Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading

The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 × 10^?3, corresponding to a stress of ～300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment.     

Mg/B化学计量比对MgB2超导电性和磁通钉扎性能的影响

采用固相反应法制备一系列的MgxB2（x=0.90,0.95,1.0,1.05,1.10）超导块材,并详细研究不同Mg/B化学计量比对MgB₂超导性能的影响。采用X射线衍射（XRD）仪,扫描电镜（SEM）和超导量子干涉（MPMS）仪分别对样品的物相、微观结构和超导性能进行表征。结果表明:名义组分为Mg_0.95B₂的样品临界电流密度Jc性能最好。由于Mg的不足,抑制了晶粒生长,同时也使得MgB₂内部Mg缺位、△Tc、FWHM、H_c2和H_irr明显增加,显著改善MgB₂的磁通钉扎性能。     

超声波对原位Mg2Si/Al复合材料中初生Mg2Si形态的影响

采用光学显微镜和场发射扫描电镜,研究超声波对原位 Mg2Si/Al 复合材料中初生 Mg2Si 形态的影响。研究结果表明：超声波处理使初生Mg2Si的晶粒尺寸从150μm降低到20μm,初生Mg2Si形态发生改变。在二维形貌中,未实施超声波振动处理的初生Mg2Si晶粒生长为含有空腔的粗大颗粒,共晶组织生长于其中,相应的三维形态为含有漏斗状空腔的八面体和十四面体。超声波处理后的初生Mg2Si晶粒变成细小、实心三维形态的颗粒,颗粒棱角已发生钝化效应。     

Manufacturing Al/Mg composite materials

The manufacturing of innovative lightweight materials and their further processing by forming allows functional dimensioning of components in addition to lightweight design. Accordingly, workpieces can be produced that have locally differing component properties. The new lateral extrusion process of composites produces near net shape lightweight composites. This process application is particularly useful when producing corrosion-resistant Al/Mg composites since it facilitates combining the favorable strength/weight ratio of magnesium with the favorable corrosion behavior of aluminum. The composite interface area is of specific significance in this respect. The presented method initiates diffusion processes with phase reformation to obtain a firmly-bonded metal joint.     

Lattice strain evolution during tensile and compressive loading of CP Ti

The micromechanics of textured Grade 1 commercially pure titanium are examined using neutron diffraction, self-consistent modelling and microscopy. It is found that twinning produces greater hardening than slip, that the residual lattice strains produced in the (0 0 0 2) are on the order of 0.001, and that both compression and tension twins are observed for both tensile and compression straining. The critical resolved shear stresses found are consistent with the macroscopic flow curves, lattice strains and textures produced, but are much lower than those found using uncorrected focused ion beam-milled micromechanical testing. The twins observed in axial compression were thicker than those found when compressing in the hoop direction, which is taken to imply that axial compression produced a greater number of twinning dislocations that could result in twin thickening.     

超声波对原位Mg_2Si／Al复合材料中初生Mg_2Si形态的影晌

采用光学显微镜和场发射扫描电镜,研究超声波对原位Mg2Si／A1复合材料中初生Mg_2Si形态的影响。研究结果表明：超声波处理使初生Mg2Si的晶粒尺寸从150μm降低到20μm,初生Mg_2Si形态发生改变。在二维形貌中,未实施超声波振动处理的初生Mg_2Si晶粒生长为含有空腔的粗大颗粒,共晶组织生长于其中,相应的三维形态为含有漏斗状空腔的八面体和十四面体。超声波处理后的初生Mg_2Si晶粒变成细小、实心三维形态的颗粒,颗粒棱角已发生钝化效应。     

Structure and stability of superconducting core of single-core MgB2/Cu,Nb tube composite with a high critical current

The core of a single-core MgB₂/Cu,Nb composite, which has been prepared by the ex-situ technique and exhibits a high critical current equal to 427 A (at 0 T and 4.2 K, j _c ≥ 10⁵ A/cm²), has been studied using various structural methods. Two kinds of MgB₂ crystals were observed; those of the first kind is large, highly dense crystals characterized by a low oxygen content (2–8 at %) and the others are fine, weakly coupled crystallites characterized by high oxygen content (4–21 at %). To perform a comparative analysis of the structures, we have also studied an MgB₂ bulk sample synthesized at 1000°C. It was found that two phases with the same lattice are formed; they differ in the magnesium and boron contents (within the homogeneity range), impurity oxygen content and microstructure as well but differ slightly in the lattice parameters. The two-phase state of MgB₂ bulk sample is due to the mechanism of its formation, which includes the melting of magnesium, the dissolution of solid boron in it, and the crystallization of MgB₂ from the melt with the formation of dendrite-like structure characterized by corresponding redistribution of components and impurities. To a certain degree, the two-phase structure of MgB₂ bulk sample is inherited by the MgB₂/Cu,Nd composite prepared by ex-situ technique (annealing of composite at 700°C). It was shown that oxygen in the MgB₂ compound is the destabilizing factor and leads to the transformation of the superconductor into MgO.     

原位合成Mg_2Si/Mg-2Al-Zn-2Gd复合材料的微观组织与断裂行为

采用多次循环塑性变形-原位反应方法制备Mg2Si/Mg-2Al-Zn-2Gd复合材料。采用XRD、SEM和TEM对复合材料的成分及微观组织进行分析和观察。结果表明:多次循环塑性变形过程对镁合金基体组织和原位合成的Mg2Si第二相粒子均有细化和均化作用;随着Mg2Si颗粒含量的增加,复合材料的弹性模量和屈服强度增加,同时断裂强度和伸长率均下降;原位反应合成的Mg2Si第二相粒子与基体结合良好,材料断裂时裂纹优先在基体中形成,断裂时Mg2Si第二相粒子能起到阻碍裂纹扩展的作用;Mg2Si/Mg-2Al-Zn-2Gd复合材料的强化机制主要为第二相强化和基体晶粒细化。     

Effect of SiC particle addition on microstructure of Mg2Si/AI composite

In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy(SEM) and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fi ber-form to a short fi ber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no signifi cant change in dendrite arm spacing(DAS) was observed in the presence of SiC particles.     

MgB2颗粒的制备及其增强铜基复合材料

采用粉末冶金反应烧结结合高能球磨的方式制备了MgB2超细粉末,烧结后X射线衍射(XRD)表明合成MgB2的纯度较高,球磨后由于晶粒尺寸减小以及晶体中微观应力增加使得MgB2衍射峰的强度下降而且宽度增加,但球磨后颗粒的高分辨透射电镜像及相应的选区电子衍射表明球磨后MgB2的晶体结构依旧完整.采用粉末冶金工艺制备了MgB2P/Cu复合材料,扫描电镜观察表明MgB2颗粒在铜基体中分布均匀.线扫描结果表明在MgB2颗粒与铜基体之间存在Mg、Cu元素的互扩散现象.性能测试结果表明,相同体积分数情况下,MgB2P/Cu复合材料的相对密度、硬度、拉伸强度以及导电性能优于TiNp/Cu复合材料和AINp/Cu复合材料,是一种有效的弥散强化相.     

镁铝轻质复合板多层挤压复合工艺

采用挤压工艺对AZ31镁合金板和6061铝合金板进行多层挤压复合,结合扫描电镜、能谱分析仪、金相显微镜、EBSD以及万能拉伸试验机等分析手段,研究了不同坯料层数对AZ31/6061复合板的微观组织及力学性能的影响。实验结果表明:复合板镁合金侧中存在大量的细小再结晶晶粒和少量变形组织,复合板铝合金侧的晶粒呈现典型的带状结构,且周围有大量细小再结晶晶粒生成;此外,复合板中Mg/Al界面具有良好的冶金结合,且有不同厚度的界面反应层生成,其中P1板的界面反应层以Mg_2Al_3为主,P2板靠近镁合金侧有Mg_(17)Al_(12)生成,靠近铝合金层有Mg_2Al_3生成。     

Load partitioning between ferrite and cementite during elasto-plastic deformation of an ultrahigh-carbon steel

An ultrahigh-carbon steel was heat-treated to form an in situ composite consisting of a fine-grained ferritic matrix with 34 vol.% submicron spheroidized cementite particles. Volume-averaged lattice elastic strains for various crystallographic planes of the α-Fe and Fe₃C phases were measured by synchrotron X-ray diffraction for a range of uniaxial tensile stresses up to 1 GPa. In the elastic range of steel deformation, no load transfer occurs between matrix and particles because both phases have nearly equivalent elastic properties. In the steel plastic range after Lüders band propagation, marked load transfer takes place from the ductile α-Fe matrix to the elastic Fe₃C particles. Reasonable agreement is achieved between phase lattice strains as experimentally measured and as computed using finite-element modeling.     

新型复合材料Mg/MWNTs的储放氢性能

通过在加氢气氛下高能球磨，制成了新型复合材料Mg／MWNTs。利用XRD，TEM—SAED等手段对该材料进行了微结构分析。采用储放氢实验装置测试了Mg／MWNTs—H2体系的PCT放氢曲线和放氢动力学性能。研究发现：复合材料Mg／MWNTs在2．0MPa氢压时，373，473，553和598K温度下，最大储氢量(质量分数)分别为0．41％，3．37％，5．70％和6．25％；复合材料Mg／MWNTs氢化物的焓变和熵变的绝对值均低于纯Mg，分别降低了10．51％和3．50％；与纳米晶Mg氢化物相比，复合材料Mg／MWNTs不仅最大储氢量显著增加，而且放氢动力学性能也明显改善。     

Microstructural characteristics of in situ Mg2Si/ Al-Si composite by low superheat pouring

To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rheo-casting of this type of material, three AI-Si matrix composites reinforced by 5wt.%, 9wt.% and 17wt.% Mg2Si with hypoeutectic, eutectic and hypereutectic compositions were prepared by the low superheat pouring （LSP） process. The effects of the pouring temperature （superheat） on the morphology and size distribution of primary phases （primary e-AI and Mg2Si）, binary （a-AI ＋ Mg2Si） eutectic cell and eutectic Mg2Si were investigated. The experimental results show that low pouring temperature （superheat） not only refines the grain structure of the primary e-AI and binary （e-AI ＋ Mg2Si） eutectic cell in three composites and promotes the formation of more non- dendritic structural semi-solid metal （SSM） slurry of these phases; but also refines the primary and eutectic Mg2Si phases, which seems to be attributed to the creation of an ideal condition for the nucleation and the acquisition of a high survival of nuclei caused by the LSP process.     

复合变质对Mg2Si/Al复合材料组织的影响

在铸造Mg2Si/A1-Si复合材料过程中,加入混合稀土氧化物与CaCO3作为变质剂,并采用光学显微镜研究了复合变质对组织的影响。双重变质后结果表明,初生Mg2Si相平均尺寸由75μm减小到25μm左右,其形态由不规则多边形、十字架形变为规则的多边形或者三角形,比单一的混合稀土氧化物、CaCO3变质效果都要好。     

Elevated temperature compressive failure behavior of a 30 vol.%ZrCp/W composite

The elevated temperature deformation behavior of a 30 vol.%ZrC_p/W composite was tested on a Gleeble-1500D thermo-mechanical simulation device under a uniaxial compressive load. The micro-failure behavior of the composite is strongly affected by the adhesive strength of ZrC/W interface and the distribution of ZrC particles. The computational results by EET theory indicate that the adhesive strength of (Zr, W)C interface is higher than that of ZrC. The microcrack initiation and propagation mechanism varies with the deformation temperature. TEM results show that the initiation and propagation of the microcracks occur in three steps in 1300–1600 °C.     

Corrosion behaviour of Mg/Al alloys with composite coatings

The corrosion behaviour of aluminium/silicon carbide (Al/SiC) composite coatings deposited by thermal spray on AZ31, AZ80 and AZ91D magnesium-aluminium alloys was investigated by electrochemical and gravimetric measurements in 3.5 wt.% NaCl solution at 22 °C. Corrosion products were examined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and low-angle X-ray diffraction (XRD). Al/SiC composite coatings in the as-sprayed state revealed high level of porosity with poor bonding at the Al/SiC and coating/substrate interfaces, which facilitated degradation of the magnesium substrates by a mechanism of galvanic corrosion. Cold-pressing post-treatment produced more compact coatings with improved corrosion performance in 3.5 wt.% NaCl compared with as-sprayed coatings.     

轴向正压力作用下新型触觉复合材料电阻机械效应研究

制备了一种纳米级导电炭黑填充热塑性弹性体的触觉敏感复合材料,并在MTS810材料万能试验机上对复合材料的力学性能和电学性能进行了同步测定。主要讨论了不同轴向加载速率对复合体系电阻机械效应的影响。结果表明,在0MPa~2.5MPa压力范围内,复合材料的压力-电阻拟合曲线接近线性;当轴向加载速率从0.25N/s增加到1.0N/s后,材料的压力-电阻拟合曲线的线性度有了一定程度的改善。     

复合变质对原位Mg2Si／Al-Si复合材料组织优化研究

在铸造Mg2Si/Al-Si复合材料过程中,研究了混合稀土氧化物、CaCO3及变质温度对初生Mg2Si变质效果的影响.采用正交试验设计方法,优化了影响因素.通过直观分析与方差分析得出的较佳工艺条件为:混合稀土氧化物的加入质量分数为0.2%,w(CaCO.)为0.3%,变质温度为820℃,此时初生Mg2 Si由原来的75μm左右减小到25 μm左右.