Effect of Ru additions on microstructure and mechanical properties of Cr–TaCr2 alloys

Early work indicated that Ru reduced the ductile-to-brittle transition temperature of Cr even at small concentrations. To evaluate the potential of Ru as a beneficial alloying element in the two-phase Cr–TaCr₂ alloys, a number of Cr–8 at.%Ta alloys with 0–10 at.%Ru were prepared, and their microstructures and mechanical properties were evaluated. The Ru addition was found to move the eutectic point of Cr–TaCr₂ to a higher Ta level, as compared to the binary Cr–Ta system. Ru partitioned preferentially in the Laves phase over in the Cr matrix, with a partitioning ratio of 2–5:1, depending on the Ru addition level. Ru was also found to mainly occupy the Cr site in the TaCr₂ Laves phase. The hardness of both the primary Cr matrix and the eutectic microconstituent increased slightly with the increase in Ru addition. At a higher Ru addition level (i.e. 10 at.%), the hardness of the primary Cr matrix increased significantly, probably due to the precipitation of extremely fine Laves-phase precipitates. The Ru addition did not noticeably affect the fracture toughness of the two-phase alloys.     

多主元高熵合金AlTiFeNiCuCrx微观结构和力学性能

研究了不同Cr含量的AlTiFeNiCuCrx多主元高熵合金的微观组织和力学性能特点.结果表明,Cr含量的增加使合金的凝固模式从亚共晶向过共晶凝固转移,铸态组织由先析出枝晶相、菊花状共晶组织和枝晶间相组成.合金仅由简单的体心立方结构和面心立方结构两相组成.Cr含量的增加对合金硬度的提高较小.该合金为低温脆性材料,但在1073 K高温时具有很好的塑性变形能力和较高的强度,当x=1-1.5时,合金具有最优的压缩强度和塑性组合.     

Microstructures,Compressive Properties,and Microhardness of NiAl-Cr(Mo) Eutectic Alloys With Various Ni Contents

The microstructures and mechanical properties of 66(Ni_xAl)-28Cr-6Mo (x?=?1.0, 1.5, 2.0, 2.5, 3.0, and 3.5) alloys were investigated using scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscope, microhardness, and compression tests. The microstructure of NiAl-28Cr-6Mo (Ni_1.0) eutectic alloy consists of NiAl and Cr(Mo) phases. With increasing the Ni content to 2.0, the microstructure changes from eutectic (Ni_1.0) to eutectic?+?primary NiAl dendrite (Ni_1.5 and Ni_2.0), and the morphologies of part of precipitates in primary NiAl dendrite evolve from granular to needle-like. When the Ni content increases further, besides eutectic and primary NiAl dendrite, the gray phase forms and is identified as an ordered FCC (L1₂) (Ni,Cr)₃(Al,Mo) phase. Moreover, the more needle-like precipitates emerge in the primary NiAl dendrite of Ni_2.5, Ni_3.0, and Ni_3.5 alloys, and the precipitate is identified as a bcc Cr(Mo) phase. The deep etching reveals that the three-dimensional morphology of Cr(Mo) precipitate is not needle-like but lath-like. Among the investigated alloys, both Ni_2.0 and Ni_2.5 alloys possess the higher fracture strength and microhardness. The relevant strengthening mechanisms are discussed.     

Investigations on the microstructure and room temperature fracture toughness of directionally solidified NiAl–Cr(Mo) eutectic alloy

The microstructures and room temperature fracture toughness of directionally solidified NiAl-xCr-6Mo (x = 28, 32 and 36 at%) alloys were investigated. Fully eutectic microstructure could be obtained in the alloys over a wide composition range. High temperature gradient could increase the planar/cellular transition rate and expand the eutectic coupled growth zone. The volume fraction of Cr(Mo) strengthening phase increased with the increasing content of Cr, accordingly, the fracture toughness of NiAl–Cr(Mo) alloys also gradually increased. The fracture toughness of 26.15 MPa m^1/2 was obtained in the NiAl-36Cr-6Mo hypereutectic alloy solidified at withdrawal rate of 10 μm/s and temperature gradient of 600 K/cm, which is the highest value in the NiAl–Cr–Mo alloy system until now. Well-aligned microstructure was beneficial to the enhancement of the fracture toughness, while the existence of primary phase seriously deteriorated the toughness. All the directionally solidified NiAl–Cr(Mo) alloy failed as brittle quasi-cleavage fracture. Some toughening mechanisms, such as crack bridging, crack nucleation, crack blunting, crack deflection, interface debonding and shear ligament toughening as well as linkage of microcracks were observed. In addition, mobile dislocation generated from the interface also had significant influence on the toughness.     

电弧熔炼Cr-40Ti-20Nb三元合金的组织与压缩性能

采用真空非自耗电弧熔炼的方法制备了Cr-40Ti-20Nb(原子分数)合金.利用光学显微镜(OM),X射线衍射(XRD),扫描电镜(SEM)分析了合金不同凝固位置处的相组成和组织形态.结果表明,合金的凝固组织主要是由Laves相Cr2(Nb,Ti)枝晶组织及丁i的固溶体组成.同时对合金的显微硬度和压缩性能进行了测试,显微硬度值在6 112～7 350MPa之间,比Laves相Cr2Nb的显微硬度低20％.另外室温压缩屈服强度可达1 334-1 524 MPa,与采用多种合金化元素的Cr-12Nb-4Re-2Al合金相当,这表明Ti元素的添加不仅可以改变Laves相Cr2Nhb合金的凝固组织,而且对其塑性也有很大程度的改善.     

晶粒细化对Cr-25Nb合金高温氧化行为的影响

采用电弧熔铸和机械合金化+热压烧结技术制备晶粒尺寸相差较大的Cr-25Nb合金,研究其在950及1200 ℃空气中的氧化行为。结果表明,熔铸态及机械合金化Cr-25Nb合金氧化后均没有发生Cr的单一外氧化,而形成了以Cr2O3为外层、NbCrO4为内层的双层氧化膜结构;机械合金化Cr-25Nb合金在950及1200 ℃的氧化速度均小于熔铸态合金,特别是在1200 ℃氧化100 h后,熔铸态Cr-25Nb合金的氧化增重是机械合金化合金的2倍多。这主要是因为晶粒细化促进了氧化膜内应力的释放,提高了氧化膜与基体的粘附性     

Oxidation resistance and mechanical properties of Laves phase reinforced Cr in-situ composites

Two-phase Cr(X)–Cr₂X (X=Nb, Ta) in-situ composites are of interest for high-temperature applications due to their high melting points and potential for high-temperature strength. A six cycle, 120 h, 1100°C cyclic oxidation screening test was used to evaluate potential for high-temperature oxidation resistance of several Cr(X)–Cr₂X in-situ composites. Alloys based on the Cr–Ta system near the Cr(Ta)–Cr₂Ta eutectic exhibited superior oxidation resistance compared to corresponding alloys based on the Cr–Nb system. The binary Cr–Ta alloys were also found to exhibit a moderate degree of room-temperature fracture toughness, in the range of 9–10 MPa√m. It was concluded that the Cr(Ta)–Cr₂Ta alloys are a promising base for future high-temperature intermetallic alloy development efforts.     

Microstructural evolution with various Ti contents in Fe-based hardfacing alloys using a GTAW technique

The aim of this study is to discuss the effect of microstructural development with different Ti contents in Fe-based hardfacing alloys. A series of Fe-Cr-C-Si-Mn-xTi alloy fillers was deposited on SS400 low carbon steel substrate using oscillating gas tungsten arc welding. The microstructure in the Fe-based hardfacing alloy without Ti content addition included: the primary γ, eutectic γ+(Fe,Cr)₃C, eutectic γ+(Fe,Cr)₂C and martensite. With increasing Ti contents, the microstructures showed the primary TiC carbide, γ phase and eutectic γ+(Fe,Cr,Ti)₃C. The amount and size of TiC carbide in the hardfacing layers increased as the Ti content increased. However, the eutectic γ+(Fe,Cr,Ti)₃C content decreased as the Ti content increased. According to the results of the hardness test, the lowest hardness value (HRC 54.93) was found with 0% wt% Ti and the highest hardness (HRC 60.29) was observed with 4.87 wt% Ti.     

AlCoCrFeMnZr近共晶高熵合金的组织形貌及耐磨性

采用真空熔炼法制备出了AlCoCrFeMnZr近共晶高熵合金,通过XRD、SEM、显微硬度计和摩擦磨损试验机测试了AlCoCrFeMnZr合金的晶体结构、组织形貌、硬度以及耐磨性能。结果表明,AlCoCrFeMnZr合金的物相结构为BCC和HCP双相结构,组织由初生相和细密的片状共晶组织组成。初生相由富Cr、Fe、Zr的HCP相组成,以树枝晶方式生长,片状共晶组织中枝晶区域(α相)主要分布Co、Cr、Fe,晶间(β相)主要分布Al和Zr,符合高熵合金组织及元素分布规律。磨损方式由粘着磨损和磨粒磨损转变为氧化磨损,摩擦因数出现先增加后减少的趋势,平均摩擦因数为0.5432,显微硬度为768.8 HV0.5,具有优良的硬度和耐磨性。     

Microstructure and properties of Fe–Cr–C hardfacing alloys reinforced with TiC–TiB2

Abstract

Different amounts of TiB₂ powder were added to flux cores of wear resistant hardfacing flux cored wires for the preparation of new flux cored wires. Fe–Cr–C hardfacing alloys reinforced with TiB₂ were produced by arc hardfacing. The microstructure, hardness and wear resistance behaviour of the hardfacing alloys were investigated using an optical micrograph, scanning electron micrograph (SEM), X-ray diffractometer, macrohardness tester, microhardness tester and abrasive wear tester. The results showed that, among the hardfacing alloys, a new hard phase, i.e. TiC–TiB₂ composite compound particles, was formed and dispersed in the primary carbides and matrix structures. The TiC–TiB₂ reinforced Fe–Cr–C hardfacing alloys imparted greater hardness and better wear resistance. The presence of TiC–TiB₂ hard phase particles is the main reason for the improvement in hardness and wear resistance of Fe–Cr–C hardfacing alloys.     

Co对Cu-Cr合金组织和性能的影响

研究了Cu-Cr-Co合金经80%变形量冷轧和450 ℃时效后的组织和性能,并与Cr-Cr合金进行了对比。结果表明, Cu-0.66Cr-0.05Co和Cu-0.62Cr-0.22Co合金的性能在450 ℃时效4 h时达到峰值,此时的抗拉强度、硬度及导电率分别为376 MPa和410 MPa、143.7 HV0.5和138.4 HV0.5、84.1%IACS和66.2%IACS。峰时效态Cu-Cr-Co合金析出相为体心立方结构(bcc),并与基体呈Nishiyama-Wassermann取向关系,Co含量对Cu-Cr-Co合金的晶粒形貌几乎没有影响。与Cu-Cr合金相比,Co的加入使合金时效的时间延长,硬度有所增加,抗软化性能提高,但抗拉强度和导电率均下降。由于Cu和Co在422 ℃以上具有一定的固溶度,在时效过程中部分Co逐渐固溶进基体中,形成固溶体,并没有与预测一样分布在析出相外围,降低了合金综合性能。     

定向凝固过共晶Nb-Si基合金的组织优化

采用液态金属冷却定向凝固炉制备Nb-16Si-24Ti-10Cr-2A1．2Hf合金,凝固速率分别为1．2、6、18、36、50mm／min,随后对定向凝固速率为50mm／min的合金进行（1400℃,10h）,（1450℃,10h）和（1500℃,10h）的热处理。研究了定向凝固速率和热处理温度对合金微观组织的影响。结果表明：合金的定向凝固组织主要由沿着试棒轴向生长的初生Nb5Si3相和耦合生长的Nbss／Nb5Si3共晶胞组成,在共晶胞边缘,有少量的Cr2Nb存在。横截面上共晶胞边界明显,随着凝固速率的增加,定向凝固组织明显细化,Nbss／Nb;Si,共晶胞形貌也发生变化。合金经过热处理,Nbss连成基体,部分CrENb相熔解,微观成分偏析减小。经过（1450℃,10h1热处理,实现了对过共晶Nb—Si基合金的组织优化。     

超高压凝固Al—Si合金的非平衡组织

研究了超高压（５．５ＧＰａ）条件下凝固的过共晶Ａｌ－Ｓｉ合金的非平衡组织。结果表明：过共晶成分合金中出现大量初生α相。并有α－β＋（α＋β）共晶的共生组织,Ｓｉ在α相中的固溶度和Ａｌ在β相中的固溶度都有极大增加。讨论了高压对凝固组织的影响。     

Cu-1.2Cr-0.6Fe合金微观组织和力学性能的研究

在大气环境下采用熔铸法制备了Cu-1．2Cr-0．6Fe合金,利用OM、XRD和EPMA分析研究了该合金铸态和热处理态的显微组织,并利用INSTRON5882电子万能材料试验机和HBE-300型电子布氏硬度计分别测试了该材料的拉伸性能和硬度。结果表明,Cr与Cu不能形成化合物,可有限同溶于纯铜中,超过部分形成过剩的第二相。Fe具有同溶强化效应和细化晶粒的作用,能改善合金力学性能。合金材料铸态试样的拉伸强度、硬度分别为247．65MPa和67．6HB。铸态合金试样经960℃×1h同溶（水淬）→470℃×6h时效（空冷）热处理后,可析出细小弥散的第二相质点,其硬度值可提高到98．7HB。     

高碳化物铁碳合金的磨粒磨损性能研究

利用销盘式磨损试验机研究了具有高碳化物含量的高铬及高钒系铁碳合金的磨粒磨损性能。结果表明,高碳化物铁碳合金的耐磨性取决于材料表面的宏观硬度与碳化物硬度、含量及分布,宏观硬度临界值约为57HRC。当材料的硬度低于临界值时,其耐磨性主要取决于宏观硬度;当宏观硬度高于临界值时,耐磨性主要取决于碳化物的硬度及含量。随着Cr7C3含量的增加,高铬系合金的耐磨性稍有提高。随着VC含量增加,高钒系合金的耐磨性迅速提高。当宏观硬度高于临界值且含量较高的VC均匀分布时,高钒合金的耐磨性是高铬铸铁的2．3—3．5倍。     

Structural stability of the Laves phase Cr2Ta in a two-phase Cr–Cr2Ta alloy

Detailed microstructural analysis of a two-phase alloy of composition Cr–9.8 at.% Ta and lying in the Cr–Cr₂Ta region of the Cr–Ta binary system confirmed that the existing phase diagram is inaccurate; in the cast and annealed condition (1273 K/24 h), blocky primary Cr₂Ta precipitates were observed although the phase diagram indicates the eutectic composition to be ∼13 at.% Ta. The eutectic structure is composed of Cr solid solution and the Laves phase Cr₂Ta; the morphology is primarily lamellar although the rod morphology was occasionally observed. The Laves phase eutectic microconstituent exhibits the C14 (2H) hexagonal structure with a low stacking fault (basal faults) density and an average composition corresponding to 28.5 at.% Ta. After a prolonged high-temperature anneal (1573 K/168 h), the morphology breaks down to form discrete particles of Cr₂Ta; the C14, C36 and C15 structures were all recognized in this annealed condition, often more than one form being present in a single precipitate. The C15 structure was not twinned but contained some stacking faults on the {111} planes. Composition measurements confirmed that these structural transformations were accompanied by composition changes, the precipitates becoming more Ta-rich as they transitioned from the C14 via the C36 to the C15 phase. These observations are coupled with the results from earlier studies to present a discussion on factors that influence the stability and C14/C36/C15 transformation kinetics.     

电弧熔炼态Laves相Cr2Nb/Cr合金的微观组织演变

采用真空非自耗电弧熔炼法制备了Cr-12％Nb(原子分数,下同)和Cr-20％Nb 2种成分合金的纽扣锭,利用XRD,OM,SEM和EDS对电弧熔炼态纽扣锭不同位置的组织及其竞争生长进行了研究.结果表明：Cr-12％Nb合金纽扣锭底部为细小的离异共晶,中部和顶部则由粗大的初生Cr相和共晶组织(Cr2Nb+Cr)组成.而...     

STUDY ON MORPHOLOGY OF CHROMIUM IN CHILLED Cu-0.14%-2.0%Cr ALLOYS

The morphology of chromium in chilled Cu-Cr alloys with 0.14%-2.0% Cr has been studied. The results showed that eutectic Cr phase takes a fibrous shape, and pre-eutectic Cr is dendritic in the studied chilled Cu-Cr alloy. During solute treatment of the eutectic and super-eutectic Cu-Cr alloys, only part of chromium particles dissolved in copper phase,some fiber and dendritic chromium still remained. Forging before solute treatment can reduce the size of primary Cr particles, which benefits the aging structure.     

Design Fe-based Eutectic Medium-Entropy Alloys Fe_2NiCrNb_x

High-entropy alloys have attracted broad research interests due to their unique and intriguing mechanical properties. As a category of high-entropy alloys, eutectic high-entropy alloys combine the advantages of eutectic and high-entropy alloys, with excellent mechanical properties and casting properties. Some eutectic high-entropy alloys have been developed and shown exciting properties. In this paper, based on the physical metallurgy of eutectic high-entropy alloy, medium-entropy alloy Fe_2NiCrNb_x was designed. The as-cast alloy is composed of FCC and Laves phases, Nb element promotes the formation of primary Laves phase, and the hardness of the alloy increases with the increase in Nb element. Among the four alloys, the eutectic chemical composition at eutectic point is Fe_2NiCrNb_(0.34); the alloy has a good strength and plastic balance. The ultimate comprehensive strength is 2267 MPa, and the fracture strain is 30.8%. The experiment data and analyses identified the eutectic points and the excellent mechanical behavior. Moreover, the expensive Co element was replaced by Fe element. This cheap medium-entropy alloy has promising prospect in the consideration of the cost performance ratio.     

Effects of Chromium on the Microstructures and Mechanical Properties of AlCoCrxFeNi2.1 Eutectic High Entropy Alloys

In the present study,a series of AlCoCrxFeNi2.1 (x=0,0.25,0.5,0.75,1.0) eutectic high entropy alloys (EHEAs) have been designed and prepared.And the effect of Cr content on the microstructures and mechanical properties of the AlCoCrxFeNi2.1 alloys was systematically investigated.The results indicate that the AlCoCrxFeNi2.1 (x ＞ 0) alloys exhibit almost complete lamellar eutectic microstructures with a mixture structure of FCC and B2 phases.And the AlCoFeNi2.1 alloy without Cr element exhibited a hypoeutectic microstructure with a primary B2 phase.In addition,the eutectic microstructures for AlCoCrxFeNi2.1 eutectic alloys do not change significantly.The room temperature compressive tests results show that with an increase in Cr content (from x =0 to x =1.0),the yield strength will first decrease,and thereafter increase.The trend is the opposite with the fracture strength and plastic strain.They show an increase trend at first,and then decrease.The AlCoCr0.5FeNi2.1 (Cr0.5) alloy shows the best comprehensive mechanical properties.The tensile yield strength,fracture strength,and elongation are 536.5 MPa,1062 MPa,and 13.8％,respectively.Furthermore,the Cr0.5 alloy also displays a high strength with a yield strength of 362 MPa at 700 ℃.In summary,by changing the Cr content,AlCoCrxFeNi2.1 eutectic high entropy alloys with excellent comprehensive mechanical properties were obtained and prepared.