Creep Of Copper Research Articles

Grain size effects during creep of copper

Results for copper single crystals and polycrystals, analysed with data for other metals and alloys, contradict the assumption that dislocation creep processes are grain size independent so the creep rate increases rapidly with decreasing grain diameter only when diffusional mechanisms are dominant at low stresses.

Participation of non-compact dislocation glide in creep of copper at high temperatures

A possible participation of dislocation glide in non-compact crystal planes of copper in the high temperature creep process is assessed by means of values of activation energy. The activation energy of creep was determined alternatively from conventional data analysis, from the concept of effective and internal stresses applied to steady-state creep, and from constant-structure creep data. The results are discussed and compared with activation enthalpies of the {001} and {110} glide calculated from the kink-pair model. The calculated values are higher than the activation enthalpy of lattice diffusion. However, the activation energy of creep, which is lower than the value for lattice self-diffusion indicates rather a participation of a process with a lower activation energy than of the relatively difficult non-compact glide.

Radiation-induced creep of copper, aluminium and their alloys

The results of creep studies on copper, aluminium and their alloys with and without neutron irradiation are presented. The experiments are carried out at the WWR-K reactor at the neutron of 1.4 · 10 16 n/m 2 · s (2.5 · 10 16 n/m 2 · s, E > 0.1 MeV). Polycrystalline copper (99.99 and 99.95%), aluminium (99.99%) and the alloys of copper with 4 at% of titanium, of aluminium with 4.2% of copper are studied within the temperature interval 0.31–0.51 T m.

Constant structure creep of copper at 973K

The results from studies indicate there is no change in the constant structure glide kinetics of copper across the 673 to 973K temperature range. The values of the obstacle strength parameter, g{sub o}, are in the range of 0.701 and 0.785, which is characteristic of medium strength obstacles such as forest dislocations. Also, the true activation area results are in agreement with the results of other FCC metals,a nd are of the order expected for forest dislocation cutting. The linear relationship between {beta} and {mu}(T)/T{sigma} does not change in this temperature range, and is in good agreement with the results from other FCC metals. Most importantly, the values of {Delta}G are similar across all of the temperatures and lie in the range of 112 to 123 kJ/mole. A good correlation exists between {Delta}G and the activation energies for creep reported by Barrett and Sherby, 117 kJ/mole, and Feltham, and Meakin, 125.5 kJ/mole, for the temperature range of 673 to 873K. The results of these constant structure creep tests demonstrate that there is no change in the dislocation glide kinetics over the temperature rage 673 to 973K.

Metallurgical reactions at the interface of Sn/Pb solder and electroless copper-plated AlN substrate

Intermetallic formation between electroless-plated copper and Sn/Pb solder is investigated. An interlayer is formed between copper and solder, and segregation of Pb-rich and Sn-rich phases are observed. X-ray diffraction and EDX analysis results suggest that the major intermetallic formed in the interlayer is Cu/sub 6/Sn/sub 5/. For the as-plated sample, the adhesion strength of Cu to the AIN substrate after 150/spl deg/C aging is affected by both the recrystallization and the creep of copper. For the soldered specimen, the presence of intermetallic compound causes cracks to propagate along the intermetallic/Cu interface and results in a decrease of the adhesion strength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of unloading time on interrupted creep in copper

The effect of unloading time on the interrupted creep behaviour of polycrystalline copper specimens was investigated over the temperature range 298–773 K. Up to 553 K, cyclic creep acceleration could be explained in terms of deformation and hardening using a dislocation glide model with recovery during unloading being due to dislocation climb. At higher temperatures, recrystallisation effects probably influence behaviour.

Creep of copper in the temperature range 423–623 K

Abstract The creep of copper in the temperature range 423–623 K was investigated and creep curves modelled by combining semi-empirical equations describing deformation and damage. Previous work has indicated that in this temperature range there is a change in the creep behaviour which is usually ascribed to a change in deformation mechanism from power law creep to power law breakdown. Evidence for this change comes mostly from measurements of steady state creep behaviour which does not account for the possibility of creep damage during testing. The purpose of this investigation is to demonstrate that if the creep curve is viewed as a whole, i.e. deformation and damage are considered simultaneously, the transition in behaviour can just as well be described in terms of a single deformation mechanism with a change in the dominant fracture mechanism.

Evidence for Nabarro-Herring creep in metals: fiction or reality?

It is shown that all creep data in metals ascribed to the Nabarro-Herring (N-H) diffusional creep mechanism cannot in fact be definitively described by the N-H creep theory. Rather, the creep mechanism is associated with either Harper-Dorn (H-D) dislocation creep or grain boundary sliding (GBS). Specific responses are presented to work by Fiala and Langdon (F-L) who have presented opposing views to the above conclusions. Creep data for copper used by F-L to support N-H creep are shown to be incompatible with the theory, since the experimental creep rates are about three orders of magnitude higher than predicted. The copper creep data, however, can be predicted by phenomenological equations for GBS and H-D creep. It is concluded that as long as rigorous and physically sound theories for creep controlled by GBS and H-D creep are not forthcoming, researchers will continue to use, erroneously in the authors' view, the N-H diffusional creep mechanism to explain low stress creep behavior of polycrustalline solids.

Effect of temperature on the grain boundary movements during creep in copper and a copper-zinc alloy

Previous work by the present authors [1] showed that the presence of second phase particles of zinc at the boundaries of copper grains blocked the absorption of lattice dislocations by these boundaries during sliding at steady state creep. This was detected from measuring the sensitivity parameter of the steady creep rate to the applied stress at wide range, either for pure copper or for copper 28 wt% zinc solid solution. In this work we cansider the effect of temperature and accordingly the redistribution and diffusion of these zinc atoms at the copper grain boundaries on this blocking phenomenon. It was found that changing the temperature from 200°C to 400°C did not alter the suppression of grain boundary movements and, accordingly, their cooperation to creep deformation was also suppressed.

Creep behavior of copper at intermediate temperatures—II. Surface microstructural observations

Detailed microstructural observations reveal the formation of three types of slip features during creep of copper at intermediate temperatures between 0.46–0.72 Tm, where Tm is the absolute melting point. Single slip occurs at the higher temperatures and lower stresses with the slip lines being inhomogeneously distributed among the grains at the lower strains. Complex wavy slip features are observed at the higher temperatures, higher stresses and with increasing strains, thereby suggesting that cross-slip mechanisms may be important under these conditions. The absence of these slip patterns at the lower temperatures and higher stresses, when mainly multiple slip morphologies are observed, suggests that cross-slip mechanisms are likely to control the creep of polycrystalline copper only in a limited range of stresses and temperatures.

Creep of copper under constant structure conditions

The purpose of the present paper is to apply the techniques developed for the analysis of data for pure aluminum to the constant structure creep behavior of pure copper. Based on a comparison of the results for aluminum and copper, it is suggested that stacking fault energy may influence structure evolution and thereby affect the kinetics of dislocation glide past intermediate strength obstacles

Creep, high-cycle fatigue and cyclic creep in copper at 500°C: Lukas, P., Kunz, L. and Sklenicka, V. Res. Mech. 1990 29, (4), 345–358

Short fatigue crack growth behavior was investigated. The crack growth was monitored using a replica technique for cracks propagating on the specimen notch from an initial length of 40–50 μm to the specimen thickness of 2.3 mm. As part of the AGARD round robin test program Al 2024-T3 and Al 7075-T6 specimens with semi-circular notches on one edge were tested under R-ratios of 0.5, 0, −1 and −2. For each R-ratio several stress levels were used. In order to compare the behavior of short and long cracks, their crack growth rate data were drawn on the same graph. The general conclusion for both aluminum alloys is that the growth rates of short cracks were faster than the rates of long cracks for R-ratios of −1 and −2, no significant differences were observed for R = 0, and the short cracks actually grew more slowly at R = 0.5.

Temperature dependence of the in-reactor creep of copper and aluminum

Temperature dependence of the in-reactor creep of copper and aluminum

Apparent activation volume for creep of copper and alpha brass at intermediate temperatures

Experimental measurements of the apparent activation volume for creep,V*, of Cu and Cu-30% Zn conducted at intermediate temperatures showed two types of strain dependencies. At the lower temperatures and higher stresses,V* decreased with increasing creep strain, e, while at higher temperatures and lower stresses,V* was essentially independent of strain. The low temperature-high stress behaviour for Cu and Cu-30% Zn was found to be consistent with the dominance of a dislocation intersection mechanism. The high temperature-low stress data for the pure metals suggest that the rate-controlling process involves the nonconservative motion of jogs on screw dislocations. For the latter conditions, an additional contribution from solute drag-limited dislocation glide also appears to be important in governing the creep behaviour of the alloy.

Kinetics of room temperature primary creep in copper and aluminium

Kinetics of room temperature primary creep in copper and aluminium

Influence of gas bubbles on creep of copper under small shear stresses

AbstractIt is known that gas bubbles on grain boundaries may grow under small applied tensile stresses and an important factor, particularly at low stress levels, is the contribution that this growth makes to the creep strain. Bubble growth also requires accommodation by volume expansion and bubble coarsening phenomena may add to further dilation. The purpose of the present experiments was to eliminate these further variables by using specimens in the form of helical coils so that the creep rate of copper could be determined under small shear stresses for material of a constant grain size with and without intergranular bubbles. Under the conditions described, the creep rate with gas bubbles is three times greater than that without gas bubbles. This can be interpreted in terms of the creep strain arising from grain boundary diffusion controlled bubble growth with consequent atom plating on grain boundaries nearly perpendicular to the tensile stress component, with the converse situation of bubble shrinkage...

Influence of gas bubbles on creep of copper under small shear stresses

Influence of gas bubbles on creep of copper under small shear stresses

Creep of copper at cryogenic temperatures

Abstract 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.

On the formation of magistral crack in high temperature creep of copper

On the formation of magistral crack in high temperature creep of copper

Long-term creep of copper at cryogenic temperatures

The equipment designed and used in this study basically consists of a constant load lever arm creep machine, a vacuum thermally isolated cryostat that is cooled by a low rate of cryogen flow, and a testing to transmit the load onto the specimen. Briefly, Figure i shows the tensile testing insert and the cryostat schematically. The tensile testing insert consists of the pull rod, the compression tube, and the specimen grips. The temperature of the specimen can be controlled with an accuracy of +l°K. The strain of the specimen was measured directly using a strain gage technique, which is capable of resolving +1 uc on the specimen. Typical creep results at 77K and 34.5 MPa initial applied stress are given in Figure 2. There is no indication of the exhaustion of creep strain when the test was terminated at i00 hours. Indeed, a steady-state creep behavior rather than a logarithmic creep claimed in another study of copper (8) was observed. The derivative of the creep curve, i.e., strain rate versus time, is also plotted in Figure 2. The onset of the steady-state region, as shown by the minimum creep rate, was determined to occur at 75 hours. The steady-state creep rate was 4 x 10 -11 sec -I. From these results, it can be concluded that long-term creep testing (about 100 hours) is necessary to study the creep behavior of materials at very low temperatures. With the current ability of conducting long-term cryogenic creep tests, more creep data will be generated to systematically investigate the long-term low temperature creep behavior of OFHC copper and other materials at the 77 K range and at 4.2K. Acknowledgments The authors wish to thank the International Copper Research Association (INCRA) and Dr. L.M. Schetky, the Technical Director, for supporting this program. We also are grate