Creep and creep fracture of polycrystalline copper

Normal creep curves are recorded over extended stress ranges at 686–823 K for fine-grain copper. Analyses of the curve shape variations, together with the results of stress change experiments, do not support the view that a transition from dislocation to diffusional creep mechanisms occurs with decreasing stress. Instead, the observed behaviour patterns suggest that dislocation processes are dominant at all stress levels. However, strain accumulation within the grains becomes progressively less important as deformation is increasingly confined to the grain boundary zones when the stress is reduced below the yield stress at the creep temperature. New approaches are then introduced for rationalization of creep rate and creep life measurements, which account for the data trends taken as evidence for major mechanism changes when the creep properties are described using power law relationships.     

Creep fracture in Al-SiC metal-matrix composites

Creep fracture behaviour of pure aluminium-matrix composites with 10–30 vol% SiC particulates at 623 K is reported. A comparison of tensile and compression creep data shows the existence of a transition stress. Above this transition stress no steady state creep is observed in tension. This transition stress is related to a transition from intergranular to transgranular fracture. The origin of transition stress is perhaps associated with the diffusional relaxation of stress concentration at the matrix/particle interface by lattice diffusion. The intergranular creep fracture of composites appears to be similar to that of unreinforced aluminium and it is power-law creep controlled. The transgranular creep fracture occurs by void nucleation and growth. The nucleation strain for voids is quite small and hence the tertiary stage starts before the end of the primary stage. The ductile fracture models overestimate the strain to fracture and do not predict the observed stress dependence of strain to fracture.     

Creep properties of sintered copper steel

The creep properties of sintered steel can be described by the normal creep laws. In particular, the activation energy for creep can apparently be identified with that for self diffusion even at temperatures far below 0.5 T _m. As might be expected the creep rupture strength of sintered steel is only a small percentage of its ultimate tensile strength. The creep rupture strength depends largely on the ductility and hence better strengths can be expected from alloys with larger ductilities.     

Creep of copper at cryogenic temperatures

The long-term creep behaviour of OFHC copper was investigated at 4.2 K and 77 K. At 77 K, steady-state creep was observed and the creep rates were tens of orders of magnitude higher than would be expected from extrapolations of ambient temperature creep data. The stress exponent obtained at 77 K is 2.2. The apparent activation energy at 77–90 K range is about 0.02 eV. At 4.2 K, transient creep was observed. TEM study of all crept specimens showed cell structures in support of the occurrence of substantial creep at cryogenic temperatures.     

Temperature dependence of fracture toughness in cleavage fracture of iron and iron alloys

In order to examine the temperature dependence of fracture toughness in cleavage fracture, exploratory work was carried out. Then effects of alloying elements and micro-structure on the low temperature fracture toughness were studied quantitatively in iron and iron alloys.The results indicate that (1) the relationship between fracture toughness G_ic and testing temperature T at low temperatures is G_ic = G_o exp (T/T_e), where G_e and T_o are the material constants; (2) G_o exhibits a stro dependence on solute carbon and nitrogen contents but is independent of micro-structure and other elements; (3) G_o values increases with increasing solute carbon and nitrogen contents; (4) T_o depends on the structure; (5) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with increasing nickel and manganese contents, to the contrary, decrease with increasing carbon, silicon and phosphorus contents; and (6) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with decreasing grain size.     

Viscoelastic phenomena in the fracture of thermosetting resins

Comparisons of stress–strain and fracture behaviour of thermosetting resins have shown viscoelastic non-linearity to be compatible with the complex fracture behaviour of thermosets. Fracture on a load controlled test machine has shown additional evidence that non-linearity is present in the material. This phenomenon is linked to previous studies of the fracture surface that have shown evidence of viscoelasticity in the formation of the surface texture. The proposed mechanism is consistent with a crack tip blunting model of stick–slip behaviour. Parallels are shown to exist between known thermoset fracture behaviour and phenomena observed in composite delamination studies.     

Spin-wave phenomena in liquid3He systems

The magnetic effects predicted by Leggett and Rice for Fermi liquids in the collisionless regime have been verified. Spin-echo measurements are reported which demonstrate the existence of spin waves and undamped spin currents in liquid³He and dilute³He-⁴He solutions. The experimental results are compared with the theoretical expressions of Leggett and Rice, and values of the Fermi liquid interaction parameter $$\lambda = \left[ {1/(1 + F_0^a )} \right] - \left\{ {1/[1 + (F_1^a /3)]} \right\}$$ are derived for three samples: liquid³He atP=0 and 27 atm, and a 6.4%³He-⁴He solution. In addition, some techniques for direct observation of individual spin-wave modes are explored and the results reported.     

Hydrogen bubbles in embrittled Al-Zn-Mg alloys

Al-Zn-Mg alloys become embrittled during exposure to moist environments due to hydrogen penetration of grain boundaries. The result of this hydrogen penetration due to surface reaction with water vapour of both bulk specimens and electron-transparent thin foils, has been studied at high resolution in the JEM 100 C transmission electron microscope as a function of alloy composition and ageing treatment. In bulk specimens of alloys solution-heated, water-quenched, and aged in water-vapour-saturated air at 70° C, the hydrogen is in the form of a mobile atomic species which is transformed to bubbles of molecular hydrogen under the action of the electron beam. However, in electron-transparent specimens of aged alloys after exposure to water vapour the accumulated hydrogen is observed directly as bubbles. These bubbles take the form of hexagonal lenses bounded by {111} planes, and are associated with grain-boundary precipitates, particularly in over-aged microstructures, and with primary intermetallic particles in alloys containing sparingly soluble transition elements. The consequence of the observed hydrogen penetration of grain boundaries in promoting environmental debilitation of mechanical properties and stress-corrosion cracking of Al-Zn-Mg alloys is discussed.     

Creep cavity observation using liquid metal embrittlement

• 1.1. To study grain boundary cavitation during creep, especially at early stages of cavity growth, new techniques are required.
• 2.2. A potential technique which, given the general susceptibility of most metals to LME attack, may be applicable to most metals involves (a) the preparation of a given microstructure, (b) exposing this material under load to liquid metal, (c) after cleaning away the LME agent, examining the intergranular fracture surface in the SEM.
• 3.3. An fcc solid-solution alloy, Ni-4 W, was chosen for study. Two liquid metals, lead and thallium, were found to be very strong embrittling agents for this alloy, and, perhaps other nickle-base alloys.
• 4.4. This alloy was cavitated during creep deformation, then exposed to liquid lead, allowing the grain boundary cavities to be examined, indicating promise as a quantitative technique to study the creep cavitation process.
• 5.5. Cavitation was found to be heterogeneous, with cavity concentration decreasing away from the specimen surface. This is consistent with an environmental, impurity-induced enhancement of cavity nucleation and/or growth near the surface.

     

Creep and creep fracture of commercial aluminium alloys

Using standard power law equations, creep rate and creep life measurements at 373–463 K are analysed for a series of aluminium alloys, namely, 2419, 2124, 8090 and 7010. The seemingly complex behaviour patterns are easily rationalized through a modified power law expression, which incorporates the activation energy for lattice diffusion in the alloy matrices (145 kJ mol⁻¹) and the value of the ultimate tensile stress at the creep temperature. By considering the changes in microstructure and creep curve shape as the test duration and temperature increase, all results are then interpreted straightforwardly in terms of the processes shown to govern strain accumulation and damage evolution. Moreover, the data rationalization procedures are also included in new relationships which superimpose the property sets onto sigmoidal ‘master curves’, allowing accurate prediction of the 100,000 h creep-rupture strengths of 2124 by extrapolation of creep lives determined from tests having a maximum duration of only around 1000 h.     

Correlation between Charpy impact energy and J fracture toughness for thermally embrittled reactor pressure vessel steel

Abstract

The Charpy impact energies of a reactor pressure vessel steel in the as received and several thermally embrittled conditions have been tentatively correlated to three J fracture toughness parameters derived under quasi-static loading regimen. Very good correlation has been achieved over the whole fracture resistance range of the structural steel, as obtained by the application of special heat treatments. It has been established that the parameters controlling the impact energy absorption capacity of the materials are the equivalent grain size of dual phase (ferrite/bainite) annealed microstructures and the bainite packet size of single phase quenched and tempered materials. The dependence of the Charpy impact energy of precracked, side grooved bend bars on the representative grain size of the microstructures tested has been disclosed as a Hall-Petch relationship.     

Simulation of iron fracture caused by a blast wave

A numerical simulation is made of the fracture of iron caused by a blast wave. The numerical method is described and results of calculations using a one-dimensional formulation of three qualitatively different explosion regimes are presented. Pis’ma Zh. Tekh. Fiz. 23, 33–39 (May 12, 1997)     

Low temperature fracture properties of DIN 22NiMoCr37 steel in fine-grained bainite and coarse-grained tempered embrittled martensite microstructures

An as-received (AR) DIN 22NiMoCr37 nuclear reactor pressure vessel steel has been heat treated for 1 h at austenitising temperatures of 1373 and 1473 K to obtain different austenite grain sizes. After austenitising, the samples were water quenched, tempered for 2 h at 923 K, water quenched and then held isothermally at 793 K for 180 h before final air-cooling. The AR condition had a tempered bainite microstructure and a prior austenite grain size of 30 μm, whereas the heat treated conditions were tempered martensite and had a prior austenite grain size of approximately 100 μm for the 1373 K condition and ‘extraordinary’ large austenite grains (>1 mm diameter) for the 1473 K condition. Their low temperature fracture properties were determined and were related to the susceptibility to segregation induced embrittlement. Despite the heat treated conditions having a larger prior austenite grain size compared to the AR condition, at a given testing temperature, the tempered martensitic 1373 K condition generally exhibited higher strength and higher fracture toughness values at 123 K. The heat treated conditions generally exhibited higher local fracture stress (σ_f) values in 0.2 mm blunt notch SE(B)-0.4T specimens at 123 and 77 K.     

Mass transport phenomena in copper nanowires at high current density

Electromigration in Cu has been extensively investigated as the root cause of typical breakdown failure in Cu interconnects. In this study, Cu nanowires connected to Au electrodes are fabricated and observed using in situ transmission electron microscopy to investigate the electro- and thermo-migration processes that are induced by direct current sweeps. We observe the dynamic evolution of different mass transport mechanisms. A current density on the order of 10⁶ A/cm² and a temperature of approximately 400 °C are sufficient to induce electro- and thermo-migration, respectively. Observations of the migration processes activated by increasing temperatures indicate that the migration direction of Cu atoms is dependent on the net force from the electric field and electron wind. This work is expected to support future design efforts to improve the robustness of Cu interconnects.

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碘量法快速测定铁矿石中的铜和铁

通过三大强酸分解试样,考虑到在共存离子影响的情况下,提出了用碘量法同时测定铁矿石中的铜和铁的新方法：通过对反应机理的分析,得出最佳的实验条件和分析方法,利用本方法多次对铁矿石中的铜和铁进行测定分析,所得结果的相对偏差均小于4．0％。该方法具有准确,快速,简便,稳定性好等特点,适用于同时测定不同铁矿石矿种中铜和铁的含量。