等轴组织BT14合金应力松弛行为及机制

研究了等轴组织BT14合金在200、400和600℃下应力松弛行为,并通过应力松弛过程中微观组织的变化研究应力松弛的微观机理.研究表明,200℃应力松驰变形中,有位错运动启动;400℃发现位错滑移带,这时应力松弛的微观机理均为位错滑移导致的微区塑性变形;600℃应力松驰变形中,发现亚晶界和位错网,其松弛机理为回复蠕变.     

β区淬火时效态TC4合金弯曲应力松弛行为

研究了卢区淬火时效的TC4合金在400℃和600℃的应力松弛行为，并对应力松弛曲线进行拟合；微观组织观察结合宏观热变形参数分析表明：400℃应力松弛机制为位错滑移和孪晶及晶界、相界的运动，孪晶为(10-11)类型；600℃位错塞积成为亚晶界，应力松弛变形机制为位错滑移、攀移和原子扩散。     

感应回火对Q550D钢组织和应力松弛效果的影响

以Q550D钢中厚钢板为研究对象,将910 ℃×1 h水淬后的试样分别进行感应回火和传统回火,将回火后的试样进行应力松弛效果测试;利用蔡司显微镜进行金相组织观察。试验结果表明,采用感应加热回火处理后的试样较传统回火工艺处理的试样晶粒细小,组织均匀,析出物弥散程度高,且应力松弛效果更好。     

魏氏组织Ti-6Al-4V合金应力松弛行为及机理

利用弯曲应力松弛方法研究了魏氏组织Ti-6Al-4V合金200℃．400℃和600℃时的应力松弛行为，并利用TEM研究了应力松弛前后微观组织变化：宏观热力学参数结合微观组织观察初步探讨应力松弛机理。研究表明：应力松弛开始时应力下降较快．随时间延长．应力下降速率降低．最后趋于应力松弛极限。TEM微观组织观察结果结合表现应力指数分析表明：200℃和400℃应力松弛变形机制为位错蠕变，a型位错滑移：而600℃变形机制则为回复蠕变和原子扩散的共同作用机制．a型和a＋c型或c型均开动．产生滑移和攀移。     

含微量Ti和Al的钴基耐热合金的应力松弛行为

采用热模拟技术研究了含微量Ti和Al钴基耐热合金在不同温度下的应力松弛行为.结果表明,当温度高于600℃时,该合金才会发生应力松弛现象.其应力松弛曲线可以用二次延迟函数来描述.透射电镜观察表明,该合金低温变形机制为层错,高温时为位错,600℃时形成大量的位错和宽度窄的层错,800℃时发生位错滑移为主的回复蠕变,而在1 000℃时发生亚晶粒长大为主的回复蠕变.     

Ti-6.5Al-2Zr-1Mo-1V钛合金低温应力松弛及组织演变

在500、550和600 ℃及不同初始应力下对Ti-6.5Al-2Zr-1Mo-1V钛合金进行了应力松弛实验。基于经典的Maxwell指数衰减函数,得到了应力松弛极限。提出了利用松弛稳定系数（C_S）和松弛速率系数（C_R）来描述Ti-6.5Al-2Zr-1Mo-1V合金的松弛特性,有利于制定残余应力消减工艺。根据Norton和Arrhenius方程计算了应力指数。通过应力指数和显微组织分析,阐明了应力松弛机理。在不同初始应力下,500 ℃时,位错的攀移和扩散主导了应力松弛过程;550 ℃时,位错滑移在应力松弛过程中起主要作用;600 ℃时,位错滑移、边界滑移和晶粒旋转控制着松弛过程。     

1Cr18Ni9钢螺旋压缩弹簧应力松弛机理

为了揭示1Cr18Ni9奥氏体不锈钢螺旋压缩弹簧的抗应力松弛性能优异的主要原因,在100、140、180和220 ℃下分别对弹簧进行了长达960 h的应力松弛试验。结果发现,经过松弛试验后,弹簧的自由长度变化较小。松驰温度为100 ℃时,在松驰过程中一阶段和二阶段间的拐点相较于其他松驰温度不明显,这是由松驰机理不同所导致的。此外,1Cr18Ni9奥氏体不锈钢螺旋压缩弹簧在100 ℃松弛时的塑性变形方式以位错的多滑移为主,而在更高的温度则以多滑移和孪生的方式发生塑性变形。     

回火温度对65Mn钢应力松弛性能的影响

测定了65Mn盘条经830℃淬火、380℃中温回火和540℃高温回火处理后的应力松弛曲线,并推导出应力松弛方程,利用透射电镜对松弛前后的形貌进行了分析,探讨了回火温度对应力松弛性能的影响.     

30MnSi预应力高强钢筋的热处理

通过感应淬火+张力回火的方法研究了30MnSi钢筋在PLC控制下的热处理工艺参数对钢筋力学性能与显微组织的影响。结果表明,随着淬火温度的升高,应力松弛率降低;回火温度对高强钢筋的应力松弛性能的影响较小;随着外加张力的增加,钢筋的应力松弛率降低。30MnSi钢筋适宜的热处理制度为900 ℃淬火+450 ℃回火,张力为15 MPa。     

回火温度对65Mn钢应力松弛性能的影响

测定了65Mn盘条经830℃淬火、380℃中温回火和540℃高温回火处理后的应力松弛曲线,并推导出应力松弛方程,利用透射电镜对松弛前后的形貌进行了分析,探讨了回火温度对应力松弛性能的影响。     

Thermomechanical fatigue mechanism in a modern single crystal nickel base superalloy TMS-82

Thermomechanical fatigue (TMF) in a 〈0 0 1〉 oriented nickel base single crystal TMS-82 superalloy was studied in an effort to clarify the mechanisms of stress relaxation and failure. Detailed observations of the microstructural evolution from the interior and outer surfaces of the specimens after TMF tests were made using transmission electron microscopy, scanning electron microscopy and optical microscopy. The stress relaxation took place during a hold time in compression at 900 °C, and the associated mechanisms varied with the following cycles. During TMF cycling, three stages of stress relaxations were identified: (1) primary stress relaxation; (2) steady stress relaxation; and (3) tertiary stress relaxation; each stage exhibits a distinct microstructural evolution. The first stage is related to the filling of dislocations in the γ channels; the second stage involves dislocation annihilation; and the final stage is associated with the de-twinning of deformation twins. The main crack was found to originate from the intersection of deformation twin plates with the specimen surface, and oxidation then assists the growth of the crack. The stress concentration at the crack tip results in a high density of deformation twins, and the propagation of the crack along the twin boundaries can lead to TMF failure of the specimen.     

Ta—O固溶体中的Snoek—Koster驰豫

试样表面镀一薄层Ｔｉ，消除内耗测最过程中氧吸附的影响．在镀Ｔｉ的Ｔａ—Ｏ试样中详细研究了Ｓｎｏｅｋ—Ｋｏｓｔｅｒ弛豫．观察到了两个内耗峰（较低温度的ＳＫ１峰和较高温度的ＳＫ２峰）．考查之退火温度和氧含量对内耗峰的形状和稳定性的影响．ＳＫ１峰和ＳＫ２峰的激活能分别为１．４和２．１ｅＶ．用Ｓｅｅｇｅｒ的螺位错上的双弯结成核和迁移以及几何弯结的迁移理论解释了实验结果．通过理论和实验比较，得到的螺位错上双弯结形成能约为０．９ｅＶ，螺位错与氧原子的结合能约为０．３ｅＶ实验还发现，进一步冷加工对Ｓｎｏｅｋ峰的影响在实验误差范围内，可以略去不计．     

Ta－O固溶体中的Snoek－K■ster弛豫

试样表面镀一薄层Ｔｉ，消除内耗测最过程中氧吸附的影响．在镀Ｔｉ的Ｔａ—Ｏ试样中详细研究了Ｓｎｏｅｋ—Ｋｏｓｔｅｒ弛豫．观察到了两个内耗峰（较低温度的ＳＫ１峰和较高温度的ＳＫ２峰）．考查之退火温度和氧含量对内耗峰的形状和稳定性的影响．ＳＫ１峰和ＳＫ２峰的激活能分别为１．４和２．１ｅＶ．用Ｓｅｅｇｅｒ的螺位错上的双弯结成核和迁移以及几何弯结的迁移理论解释了实验结果．通过理论和实验比较，得到的螺位错上双弯结形成能约为０．９ｅＶ，螺位错与氧原子的结合能约为０．３ｅＶ实验还发现，进一步冷加工对Ｓｎｏｅｋ峰的影响在实验误差范围内，可以略去不计．     

螺旋压缩弹簧的加速贮存行为研究

为评价T9A螺旋压缩弹簧的室温松弛特性,利用小吨位电子式万能材料试验机,对其在不同温度条件下进行高温压缩加速试验,研究弹簧的应力松弛行为。基于粘弹性体模型,揭示应力松弛过程中弹性应变向塑性应变的转化特性与塑性应变随松弛时间的变化规律。结果表明:螺旋压缩弹簧的应力松弛行为与标准的金属相似,均分为2个阶段;温度对第二阶段的松弛速率具有显著影响。基于应力松弛过程的热激活特性,建立T9A螺旋压缩弹簧的贮存寿命预测方程,并对弹簧的室温贮存寿命进行合理预测:在保持126 N的压缩载荷条件下,弹簧在25 ℃室温下,满足载荷损失率（?P/P）小于12%的贮存20 a的寿命要求。     

The influence of thermal annealing on residual stresses and mechanical properties of arc-evaporated TiCxN1−x (x=0, 0.15 and 0.45) thin films

We report the stress relaxation behavior of arc-evaporated TiC_xN_1−x thin films during isothermal annealing between 350 and 900°C. Films with x=0, 0.15, and 0.45, each having an initial compressive intrinsic stress σ_int=−5.4 GPa, were deposited by varying the substrate bias V_s and the gas composition. Annealing above the deposition temperature leads to a steep decrease in the magnitude of σ_int to a saturation stress value, which is a function of the annealing temperature. The corresponding apparent activation energies for stress relaxation are E_a=2.4, 2.9, and 3.1 eV, for x=0, 0.15, and 0.45, respectively. TiC_0.45N_0.55 films with a lower initial stress σ_int=−3 GPa, obtained using a high substrate bias, show a higher activation energy E_a=4.2 eV. In all the films, stress relaxation is accompanied by a decrease in defect density indicated by the decreased width of X-ray diffraction peaks and decreased strain contrast in transmission electron micrographs. Correlation of these results with film hardness and microstructure measurements indicates that the stress relaxation is a result of point-defect annihilation taking place both during short-lived metal-ion surface collision cascades during deposition, and during post-deposition annealing by thermally activated processes. The difference in E_a for the films of the same composition deposited at different V_s suggests the existence of different types of point-defect configurations and recombination mechanisms.     

多孔铜的阻尼性能研究

运用空气加压渗流法制备了直径约1.0 mm、孔隙率高达60%的多孔铜样品,并利用多功能内耗仪对材料的阻尼行为进行了研究。结果表明,多孔铜的阻尼能力比致密铜的阻尼能力有了很大提高,同时在内耗-温度谱上发现有两个内耗峰,分别出现在280℃和400℃左右,激活能分别是1.69 eV和2.30 eV。TEM分析发现基体晶界附近存在大量的位错。经分析认为,低温峰起因于位错与晶界交互作用所引起的对晶界粘性滑移限制,高温峰则由晶界弛豫引起。     

An experimental study of the formation of typical dislocation patterns in polycrystalline copper under cyclic shear

The typical slip patterns and dislocation substructures of polycrystalline copper under cyclic torsion were experimentally investigated. The cyclic stress–strain curve of the material consisted of three regions, resembling those of single crystal copper oriented for single slip. During the formation of persistent slip bands, cross slip bands between primary slip bands were often observed. Under cyclic torsion at a high shear strain amplitude, cross slip between slip bands of each slip system was an important process for the collapse of dislocation tangles into dislocation cell walls. During the transient stage of the formation of dislocation cells, the stress amplitude was inversely proportional to the average diameter of dislocation cells. This relationship is identical to that between the saturated stress magnitude and the corresponding dislocation cell size. The formation of typical dislocation patterns in copper under cyclic loading is closely associated with cross slip of screw dislocations.     

Motion of 1 0 0-tilt grain boundaries

The motion of planar symmetrical 1 0 0-tilt boundaries in high-purity aluminum was investigated in situ under the influence of an external mechanical stress field. It was observed that the motion of planar 1 0 0-tilt boundaries could be activated by an applied shear stress which acts perpendicular to the grain boundary plane. The motion of the grain boundaries is thermally activated so that we could derive the activation parameters for the motion from the in situ data of the mobility at different temperatures. A sharp transition between low angle grain boundaries and high angle grain boundaries was observed for the planar tilt boundaries at 8.6° which was apparent from a step change in the activation enthalpy for the stress induced grain boundary motion. The observed activation parameters for the stress-induced motion can be correlated to the activation parameters of self-diffusion for the motion of low angle boundaries and to the activation parameters of grain boundary diffusion for the motion of high angle grain boundaries. From these correlations, it seems obvious that the motion of planar low and high angle grain boundaries under the influence of a mechanical stress field can be attributed to the movement of the grain boundary dislocations which comprise the structure of the boundary.     

Motion of 〈1 0 0〉-tilt grain boundaries

The motion of planar symmetrical 〈1 0 0〉-tilt boundaries in high-purity aluminum was investigated in situ under the influence of an external mechanical stress field. It was observed that the motion of planar 〈1 0 0〉-tilt boundaries could be activated by an applied shear stress which acts perpendicular to the grain boundary plane. The motion of the grain boundaries is thermally activated so that we could derive the activation parameters for the motion from the in situ data of the mobility at different temperatures. A sharp transition between low angle grain boundaries and high angle grain boundaries was observed for the planar tilt boundaries at 8.6° which was apparent from a step change in the activation enthalpy for the stress induced grain boundary motion. The observed activation parameters for the stress-induced motion can be correlated to the activation parameters of self-diffusion for the motion of low angle boundaries and to the activation parameters of grain boundary diffusion for the motion of high angle grain boundaries. From these correlations, it seems obvious that the motion of planar low and high angle grain boundaries under the influence of a mechanical stress field can be attributed to the movement of the grain boundary dislocations which comprise the structure of the boundary.     

Dislocation accumulation and strengthening in Cu thin films

An analysis that addresses the strain-hardening behavior of thin metallic films on substrates is presented. Stress measurements were made on 0.5 μm thick Cu films on Si substrates during thermal cycling, during stress relaxation at room temperature (RT), and after quenching in liquid nitrogen. Significant strengthening was observed in the thermal cycle during cooling. The stress relaxation at RT shows a decrease of the stress from 360 MPa to 290 MPa within 15 months. A theoretical approach to the strengthening phenomenon is made on the basis of the Peach–Koehler dislocation-interaction forces. It shows that adding threading dislocations into a parallel array of dislocations at the film–substrate interface can contribute significantly to the strain hardening of thin films. The calculated strain hardening accounts for a large portion of the observed strengthening.