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.     

AlCoCrFeNiBx 高熵合金微结构与性能

本文系统研究了 B 元素对高熵AlCoCrFeNiBx (x denotes the atomic fraction of B element 0, 0.1, 0.25, 0.5, 0.75 and 1.0)合金的微结构和性能的影响。其中添加的B元素含量为0.1时AlCoCrFeNi 高熵合金的形貌从等轴晶转变为枝晶形貌。 其中在等轴晶的内部可以观测到调幅分解结构。当 x>0.1时, 枝晶和调幅分解结构都逐渐消失了,但是越来越多的硼化物开始出现了。这个转变归因于 Cr-B 和Co-B之间高的负混合焓.随着B元素的增加, AlCoCrFeNiBx高熵合金的结构从B2 BCC 结构向B2 BCC FCC 结构的转变, 最后形成了 B2 BCC FCC 以及硼化物的混合结构。 随着B元素的添加硬度值从 HV486.0 下降到了 HV460.7, 然后增加到 HV615.7,其中x=0.1时合金的硬度最低。合金的压缩强度随B元素的增加明显下降,当x=0.25时,合金具有最大的压缩强度,但是当x =0.75时, 由于硼化物的大量生成合金在弹性变形阶段就发生了断裂。随着B含量增多合金的矫顽力和饱和磁化强度开始下降. 下降的矫顽力显示合金具有很好的软磁性能。     

热处理工艺对Mg-6Zn-2.5Cu镁合金显微组织和力学性能的影响

利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)和力学试验机等研究了铸造Mg-6Zn-2.5Cu合金在铸态、固溶和时效处理下的显微组织和力学性能。结果表明:合金的铸态组织主要由α-Mg和(α-Mg+MgZn2+Mg2Cu+CuZnMg)共晶相组成。在455℃固溶12~36 h时,随着时间增加,固溶效果逐渐增强,且在20 h时合金获得了较理想的显微组织及218 MPa的抗拉强度和8.68%的伸长率。随后在180℃时效6~72 h后,合金的拉伸性能随时效时间的增加呈先增加后减小的趋势,其中时效24 h时后,合金的抗拉强度和硬度达到峰值,分别为249.5 MPa和64.6 HV0.1,比铸态的分别提高了66.5 MPa和26.29%,伸长率在时效12 h时后达到了峰值6.72%。铸态合金的断裂方式以沿晶断裂为主,时效处理后合金的断裂方式为准解理断裂。     

Effects of Cu addition on microstructure and mechanical properties of as-cast Mg-6Zn magnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.     

时效处理对Mg-6Al-1Nd-xGd合金组织及高温力学性能的影响

采用光学显微镜(OM)、扫描电镜(SEM)、EDS能谱分析等手段研究了Mg-6Al1Nd-xGd(0,0.5,1,1.5)合金的时效硬化行为及时效处理(T6)对合金高温拉伸性能的影响,结果表明:Gd元素的加入使Mg-6Al-1Nd合金的时效过程延长,随Gd含量的增多,合金在200℃时效时的硬度峰值从28 h延迟到36 h附近,且Gd含量为1%时合金峰值硬度最大,达到HV51.1。T6处理后,合金的强度及塑性都有所提升,Mg-6Al-1Nd-1Gd合金在200℃的抗拉强度为146 MPa,伸长率为22.3%,较铸态分别提高27.5%和29.7%,合金表现出良好的综合高温拉伸性能。     

Effects of V Addition on Microstructural Evolution and Mechanical Properties of AlCrFe2Ni2 High-Entropy Alloys

The effects of vanadium addition on the microstructural evolution and mechanical properties of AlCrFe₂Ni₂ high-entropy alloy (HEA) were investigated. The results showed that the AlCrFe₂Ni₂V_0.2 HEA was composed of FCC phase, disordered BCC phase, and ordered BCC (B2) phase. With the increase in vanadium content, the formation of FCC phase was inhibited, and a transition from FCC phase to BCC phase occurred. The FCC phase disappeared completely when the value of x exceeds 0.4 in AlCrFe₂Ni₂V_x HEAs. Besides, the amplitude-modulated microstructure morphology transformed from a B2 phase matrix with dispersed BCC nano-phase into an alternating interconnected B2 and BCC phases. Vanadium element has the function of stabilizing BCC phase and B2 phase in AlCrFe₂Ni₂V_x alloys. The hardness of AlCrFe₂Ni₂V_x alloys increased from HV 332.4 to HV 590.7, while the yield strength increased from 765 to 1744.6 MPa with increasing vanadium content, which was mainly due to the decreasing content of FCC phase and the solid solution strengthening of vanadium element. At the same time, the compression ratio of the alloys decreased with the disappearance of the FCC phase. Among the alloys, the AlCrFe₂Ni₂V_0.2 alloy possessed the most excellent comprehensive mechanical properties with yield strength, fracture strength, and compressive ratio 1231.1, 2861.9 MPa, and 44.5%, respectively.     

Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Near-Eutectic AlCoCrFeNi<Subscript>2</Subscript> High-Entropy Alloy

The effects of tungsten addition on the microstructure and mechanical properties of near-eutectic AlCoCrFeNi₂ high-entropy alloy were investigated in this paper. The AlCoCrFeNi₂W _x alloys comprised the primary BCC phase plus eutectic FCC/BCC phases. It was found that W element can both promote the formation of the primary BCC phase and act as a solid solution strengthening element. The hardness of the AlCoCrFeNi₂W _x alloys increased from HV 293 to HV 356.2 with the increase in W content. The addition of W element improved the strength of alloys but reduced ductility. Thereinto, the AlCoCrFeNi₂W_0.2 alloy showed the most excellent compressive properties with the fracture strength of 2785.9 MPa and the plastic strain of 0.42, respectively, which implied the potential industrial application values.     

Effects of heat treatment on microstructure and mechanical properties of Mg-6Zn-4Sm-0.4Zr alloy

A new rare earth magnesium alloy(Mg-6 Zn-4 Sm-0.4 Zr, wt.%) was prepared by permanent mould casting. The microstructure and mechanical properties of the alloy sample in as-cast and various heat treatment situations were characterized with an optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) equipped with energy dispersive spectroscope(EDS), transmission electron microscope(TEM) and mechanical tests at room temperature, respectively. The experimental results show that the as-cast alloy mainly consists of α-Mg, eutectic Mg_2Zn_3, MgZnSm and Mg_(41)Sm_5. These eutectic phases with continuous or semicontinuous morphology principally distribute along grain boundaries. Almost all the eutectic compounds dissolve in α-Mg and the grains have no obvious growth trend after optimum solution treatment at 490 °C for 18 h. Meanwhile, the ultimate tensile strength(UTS) of 229 MPa and elongation(EL) to rupture of 9.78% can be achieved through the optimal solution treatment, which increase by 37 MPa and 57.74%, respectively, compared with that of the as-cast alloy. Further aging treatments at 200 °C for different durations lead to the conspicuous increment of mechanical properties and prominent age-hardening response. Peak-aged alloy(treated at 200 °C for 12 h) reveals better mechanical properties(UTS 258 MPa, EL 9.42%, hardness 73.4 HV) compared with the same alloy treated in other aging conditions, which is mainly ascribed to precipitated Mg_2Zn_3 and MgZn_2 phases. Fracture analysis demonstrates that the as-cast alloy belongs to inter-granular and cleavage fracture patterns, while the solutionized alloy(treated at 490 °C for 18 h) reveals trans-granular and quasi-cleavage fracture modes. For the peak-aged alloy, the fracture pattern obeys the mixture of trans-granular and cleavage modes.     

轻质MgAlSnZnCu高熵合金的微观组织和力学性能

为了提高阻隔层的稳定性,研究采用电磁感应加热方法,在覆盖剂和氩气保护作用下制备MgAlSnZnCu系列轻质高熵合金。使用扫描电镜(SEM)、X射线衍射(XRD)、能谱分析(EDS)对合金的铸造组织、退火组织和物相进行了表征和分析,同时采用显微硬度测试方法对其硬度进行了研究。结果表明,铸态MgAlSnZnCu合金组织由(AlMgZnCu)-FCC相和Mg₂Sn相组成,Mg₂Sn相的形态为2~6 μm粒状和不规则块状。Mg的含量由22%降低到12%,其合金的硬度由277 HV0.2增加到326 HV0.2,抗压强度由223 MPa增加到237 MPa。Sn和Zn含量降低后组织中出现了针状和片状的杂质相,且硬度值分散度较大,在450 ℃保温6 h的退火工艺条件下,组织中的杂质相出现明显的积聚长大的趋势。力学性能测试显示退火对抗压强度和硬度的影响不大,MgAlSnZnCu系列合金在450 ℃的条件下能保持较好的热稳定性。     

Combined effects of Bi and Sb elements on microstructure,thermal and mechanical properties of Sn-0.7Ag-0.5Cu solder alloys

This research investigated the combined effects of addition of Bi and Sb elements on the microstructure, thermal properties, ultimate tensile strength, ductility, and hardness of Sn-0.7Ag-0.5Cu (SAC0705) solder alloys. The results indicated that the addition of Bi and Sb significantly reduced the undercooling of solders, refined the β-Sn phase and extended the eutectic areas of the solders. Moreover, the formation of SbSn and Bi phases in the solder matrix affected the mechanical properties of the solder. With the addition of 3 wt.% Bi and 3 wt.% Sb, the ultimate tensile strength and hardness of the SAC0705 base alloy increased from 31.26 MPa and 15.07 HV to 63.15 MPa and 23.68 HV, respectively. Ductility decreased due to grain boundary strengthening, solid solution strengthening, and precipitation strengthening effects, and the change in the fracture mechanism of the solder alloys.     

消失模壳型铸造A356铸态和T6态铝合金的组织、性能及拉伸断口(英文)

对采用消失模壳型铸造制备的A356铝合金在铸态和T6热处理态下的微观组织、拉伸性能以及拉伸断口进行了研究,并与消失模铸造A356铝合金进行了对比分析。结果表明:消失模壳型铸造A356铝合金组织主要有α(Al)初生相、共晶硅相以及Mg2Si相组成。经过T6热处理后,共晶硅形貌更加球化,均匀地分布于晶界处;且共晶硅粒子的平均长度、宽度和长宽比都比铸态条件下的小。与消失模铸造相比,组织中的初生相和共晶硅相都明显细化。经T6处理后,消失模壳型铸造A356合金的力学性能得到明显提高,其中抗拉强度、延伸率和布氏硬度分别达到260.53MPa、6.15%和86.0,其与消失模铸造相比具有明显优势。此外,消失模壳型铸造A356铝合金拉伸断口为具有准解理面和韧窝形貌的混合断口,最终表现为穿晶断裂模式。而消失模铸造A356铝合金拉伸断口为明显的脆性断口。     

时效工艺对WE43镁合金组织与力学性能的影响

研究了WE43稀土镁合金在不同热处理工艺下显微组织、力学性能的变化规律,从而得出最佳的热处理工艺。研究结果表明WE43稀土镁合金铸态组织为等轴状晶粒,比较均匀,平均晶粒尺寸为40 μm;铸造冷却凝固的过程中,在晶界处形成了离异共晶组织;经520 ℃×8 h固溶处理后的组织,共晶相的数量和形态发生了明显的变化,枝晶偏析基本消除,晶界上仍有少量未溶的第二相。230 ℃×8 h时效后稀土第二相的数量增加,并且在晶粒内部析出了点状弥散的稀土相;经过250 ℃×16 h的时效后,合金的硬度达到了峰值,随着时效时间的继续延长,合金的硬度下降。固溶处理后WE43稀土镁合金的抗拉强度为162.59 MPa左右,断后伸长率约为5.0%;而经过250 ℃时效处理后,其抗拉强度明显增加,断后伸长率在4%左右。     

Microstructures and Mechanical Properties of Multi-component Al_xCrFe_2Ni_2Mo_(0.2) High-Entropy Alloys

A series of Al_xCrFe_2 Ni_2 Mo_(0.2) alloy consisting of FCC+BCC phases have been designed,and their as-cast microstructures and mechanical properties were also investigated with x ranging from 0.6 to 0.9.It was found that with the addition of Al element,the solidified structures changed from dendrite to columnar crystal then back to dendrite again.Moreover,the increased amount of BCC phase resulted in finer and more uniform microstructures of FCC [FeCrNi(Mo)] and BCC(Al-Ni)phases.Tensile yield strength and hardness of alloys showed a similar increasing trend as the volume fraction of BCC phase increased.Both strain hardening rate and strain hardening exponent were calculated to assess the tensile properties of the alloys.It was shown that A1_(0.6)CrFe_2 Ni_2 Mo_(0.2) exhibited the most excellent and comprehensive mechanical properties due to its high work hardening ability and stable strain hardening rate.The product of strength and elongation of Al_(0.6)CrFe_2 Ni_2 Mo_(0.2)reached up to 38.6 GPa%,which was higher than most of the reported as-cast high-entropy alloys.     

Mg含量对Al-Zn-Mg铝合金组织及性能的影响

通过改变镁的含量,设计了4种不同成分的Al-6.0Zn-xMg合金。采用光学显微镜(OM)、扫描电镜(SEM)、差式扫描量热分析仪(DSC)、硬度、导电率以及室温拉伸等分析测试方法,研究了Mg含量对Al-Zn-Mg合金铸态、均匀化态组织性能及T6态力学性能的影响。结果表明:4种铸态合金组织晶界附近存在大量共晶网状结构与链状第二相,主要为α(Al)+三元T(AlZnMg)相,合金中还存在少量的Al₃(Zr,Ti)相和富铁相,提高Mg含量会使合金组织中的非平衡共晶相增加。合金均匀化处理后空冷,基体内有大量细小弥散的针状η(MgZn₂)相析出,且随着Mg含量的提高,这种针状η(MgZn₂)相的析出数量也逐渐增多。随着Mg含量增加,硬度逐渐增加,导电率逐渐下降,且均匀化态合金的硬度及导电率比铸态的高。4种T6态合金中Al-6.0Zn-2Mg合金的综合力学性能最佳。     

MICROSTRUCTURE ANALYSIS AND MECHANICAL PROPERTIES OF Zn—Al ALLOY ROD PRODUCED BY HEATED MOLD CONTINUOUS CASTING

The new technology of continuous casting by heated mold was used to produce directional solidification ZA alloy lines to eliminate the inter defects of these lines and increase their mechanical properties. The results are as follows: (1) The microstruc-ture of the ZA alloy lines is the parallel directional dendritic columnar crystal. Every dendritic crystal of eutectic alloy ZA5 was composed of many layer eutectic β and η phases. The micro structure of hypereutectic ZA alloys is primary dendritic crystal and interdendritic eutectic structure. The primary phase of ZA8 and ZA12 is β, among them, but the primary phase of ZA22 and ZA27 is a. (2) Through the test to the as-cast ZA alloy lines made in continuous casting by heated mold, it is found that the tensile strength and hardness increase greatly, but the elongation decreases. With the increase of aluminum amount from ZA 5 to ZA 12, ZA22 and ZA27, the tensile strength increases gradually. ZA27 has the best comprehensive mechanical properties in these     

Microstructure,tensile properties and fractography of A356 alloy under as-cast and T6 obtained with expendable pattern shell casting process

The microstructure, tensile properties and fractography of A356 alloy were studied under as-cast and T6 conditions obtained with expendable pattern shell casting, and the results were compared with lost foam casting (LFC). The results indicate that a(Al) primary, eutectic silicon and Mg₂Si are the main phases in the microstructure of A356 alloy obtained with this casting process. The eutectic silicon particles are spheroidized and uniformly distributed at the grain boundaries after T6 treatment. The average length, average width and aspect ratio of eutectic silicon particles after T6 condition decrease. The sizes of a(Al) primary phase and eutectic silicon of this casting process are smaller than those of LFC. The tensile strength, elongation and hardness of A356 alloy after T6 obviously increase, they reach 260.53 MPa, 6.15% and 86.0, respectively and have a significant improvement compared to LFC. The fracture surfaces of expendable pattern shell casting show a mixed quasi-cleavage and dimple fracture morphology as a transgranular fracture nature. However, the fracture surfaces of LFC display a brittle fracture.     

Influence of Sr on microstructure and mechanical properties of ZL114 cast alloy

In the present work,the effects of trace element Sr on the microstructure,tensile properties,fractography and morphology of the eutectic Si of ZL114A (Al-7Si) cast alloy were investigated.The cast ZL114A aluminum alloy was prepared using a metal mold,and then heat treated with the T6 technique.The test results of mechanical properties show that modification element Sr can improve significantly the ultimate tensile strength,elongation and hardness of the ZL114A-T6 aluminum alloy.By adding 0.04％Sr,the values of the tensile strength Rm,elongation A and hardness HB increase from 230 MPa,1％ and 65 to the maximum of 305 MPa,8％,and 100,respectively.SEM analysis indicates that the near tensile fracture surface on longitudinal section of the ZL114A-T6 alloy reveals a transgranular fracture mode without Sr modification,while the tensile fracture is an intergranular fracture mode after Sr modification.The morphology of the eutectic Si phase is changed from acicular to fine fibrous.     

均匀化处理对Al-Cu-Mg合金组织和性能的影响

利用光学显微镜、扫描电镜、能谱分析、差热分析、硬度测试和拉伸测试等方法研究了均匀化处理对Al-4.5Cu-0.8Mg合金的组织和性能的影响。结果表明:Al-4.5Cu-0.8Mg铸态组织中存在较严重的枝晶偏析现象,晶界及晶界交汇处有大量Al2Cu相及Al2Cu和Al2CuMg的共晶相,合金经480℃×12 h均匀化处理后,组织中的非平衡相已基本溶解,综合力学性能较好,抗拉强度为320 MPa,屈服强度为246 MPa,伸长率为10.2%,硬度为139.2 HV。     

Microstructure,Mechanical and Corrosion Properties of AlCoCrFeNi High-Entropy Alloy Prepared by Spark Plasma Sintering

AlCoCrFeNi is one of the most widely studied alloy systems in the high-entropy alloy(HEA) area due to the interesting microstructure and mechanical properties.In this study,the AlCoCrFeNi alloy was prepared using spark plasma sintering(SPS) with pre-alloy powders obtained through gas atomization.Then,the sintered samples were annealed at 700,800 and900℃,and the effect of annealing temperature on the microstructure,mechanical and corrosion properties was studied.The results show that phase formation takes place during annealing process with the new phase(σ) and some nano scale BCC precipitates formation.The size and quantity of the nanoscale precipitates increase with increasing annealing temperature.The twin is also observed after annealing at 900℃.The annealing temperature has an obvious effect on the mechanical properties and corrosion resistance of the spark plasma sintered AlCoCrFeNi HEA.When the annealing temperature is 700℃,the hardness,yield strength and fracture strength reach the maximum with the value of 545 HV,1430 MPa and 2230 MPa,respectively.The compressive ratio reaches the maximum of 17.2%,with the annealing temperature increasing to 800℃.The corrosion resistance of the samples decreases with increasing the annealing temperature.