Tungsten wires and porous NiAl prepared through directional solidification and selective dissolution

The combination of directional solidification and selective dissolution was applied to fabricate tungsten (W) wires and porous NiAl matrix. A NiAl–W pseudobinary eutectic alloy with 1.5?at.% tungsten was directionally solidified in a Bridgman-type oven at 1700°C. Results confirmed that the relationships of the growth rate with the interfibrous spacing and diameter of W fibrous phases in the directionally solidified samples are in accordance with the Jackson and Hunt (J?H) model. Afterward, the NiAl matrix was selectively dissolved in an HCl:H₂O₂ solution to reveal W wires, which present various three-dimensional (3D) morphologies at different growth rates. The W fibrous phases in the NiAl–W alloy samples were then selectively removed with a mixed etchant of ammonium acetate to form a porous NiAl matrix at a constant potential. Dynamic corrosion curves revealed that etching W from the NiAl matrix was inhibited after 2–3?h. The porous structures of NiAl after removing W phases are linked to the 3D morphologies of W fibrous phases embedded in the NiAl matrix. The aspect ratio of W wires and the structures of porous NiAl can be adjusted by selecting the process parameters of this combined technology.     

Fracture investigation of U‐notch made of tungsten–copper functionally graded materials by means of strain energy density

The averaged strain energy density over a well‐defined control volume was employed to assess the fracture of U‐notched specimens made of tungsten–copper functionally graded materials under prevalent mode II loading. The boundary of control volume was evaluated by using a numerical method. Power law function was employed to describe the mechanical properties (elasticity modulus, Poisson's ratio, fracture toughness and ultimate tensile stress) through the specimen width. The effect of notch tip radius and notch depth on notch stress intensity factors and mode mixity parameter χ were assessed. In addition, a comparison based on fracture load between functionally graded and homogeneous W–Cu was made. Furthermore, in this research, it was shown that the mean value of the strain energy density over the control volume can be accurately determined using coarse meshes for functionally graded materials.     

Effects of microstructural heterogeneity on very high cycle fatigue properties of 7050-T7451 aluminum alloy friction stir butt welds

In this study, the very high cycle fatigue (VHCF) properties of 7050-T7451 aluminum alloy and its friction stir welding (FSW) butt welds have been investigated. The results show that the failure of FSW joints still occurs at 7.0 × 10⁸ cycles. The fatigue properties of the FSW joints are superior to those of the base material, especially in the super long life regime. Most fatigue cracks initiate at the thermo-mechanically affected zone and heat affected zone on the advancing side of the FSW joints, and the susceptibility of these zones to fatigue is attributed to the metallurgical heterogeneity.     

面向等离子体材料钨中氘/氦滞留行为的研究进展

作为面向等离子体材料,钨(W)在服役的过程中不仅受到等离子体造成的高能热负荷的作用,还受到高束流粒子如氘(D)、氚(T)、氦(He)等的轰击和D-T聚变反应产生的高能中子的影响。W中D、T、He的滞留和起泡,仍是聚变堆装置中有待解决的关键问题之一。综述了D、T和He的滞留行为及其气泡形成与辐照条件之间的关系,简要评述了W的服役性能和强化机理。通过降低W中D/He滞留量、抑制气泡的形成可有效改善W的服役性能。深入研究D/He滞留行为与辐照缺陷之间的相互作用关系,进而构建D/He的宏观热脱附行为与其微观状态之间的对应关系,为寻找合适途径来改善W的服役性能提供理论支撑。     

氧化镧改善钨材料性能的研究现状

制备钨合金面临着再结晶温度低、韧脆转变温度高、高温强度低及寿命短等问题。稀土氧化物氧化镧(La2O3)添加到钨合金内,再结晶温度提高、韧脆转变温度下降、高温强度提高,所以钨材料内添加La2O3是最近几年国内外的热门研究课题之一。主要介绍了高温强度强、再结晶温度低、寿命长的W-La2O3合金的最佳La2O3添加含量以及改善这些性质的一些方法,最后指出了该合金待解决的一些问题及其发展趋势。     

Microstructure and Processing of 3D Printed Tungsten Microlattices and Infiltrated W–Cu Composites

Tungsten is of industrial relevance due its outstanding intrinsic properties (e.g., highest melting‐point of all elements) and therefore difficult to 3D‐print by conventional methods. Here, tungsten micro‐lattices are produced by room‐temperature extrusion‐based 3D‐printing of an ink comprising WO₃–0.5%NiO submicron powders, followed by H₂‐reduction and Ni‐activated sintering. The green bodies underwent isotropic linear shrinkage of ≈50% during the thermal treatment resulting in micro‐lattices, with overall 35–60% open‐porosity, consisting of 95–100% dense W–0.5%Ni struts having ≈80–300 μm diameter. Ball‐milling the powders and inks reduced the sintering temperature needed to achieve full densification from 1400 to 1200 °C and enabled the ink to be extruded through finer nozzles (200 μm). Partial sintering of the struts is achieved when NiO is omitted from the ink, with submicron interconnected‐porosity of ≈34%. Several tungsten micro‐lattices are infiltrated with molten copper at 1300 °C under vacuum, resulting in dense, anisotropic W–Cu composites with 40–65% tungsten volume fraction. Partially sintered struts (containing nickel) with submicron open porosity are also infiltrated with Cu, resulting in co‐continuous W–Cu composites with wide W struts/Cu channels at the lattice scale (hundreds of micrometers), and fine W–Cu interpenetrating network at the strut scale (hundreds of nanometers) allowing for the design of anisotropic mechanical and electrical properties.

     

Magnetic Properties of Thermal Sprayed Tungsten Carbide–Cobalt Coatings

In the information age, the storage and accessibility of data is of vital importance. There are several possibilities to fulfill this task. Magnetic storage of data is a well‐established method and the range of materials used is continuously extended. In this study, the magnetic remanence of thermally sprayed tungsten carbide–cobalt (WCCo)‐coatings in dependence of their thickness is examined. Two magnetic fields differing in value and geometry are imprinted into the coatings and the resulting remanence field is measured. It is found that there are two effects, which in combination determine the effective value of the magnetic remanence usable for magnetic data storage.

     

微量Sc对Al-Zn-Mg合金焊接接头组织和性能的影响

使用光学显微镜、扫描电镜和透射电镜分析了Al-Zn-Mg合金和含微量钪的Al-Zn-Mg合金钨极氩弧焊接头的微观组织,并对其力学性能和耐应力腐蚀性能进行了对比。结果表明：在传统Al-Zn-Mg合金板材熔合线附近的热影响区出现再结晶和晶粒异常长大,而含钪Al-Zn-Mg合金基体中热稳定性优良的纳米Al₃(Sc, Zr, Ti)相在焊接过程中能阻碍晶界迁移,抑制再结晶晶粒的形核和长大,进而细化熔合线附近的组织。同时,含微量钪的Al-Zn-Mg合金焊接接头的强度明显比传统合金的高,其强化效果主要来源于熔合线附近区域的细晶强化和二次Al₃(Sc, Zr, Ti)相的弥散强化。