固溶处理对铸造625合金显微组织和拉伸性能的影响

研究1050～1250℃ 固溶处理对铸造625合金显微组织和拉伸性能的影响.采用SEM、EDS、EPMA和DTA研究合金的显微组织及凝固特征.结果表明,合金的凝固顺序为L→L+γ→L+γ+MC→L+γ+MC+γ/Laves→ γ+MC+γ/Laves.经1225和1250℃固溶处理后,组织中Laves相发生初熔.经不同...     

Al9Fe0.7Ni1.3相对喷射沉积Al-Zn-Mg-Cu-Ni合金组织和性能的影响

本文利用喷射沉积技术合成含Ni的Al-Zn-Mg-Cu合金,合金中的Ni元素以亚微米球状Al₉Fe_0.7Ni_1.3化合物的形式存在。利用扫描电镜和电子背散射衍射、透射电镜以及拉伸测试研究了Al₉Fe_0.7Ni_1.3颗粒对合金固溶处理后组织和性能的影响。结果发现：Al₉Fe_0.7Ni_1.3颗粒主要在晶界附近分布,说明该颗粒在固溶过程中具有有力的抑制再结晶作用。固溶处理后,合金的拉伸强度为603 MPa,断裂延伸率为11.79%,主要断裂方式为穿晶延性断裂。实验结果表明亚微米球状Al₉Fe_0.7Ni_1.3化合物对合金性能有重要影响,可以产生细晶强化和Orowan强化,是合金发生穿晶延性断裂的主要原因。     

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.     

真空热处理对微波烧结93W-Ni-Fe合金显微组织及力学性能的影响

研究真空热处理对微波烧结挤压棒坯93W-Ni-Fe合金显微组织及力学性能的影响,采用高倍SEM和光学金相分别对合金断口和显微组织进行观察,采用能谱分析仪对合金真空热处理前后各元素含量进行定量分析,并对真空热处理样的相对密度、抗拉强度、延伸率和硬度进行测定和分析.结果表明:经真空热处理后,钨合金的各项力学性能都得到了提高,抗拉强度和延伸率提高显著,抗拉强度从920 MPa提高到了988 MPa,延伸率从9.7％提高到了18.6％;真空热处理后,显微组织中钨晶粒的连接度降低,合金断口中钨晶粒的穿晶解理断裂和粘结相的延性撕裂增多;真空热处理后合金粘结相中的钨含量明显降低.     

Ti-Al-Nb三元合金组织对力学性能的影响

通过合金设计的方法分别制备了具有单相(γ-TiAl)组织的合金A、二相(γ-TiAl+α2-Ti3Al)层片组织的合金B和三相(γ-TiAl+α2-Ti3Al+Nb2Al)混合组织的合金C3种Ti-Al-Nb三元合金,通过XRD、EPMA以及SEM等手段确定了这3种合金的组织结构和分布形态,并对这3种合金进行了室温和1173K的拉伸试验。结果表明,合金的显微组织与其性能密切相关,室温下合金B的塑性变形能力好于另外两种合金,这主要是因为α2相的存在降低了合金平均晶粒尺寸,由γ和α2两相构成的层片组织结构以及大量的γ/α2相界面。温度升高可以显著改善合金B的塑性变形能力,合金B在1173K时的拉伸延性达到40.4%,并且断裂方式从室温时的穿晶脆性断裂向1173K时的韧性断裂方式转变,而合金A、C不管在室温还是1173K,都显示出穿晶脆性断裂方式。合金C在室温和高温都很脆,是由于Nb2Al相的出现,降低了(γ+α2)两相层片组织的连续程度。     

热处理对选区激光熔化GH3536合金晶界与拉伸行为的影响

采用选区激光熔化制备了GH3536合金,并分别进行固溶处理和热等静压处理,研究不同热处理手段对GH3536合金的组织形貌、晶界形态及室温拉伸行为的影响。结果表明:沉积态试样的组织由超细柱状亚晶粒与熔池界组成,存在气孔与微裂纹等缺陷;选区激光熔化试样分别经固溶处理和热等静压处理后,二者致密度均上升,组织转变为由交替分布的大小不等等轴晶粒组成,但热等静压的沿晶界析出M_(23)C_6相,形成锯齿状的弯曲晶界;沉积态试样的拉伸性能表现出各向异性的特点,固溶处理可消除拉伸性能的各向异性,但抗拉强度和屈服强度均有下降,延伸率明显上升。热等静压态试样与固溶态试样相类似,但其抗拉强度、屈服强度和延伸率均有进一步的提高;3种形态合金的断裂机制均为微孔聚集型的韧性断裂。     

Microstructure and mechanical properties of a spark plasma sinteredTi–45Al–8.5Nb–0.2W–0.2B–0.1Y alloy

A high Nb containing TiAl alloy from pre-alloyed powder of Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y was processed by spark plasma sintering (SPS). The effects of sintering temperature on the microstructure and mechanical properties were studied. The optimized conditions yield high densities and uniform microstructure. Specimens sintered at 1100 °C are characterized by fine duplex microstructure, leading to superior room temperature mechanical properties with a tensile strength of 1024 MPa and an elongation of 1.16%. Specimens sintered at 1200 °C are of fully lamellar microstructure with a tensile strength of 964 MPa and an elongation of 0.88%. The main fracture mode in the duplex microstructure was transgranular in the equiaxed γ grains and interlamellar in the lamellar colonies. For the fully lamellar structure, the fracture mode was dominated by interlamellar, translamellar and stepwise failure.     

Effects of minor Y,Zr and Er addition on microstructure and properties of Al-5Cu-0.4Mn alloy

The effect of different contents of Y, Zr and Er on microstructure and properties of Al-5 Cu-0.4 Mn alloy was investigated. T6 heat treatment, OM, SEM and EDS methods were applied to the alloy. The results showed that fluidity and elongation of alloy adding Y, Zr and Er were improved, while with the increase of addition amounts, θ phase increased and grains were trended to grow up gradually. The Al-5 Cu-0.4 Mn alloy presented the maxed style of ductile and brittle fracture. After T6 heat treatment, the precipitation amounts of θ phase decreased dramatically and tensile strength and hardness significantly increased. Especially when addition contents were among 0.1-0.3 wt.%, tensile strength and hardness of heat-treated alloy increased greatly, almost doubled as that of the as-cast state. The tensile strength reached its maximum of 378.43 MPa when the addition amount was 0.3 wt.%. With the further increase of addition amounts, the elongation deteriorated and the proportion of ductile fracture reduced due to the limited dispersion strengthening effect of θ phase and Al_8Cu_4 Er. It demonstrated that addition of 0.1-0.3 wt.% Y, Zr and Er would generate positive effects and influences on Al-5 Cu-0.4 Mn alloy, which is significant for optimizing components and improving properties of Al-5 Cu-0.4 Mn alloy.     

Effect of La addition on microstructure and mechanical properties of hypoeutectic Al-7Si aluminum alloy

The effect of La addition (0, 0.1, 0.2, 0.4, wt.%) on the microstructure, tensile properties and fracture behavior of Al-7Si alloy was investigated systematically. It is found that the La appears in the Al-7Si alloy in the form of Al₄La and Al₂Si₂La phases. La addition can refine the secondary dendrite arm spacing (SDAS) and eutectic Si particles, which are decreased by 7.9% and 7%, respectively, with the optimal La content of 0.1wt.%. Because when 0.1wt.% La is added, a relatively higher nucleation undercooling of 37.47 °C is observed. Higher undercooling degree suggests that nucleation is accelerated and subsequent growth is restrained. After T6 heat treatment, compared with the without La, the ultimate tensile strength of the alloy with 0.1wt.% La is enhanced by 5.2% from 333 MPa to 350.2 MPa and the elongation increases by 73% from 7.37% to 12.75%, correspondingly. The fracture mode evolves from the ductile-brittle mixed fracture to ductile fracture mode. However, when La element content reaches a certain value of 0.4wt.%, serious segregation takes place during the solidification process. The formed brittle phases deteriorate the tensile properties of the alloy and the fracture mode of Al-7Si-0.2/0.4 La changes to mixed ductile-brittle fracture mode.

     

热加工对电子束焊接TC11/Ti2AlNb双合金接头组织和性能的影响（英文）

研究热加工对电子束焊接TC11/Ti2Al Nb双合金接头显微组织的影响,对焊接件热暴露前后的室温拉伸性能进行测试。结果表明:电子束焊接TC11/Ti2Al Nb双合金熔合区主要由β相组成;经过变形和热处理后,熔合区主要由β、α2和α相组成,同时原始铸态的晶界在变形过程中破碎。在拉伸试验中,熔合区是薄弱区域;在不同的变形条件下,试样(热暴露前后)在此区域发生断裂。热处理后试样的最大室温拉伸强度达到1190 MPa;锻后水冷试样具有较好的塑性,其伸长率达到4.4%。相比较而言,经过(500°C,100 h)的热暴露后,试样的室温拉伸强度略有上升,但塑性变化较小。拉伸断口SEM观察显示,在不同变形条件下穿晶断裂为主要的断裂机制。     

Nb含量对Fe0.5MnNi1.5CrNb x 高熵合金微观结构和力学性能的影响

采用真空感应熔炼法制备了Fe_0.5MnNi_1.5CrNb_x（x=0,0.05,0.1,摩尔比）高熵合金,并分析了不同Nb含量对其组织和力学性能的影响。结果表明,不含Nb元素的合金具有单相fcc结构,其抗拉强度和断裂延伸率（即延展性）分别为519 MPa和47%。添加少量的Nb(x=0.05)后出现(200)织构和少量Fe₂Nb Laves相,合金的延展性增加到55%,并且抗拉强度增加到570 MPa。当Nb含量增加到x=0.1时,织构减少,而Fe₂Nb Laves相增多,抗拉强度和延展性分别为650 MPa和45%。     

Mechanical behavior and microstructure of Al-10wt.%Nb alloy fabricated by Mechanical Alloying

Al-10%Nb alloy powders were fabricated by mechanical alloying and their mechanical behavior and microstructure were investigated by means of tensile testing, differential scanning calorimetry, X-ray diffraction and electron microscopy. An intermetallic compound of Al₃Nb was partially formed in the mechanically alloyed powders. The grain size was 50 run after mechanical alloying for 20 hours, and increased to 500 nm after hot extrusion at 400°C. However the 20 size of the intermetallic compounds of precipitated Al₃Nb in an Al matrix, did not vary with hot extrusion. The density of the consolidated Al-Nb alloy was over 97% relatively with hot extrusion. Both the tensile strength and elongation decreased at the elevated temperature. As the temperature increased, the dimples in the fracture surface were large and of coalescent shape, and the fracture was caused by the precipitated phases of Al₃Nb.     

Microstructure and Mechanical Properties of a Refractory CoCrMoNbTi High-Entropy Alloy

In this work, a new refractory high-entropy alloy, the Co-Cr-Mo-Nb-Ti system, was proposed as a family of candidate materials for high-temperature structural applications. CoCrMoNbTi _x (x values in terms of molar ratios, x = 0, 0.2, 0.4, 0.5 and 1.0) alloys were prepared by vacuum arc melting. The effects of variations in the Ti content on the phase constituents, microstructure and mechanical properties of the alloys were investigated using x-ray diffractometry, scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy and compressive testing. The results showed that the CoCrMoNbTi_0.4 alloy possessed a typical cast dendritic microstructure consisting of a single body-centered cubic (BCC) solid solution. Laves phases (Cr₂Nb and Co₂Ti) were formed in other alloys with different Ti contents. The results were discussed in terms of the mixing enthalpy, atomic size difference, electronegativity difference and valance electron concentrations among the elements within alloys. The alloy hardness exhibited a slightly decreasing trend as the Ti content increased, resulting from the coarser microstructure and reduced amount of Laves phases. Augmented Ti content increased the compressive strength, but decreased the ductility. Particularly, for the CoCrMoNbTi_0.2 alloy, the hardness, compressive strength and fracture strain were as high as 916.46 HV_0.5, 1906 MPa and 5.07%, respectively. The solid solution strengthening of the BCC matrix and the formation of hard Laves phases were two main factors contributing to alloy strengthening.     

Effects of Homogenized Treatment on Microstructure and Mechanical Properties of AlCoCrFeNi_(2.2) Near-Eutectic High-Entropy Alloy

A 4 kg AlCoCrFeNi_(2.2) near-eutectic high-entropy alloy ingot was prepared by vacuum medium frequency induction melting. The effects of homogenized treatment on microstructure and mechanical properties of AlCoCrFeNi_(2.2) were studied. The results showed that all the alloys consisted of the primary FCC phases and eutectic FCC/B2 phases. After homogenized treatment, lots of precipitated phases appeared in the primary phase. The hardness of the as-cast alloy was HV296. The hardness values of samples were decreased and were around HV250 after homogenized treatment. The tensile fracture strength of the as-cast alloy reached 900 MPa, while the elongation was 18%. After homogenized treatment at 900 ℃, the alloy showed the most excellent mechanical properties with the fracture strength 880 MPa and the elongation was 29%, respectively. All the alloys displayed a mixture fracture mechanism, including ductile fracture in primary FCC phases and eutectic FCC phases, and brittle quasi-cleavage fracture in eutectic B2 phases. Through a simple heat treatment method, the strength of the alloy was not reduced but the plasticity was greatly enhanced, which was more conducive to the industrial application prospects.     

The effect of annealing on microstructure and tensile properties of Ti–22Al–25Nb electron beam weld joint

This study investigated the microstructure evolution and tensile properties of Ti–22Al–25Nb EBW joints. The fusion zone of the as-welded joint exhibited a fully B₂ microstructure. Widmanstätten O particles precipitated out of B₂ matrix after annealing and their size increased within a temperature range from 750 °C to 900 °C. In the heat affected zone, there was a transition of microstructure moving away from the fusion zone towards the base material. Strength and elongation of the as-welded sample were significantly improved after annealing, which was attributed to the strengthening effect of O precipitates and the slip transmission between O and B₂ phases. Samples tensile tested at 650 °C all failed within the fusion zone and exhibited intergranular failure instead of transgranular failure at room temperature. The room temperature strength and hardness of the joints decreased with annealing temperature due to the coarsening of O precipitates. At 650 °C, failure occurred by intergranular fracture in the fusion zone and the joint strength of all annealed samples was similar due to similar B₂ grain boundary strength.     

Physical metallurgy and mechanical properties of transition-metal Laves phase alloys

This paper provides a comprehensive review of the recent research on the phase stability, point defects, and fracture toughness of AB₂ Laves phases, and on the alloy design of dual-phase alloys based on a soft Cr solid solution reinforced with hard XCr₂ second phases (where X=Nb, Ta and Zr). Anti-site defects were detected on both sides of the stoichiometric composition of NbCr₂, NbCo₂, and NbFe₂, while they were observed only on the Co-rich side of ZrCo₂. Only thermal vacancies were detected in the Laves phase alloys quenched from high temperatures. The room-temperature fracture toughness cannot be effectively improved by increasing thermal vacancy or reducing stacking fault energy through control of phase stability. Microstructures, mechanical properties, and oxidation resistance of dual-phase alloys based on Cr–NbCr₂, Cr–TaCr₂, and Cr–ZrCr₂ were studied as functions of heat treatment and test temperature at temperatures to 1200°C. Among the three alloy systems, Cr–TaCr₂ alloys possess the best combination of mechanical and metallurgical properties for structural use at elevated temperatures.     

挤压铸造AZ81镁合金均匀化热处理工艺研究

为改善挤压铸造AZ81镁合金组织的不均匀性,对铸态试样进行均匀化热处理。采用金相显微镜、X射线衍射仪和扫描电镜对AZ81镁合金的组织与性能进行分析。结果表明:经400℃、8h均匀化处理后,AZ81合金有效地消除了枝晶偏析,改善了材料的组织状态;合金硬度由HRE73.72下降到HRE57.68,屈服强度由130MPa增加到138MPa,抗拉强度由226MPa增加到258MPa,伸长率则由7.6%增加到13.6%;试样的室温拉伸断口均为准解理断裂,经均匀化处理后断裂方式由沿晶界的脆性断裂转变为韧性穿晶断裂。     

Control of Laves phase in Inconel 718 GTA welds with current pulsing

Abstract

The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.     

Effects of Nb additions on the microstructure and mechanical property of CoCrFeNi high-entropy alloys

A series of five-component CoCrFeNiNb_x high entropy alloys (HEAs) were synthesized to investigate alloying effects of the large atom Nb on the structure and tensile properties. Microstructures of these alloys were examined using scanning electron microscopy and the phase evolution was characterized and compared using the ΔH_mix–δ and ΔX criteria. It was found that the microstructure changes from the initial single face-centered cubic (FCC) to duplex FCC plus hexagonal close-packed (HCP) structure with additions of Nb. The current alloy system exhibits a hypoeutectic structure and the volume fraction of the Nb-enriched Laves phase with the HCP structure increases with increasing the Nb content, which is mainly responsible for the increment in the yield and fracture strength. Particularly, the Nb_0.155 alloy containing a 9.3% Nb-enriched Laves phase exhibits the most promising mechanical properties with the yield strength and plastic strain as high as 321 MPa and 21.3%, respectively. The ΔH_mix–δ criteria well describe the phase selection for the thermally treated alloys, while the physical parameter ΔX fails to predict the appearance of the Nb-enriched Laves phase in this alloy system.     

Effect of swaging on microstructure and mechanical properties of liquid-phase sintered 93W-4.9(Ni,Co)-2.1Fe alloy

The effect of swaging on the microstructure and mechanical properties of 93W-4.9Ni-2.1Fe alloy was investigated. The alloy was prepared by liquid-phase sintering under hydrogen atmosphere followed by vacuum heat treatment and swaging at 600 °C with different area reductions (ranging from 15.0% to 84.8%). The as-swaged alloy with area reduction 84.8% exhibits the highest ultimate tensile strength (about 1490 MPa) and the lowest elongation (about 2.5%), which has been attributed to higher fraction of tungsten cleavage. For the as-sintered alloys, the fracture modes are a combination of the ductile rupture of W-Ni-Fe-Co matrix, transgranular cleavage of the tungsten particles, W-W interfacial segregation and W-M interfacial debonding, whereas transgranular cleavage of the tungsten particles is the main characteristic in the as-swaged alloy. Transmission electron microscopy images indicate that tungsten grains and W-Ni-Fe-Co matrix phase are composed of high-density dislocations. Based on the results, when running the swaging of 93W-4.9(Ni, Co)-2.1Fe alloy at 600 °C, the strengthening mechanism can be mainly due to the working-hardening.