The application of an approximate analysis of the diffusion process for a description of creep and creep rupture

An analysis of the environmental effect on creep and creep rupture of metals is presented. It is pointed that the investigation of the diffusion processes leads to significant computational difficulties. These difficulties arise on representing the solution of the diffusion equation with variable boundaries in the form convenient for analysis.The process of damage accumulation is modelled for a material, which is subjected to the combined action of mechanical loads and the aggressive environment. The Rabotnov kinetic theory is applied in which two parameters are taken into account: the damage of the material and the concentration of chemical elements reducing the resistance of the material to mechanical loads. An approximate solution of the diffusion equation is suggested for rod or shell subjected to axial tension. This solution is based on dividing the cross-section of rod or shell into the disturbed and undisturbed parts and determining the motion of the boundary between these parts. The system of constitutive equations which describe the interaction between the diffusion and rupture fronts during the creep process until failure is obtained. A good quantitative agreement between experimental and theoretical results has been received.     

FORMATION OF AMORPHOUS Al_(80)Fe_(20)BY MECHANICAL ALLOYING

Amorphous Al_(80)Fe_(20) powder which can hardly be obtained using conventional rapid quenchingtechnique was directly prepared from crystalline Fe and A1 powders by means of mechanicalalloying process.The amorphization process was examined by X-ray analysis and M(?)ssbauerspectroscopy,and the thermal behaviour was studied by DSC.The results show that the rateof amorphization is controlled by the diffusion reaction at the interfaces and changes with themilling time.The effect of milling conditions on amorphization by mechanical alloying was al-so investigated.     

船用大型螺旋桨材料研究的进展

本文综述了大型船用螺旋桨材料的最新研究进展,包括桨叶失效分析。实用热处理技术以及满足铸态船用螺旋桨冲击韧性和強度的铝、锰含量。     

PHASE DIAGRAM OF Nd-Pd(Nd≤50at.-％) BINARY SYSTEM

采用X射线衍射,示差热分析和金相等方法研究了Nd-Pd系相图中含0—50at-％Nd的区域。发现在该区域内存在6个金属间化合物:NdPd_5,NdPd_3,NdPd_2,Nd_2Pd_3,Nd_1Pd_5和NdPd。其中,NdPd_3,Nd_4Pd_5和NdPd是固液共熔化合物。还测出NdPd_5为SmPt_5型结构,NdPd_?为AuCu_3型结构,低于708±4℃的NdPd为CrB型结构。在该区域内共有3个共晶反应和3个包晶反应。     

大气腐蚀的模拟加速试验方法研究(摘要)

大气腐蚀的模拟加速试验方法研究(摘要)金蕾,唐其环,彭长灏,牟献良(中国兵器工业第五九研究所,重庆630039)试样材料为20fi4比学成分《ql.):C017SI020.Mfl04(1.P001,50017,Cfl002、N1001.Cll001、A1001试验方法采用表1列出的加速试验TablelAcceleratedtestingconditions!相关性由于本研究中只m了一种材料,因此不能采用相关系数法定量计算,对相关性只作定性评价1刽1、2分别是加速试验和户外暴露试验结果从图中曲线看,加速试验     

ICP－AES法对Pt－Pd－Rh－RE合金中各组分的同时测定

研究了ＩＣＰ─ＡＥＳ法对ＰｔＰｄＲｈ、ＰｔＰｄＲｈＣｅ、ＰｔＰｄＲｈＹ合金中Ｐｄ、Ｒｈ、Ｃｅ、Ｙ的同时测定方法。通过对同一样品不同测定方法对照，认为本方法简便、快速、适用性广。本法测定的范围是；Ｃｃ、Ｙ０．１～１％；Ｒｈ０．６～６％；Ｐｄ２～２０％。相对误差最大为２％，变差系数＜１％。     

Thermodynamic analysis of inclusion in weld

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Finite-element simulation of moving induction heat treatment

An efficient finite-element procedure with a remesh scheme has been developed for the analysis of the moving induction heat treatment process, wherein relative motion occurs between the coil and the workpiece. In this procedure, the magnetic field is first simulated by using an updated mesh that tracks the moving coil position; the moving heat source within the workpiece material is derived from the magnetic field. The heat equation is then solved to obtain the temperature field created by the heat source. The procedure has been applied to calculate the temperature distributions in 1080 carbon steel cylinders during induction heating. The calculations have been validated by comparison with analytical solutions for the temperature distribution obtained using Green’s function methods. Finally, the temperature, residual stress, and microstructure distributions in quenched 1080 steel cylinders have been obtained using the finite-element procedure. Quenching of the heated cylinders, by both a moving cooling ring and a stationary liquid bath, has been analyzed. The finite-element procedure presented incorporates temperature-dependent material properties, phase transformations occurring in the 1080 steel, the change in magnetic permeability of the 1080 steel at the Curie temperature, and an elastoplastic stress model based on a mixed hardening rule. The simulation results demonstrate that the finite-element procedure could be applied to a variety of moving induction heat treatment problems to determine the residual stress and microstructure distributions in the heat-treated component. It also could be used in the design of process parameters and coils.     

Microstructures and Properties of Laser-Glazed Plasma-Sprayed ZrO2-YO1.5/Ni-22Cr-10AI-1Y Thermal Barrier Coatings

Thermal barrier coatings (TBCs) consisting of two layers with various yttria contents (ZrO ₂- YO_1.5/Ni-22Cr-10Al- lY) were plasma sprayed, and parts of the various specimens were glazed by using a pulsed CO₂ laser. All the specimens were then subjected to furnace thermal cycling tests at 1100 °C; the effect of laser glazing on the durability and failure mechanism of the TBCs was then evaluated. From these results, two models were developed to show the failure mechanism of as- sprayed and laser- glazed TBCs: model A, which is thermal-stress dominant, and model V, which is oxidation-stress dominant. For top coats containing cubic phase, cubic and monoclinic phases, or tetragonal and a relatively larger amount of monoclinic phases, whose degradation is thermal- stress dominant, laser glazing improved the durability of TBCs by a factor of about two to six. Segmented cracks that occurred during glazing proved beneficial for accommodating thermal stress and raising the tolerance to oxidation, which resulted in a higher durability. Thermal barrier coatings with top coats containing tetragonal phase had the highest durability. Degradation of such TBCs resulted mainly from oxidation of the bond coats. For top coats with a greater amount of monoclinic phase, thermal mismatch stress occurred during cooling and detrimentally affected durability.     

A critique of internal oxidation in alloys during the post-wagner era

Wagner's classical treatment of internal oxidation (generic name allowing for reaction with oxygen, nitrogen, carbon or sulfur) assumed ideal conditions such as uninhibited dissolution of the gas, formation of spherical particles, diffusion of the oxidant in the solvent as the rate-controlling step, equilibrium conditions, etc. However, during the 45 years since his treatment, many observations have been made to complicate the idealized situation suggested by Wagner. This paper examines the most important modifications with respect to Wagner's original analysis. The following items are discussed. (a) The role of solute concentration: The parabolic kinetics are much higher than expected for Ni–Al alloys due to rapid interfacial diffusion of oxygen along the interfaces between cylindrical rods of Al₂O₃ (perpendicular to the surface) and the matrix. (b) Precipitate morphology: Spherical precipitates seem almost to be the exception. A wide variety of forms have been observed, including Widmanstätten platelets, cylindrical rods, hexagonal plates, dendritic or fishbone products, etc. The competition between nucleation and growth is useful to explain the observed structures. (c) Intergranular internal oxidation: Rapid oxygen diffusion in grain boundaries may lead to a wide variety of intergranular-precipitate structures. (d) Internal-oxide bands: Wavy, approximately parallel bands form at a finite distance beneath the surface in certain alloys having very reactive solutes, e.g., Ag–Mg. It is postulated that high stresses generated by precipitation play a major role. (e) Surface nodules of pure solvent metal: High stresses generated during precipitation cause extrusion of solute through dislocation pipes, leading to extensive nodule formation on either grain boundaries or on the grains (or both), depending on the alloy and oxidizing conditions. (f) Nonstoichiometric precipitates: Either hypo- or hyperstoichiometric particles can form as very small clusters in certain alloys (Ag–Al). The nature of precursors and changes in stoichiometry during reaction are discussed. (g) Trapping of oxidant: Diffusion of the oxidant may be slowed appreciably by trapping with the solute, although no precipitates need to form. Lower-than-expected kinetics (based on normal diffusivities of the oxidant) result. (h) High-solubility-product precipitates: Concentration profiles of solute, oxidant and precipitate are quite different than those expected for low-solubility-product precipitates as considered by Wagner. In particular, a variable mole fraction of precipitate exists, and further precipitation occurs in the reaction zone after the front has passed by. Linear kinetics have been observed for some Nb-base alloys at very high temperatures and low oxygen pressures. The rate-controlling step is the arrival of oxygen at the surface and not oxygen diffusion in the metal. (i) Dual oxidants: Two gases may diffuse·simultaneously and each forms its own product with the solute. The thermodynamically most-stable compound forms near the surface, and the less-stable compound deeper in the alloy. The less-stable compound is subsequently converted to the more-stable compound with a concomitant release of the second oxidant. Although numerous examples have been reported of systems which do not behave as predicted by Wagner, his theory still remains as the cornerstone of our understanding and is still the starting point for virtually every study in internal oxidation.