Influence of Grain Boundary Character on Creep Void Formation in Alloy 617

Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP), which will operate at temperatures exceeding 760 °C and a helium pressure of approximately 7 MPa. Observations of the crept microstructure using optical microscopy indicate creep stress does not significantly influence the creep void fraction at a given creep strain over the relatively narrow set of creep conditions studied. Void formation was found to occur only after significant creep in the tertiary regime (>5 pct total creep strain) had occurred. Also, orientation imaging microscopy (OIM) was used to characterize the grain boundaries in the vicinity of creep voids that develop during high-temperature creep tests (900 °C to 1000 °C at creep stresses ranging from 20 to 40 MPa) terminated at creep strains ranging from 5 to 40 pct. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular, or 45 deg to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids, while coincident site lattice (CSL)–related grain boundaries did not appear to be consistently associated with void development. Similar results were found in oxygen-free, high-conductivity (OFHC) copper, severely deformed using equal channel angular extrusion, and creep tested at 450 °C and 14 MPa.     

Observation of Deformation and Lattice Rotation in a Cu Bicrystal

The current work examines deformation at grain boundaries from an experimental viewpoint. The orientation images of a pseudointernal surface during interrupted channel die deformations of a Cu bicrystal show the evolution of lattice orientation and crystallite fragmentation near the grain boundary. The experiments demonstrate that a region near the boundary is influenced strongly by neighboring grain deformation and lends support to the development of deformation models that include the effects of boundary character and nonlocal slip system interaction. Two crystal plasticity models of the experiment were implemented with a limited degree of success in modeling the observed behavior.     

工业纯钛TA2的高温变形机制研究

研究了纯钛TA2 在 70 0 ,75 0 ,80 0℃的室温下及变形速度为 4.5 ,12和 45mm·min- 1 )时的拉伸变形行为 ,分析了其真应力 真应变 (σ ε)的对应关系及显微组织的变化规律。结果表明 ,σ ε曲线上 ,在给定温度下 ,随着应变速率增大 ,应力增大 ;在固定应变速率时 ,随着温度升高 ,应力降低。随着应变速率增大 ,TA2 的显微组织呈现细化趋势 ,并且组织中亚晶粒比例增加。TA2 高温变形的变形激活能Q为 3 47 60 18kJ·mol- 1 ,说明该金属的高温变形机制为杂质元素与位错相互作用的过程 ,得到了高温变形的本构方程。     

Effect of Nb on Austenite Recrystallization in High Temperature Deformation Process

By analyzing the stepped test pieces with optical microscope,the influence of the technological parameters including rolling temperature and reduction on the austenite recrystallization fraction of steel with Nb content of 0.08% deformed at high temperature processing was studied,and the deformed austenite recrystallization figures of the test steel were obtained.The result indicates that when the reduction is 60%,the critical temperature of complete recrystallization is 1070 ℃ and the borderline temperature of non-recrystallization is 900 ℃.In contrast with general HSLA steel,the recrystallization and non-recrystallization temperatures are respectively 120 ℃ and 100 ℃ higher than those of ordinary HSLA,so the steel with high content of Nb has better hot processing performance because Nb has great function of holding back recrystallization.     

镁在高温合金中的晶界效应和作用机制

偏聚到晶界的镁原子可将原子错配度较小的其它溶质原子从晶界驱逐到晶内点阵或晶界相中,并可增强间隙原子向晶界的偏聚;镁原子可进入晶界相的单胞中,从而促使晶界相球化,并降低其稳定性。     

M963合金高温蠕变过程中显微组织的演化及断裂机理

研究了M963合金在975℃×225MPa条件下蠕变过程中的组织演化及断裂机理.结果表明M963合金的蠕变曲线呈现出明显的3个阶段且稳态蠕变速率较低;蠕变过程中,γ'相粒子逐渐筏形化,由初始阶段分布在γ基体中的立方状孤立相转变为蠕变后期包围γ相的连续相;在枝晶干上有颗粒状M6C碳化物析出;蠕变变形机制从初始阶段的Orowan绕过γ'相粒子变为蠕变后期的位错切过γ'相粒子.     

Influence of Grain Coarsening on the Creep Parameters During the Superplastic Deformation of a Severely Friction Stir Processed Al-Zn-Mg-Cu Alloy

During grain boundary sliding in ultrafine-grain materials at intermediate temperatures and high strain rates (~10^?2 s^?1), apparent creep parameters usually deviate from the theoretical values, due to microstructural coarsening. An analysis has been carried out in a severely friction stir processed (FSP) 7075 alloy with three different ultra-fine grain sizes (L), obtaining explicit grain size dependence of the creep parameters n _ap = n _ap(L) and Q _ap = Q _ap(L), confirming the validity of the theoretical values of these parameters in the constitutive equation.     

热轧细晶高强度汽车板冷弯微裂纹的成因

对CSP生产线上生产的细晶高强度热轧汽车板冷弯时的微裂形成的原因进行了实验和分析。结果表明：表面微裂纹与表面的粗晶和混晶有关；而横向冷弯时的微裂纹主要与次表层被压扁和成方向性的晶粒及混晶有关；消除混晶和方向性的变形晶粒，则冷弯微裂纹即可避免。     

变形速度及晶粒度对GH4169合金高温拉伸性能和组织的影响

研究了温度、变形速度、原始晶粒度对GH4169合金高温拉伸性能和组织的影响.随变形速度的提高,合金的强度升高,塑性下降.原始粗晶组织的强度明显高于原始细晶组织的相应值,而塑性则有不同程度的下降.在动态再结晶温度以上的950～980℃,原始细晶组织试样的适量变形区具有均匀的10～13级晶粒.890℃、950℃和1030℃适量变形区在正常热处理后晶界δ相分别呈现大量聚集针状、适量短棒和小颗粒状以及少量小片状和薄膜状的析出特征.在热模锻条件下,选用合适的细晶坯料和950℃左右的模具温度,预计锻件可获得均匀细小的晶粒、良好的晶界状态及性能.     

变形晶界对低碳钢显微组织的影响

对不同温度下变形和变形后再加热到奥氏体区的低碳钢SS400的显微组织进行了研究,结果表明：变形使奥氏体和铁素体晶界呈锯齿状,锯齿状的奥氏体晶界优先成为铁素体的形核位置,锯齿状的铁素体晶界有利于铁素体再结晶核心的形成。     

The Influence of Alloying Elements on Impurity Induced Grain Boundary Embrittlement

A nonequilibrium thermodynamic model which describes the effect of solute grain boundary segregation on grain boundary cohesion was extended to Fe ternary systems. The extended model directly and simply predicts the effect of alloying elements on impurity-induced grain boundary embrittlement. According to the extended model, Mo, W, and Zr strongly reduce, Ni, Ti, and V slightly reduce, and Cr and Mn enhance impurity-induced grain boundary embrittlement in an Fe ternary system. For the evaluation of the extended model, Fe-P, Fe-P-Mn, Fe-P-Mo, and Fe-P-W alloys were studied by Auger electron spectroscopy, scanning electron microscopy, 4-point slow bend tests, and tension tests. The experimental results show that for a given amount of P grain boundary segregation the grain boundary strength increases with increasing Mo or W grain boundary segregation and decreases with increasing Mn grain boundary segregation. These experimental results showing the remedial effect of Mo or W and the embrittling effect of Mn on P-induced grain boundary embrittlement are consistent with the predicted results from the extended model. The nonequilibrium model is also used to evaluate impurity-induced interfacial embrittlement in continuous fiber metal matrix composite materials.     

Effect of Post-annealing on Grain Boundary of Nano-crystalline Cu Processed by Powder High-Pressure Torsion

High tensile strength of 616 MPa and improved ductility of 7.6 pct were obtained in powder-consolidated pure Cu processed by high-pressure torsion (HPT) at room temperature followed by post-annealing at 673 K (400 °C). The powder-HPT consolidation process maintained nano-crystalline microstructures even after post-annealing due to the presence of well-dispersed oxide particles in the matrix. Higher ductility in the post-annealed specimen is attributed to higher fraction of stable Σ3 coincidence site lattice boundaries than that in the HPT-processed Cu.     

The Effect of Solute Atoms on Aluminum Grain Boundary Sliding at Elevated Temperature

Grain boundary sliding (GBS) is an important deformation mechanism for elevated temperature forming processes. Molecular dynamics simulations are used to investigate the effect of solute atoms in near grain boundaries (GBs) on the sliding of Al bicrystals at 750 K (477 °C). The threshold stress for GBS is computed for a variety of GBs with different structures and energies. Without solute atoms, low-energy GBs tend to exhibit significantly less sliding than high-energy GBs. Simulation results show that elements which tend to phase segregate from Al, such as Si, can enhance GBS in high-energy GBs by weakening Al bonds and by increasing atomic mobility. In comparison, intermetallic forming elements, such as Mg, will form immobile Mg-Al clusters, decrease diffusivity, and inhibit GBS.     

H68合金退火料温对其晶粒度的影响

本文对深冲用H68合金成品退火的晶粒度之影响因素进行分析,通过对原始晶粒度冷轧后（ε〉50%）的各种不同料温的晶粒度测试试验作出了不同料温情况下晶粒度的关系图,最后得出了两点结论,第一,H68合金板带的成品退火晶粒度不受原始晶粒度的影响,退火前冷加工率超过50%成品软态的晶粒度可获得最佳值;第二,H68合金板带的晶粒度与退火料温的关系是在550℃以下呈线性变化,大于550℃后变化不明显。     

H68合金退火料温对其晶粒度的影响(续)

2试验方案和退火工艺 2．1试验方案 根据前节分析,H68合金属单相α高锌合金,第一再结晶温度低,第二晶粒易长大。结晶理论指出,原始晶粒粗大,加工退火后再结晶晶粒亦大,H68合金在成品冷轧前需经两次中间退火（6．5mm热轧卷坯退火,2．3mm冷轧卷坯退火）,     

高温蠕变理论在耐材支架设计中的应用研究

在机器的设计和制造过程中,不仅需要保证设备的主功能够满足用户的使用要求,也必须确保辅助结构的运行稳定和可靠,任何结构的故障都会严重影响机组的正常生产,造成重大经济损失。以感应加热器的耐材支架故障为例,应用材料的高温蠕变理论,对支架故障原因进行了研究和分析,提出了满足使用要求的改进办法。实践表明本次改造是成功和有效的,为工程项目管理中类似问题的解决提供了经验和方法。     

细晶高强钢筋生产工艺研究

简要介绍了开发生产细晶高强钢筋的工艺过程,通过采用控制轧制和控制冷却的方法轧制出细晶粒的高强度钢筋,达到节能降耗、降低生产成本的目的。     

Effect of Deformation Temperature on Deformation Mechanism of Fe-6.5Si Alloys with Different Initial Microstructures

Deformation behaviors and mechanisms under different temperatures for columnar-grained Fe-6.5Si(mass%)alloys fabricated by directional solidification and equiaxed-grained Fe-6.5Si alloy fabricated by forging were comparatively investigated.The results showed that,with increasing the deformation temperature from 300 ℃ to500 ℃,the elongation increased from 2.9%to 30.1%for the equiaxed-grained Fe-6.5Si alloy,while from 6.6%to about 51%for the columnar-grained Fe-6.5Si alloy.The deformation mode of equiaxed-grained Fe-6.5Si alloy transferred from nearly negligible plastic deformation to large plastic deformation dominated by dislocation slipping.Comparatively,the deformation mode of the columnar-grained alloy transferred from nearly negligible plastic deformation to plastic deformation dominated by the twining,and finally to plastic deformation dominated by dislocation slipping.Meanwhile,compared with the alloy with equiaxed grains,it was found that ultimate tensile strength and elongation could be increased simultaneously,which was ascribed for the twinning deformation in columnar-grained Fe-6.5Si alloy.This work would assist us to further understand the plastic deformation mechanism of Fe-6.5Si alloy and provide more clues for high-efficiency production of the alloy.     

热处理温度对Cu/Ni-P镀层的影响

研究了不同热处理温度对Cu／Ni-P合金镀层表面形貌、硬度及耐蚀性的影响；通过对比分析，确定最佳热处理温度为400℃。