Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu61.13Zn33.94Al4.93 alloys

The phase transformation activation energy of the Cu_61.13Zn_33.94Al_4.93 alloys, which were treated at 4 GPa and 700 °C for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu_61.13Zn_33.94Al_4.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from (111) to (200) of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β' → β and β → β ' transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5--20 °C/min.     

Effect of local atomic disorder on the half-metallicity of full-Heusler Co2FeSi alloy: a first-principles study

This paper investigates the effect of atomic disorder on the electronic structure, magnetism, and half-metallicity of full-Heusler Co₂FeSi alloy by using the full-potential linearized augmented plane wave method within the generalized gradient approximation (GGA) and GGA+U schemes. It considers three types of atomic disorders in Co₂FeSi alloy: the Co--Fe, Co--Si, and Fe--Si disorders. Total energy calculations show that of the three types of disorders, the Fe--Si disorder is more likely to occur. It finds that for the Co--Si disorder, additional states appear in the minority band-gap at the E_F and the half-metallcity is substantially destroyed, regardless of the disorder level. On the other hand, the Co--Fe and Fe--Si disorders have little effect on the half-metallicity at a low disorder level. When increasing the disorder levels, the half-metallcity is destroyed at about 9 % of the Co--Fe disorder level, while that stays at 25 % of the Fe--Si disorder level.     

Si含量对镍基合金氧化保护膜影响机制的研究

本文对镍基合金中Si在弱氧化环境下表面氧化成膜特性进行了研究。利用XRD、SEM、EDS等检测手段对试样进行了检测分析,结果发现:合金表面氧化膜的形成动力学对镍基合金的Si含量非常敏感。当合金元素Si的含量较高时,由于连续的非晶SiO2膜在表层氧化铬与奥氏体基体之间的富集阻碍了Cr离子的向外扩散,导致在奥氏体区之上形成了较薄的氧化铬膜;共晶组织区域由于不会形成连续的SiO2非晶膜,仍然可以作为Cr离子的快速扩散通道,使得在该组织区域形成大量的脊状氧化物。奥氏体组织之上的氧化膜厚度与基体的Si含量成反比。     

Seismic behaviour of self‐centring braced frame buildings with reusable hysteretic damping brace

This paper presents the seismic behaviour of a concentrically braced frame system with self‐centring capability, in which a special type of bracing element termed reusable hysteretic damping brace (RHDB) is used. The RHDB is a passive energy dissipation device with its core energy‐dissipating component made of superelastic Nitinol wires. Compared with conventional bracing in steel structures, RHDB has a few prominent performance characteristics: damage free under frequent and design basis earthquakes in earthquake prone areas; minimal residual drifts due to the self‐centring capability of RHDB frame; and ability to survive several strong earthquakes without the need for repair or replacement. This paper also includes a brief discussion of the RHDB's mechanical configuration and analytical model for RHDB. The seismic performance study of RHDB frame was carried out through a non‐linear time history analysis of 3‐storey and 6‐storey RHDB frame buildings subjected to two suites of 20 earthquake ground motions. The analysis results were compared with buckling‐restrained brace (BRB) frames. This study shows that RHDB frame has a potential to outperform BRB frames by eliminating the residual drift problem. Copyright © 2007 John Wiley & Sons, Ltd.     

以镁、锌、铝为主要合金元素的应用合金研究进展

以镁、铝、锌为主要合金元素的镁铝合金材料是轻合金的基础,评述了镁合金和铝合金的优缺点及应用概况,介绍了Zn、RE、Mn、Cu等主要元素对合金微观组织、铸造性能、力学性能和抗腐蚀性能的影响。随着轻合金综合性能不断提高和改进,其应用前景更加广阔。     

煤矿用钛合金无磁钻杆的中试研究

目前,国内外煤矿坑道水平定向钻探用无磁钻杆材料均选用铍铜QBe2（ C17200）,该合金材料的延伸率低,钻杆易出现断裂事故。为解决这一问题,研究了高强度钛合金钻杆,探讨了钻杆的材料选择及螺纹结构设计。试验了钻杆的加厚工艺,其强度达到了设计要求,并通过现场试验验证了钻杆的使用效果。     

铬的迁移形式、成矿机理新探

通过对地球深部富氢流体、若干金属氢化物及合金氢化物的形成条件与性质、铬矿物的化学成分及其共生伴生矿物的研讨,结合铬铁矿成矿的地质背景,认为铬氢化物、铬合金氢化物是铬成矿的主要迁移形式。它们从地球深部富氢强还原环境随岩浆迁移至地壳浅部,由于H2,CO,CH4等逃逸、氧化,氧逸度大增,温度、压力下降,铬氢化物和铬合金氢化物分解、氧化、固化富集成铬矿床。     

Shaking table tests of steel frame with superelastic Cu–Al–Mn SMA tension braces

Shaking table tests are performed on a one‐bay one‐story steel frame with superelastic Cu–Al–Mn shape memory alloy (SMA) tension braces. The frame is subjected to a series of scaled ground motions recorded during the 1995 Kobe earthquake, Japan. The test results demonstrate that the SMA braces are effective to prevent residual deformations and pinching. It is also shown that the time history responses observed from the shaking table tests agree well with the numerical predictions using a rate‐independent piecewise‐linear constitutive model calibrated to the quasi‐static component tests of the SMA braces. This suggests that the loading rate dependence of Cu–Al–Mn SMAs as well as the modeling error due to the piecewise linear approximation can be neglected in capturing the global response of the steel frame. Numerical simulations under a suite of near‐fault ground motion records are further performed using the calibrated analytical models to demonstrate the effectiveness of the SMA braces when the variability of near‐fault ground motions is taken into account. A stopper, or a deformation restraining device, is also proposed to prevent premature fracture of SMA bars in unexpectedly large ground motions while keeping the self‐centering capability in moderate to large ground motions. The effectiveness of the stopper is also demonstrated in the quasi‐static component and shaking table tests. Copyright © 2015 John Wiley & Sons, Ltd.     

形状记忆合金橡胶对高架桥梁碰撞减震效果的试验研究

地震作用下,高架桥梁相邻主梁间的碰撞会引起结构位移和加速度响应增大、应力提高,导致混凝土开裂、脱落和伸缩缝被挤压破坏,甚至引发桥梁落梁和倒塌等,因此采取减轻或者避免桥梁结构在地震作用下碰撞的措施显得尤为必要。设计制备了具有变形自恢复能力的形状记忆合金橡胶碰撞缓冲器,通过桥梁地震碰撞的振动台试验,研究了形状记忆合金橡胶缓冲器对桥梁碰撞的控制效果,提出了碰撞缓冲器吸能效率和结构自身耗能控制率指标。研究表明,形状记忆合金橡胶碰撞缓冲器具有稳定的吸能效率,能够大幅度降低桥梁结构碰撞加速度和碰撞力,这对于提高城市交通网络的地震安全性能具有重要意义。     

Penetration of molten iron alloy into the lower mantle phase

The core–mantle boundary is the only interface where the metallic core and the silicate mantle interact physically and chemically. Many geophysical anomalies such as low shear velocity and high electrical conductivity have been observed at the bottom of the mantle. Perturbations in the Earth's rotation rate at decadal time periods require the existence of a thin conductive layer with a conductance of 10⁸ S. Substantial additions of molten iron from the outer core into the mantle may produce these geophysical anomalies. Although iron enrichment by penetration has only been observed in (Mg,Fe)O, the second dominant mineral in the lower mantle, the penetration process leading to iron enrichment in the silicate mantle has not been experimentally confirmed. In this study, high-pressure and high-temperature experiments were conducted to investigate the penetration of molten iron alloy into lower mantle phases; postspinel, polycrystalline bridgmanite and polycrystalline (Mg,Fe)O. At the interface between (Mg,Fe)O aggregate and molten iron alloy, liquid metal penetrated the (Mg,Fe)O aggregate along grain boundaries and formed a thin layer containing metal-rich blobs. In contrast, no penetration of molten iron alloy was observed at the interface between molten iron alloy and silicate phases. Penetration of liquid iron alloy into the (Mg,Fe)O aggregate is caused by the capillarity phenomenon or Mullins–Sekerka instability. Neither mechanism occurs at the boundary of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential role in this phenomenon. Infiltration of molten iron alloy along grain boundaries (capillarity phenomenon) is the dominant process and precedes penetration due to the Mullins–Sekerka instability. The capillarity phenomenon is governed by the balance of forces between surface tension and gravity. In the case where the ultralow velocity zone (ULVZ) with a low shear velocity is composed of Fe-rich (Mg,Fe)O, the maximum penetration distance of molten iron alloy by capillary rise is limited to 20 m. The addition of iron-rich melt to the base of the mantle is therefore unlikely to be the main cause of the high conductance of the CMB region predicted from decadal variation of the length of day. Furthermore, the absence of molten iron alloy penetration into silicate phases does not allow an extensive modification of the chemical composition of the mantle by core–mantle interaction.