喷射成形粉末高温合金FGH4095M的制备及组织特征

喷射成形是一种近净成形的在粉末冶金气体雾化制粉技术基础上发展起来的快速凝固技术. 本文采用喷射成形技术制备成分优化后的FGH4095M合金, 研究了喷射成形FGH4095M合金沉积坯的致密度、显微组织特征, 特别是研究了喷射成形高温合金组织中特殊形貌的γ’相. 研究表明, 致密度与沉积坯部位有关, 底部致密度最高, 可达99.63%, 热等静压后的致密度可达100%. 喷射成形合金组织以均匀细小的等轴晶为主, 不存在原始颗粒边界; 一次γ’ 相尺寸约为0.6-0.8 μm, 二次γ’相尺寸约为0.1-0.5 μm, 在二次γ’相的间隙中有少量尺寸约为10-20 nm的三次γ’相. 喷射成形FGH4095M 合金中的二次 γ’相中出现特殊形貌的γ’相, 这是由单个γ’颗粒分裂形成, 与沉积过程的低冷却速度有关. 分裂过程是γ’颗粒总能量降低的过程, γ’颗粒间的弹性交互作用能起到主导作用. 对分裂γ’相的等效直径进行统计, 得到γ’ 相等效直径超过0.40 μm 后, 会出现分裂趋势. 合金具备优异的拉伸性能, 室温塑性得到显著提高, 出现γ’ 相分裂的特殊形貌组织是否对合金性能的提高产生直接影响仍需进行进一步的研究.     

氮气喷射成形FGH4095的组织特征

以氮气为雾化气体采用喷射成形工艺制备了FGH4095高温合金沉积坯, 记录了沉积过程坯体表面温度曲线, 并采用定量金相法、排水法测试了坯体致密度, 观察了坯体晶粒及γ'相的形貌. 结果表明采用氮气作为雾化介质进行喷射成型喷射沉积坯基体致密度可达99%以上, 但也存在着较大的(1—2μm)的气孔, 经热等静压和近等温锻后宏观气孔闭合, 氮以尺寸不超过1 μm的碳氮化物形式存在. 喷射沉积坯以等轴晶组织为主, 坯体内部平均晶粒尺寸约为20—40 μm, 近表面区域晶粒较细, 约为13 μm; 一次γ' 相多数呈尺寸约0.3—0.5 μm不规则块状形貌. 喷射成形坯组织结构的形成与喷射成形过程的降温过程有密切关系.     

喷射成型FGH4095静态再结晶组织特征

为了研究喷射成型FGH4095高温合金经热等静压、近等温锻后固溶热处理的组织特征,采用喷射成型高温合金,经1170℃,120 MPa,3 h热等静压和75%压缩量的近等温锻,经1120℃,1140℃,1160℃保温10,20,40 min固溶热处理,再经油淬后研究其再结晶过程及晶粒尺寸、析出相的变化规律.结果表明,固溶温度强烈影响静态再结晶过程及固溶后的组织.在1120℃下固溶20 min,由于区域化的不完全再结晶,可形成项链组织;1140℃下固溶40 min可基本完成再结晶,并得到细化的再结晶组织,平均晶粒尺寸约为8μm;1160℃下固溶10 min即可基本完成再结晶,晶粒尺寸长大到约18μm.     

考虑相变的热弹塑性本构方程及其应用

将在热加工及热处理过程中发生相变的材料考虑为热弹塑性的多相混合物,基于连续介质物理学及含内变量的不可逆热力学,推导出考虑相变的热弹塑性本构方程.根据一组不同温度水平下的高温短时拉力试验,确定本构方程中的材料参数及其随温度的变化关系.同时,提出了考虑相变的热传导方程和计及应力影响的相变动力学方程.基于这些方程编制相应有限元分析程序,用其分析计算了1Cr12WMoV不锈钢管通的焊接残余应力分布.计算所得结果与通过X射线衍射测试的实验结果具有较好的一致性. 关键词： 相变 热弹塑性 本构方程 焊接     

钨合金的高压本构研究

通过静高压实验、动高压实验及理论计算相结合的方法，确定了钨合金的一种高压本构方程 （Steinberg模型方程）中的各参数.用数值模拟计算方法，采用几种不同的本构模型进行了 计算，并与实测结果进行了比较.结果显示，确定的高压本构方程计算值与实测值符合最好. 关键词： 高压本构方程 Steinberg 模型 数值模拟计算 粒子速度波形     

从热质理论到能质理论

现有流变学本构方程大多是基于唯象模型或者通过对线性定律进行修正而导出的,物理意义不够清晰。本文借鉴热质理论,提出连续介质微元的动能同样具有当量质量,可以用能质控制方程导出普适动能输运定律。普适动能输运定律在不同问题背景下,可以导出牛顿黏性定律,胡克定律以及流变学中较为基础的线性黏弹性本构方程。能质理论推导流变学本构方程的过程是基于第一性原理,不仅物理意义清晰,而上揭示了热输运与动能输运之间的内在统一规律。     

Spray forming and mechanical properties of a new type powder metallurgy superalloy

The deposited billet of a new type powder metallurgy(PM) superalloy FGH4095 M for use in turbine disk manufacturing has been fabricated using spray forming technology. The metallurgical quality of the deposited billet was analyzed in terms of density, texture, and grain size. Comparative research was done on the microstructure and mechanical properties between the flat disk preform prepared with hot isostatic pressing(HIP) and the same alloy forgings prepared with HIP followed by isothermal forging(IF). The results show that the density of the spray-formed and nitrogen-atomized deposit billet is above 99% of the theoretical density, indicating a compact structure. The grains are uniform and fine. The billet has weak texture with a random distribution in the spray deposition direction and perpendicular to the direction of deposition.A part of atomizing nitrogen exists in the preform in the form of carbonitride. Nitrogen-induced microporosity causes the density reduction of the preform. Compared with the process of HIP+IF, the superalloy FGH4095 M after HIP has better mechanical properties at both room temperature and high temperature. The sizes of the γphase are finer in microstructure of the preform after HIP in comparison with the forgings after HIP+IF. This work shows that SF+HIP is a viable processing route for FGH4095 M as a turbine-disk material.     

基于孔洞体胞模型铸造镁合金ML308的本构方程

铸造镁合金不可避免地包含许多微孔洞,这些微孔洞在材料的后续加工及服役过程中将发生演化,并对材料的力学行为产生重要影响.基于球形孔洞体胞模型,提出微孔洞长大及形核方程,它们构成微孔洞的演化方程.根据孔洞演化将造成材料性质弱化的物理机制,将微孔洞演化以弱化函数的形式引入到非经典弹塑性本构方程,得到考虑孔洞演化的铸造镁合金弹塑性本构方程.发展与本构方程相应的有限元数值分析程序,用其模拟了铸造镁合金ML308的微孔洞演化及力学行为,计算结果与实验结果符合较好. 关键词： 铸造镁合金 孔洞体胞模型 孔洞演化方程 本构方程     

炸药爆轰的连续介质本构模型和数值计算方法

假定炸药和爆轰产物处于局部热力学平衡状态, 即它们的压力和温度相同, 利用热力学基本关系建立炸药爆轰过程的连续介质本构模型的一般理论框架. 在此框架下, 炸药爆轰本构模型由一组常微分方程构成, 包括炸药和爆轰产物的状态方程、简单混合法则、化学反应速率方程和能量守恒方程, 易于由成熟的计算方法如梯形法等进行求解. 一组广义Maxwell型非线性固体本构形式的微分方程描述了压力和温度随时间的演化速率与应变率和化学反应速率的关系, 借助简单混合物理论, 其中的系数由炸药和爆轰产物的材料参数确定. 未反应的炸药和爆轰产物采用JWL状态方程, 化学反应率方程采用Lee-Tarver点火-燃烧二项式模型, 模拟PBX-9404炸药的一维冲击波起爆过程和爆轰波传播过程. 计算结果表明了本文给出的本构模型和相应计算方法的有效性. 关键词： 炸药爆轰 本构模型 化学反应率方程 数值模拟     

正交各向异性材料的三维动态本构模型及其在脉冲X射线热击波模拟中的应用

基于三维应变条件下的应力-应变关系,利用Grüneisen物态方程、PUFF物态方程以及Tsai-Hill屈服准则和Johnson-Cook强度模型,建立了正交各向异性复合材料的三维动态本构模型。在此基础上,对一种碳酚醛材料在高能脉冲X射线辐照下所产生的热击波传播现象进行了三维模拟,得到了热击波模拟结果,并将各向异性本构模型与各向同性本构模型的模拟结果进行对比。分析表明,各向异性本构模型不仅反映了固体材料各向异性的特点,而且还能描述材料转变为气体后的动力学行为。模型的建立为各向异性复合材料在脉冲辐照环境下的应用打下重要的理论基础。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.