406 to 506?MPa) along with high ductility (30 to 47?pct) has been achieved in the selected range of finish rolling temperatures. Superior impact toughness value in the range of 153 to 162?J is obtained in the subsize specimen even at subzero temperatures (233?K [?40?°C]), which is attributed to fine average ferrite grain size. The acicular ferrite dominated microstructure obtained at the 1023?K (750?°C) finish rolling temperature is the most attractive microstructure for pipeline applications due to its excellent combination of strength and toughness.     

轻质Al-Mg-Li合金的微观组织与力学性能

采用熔炼和热挤压制备轻质Al-5.5Mg-2.0Li-0.1Zr-0.2Sc合金,利用X射线衍射仪、差示扫描量热仪、金相显微镜、扫描电子显微镜、显微硬度计及拉伸试验机对合金的物相组成、微观组织、力学性能及断口形貌进行检测分析,研究时效工艺温度（120 ℃和160 ℃）对合金微观组织和力学性能的影响.结果表明:Al-Mg-Li合金挤压后晶粒组织呈纤维状,存在一定数量的Al₃Li（δ′）和Al₂MgLi（S）相;经固溶和时效处理后,再结晶晶粒尺寸变大,主要析出相为δ′相S相;160 ℃时效处理容易加速时效析出行为,导致析出相粗化,强化效果减弱;经120 ℃/20 h峰时效处理后,合金的抗拉强度、屈服强度和延伸率分别达到532 MPa、475 MPa和4.4 %.      

微合金化对电子封装用高硅铝合金微观组织与性能的影响

采用快速凝固-粉末冶金法制备电子封装用高硅铝合金（Al-50 %Si）,研究添加单质Cu粉对微观组织、力学性能和热物理性能的影响.采用扫描电子显微电镜（SEM）、X射线衍射仪（XRD）等手段,分析Cu含量（0~2 %）对微观组织和相组成的影响,并建立与力学性能和热物理性能之间的关系.结果表明:当Cu含量不高于1 %时,高硅铝合金微观组织中Si相尺寸和形貌改变不明显;拉伸强度和抗弯强度均随着Cu含量增加而迅速上升,并在2 %Cu时达到极大值268.4 MPa和422.6 MPa,相对于合金化前提高44.9 %和46.7 %;Cu含量对合金热膨胀系数（CTE）的影响不明显,但是基体中细小的Al₂Cu相不利于导热性能（热导率下降7.5 %）.综上,电子封装用高硅铝合金中添加1 %Cu时,可以在基本保持原有组织和热物理性能的情况下,提高强度20 %以上.      

Microstructure and Mechanical Properties of GMAW Weld Metal of 890MPa Class Steel

The relationship between microstructure and mechanical properties of gas metal arc weld metal with strength over 890 MPa is discussed. The microstructure of the weld metals is characterized with OM, SEM, TEM and EBSD. The microstructure of the weld metals is mainly composed of martensite and bainite. Experimental results show that the microstructure with predominant fine lath bainite possesses good toughness of 77 .l, while its yield strength is less than 800 MPa. The microstructure of coarse lath martensite and bainite has the lowest toughness of 43 J and its yield strength is 820 MPa. The mixed microstructure with fine martensite, bainite and retained austenite films bears good combination of toughness and yield strength （62 J and 880 MPa, respectively）. It is concluded that fine effective grain size and ductile phase of austenite films are two main factors to achieve good mechanical properties.     

Y2O3对AlCoCrFeNi高熵合金涂层组织及力学性能的影响

利用激光熔覆技术在Q235钢基体表面分别制备出添加不同质量分数Y₂O₃的AlCoCrFeNi高熵合金涂层。采用X射线衍射仪、扫描电子显微镜、显微硬度计和摩擦磨损试验机对AlCoCrFeNi高熵合金涂层的微观组织、硬度及摩擦磨损性能进行了分析。结果表明:AlCoCrFeNi高熵合金涂层由面心立方结构（FCC）和体心立方结构（BCC）两相构成;随着Y₂O₃质量分数的提高,其体心立方结构相体积分数增加,而面心立方结构相的体积分数变化呈相反趋势。AlCoCrFeNi高熵合金涂层组织由等轴晶构成,加入Y₂O₃后,促进了熔池流动,使气孔逐渐消失,致密性提高,晶粒明显细化。添加质量分数5%Y₂O₃的涂层组织呈树枝晶状,形成弥散分布的YAl₂和Y₂O₃相;涂层的显微硬度可达HV 350,约为AlCoCrFeNi高熵合金涂层硬度的2倍,强化效果明显。Y₂O₃的添加有利于促进涂层中体心立方相的形成和YAl₂相的析出,能有效提高高熵合金涂层的硬度及耐磨性能。     

冷轧双相钢DP800生产工艺及性能研究

探讨了800 MPa级冷轧双相钢的成分体系、冷却处理工艺、组织及性能;研究了退火温度、冷却速率对双相钢性能的影响,分析了双相钢的强化机理,并且优化了退火工艺参数。结果表明,冶炼过程采用C-Si-Mn-Cr-V成分体系,轧制过程采用650℃±20℃的中温卷取,连续退火过程中快冷段投入高氢(H2含量20%)冷却,冷速达到42~50℃/s,能够得到由铁素体和马氏体组成的冷轧双相钢DP800,综合力学性能优良。     

60 mm厚低屈强比高强钢板Q500qE组织与性能研究

通过JMatpro软件、扫描电镜、力学性能测试,对Q500qE 60 mm厚度500 MPa级低屈强比高强钢板进行了连续冷却转变(CCT)曲线、钢板显微组织与力学性能、焊接接头力学性能分析。结果表明,通过控轧控冷工艺：终轧温度800～840℃,入水温度660～680℃和终冷温度400～450℃,该钢组织为铁素体+贝氏体+马氏体/奥氏体岛,两相交界处和贝氏体内部存在大量大角度晶界。钢板1/4和1/2厚度位置屈服强度≥500 MPa,抗拉强度≥640 MPa,屈强比≤0.80,-40℃低温冲击功≥200 J,焊接热影响区-40℃低温冲击功≥100 J     

高能球磨制备WC/Al2O3-Cr-Mo-Ni金属陶瓷及其组织和力学性能

以亚微米级WC粉、Al2O3粉、Cr粉、Mo粉与Ni粉为原料,采用高能球磨+热压工艺制备WC/Al2O3-Cr-Mo-Ni金属陶瓷材料,利用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)分析材料的物相组成和显微组织结构以及断裂方式,研究粘结相Ni和陶瓷相Al2O3的含量(均为质量分数)对该材料力学性能和微观结构的影响。研究表明:金属陶瓷的抗弯强度及断裂韧性随Ni含量增加而提高,随Al2O3含量增加而降低,硬度的变化趋势则相反。当Ni含量为7%、Al2O3含量为10%时,该金属陶瓷具有良好的综合性能,抗弯强度为567 MPa,断裂韧性为7.46(MPa.m1/2),维氏硬度为15.24 GPa,基本达到现用模具材料的水平。随着Ni含量增加,金属陶瓷的断裂方式由沿晶断裂向沿晶断裂与穿晶断裂相混合的方式转变。     

1 500 MPa级高伸长率双相钢的组织性能分析

为了进一步提高双相钢的性能,通过合理的化学成分设计,在实验室研发了 1 500 MPa级Nb-Ti微合金化的高伸长率冷轧双相钢,并且利用连退模拟试验机、扫描电镜等设备,系统研究了退火温度和过时效温度对双相钢组织性能的影响.结果表明,抗拉强度随着退火温度的升高而增大,在840℃时可达到1 650 MPa.当温度继续升高时...