Ag颗粒增强复合钎料钎焊接头蠕变断裂及强化机理研究

测定了不同应力和温度下Ag颗粒增强复合钎料及基体钎料63Sn37Pb钎焊接头蠕变寿命,分析了Ag颗粒增强复合钎料及基体钎料钎焊接头蠕变断裂机理.表明:Ag颗粒增强复合钎料钎焊接头蠕变寿命优于基体钎料;Ag颗粒表面Ag-Sn金属间化合物形成及Ag颗粒对富Pb层阻碍作用是复合钎料钎焊接头蠕变性能提高的主要因素;钎焊接头Cu基板上一薄层富Pb相区形成是蠕变裂纹主要原因.     

Creep rupture and fatigue properties of transient liquid phase bonded joints of Ni base single crystal superalloy

Abstract

Creep rupture and fatigue properties of transient liquid phase (TLP) bonded joints of Ni base single crystal superalloy, CMSX-2, were investigated using MBF-80 insert metal. CMSX-2 was bonded at 1523 K for 1.8 ks in vacuum, which was determined as the optimum bonding condition. The (100) orientation of a bonded specimen was aligned perpendicular to the joint interface. The creep rupture strength and rupture lives of all joints were almost identical to those of the base metal. Elongation and reduction area values of joints were comparable to those of base metal, while creep rupture at high temperature was worsened. The low cycle fatigue properties of all joints were also the same as those of base metal. SEM observation of the fracture surfaces of joints after creep rupture tests revealed that the fracture surfaces were classified into three regions, and that the elongation and reduction of area values decreased sharply with increase in the area fraction of interfacial fracture surface.     

Creep of PE-10 nickel-base superalloy at 973 K

Creep data, at 973 K and stresses between 355 and 512 MPa, in flat specimens of PE-10 nickel-base superalloy are reported. The data have been interpreted in terms of a constitutive equation based on a creep model involving dislocation climb and cross-slip over the strengthening phase. Strain-rate sensitivity and apparent activation energy have also been measured and analysed in the frame of the proposed model.     

Creep behaviour of butt-welded joints

A theoretical investigation has been made of the strains accumulating in the steady state creep of butt-welded joints. This was done by using a refined plate theory-Cosserat plate theory. Appropriate constitutive equations were developed for the theory which correspond to standard uniaxial and three-dimensional equations. In particular, a choice of Norton's Law, $\text{? = Aσ}{}^{\mathrm{n}}$ was made. Then, the plane strain problem of a plate containing a weld of different mechanical and creep properties was solved for the case of tensile loading. Results were obtained both numerically and analytically for a wide range of parameter values: for different ratios of the creep strengths, $\text{A}$, of the parent and weld metals, for values of the index, $\text{n}$, (including the limit $\text{n}$ → ∞) and for values of the length, $\text{l}$, of the weld (including the limit $\text{l}$ → 0).     

Variation of the properties of thin-walled shells of AMg6 alloy after long-term service

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 79–83, March–April, 1990.     

Creep rupture and viscoelastoplasticity of polypropylene

Observations are reported on isotactic polypropylene in tensile tests with various strain rates, relaxation tests at various strains, and creep tests with various stresses at room temperature. Constitutive equations are derived for the viscoelastic and viscoplastic responses of semicrystalline polymers at three-dimensional deformations with small strains. The stress-strain relations involve eight material constants that are found by fitting the experimental data. The model is applied to the numerical analysis of creep failure of polypropylene under various deformation modes (uniaxial tension, equi-biaxial tension, shear, multiple-step creep tests).     

Increasing the service properties of weld joints by electrohydroimpulse treatment

Known examples of the positive influence of electrohydroimpulse treatment on the quality of weld joints of various steels, particularly including an increase in their long-term and cyclic strength and also corrosion resistance, are analyzed. It is shown that in this case there is a reduction in residual macro- and micro-stresses and also a change in the parameters of the dislocation structure of the joint metal in the direction of stabilization of it.Translated from Problemy Prochnosti, No. 4, pp. 119–123, April, 1996.     

Creep rupture of a phenolic-alumina particulate composite

The creep and creep rupture behaviour of a phenolic-alumina particulate composite was determined in an aqueous environment. Flexural creep tests were carried out in which the loading-point displacement was measured as a function of applied stress and time. The material exhibits power-law creep behaviour in which the steady-state creep rate is a power function of the initial applied elastic stress. The creep exponent was found to be 5.3. The creep rupture behaviour can be explained using a modified Monkman-Grant relationship which provides a failure criterion that is independent of applied stress and stress state.     

Creep crack growth in joints of a thermoplastic

An investigation of creep crack growth in butt heat fusion joints in a high density polyethylene (HDPE) is performed to quantify their life expectancy. Three point bend specimens containing a centrally located notched joint are used in creep crack growth tests at ambient and elevated temperatures. A quasi-nonlinear viscoelastic fracture mechanics model is used to deduce the crack growth histories from the measured load-point displacement histories. The initiation time for crack growth and the rate of crack growth are correlated with the stress intensity factor for combinations of initial crack lengths, applied loads and test temperatures. The elevated temperature data are shifted bidirectionally, utilizing shift functions derived from stress relaxation tests, to develop master curves for the initiation time and rate of crack growth. These master curves are used to predict the life of a girth joint containing an initial circumferential surface crack extending through 10 percent of the thickness of a pressurized pipe.     

Creep rupture studies of two alumina-based ceramic fibres

Creep rupture tests were performed in air on two polycrystalline oxide fibres (Al₂O₃, Al₂O₃-ZrO₂) using both filament bundles and single filaments. Tests were performed at applied stresses ranging from 50–150 MPa over the temperature range 1150–1250 °C. Under these conditions, creep rates for the alumina-zirconia fibre ranged from 4.12 × 10^–8–7.70 × 10^–6s^–1. At a given applied stress, at 1200°C, creep rates for the alumina fibre were 2–10 times greater than those of the alumina-zirconia fibre. Stress exponents for both fibres ranged from 1.2–2.8, while the apparent activation energy for creep of bundles of the alumina-zirconia fibre was determined to be 648 ± 100kJmol^–1. For the alumina-zirconia fibre, the two test methods yielded similar steady-state creep rates, but the rupture times were generally found to be longer for bundles than for single filaments. The steady-state creep behaviour of these alumina-based fibres is consistent with an interface-reaction-controlled diffusion-controlling mechanism.     

Creep deformation and rupture behavior of Alloy 617

A series of creep data was obtained from creep tests at different applied stresses at the temperatures of 850 °C, 900 °C, and 950 °C for Alloy 617, which is a leading candidate material for high-temperature components in Gen-IV nuclear reactor systems. The creep deformation and rupture behavior were investigated in terms of Norton's power law, Monkman–Grant relation (MGR), modified Monkman–Grant relation (MMGR), creep damage tolerance factor (λ), Zener–Hollomon Parameter (Z), and fracture behavior. Alloy 617 did not exhibit textbook creep behavior and revealed somewhat differences from typical heat resistant steels. The MMGR provided improved correlation between creep rate and rupture life in Alloy 617. The Z parameter obeyed a good agreement for a function of Z = 2.30 × 10³³ (σ/E)^5.87, and the same creep mechanism was operative within the ranges tested in the present study. The value of λ for Alloy 617 was found to be 2.40, and this was in agreement with materials exhibiting typical cavitation damage. The creep failure analysis revealed a dominant intergranular fracture mode, which proceeds via initiation, linking, and incorporation of the cavities.     

Creep damage in welded joints of 0.5CrMoV steel

The creep damage in two components along a main steam pipe in a fossil-fired power plant has been investigated using plastic replicas. Extensive damage in the weldedjoints was found in both components including several macrocracks. Out of eight analysedjoints, five showed significant damage. All stages of damage from single cavities to macrocracks were present. At a number of positions around thejoints damage was observed in the weld metal, the heat affected zone and the parent metal. For comparison cavitation was also examined in crossweld specimens from creep tests. Characteristic features of the cavitation in power plant were reproduced. In the heat affected zone adjacent to the parent metal a high density of separate cavities was observed. In the coarse grained part of the heat affected zone rows ofcavities were present in some grain boundaries.     

Creep behavior and in-depth microstructural characterization of dissimilar joints

Abstract

The 700 °C power plants currently under development will utilize Ni-base alloys such as alloy 617 for components to be operated at temperatures >650 °C. Due to economic reasons for components or parts of components which are subjected to temperatures <650 °C, 2% Cr or 9–12% Cr steels is used, depending on the required mechanical properties. This makes the dissimilar joining of Ni-base alloys and Cr steels a necessity in these plants. Experimental investigations show that these joints have to be identified as weak points with regard to damage development under creep and creep-fatigue loading. The present investigation focuses on welds between the alloy 617 and 2% Cr steel. Under creep load the fracture occurs near the fusion line between the 2% Cr steel base metal and alloy 617 weld metal. To explain the reasons for this fracture location, the microstructure of this fusion line was investigated using TEM and FIB techniques after welding and after creep loading. The TEM investigations have shown a small zone in the weld metal near the fusion line exhibiting chromium depletion and clearly reduced amounts of chromium carbides, leading to a weakening of this zone.     

Creep and long-term strength of herringbone lock joints of gas-turbine engines under the combined action of static and cyclic loads

We propose a method for the investigation of creep and long-term strength of statically and cyclically loaded elements of power-generating units. We present the results of numerical analysis of creep and fracture of herringbone lock joints of the blades of the second stage of gas-turbine engines as well as of their stress-strain state and accumulation of damage caused by creep. We determined the periods of time to the termination of the processes of latent and complete fracture of the investigated lock joints. It is shown that the effects of high-frequency cyclic loading on the relaxation of stresses, deformation, and fracture of the lock joint are significant. Kharkov State Polytechnical University, Kharkov, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 34 – 41, January – February, 1998.     

Creep rupture behaviour of low alloy ferritic steel weldments

To establish differences in rupture lives and ductilities between parent metal, weld metal and weldjoint, a commercial heat of lCrMoV cast steel welded with 21/4Cr1M0 steel electrodes was creep tested over a range of stresses at 550°C using constant load creep testing units. The results indicate that, while there is no significant variation in rupture lives, ductility in the weldjoint showed a decreasing trend over longer periods of testing. In weldjoint specimens that comprised parent metal, heat affected zone (HAZ) and weld metal, fracture occurred in the weld metal quite near to the fusion boundary over the entire range of stresses. The rupture ductility in the weldjoint was found to be lower than in parent or weld metal.

Scanning electron microscopy (SEM) revealed the fracture surfaces of parent and weld metal to be heavily dimpled, the dimples originating mostly around carbide precipitates, whereas the fracture surfaces of the weldjoint were found to be somewhat faceted.

The results of the present work suggest that weldments made with 2114CrlMo steel deposits possess comparable creep lives to the parent metal of 1CrMoV steel, and the weld metal in the weldjoint near the fusion boundary exhibits a tendency to embrittle over longer periods of testing.