Steady-State Creep Behavior of Super304H Austenitic Steel at Elevated Temperatures

Creep behavior of Super304 H austenitic steel has been investigated at elevated temperatures of 923-973 K and at applied stress of 190-210 MPa.The results show that the apparent stress exponent and activation energy in the creep deformation range from 16.2 to 27.4 and from 602.1 to 769.3 kJ/mol at different temperatures,respectively.These high values imply the presence of a threshold stress due to an interaction between the dislocations and Cu-rich precipitates during creep deformation.The creep mechanism is associated with the dislocation climbing governed by the matrix lattice diffusion.The origin of the threshold stress is mainly attributed to the coherency strain induced in the matrix by Cu-rich precipitates.The theoretically estimated threshold stresses from Cu-rich precipitates agree reasonably with the experimental results.     

复合加工制备的超细晶工业纯钛室温蠕变行为研究

采用工业纯钛TA1经等径弯曲通道变形(Equal channel angular pressing,ECAP)+冷轧(Cold Rolling,CR)+旋锻(Swaging)的方法制得晶粒尺寸约为120nm的超细晶工业纯钛,通过单轴拉伸蠕变实验、透射电子显微镜(TEM)、扫描电子显微镜(SEM)等方法,研究室温下超细晶工业纯钛蠕变变形行为及机理。结果表明:在实验应力范围内,超细晶工业纯钛存在明显的室温蠕变现象;随加载应力的升高(640～760 MPa),蠕变量增加,稳态蠕变速率增大(2.8×10~(-7)～1.5×10~(-4)s~(-1));在相同蠕变应力水平(0.8σ_s)下,超细晶工业纯钛稳态蠕变速率(2.8×10~(-7)s~(-1))低于粗晶工业纯钛(8.6×10~(-6)s~(-1)),抗蠕变性能优于粗晶工业纯钛;位错滑移机理是其主要蠕变变形机理,蠕变断裂机制为韧性断裂。     

热处理冷速对FGH97盘件显微组织和蠕变性能的影响

对FGH97粉末高温合金盘件进行热处理,采用光学显微镜、扫描电子显微镜、能谱仪和蠕变试验机研究了不同固溶冷速下合金的显微组织、蠕变性能和蠕变机制。研究表明:随固溶冷速的增加,γ′相尺寸减小,富Ti、Nb、Hf的MC型碳化物由连续析出变为颗粒状弥散析出。在750℃/450 MPa蠕变试验条件下,固溶冷速为94℃/min的样品性能明显优于43℃/min。FGH97粉末高温合金在750℃/450MPa条件下的蠕变机制为位错切割γ′相,在晶界处产生应力集中导致裂纹的萌生,裂纹沿着晶界碳化物扩展,最终导致材料的断裂。弥散颗粒状分布的碳化物能有效抑制微裂纹的贯通。     

Performance investigation of resin bonded ferro-silicon nitride-corundum refractories after creep at 1300 °C

Novel tempered resin bonded ferro-silicon nitride-corundum refractories containing 0 wt%, 15 wt% and 25 wt% ferro-silicon nitride were prepared respectively. Creep tests were performed under a load of 0.2 MPa at a temperature of 1300 °C for 50 h in air. The results showed that creep performance was significantly improved by the addition of ferro-silicon nitride. Ferro-silicon nitride-corundum containing 15 wt% ferro-silicon nitride initially presented a steady-state stage and was able to remain stable from the beginning of the holding time until 50 h of creep testing. All the specimens exhibited cold crushing strength more than 100 MPa both before and after creep testing. Phase composition and microstructure were analyzed following the creep experiments. The results showed that Si₂N₂O and O’-sialon crystals formed in situ during creep testing, in addition to the conversion of α-Si₃N₄ to β-Si₃N₄. Liquid Fe₃Si from the ferro-silicon nitride component accelerated the formation of the O’-sialon and prolonged the growth of β-Si₃N₄, which improved the creep performance significantly. Fe₃Si liquid migrated into the pores, and some Fe₃Si coexisted with residual carbon from the resin, which filled a part of pores and protected the specimens from severe oxidation.     

小冲杆蠕变试验微试样的应变分析

在假设以弹塑性薄膜变形分析所获得的试样中心挠度与非蠕变中心应变之间的关系近似等于蠕变时试样中心挠度与中心蠕变应变之间的关系的基础上 ,使用塑性薄膜伸张变形模型模拟小冲杆试样的蠕变变形过程 ,设计了以小冲杆试验实测中心挠度数据估算试样中心蠕变应变以至材料蠕变性能的方法 ,并具体推导得到了特定小冲杆试验装置和试样尺寸对应的蠕变应变工程估算方程     

塔里木盆地A区深部盐层蠕变特性试验研究

钻井过程中钻遇盐层时,由于盐层本身所具有的蠕变特性,经常给井下施工带来极大的干扰和破坏,不同地区不同埋深的盐层具有不同的蠕变特性。正确地认识盐层的蠕变特性,找出其变化的规律,无疑对该地层的施工具有很好的指导意义。     

转化管蠕变参量的二元回归分析

对于以温度和应力为变量的幂函数型蠕变参量,本文提出了一种二元回归分析方法,计算了ＨＫ４０转化炉管新材料的稳态蠕变速率参量和蠕变损伤速率参量的咽归系数,并搪塞了材料常数对这两个蠕变参量的影响。回归出的蠕变参量解析式与试验数据拟合得颇好。特别对于极少量的试验数据,更能显示本文方法的有效性。     

露天矿顺层蠕动边坡稳定性动态分析探讨

进行了阜新海州露天矿北帮东部一号断层区顺层蠕动边坡变形、失稳机理分析讨论。根据老化理论提出了软弱夹层的一般流变方程τ =Ao( 1 δ·tα) ·γm ( 1 σmH) ,确定由等速蠕变向加速蠕变过渡的临界应变量作为破坏时刻的破坏应变量γs,从而建立长期抗剪强度与应力作用时间变化的关系τ =Ao·γs( 1 δ·tα) Ao·γsH ( 1 δ·tα) ·σm=c σm·tgφ ,对于非稳定蠕动变形 ,等速蠕变阶段的应变速率与剪应力超过长期极限强度的程度有关 ,在此基础上探讨并建立顺层蠕动边坡的流变稳定性分析方法 ,评价蠕动边坡变形、失稳的动态演化     

Fabrication and mechanical performance of Ti2AlN prepared by FAST/SPS

Highly dense bulk Ti₂AlN with high purity was successfully fabricated at 1400 °C by Field Assisted Sintering Technology (FAST/SPS) using Ti, Al, TiN as starting powders. Aluminum content appears to play a determinant role to attain high phase purity, where the optimum content has been achieved for a starting molar composition of 1:1.02:1 for Ti, Al, and TiN, respectively. Elastic modulus and hardness were determined via micro-indentation testing at room temperature. Regarding abrasive behavior, sandblasting tests with compressed air of 2 bar were carried out. In addition, creep tests in air in the temperature range of 900−1200 °C were performed to characterize the steady state deformation behavior under constant applied stresses ranging from 20−100 MPa.     

Tensile creep behavior of SiCf/SiC ceramic matrix minicomposites

Single fiber-tow minicomposites represent the major load-bearing element of woven and laminate ceramic matrix composites (CMCs). To understand the effects of fiber type, fiber content, and matrix cracking on tensile creep in SiC_f/SiC CMCs, single-tow SiC_f/SiC minicomposites with different fiber types and contents were investigated. The minicomposites studied contained either Hi-Nicalon™ or Hi-Nicalon™ Type S SiC fibers with a boron nitride (BN) interphase and a chemical-vapor-infiltrated-silicon-carbide (CVI-SiC) matrix. Tensile creep was performed at 1200 °C in air. A bottom-up creep modeling approach was applied where creep parameters of the fibers and matrix were obtained separately at 1200 °C. Next, a theoretical model based on the rule of mixtures was derived to model the fiber and matrix creep-time-dependent stress redistribution. Fiber and matrix creep parameters, load transfer model results, and numerical modeling were used to construct a creep strain model to predict creep damage evolution of minicomposites with different fiber types and contents.