一种[001]取向镍基单晶高温合金蠕变特征

研究了一种[001]取向镍基单晶合金的蠕变特征和变形期间的微观组织结构.结果表明:在低温高应力和高温低应力条件下,合金具有较长的蠕变寿命和较低的稳态蠕变速率;在700℃,720MPa条件下,透射电镜(TEM)观察显示蠕变期间的变形特征是$\\frac{1}{2}研究了一种[001]取向镍基单晶合金的蠕变特征和变形期间的微观组织结构.结果表明:在低温高应力和高温低应力条件下,合金具有较长的蠕变寿命和较低的稳态蠕变速率;在700℃,720MPa条件下,透射电镜(TEM)观察显示蠕变期间的变形特征是1/2110位错在基体中运动,发生反应形成1/3112超肖克利(Shockley)不全位错,切入γ′相后产生层错.在900℃,450MPa条件下,没有出现蠕变初始阶段,γ′相从立方体形态演化成筏形;在加速蠕变阶段,多系滑移开动,大量位错剪切γ′相是变形的主要机制.在1070℃,150MPa条件下,γ′相逐渐转变成筏形组织,并在γ/γ′界面处形成致密的六边形位错网,位错网可以阻止位错切入γ′相,提高蠕变抗力;在蠕变后期,位错以位错对形式切入γ′相,是合金变形的主要方式.     

Development of (110) [001] texture in iron by diffusion of sulfur into grain boundaries

Secondary recrystallization selective to a (110)[00l] texture was obtained in 0.15 mm thick iron sheet processed in the α-phase and having final cold reductions in the range between 50 to 70 pct. Grain boundary inhibition was induced by the addition of elemental sulfur to an inert separator. The diffusion of sulfur, being more rapid in the primary grain boundaries than in bulk iron, produced inhibition by solute-induced grain boundary restraint. Improved magnetic properties were obtained by comparison to iron textured by the conventional MnS process.     

Formation of crystallographic texture in titanium nickelide single crystals during rolling

The texture formation in the single crystals of the Ti-48 at % Ni-2 at % Fe alloy rolled at a temperature of 350°C up to a strain of 80% in eleven different initial orientations is examined. There are three stable initial orientations that remain unchanged in rolling: {011}〈011〉, {111}〈011〉, and {111}〈112〉. The TiNi single crystals are shown to be deformed by means of a combined action of slip in systems {011}〈001〉 and twinning in systems {114}〈221〉 and {118}〈441〉. The types of formed rolling texture in the single crystals depend on their initial orientation and strain.     

轧制工艺对体心立方金属冷轧织构的影响

摘要：采用取向分布函数和取向线分析法研究了初始随机分布的体心立方金属α-Fe经过不同轧制工艺的织构演变,．体心立方金属α-Fe经过普通同步轧制后,其织构组分主要为高斯织构。经过工艺改变的异步轧制后,材料发生强烈的剪切应变,与轧制固有的平面压应变共同作用,获得了完全不同于同步轧制织构组分的{100}面织构。     

A'-form RNA double helix in the single crystal structure of r(UGAGCUUCGGCUC)

Here we demonstrate the presence of the A'-RNA conformation using the single crystal structure of a tridecamer: r(UGAGCUUCGGCUC). The average A'-RNA conformation deduced from X-ray fiber diffraction data had only been available previously, but now the presence of the A'-RNA conformation has been found in a single crystal structure for the first time. Statistical analysis showed that the A'-RNA conformation is distinguishable from the A-RNA conformation in a plot of the major groove width against the base pair inclination angle. The major groove of the A'-RNA conformation is wide enough to accommodate a protein or peptide while that of the A-RNA conformation is too narrow to do so. The presence of the A'-RNA conformation is significant for protein-RNA interaction.     

Three-dimensional investigation of long-range internal stresses in a single crystal deforming by nonsymmetrical slip

Long-range internal stresses (LRIS) are investigated in a [112]-oriented tensile-copper single crystal. The three-dimensional investigation of asymmetric X-ray profiles, measured by a high resolution diffractometer and using all Bragg reflections, allows the determination of the full long-range strain tensor. The corresponding stress tensor, determined by the generalized Hooke’s law, reveals a complicated behavior inconsistent with a uniaxial stress state in the [112] direction. It reveals, instead, a principal stress axis in the [001] direction. This stress state is different from the applied stress state predicted by numerical simulations of the tensile test. The LRIS and applied stresses are both deviated from the initial tensile axis in two opposite directions. An interpretation of these results is proposed in this article, taking into account active slip mechanisms and the geometrical contrast of interface dislocations introduced in the composite model of Mughrabi.     

Hydrogen effects in [001] oriented nickel-base superalloy single crystals

The entry and subsequent interaction of hydrogen on the mechanical properties of the single crystal nickel-base super alloy CMSX-2 has been studied. Significant amounts of hydrogen were introduced by high temperature hydrogen charging in molten salts which led to an increased lattice parameter and microhardness and to a degradation in tensile elongation to failure whose extent scales with the depth of the hydrogenated zone. In this region a fracture mode change from a {111} to a {100} type also occurred. The values of the binding energy of hydrogen to solidification voids and the effective hydrogen pressure in the voids were estimate.