镍基单晶高温合金磨削表面质量及亚表面微观组织试验

采用正交试验的方法,研究了镍基单晶高温合金DD5表面质量影响因素和亚表面微观组织.进行DD5平面槽磨削正交试验,得到砂轮线速度、磨削深度和进给速度对表面质量的影响规律,优选出最优工艺参数组合,并对磨削亚表面微观组织和磨屑形貌进行观察.结果表明:砂轮线速度对磨削表面粗糙度R_○a影响最大;随着砂轮线速度的增大,表面粗糙度R_○a不断减小;随着磨削深度和进给速度的增大,表面粗糙度R_○a不断增大.选出的镍基单晶高温合金DD5平面磨削试验参数范围内的最优工艺参数组合:砂轮线速度为30m/s,磨削深度为20μm,进给速度为0.2m/min.磨削亚表面出现了塑性变形层和加工硬化层.磨屑主要呈现出一节一节的锯齿状特征.     

高温下钨断裂及氢影响钨断裂的分子动力学模拟

用分子动力学模拟在1000K温度下单晶钨在单轴应变的情形下断裂和氢对钨断裂的影响。结果表明:{100}面的辟裂比{110}面要容易。{100}面的辟裂与裂纹尖端的取向有关,模拟结果与低温下的实验结果符合得比较好。{110}面<111>方向的断裂不是辟裂方式。切应变的模拟结果也与实验相符。氢的加入对裂纹尖端影响比较大,能显著降低应力。     

不同晶向取向的裂纹扩展演化模拟

【目的】研究具有不同初始晶向倾角的样品在单轴拉应变作用下的纳观尺度裂纹扩展行为,了解裂纹的生长特征和扩展规律,揭示纳米级裂纹扩展机理及其对材料断裂的影响。【方法】采用晶体相场法观察不同晶向倾角下裂纹的扩展演化图及对应的应力分布图。【结果】当拉应变作用达到临界值时,无预应变的样品裂口开始起裂,并伴随着位错出现。在晶向倾角为0°、5°时,裂口在起裂时,缺口两端裂纹和裂口相连接,裂纹主要是解理脆性断裂模式扩展;在晶向倾角为10°时,裂口向左右两边各发射一个位错,位错在滑移过程中留下一系列空位,空位连通形成裂纹再与主裂口相连,裂纹主要是韧性断裂模式扩展。【结论】不同晶向取向对裂纹的扩展演化有重要影响。     

5 Cr9 Si3钢的高温变形行为及流变应力异常变化机理

通过不同热加工参数下的热压缩试验,研究了新型阀门钢5Cr9Si3的高温变形行为.5Cr9Si3钢在850~900℃和1000~1100℃温度区间内峰值应力分别随温度的升高而减小,而在900~1000℃温度区间内出现峰值应力随温度升高而增大的异常现象.进一步的微观组织及相结构演化分析表明：5Cr9Si3钢在900~1000℃温度区间内发生了由铁素体向奥氏体的转变,产生奥氏体相变强化;同时,随着变形温度的提高,碳化物的回溶造成碳元素和铬元素对5Cr9Si3基体固溶强化效果增强.相变强化和固溶强化是导致5Cr9Si3在900~1000℃温度区间内流变应力异常变化的主要原因.     

Effects of overaging temperature on the microstructure and properties of 600 MPa cold-rolled dual-phase steel

C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining (2%) and baking treatments (170°C for 20 min) to measure their bake-hardening (BH2) values. The effects of overaging temperature on the microstructure, mechanical properties, and BH2 behavior of 600 MPa cold-rolled dual-phase (DP) steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH2 value initially increases and then decreases. The maximum BH2 value of 83 MPa was observed for the specimen overaged at 350°C.     

Microstructure and heat treatment for Ni3Al-based single crystal alloy with different crystal orientations

Ni₃Al-based single crystal alloy IC6SX with different crystal orientations were prepared by seed crystal method. The microstructure and heat treatment of the alloy were investigated. The results showed that the microstructure of the alloy was in dendrite structure, and the crystal orientation had significant effect on the dendrite morphology of this alloy. The precipitated phases of (MoNi)₆C and NiMo appeared in the microstructure of the three alloys with different crystal orientations during solidification process. Compared with other two alloys, the volume fractions of precipitated phases of both (MoNi)₆C and NiMo was the most in the alloy with [111] orientation and the least in the alloy with [001] orientation. The solidus and liquidus temperatures of the alloy IC6SX tested by differential scanning calorimetry (DSC) were 1356 °C and 1387 °C, respectively. Meanwhile, the effect of different solution temperatures on the microstructure of the alloy with different orientations was studied. The results showed that the precipitated phases of (MoNi)₆C and NiMo were eliminated with the solid solution treatment under the condition of 1300 °C/10 h. However, the incipient melting of the alloys occurred due to the dissolution of low melting point phases. As the temperature dropped to 1280 °C, the area of incipient melting in the alloy with different orientations decreased gradually. However, there was no incipient melting appearing in the three alloys with different orientations when the solution treatment temperature dropped to 1260 °C.     

Influence of sintering temperature on the thermoelectric properties of Ba8Ga16Si30 clathrate treated by spark plasma sintering

A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering (SPS). X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750°C. Lattice contraction recurred when the SPS temperature was further increased in the range of 750–1000°C. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800°C. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT–T curve.     

Tensile properties of tungsten-rhenium wires with nanofibrous structure

In this study, the mechanical properties of tungsten-rhenium wires with nanofibrous microstructure were investigated at both room temperature (RT) and 800℃. The strengthening mechanism associated to the nanofibrous microstructure was discussed. The results showed that the tungsten-rhenium wires with nanofibrous grains exhibited a very high tensile strength reaching values of 3.5 GPa and 4.4 GPa for the coarse (grains diameter of 240 nm) and fine (grains diameter of 80 nm) wires, respectively. With increasing the temperature from RT to 800℃, the tensile strength decreased slightly but still held high values (1.8 GPa and 3.8 GPa). All the fracture surfaces exhibited apparent necking and characteristics of spear-edge shaped fracture surface, indicating excellent ductility of the wires. A model of the strengthening mechanism of these tungsten-rhenium wires was proposed.     

Creep behavior and dislocation mechanism of Ni3Al based single crystal alloy IC6SX at 760°C

The creep behavior and dislocation mechanism of Ni₃Al-based single crystal alloys IC6SX with crystal orientation [001] which was prepared by seed crystal method under the testing conditions of 760 ​°C/500 ​MPa,760 ​°C/540 ​MPa and 760 ​°C/580 ​MPa were investigated. The experimental results showed that the creep properties, dislocation morphology and mechanism of this alloy were different under different stress conditions. With the stress increasing from 500 ​MPa to 580 ​MPa, the creep life decreased from more than 1000h to 32.64h. The cubic degree of γ′ phase in single crystal alloy decreased obviously and the size of γ′ phase increased. The mechanism of dislocation movement also changed with the increasing stress. It was found that after the specimen was tested under the condition of 760 ​°C/500 ​MPa the dislocation network prevented the movement of dislocations and it was difficult for dislocations to enter the γ′ phase from the γ/γ′ interface. When the stress was 540 ​MPa, the dislocations cut into the γ′ phase by stacking fault. Furthermore, with the stress increasing to 580 ​MPa, the dislocation entered the γ′ phase in the form of extended dislocation and Lomer-Cottrell dislocation.     

单晶镍基高温合金微铣削力试验

以单晶镍基高温合金DD98为研究对象,从单晶高温合金微观组织分析材料去除机理,得出DD98滑移面为密排面{111},滑移向为密排方向110,克服阻力最小,最易滑移.采用双刃微铣刀对单晶镍基高温合金DD98进行正交试验,通过极差分析比较获得切削参数对微铣削力的影响程度.结果表明,主轴转速的影响最大,进给速度其次,铣削深度最小.通过优化获得理想的切削参数为:主轴转速36 000 r/min,铣削深度5μm,进给速度20μm/s,此时微铣削力最小.并对其原因进行深入分析,为单晶高温合金的微加工理论的机理揭示提供理论参考和试验依据.     

Influence of aluminium nitride as a foaming agent on the preparation of foam glass-ceramics from high-titanium blast furnace slag

To effectively reuse high-titanium blast furnace slag (TS), foam glass-ceramics were successfully prepared by powder sintering at 1000℃. TS and waste glass were used as the main raw materials, aluminium nitride (AlN) as the foaming agent, and borax as the fluxing agent. The influence of the amount of AlN added (1wt%–5wt%) on the crystalline phases, microstructure, and properties of the produced foam glass-ceramics was studied. The results showed that the main crystal phases were perovskite, diopside, and augite. With increasing AlN content, a transformation from diopside to augite occurred and the crystallinity of the pyroxene phases slightly decreased. Initially, the average pore size and porosity of the foam glass-ceramics increased and subsequently decreased; similarly, their bulk density and compressive strength decreased and subsequently increased. The optimal properties were obtained when the foam glass-ceramics were prepared by adding 4wt% AlN.     

Effect of temper rolling on the bake-hardening behavior of low carbon steel

In a typical process, low carbon steel was annealed at two different temperatures (660℃ and 750℃), and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subsequently carried out to measure the bake-hardening (BH) values. The influences of annealing temperature and temper rolling on the BH behavior of the steel were investigated. The results indicated that the microstructure evolution during temper rolling was related to carbon atoms and dislocations. After an apparent increase, the BH value of the steel significantly decreased when the temper rolling reduction was increased from 0% to 5%. This was attributed to the increase in solute carbon concentration and dislocation density. The maximum BH values of the steel annealed at 660℃ and 750℃ were 80 MPa and 89 MPa at the reductions of 3% and 4%, respectively. Moreover, increasing the annealing temperature from 660 to 750℃ resulted in an obvious increase in the BH value due to carbide dissolution.     

DD3单晶镍基超合金高温力学性能

采用扫描电镜（ＳＥＭ）研究了单晶镍基高温合金ＤＤ３的高温蠕变性能和低应变速率下的拉伸行为。结果表明，ＤＤ３合金表现出良好的蠕变强度和较高的蠕变寿命；拉伸过程中合金的屈服强度在室温１１０３３Ｋ之间保持不变，当温度大于１０３３Ｋ后，屈服强度显著降低。断口分析表明，这类材料具有独特的断裂方式，断口为混合型，即包括韧性断裂和局部区域的解理断裂特征。     

Ductile fracture behavior of TA15 titanium alloy at elevated temperatures

To better understand the fracture behavior of TA15 titanium alloy during hot forming, three groups of experiments were conducted to investigate the influence of deformation temperature, strain rate, initial microstructure, and stress triaxiality on the fracture behavior of TA15 titanium alloy. The microstructure and fracture surface of the alloy were observed by scanning electronic microscopy to analyze the potential fracture mechanisms under the experimental deformation conditions. The experimental results indicate that the fracture strain increases with increasing deformation temperature, decreasing strain rate, and decreasing stress triaxiality. Fracture is mainly caused by the nucleation, growth, and coalescence of microvoids because of the breakdown of compatibility requirements at the α/β interface. In the equiaxed microstructure, the fracture strain decreases with decreasing volume fraction of the primary α-phase (α_p) and increasing α/β-interface length. In the bimodal microstructure, the fracture strain is mainly affected by α-lamella width.     

一种镍基单晶高温合金的反相热机械疲劳行为

采用扫描电镜、透射电镜等方法研究了一种镍基单晶高温合金在600~900℃的反相位热机械疲劳行为,旨在探讨单晶合金的热疲劳变形及断裂机制,丰富单晶合金热机械疲劳理论。试验结果表明：当应变幅由0.6%增大至0.9%时,热机械疲劳寿命下降,塑性应变量和应力范围增大。合金的循环应力响应曲线在低温半周表现为循环硬化行为,而在高温半周则表现为循环软化行为。合金主要的变形特征是局部区域滑移带的运动。热机械疲劳裂纹起始于试样表面应力集中处,并沿着滑移带在{111}面向合金内部扩展,拉应力对合金的断裂起到了主导作用。     

沉积温度对NbN膜层微观结构的影响

利用有磁过滤器的等离子体沉积装置,在不同温度的Si基底上沉积氮化铌（NbN）薄膜,通过XRD,XPS,SEM等分析,研究了NbN薄的表面表貌与微观结构跟温度的关系,发现沉积温度对掺优取向有较强的影响：从室温到约300℃得到的薄膜在（220）峰表现出很强的择优取向,500℃（220）峰变得很弱,（200）峰表现出择优取向,但不明显,同时,膜层中N和Nb的原子比先随温度的升高而升高,后稍有降低,温度升高,δ-NbN的晶粒变大,室温到300℃很难得到完整的NbN膜,而在500℃得以的薄膜完整且光滑,膜层中得到单一的δ-NbN相。     

B位Mn掺杂Sr2Fe1.5Mo0.5O6-δ作为中温固体氧化物燃料电池阳极的性能

采用溶胶-凝胶燃烧法合成出Sr₂Fe_1.4Mn_0.1Mo_0.5O_6-δ（SFMn0.1M）材料,并将其作为中温固体氧化物燃料电池的阳极.表征了SFMn0.1M材料的晶体结构、微观形貌、元素价态、电导率和电化学性能.X射线衍射表明Mn取代后,SFMn0.1M依然保持了立方钙钛矿结构,扫描电子显微镜观察到其微观形貌为三维多孔结构.SFMn0.1M作为SOFCs阳极显示出优异的电化学性能,在800℃下SFMn0.1M的电导率为14.7 S·cm-1,以SFMn0.1M为阳极材料组装单电池,H₂作为燃料,其最大功率密度在800,750,700和650℃下分别为565.2,385.2,303.9和141.2 mW·cm-2.因此,SFMn0.1M在作为IT-SOFC阳极材料时表现出巨大的潜力.      

纯镍N6平面热压缩变形行为及加工图

利用Gleeble-3800热模拟试验机对纯镍N6在变形温度800~1100℃,应变速率5~40 s-1,应变量70%条件下进行了高温塑性变形压缩试验,分析纯镍N6高温高应变速率热变形行为,得到了材料在不同变形参数条件下的组织变化规律及流变应力变化曲线,利用动态材料模型绘制出了纯镍N6在不同应变条件下的热加工图。通过对组织及热加工图的分析研究,得出变形温度为1000~1100℃,应变速率为5~7 s-1或20~40 s-1以及变形温度为800~900℃,应变速率为5~10 s-1为纯镍N6材料高温高应变速率热变形的两个合理变形参数区间,在参数区间内N6组织均匀;而流变失稳区变形参数条件下得到的组织比较紊乱,晶粒大小不一。纯镍N6热变形后的晶粒尺寸随变形温度升高及应变速率减小而增大。     

形成新生断裂的临界角度及其与强烈地震发生的关系

选取具有薄弱面或破裂面的细粒花岗岩块状露头标本,在实验室模拟高温高压环境条件进行测试,研究岩石产生新破裂面的受力临界角度。在温度100℃、围压100 MPa和温度200℃、围压200 MPa的环境条件下,按照与主应力夹角的不同度数变化分别进行实验。实验结果表明,当夹角α处于0°~30°时,岩石沿原破裂面稳滑;夹角α处于30°~60°时,以粘滑为主;夹角α处于60°~90°时,以新破裂面的产生为主;可能产生新破裂面的临界角度范围为50°~65°,当夹角α大于65°时,新破裂产生。对岩石出现的稳滑-粘滑-新破裂现象,通过分析切面所受应力(σ)与应变率(ε)的关系进行了解释。根据莫尔圆理论认为,复杂断裂背景下,岩石的受力角度对于新破裂面的产生将有着决定性作用,而作用力状态一定时,新破裂产生的临界角度60°是可能导致强烈地震发生的危险值。     

热作模具钢淬火回火态的内耗谱分析

对热作模具钢淬火后回火态试样的内耗谱进行了分析.研究表明，淬火态试样的内耗谱由3部分构成.其中：157.2 °C处的内耗峰是由于体心立方结构的马氏体晶格畸变引起应力感生碳原子微扩散的结果；225.5 °C处为溶质原子与位错交互作用产生的SKK峰及其背景内耗峰.随着回火温度升高，SKK峰的弛豫强度逐渐减小，此时，碳原子与部分合金元素以碳化物形式结合而从基体中析出，使得其晶格畸变减弱，157.2 °C处的内耗峰消失；部分碳化物在位错处形核并使位错段增长、弛豫时间增大；内耗峰位置的移动主要归因于合金元素与碳原子的作用.