Electron backscatter diffraction investigation of duplex-phase microstructure in a forged Zr-2.5Nb alloy

Microstructural features of a duplex-phase Zr-2.5Nb alloy were investigated in detail using electron channeling contrast(ECC)imaging and electron backscatter diffraction(EBSD)technique in an emission gun scanning electron microscope(FEGSEM).The excellent resolution provided by the FEGSEM promises the combined utilization of both techniques to be quite adequate for characterizing the duplex-phase microstructures.Results show that the microstructure of the Zr-2.5Nb alloy is composed of bulkαgrains(majority)in equiaxed or plate shape and thinβfilms(minority)surrounding the bulk grains,with their average grain size and thickness measured to be 1.4μm and 72 nm,respectively.Analyses onα-grain boundaries reveal a number of low angle boundaries,most of which belong to deformation-induced dislocation boundaries.Measurements on relative proportions of various Burgers boundaries suggest very weak(if any)variant selection duringβ→αcooling,which should be related to deformation-induced higher nucleation rate ofαphases.Compared to earlier attempts,more satisfactory indexing of fineβphases(down to nanoscale)is attained by the FEGSEM-based EBSD.Examples are presented to clearly reveal well-obeyed Burgers orientation relationships between adjacentαandβphases.Finally,it is deduced that continuing application of the FEGSEM-based EBSD to duplex-phase Zr alloys could help clarify controversies like the deformation priority of the two phases.     

Zr-4合金显微组织结构分析

利用XRD,SEM和TEM对Zr-4合金的组织进行了分析.实验结果表明Zr-4合金中主要以Zr为主还溶有少量Cr,Sn,Cu元素.Zr-4中主要物相为α-Zr相.     

Microstructural evolution of plastic deformation of NiTi shape memory alloy at low temperature

Nickel-titanium shape memory alloy (NiTi SMA) which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature (?150 °C) by means of local canning compression. The microstructural evolution of NiTi SMA at the different deformation degree was investigated by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). At the deformation degree by 15%, a high density of dislocations occurs in the deformed NiTi sample. At the deformation degree by 25%, the deformed NiTi sample exhibits the martensite morphology due to the pinning of dislocations at the grain boundaries. At the deformation degree by 50%, a small amount of nanocrystalline phase arises in the deformed NiTi sample. At the deformation degree by 80%, severe plastic deformation (SPD) leads to the occurrence of a great deal of amorphous and nanocrystalline phase.     

Microstructural characteristics and mechanical properties of Al-2024 alloy processed via a rheocasting route

This article reports the effects of stirring speed and T6 heat treatment on the microstructure and mechanical properties of Al-2024 alloy synthesized by a rheocasting process. There was a decrease in g...     

Microstructural characterization of internal oxidation of AgCu alloy

The internal oxidation of AgCu alloys with atomic percentage 0.8,3 3, 6 3 and 9 5 of Cu in air at 750℃ and 850℃ has been studied. It was found that CuO particles precipitated homogeneously on the surface of AgCu alloys except for Ag-9.5% (atomic percentage) Cu. The latter exhibited the agglomerated precipitation of CuO particle cluster on the surface. The experimental results also revealed that the nucleation and growth of CuO oxide evidently varied with the change of Cu contents or oxidation temperature. When both Cu content and exposure temperature were low, the precipitation and the growth of internal CuO oxide were consistent with the prediction by the classical Bohm-Kahlweit mode, but the abnormal phenomenon of nucleation and growth of the CuO oxide was observed when the Cu content or the exposure temperature was increased. As a result of investigation of the atomic structure of different internally oxidized AgCu alloys, it is proposed that the stacking fault tetrahedra(SFT), which were found in     

AFM research on the mechanism of Fe-based alloy stress annealed inducing magnetic anisotropy

The cross-section of the Fe-based alloy (Fe_73.5Cu₁Nb₃Si_13.5B₉) ribbon annealed at 540°C under various tensile stress was investigated with atomic force microscope (AFM). The stress effect mechanism in Fe-based alloy ribbon tensile stress annealed inducing transverse magnetic anisotropy field was studied using the X-ray diffraction spectra and longitudinal drive giant magneto-impedance effect curves, and the model of direction dominant in encapsulated grain agglomeration was established. The relationship between the direction dominant in encapsulated grain agglomeration and magnetic anisotropy field was disclosed. Supported by the Natural Science Foundation of Zhejiang Province (Grant No. Y405021), Key Project of Science and Technology of Zhejiang Province (Grant No. 2006C21109) and Key Project of Science and Technology Research of China Ministry of Education (Grant No. 204059)     

Microstructural evolution of ECAPed 1050 alloy under magnetic annealing

Hardness and microstructure evolutions in 1050 aluminum alloy prepared by equal-channel angular pressing （ECAP） were inves- tigated by hardness testing, optical microscopy, and transmission electron microscopy after samples were annealed at different temperatures for 1 h both in the absence and presence of a 12-T magnetic field. The results showed that the hardness of samples after magnetic annealing were lower than that of samples after normal annealing at 150-250℃, but it was higher than that of samples after normal annealing at 〉250℃. During annealing, the rate of softening was faster, and the grains were more homogeneous in 8-ECAPed samples than in 2-ECAPed samples. A rapid grain growth occurred when 2-ECAPed samples were annealed at high temperature （〉300℃）. The magnetic field enhanced the mobility of dislocations and grain boundaries. A more homogeneous grain size was observed in samples prepared under an applied magnetic field.     

Si3N4/（Cu，Nb）/Ni/Inconel600高温合金部分液相扩散连接接头的组织与力学性能

为了在较低的连接温度、连接压力和连接时间下获得高温稳定性好的陶瓷/金属接头，通过设计非对称中间层（Cu，Nb）/Ni，在连接温度为1403K/1373K，连接时间为50min，连接压力为7.5MPa，冷却速度为10K/min的工艺条件下，采用真空扩散连接设备，进行了Si₃N₄/Inconel600高温合金接头的部分液相扩散连接（Partial Liquid Phase Diffusion Bonding，PLPDB）.接头的强度通过剪切试验评价，接头组织形态采用扫描电子显微镜（SEM）进行了观察和分析.实验结果表明，Cu，Nb配比、（Cu，Nb）层的厚度和连接温度影响接头的组织形态、强度与断裂.在连接温度为1403K时，Cu，Nb配比增加，接头中的孔洞缺陷减小，接头强度提高，断裂位置从陶瓷/中间层界面向陶瓷转变.当连接温度为1403K，Cu，Nb配比为10，(Cu,Nb)层厚度不超过0.2mm时，随着(Cu,Nb)层厚度的增加，接头强度提高.当连接温度从1403K降到1373K时，接头强度明显提高.     

非晶SiO2涂层的制备及其对Ti-22Al-26Nb合金的高温防护

以商业硅胶为原料,采用溶胶-凝胶法在Ti-22Al-26Nb合金表面浸涂制备非晶氧化硅涂层.涂层样品和空白样品在800和900℃静态空气中进行等温氧化实验,900℃静态空气中进行循环氧化实验.采用热重分析（TGA）、扫描电子显微镜（SEM）和X射线衍射（XRD）对结果进行分析,研究涂层对Ti-22Al-26Nb合金氧化行为的影响.结果表明：涂层样品的氧化抛物线速率常数较空白样品降低,涂层提高了合金在空气中的抗氧化能力.合金表面生成氧化膜主要由TiO2,Nb2TiO7和AlNbO4组成,涂层抑制了氧化物的生长.探讨了涂层的作用机制.     

Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

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Microstructural feature of As-cast A-356 alloy modifiers with the addition of SrO

To explore the effect of strontium on the structure of as-cast A356 alloy, the strontium was incorporated to the alloy by metallothermic reduction of SrO where the mineral was added to the melt through the submerged powders injection technique. The evaluation of the modification of the eutectie silicon and the chemical analysis of samples were done using optical microscopy （OP） and inductively coupled plasma （ICP）, respectively, while microstructural analyses by scanning electron microscopy （SEM）, and the injection time was variable. Magnesium was added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 0.027% after 20 minutes treatment. This concentration was sufficient to bring about full modification structure of eutectic silicon of as cast alloy A 356 and the acceptable quality metallurgical of alloy.     

Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7...     

置氢TC4钛合金等温锻造叶片组织演变规律

为了降低钛合金叶片的锻造温度和改善其组织性能,基于氢致钛合金高温增塑机理,将热氢处理技术应用于钛合金叶片的等温锻造成形工艺中.观察和对比分析了未置氢TC4钛合金和置氢TC4钛合金叶片等温锻造后的组织以及真空除氢热处理和普通热处理工艺下的组织演变.实验结果表明:置氢降低了TC4钛合金叶片的等温锻造载荷,除氢热处理后组织得到改善,获得了含有细小、等轴α晶粒的双态组织.确定了置氢量为0.25%(质量分数)的TC4钛合金适宜的热处理工艺为:锻后在750℃真空脱氢保温5h,900℃退火1h后再450℃时效4h.     

Microstructural formation of semi-solid AZ91D alloy stirred by electromagnetic field

With the help of an electromagnetic stirring device, alloy melt quenching and EBSD (electron back scatter diffraction)analysis technology, the microstructure of the semi-solid AZ91D magnesium alloy slurry stirred by rotational electromagnetic field under different stirring power conditions has been studied. The results show that the size of primary α-Mg phase is reduced obviously when the solidifying alloy melt is stirred by rotational electromagnetic field, moreover, the primary α-Mg grains are changed to fine rosette grains or spherical grains which are proved to belong to the different grains in three-dimension by the EBSD analysis technology. The results also show that the stirring power is an important processing parameter in the preparation of the semi-solid AZ91D magnesium alloy slurry. The larger the stirring power, the finer the primary α-Mg grains, the less the rosette primary α-Mg grains, and the more the spherical primary α-Mg grains. Theoretical analysis indicates that a stronger flow motion leads to a more even temperature field and solute field and a stronger man-made temperature fluctuation in the alloy melt so that the specially fine rosette and/or spherical primary α-Mg grains are formed in the semi-solid AZ91D magnesium alloy slurry.     

Nb对低碳微合金钢相变的影响

采用Gleeble-1500D型热模拟机测定了不同含铌量低碳微合金钢在不同冷却速度下,过冷奥氏体连续冷却相变点,分析观察了显微组织,测定了其显微硬度.得出:在同一冷却速度下,随着含铌量的提高,过冷奥氏体连续冷却相变点降低,容易出现条片状贝氏体铁素体,显微硬度提高;在相同成分下,随着冷却速度的增加,含铌钢中铁素体越来越细小,由等轴状大块铁素体组织向条片状贝氏体铁素体转变.     

Al-Mg-Si-Cu合金近液相线半连续铸造组织研究

采用近液相线半连续铸造方法制备了Al-1.2Mg-0.8Si-0.4Cu合金半固态锭坯,研究了浇注温度和铸造速度对锭坯微观组织的影响.合金熔体在750℃下浇注,组织不均匀,边部是细小的晶粒,1/2半径和中心部位是粗大的枝晶,最小晶粒直径25μm,最大晶粒直径达220μm;660℃保温后浇注,可以获得适合半固态加工的均匀、细小的近球形组织,锭坯中心和边部组织差异小,平均晶粒尺寸为36.5μm;铸造速度达150 mm/min时有利于均匀、细小的近球形组织形成.结果表明,对于Al-1.2Mg-0.8Si-0.4Cu铝合金采用近液相线半连续铸造可以获得理想的半固态浆料.     

Hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with acicular microstructure

The characteristics of hot deformation of an α+β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s-1 at 860-1 100 °C. The true stress-true strain curves of alloy hot-compressed in the α+β region exhibit a peak stress followed by continuous flow softening; whereas in the β region,the flow stress attains a steady-state regime. At a strain rate of 10 s-1 and in a wide temperature range,the alloy exhibit...