Superplastic Behavior of the Sn-Pb Eutectic in the As-Worked State
01 Jan 1982-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 13, Iss: 1, pp 53-58
TL;DR: In this article, the superplastic behavior of the Sn-Pb eutectic was studied in the as-worked state by mechanically working the cast material to varying degrees.
Abstract: Superplastic behavior of the Sn-Pb eutectic was studied in the as-worked state by mechanically working the cast material to varying degrees. The flow behavior was explored in the temperature range of 298 to 443 K and metallographic observations of longitudinal and transverse sections were made. The microstructure was inhomogeneous for low degrees of working, while at high reductions the grains were nonequiaxed. There was strain softening or hardening up to some strain depending on the test conditions. The grains became more equiaxed and coarser in size with increasing deformation. Due to these changes in microstructure and the nonunique stress-strain rate relation, the as-worked material is not suitable from the viewpoint of assessing the mechanisms of superplastic flow based on steady state. Strain dependency of flow stress was also observed in specimens specially processed to obtain equiaxed grains in the as-worked state.
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01 Jan 1991
TL;DR: The Pb-Sn eutectic alloy is widely used as a joining material in the electronics industry as discussed by the authors and it is known that the mismatched thermal expansion characteristics of the materials joined by the solder and the cyclic temperature fluctuations normally encountered during service constitute a condition of thermal fatigue for the constrained solder.
Abstract: The Pb-Sn eutectic alloy is widely used as a joining material in the electronics industry. In this application the solder acts as both an electrical and mechanical connection within and among the different packaging levels in an electronic device. Advances in packaging technologies driven by the desire for miniaturization and increased circuit speed result in severe operating conditions for the solder joint and thus solder joint reliability problems. Specifically, the mismatched thermal expansion characteristics of the materials joined by the solder and the cyclic temperature fluctuations normally encountered during service constitute a condition of thermal fatigue for the constrained solder. This is especially a problem in the surface mounting of leadless components where a shearing of the solder joint occurs with each temperature excursion. Repeated temperature cycling, such as that associated with Joule heating as the device is turned on and off, and environmental temperature changes fatigue the solder joint ultimately causing its failure. Increased solder joint reliability and the development of new more fatigue-resistant solder alloys require a fundamental understanding of the metallurgical mechanisms operative during the fatigue cycle and, hence, an understanding of the solder microstructure.
60 citations
TL;DR: In this paper, the authors describe the service life of electronic packaging, such as in automotive, airplane, military and mobile electronic devices, and discuss the effects of concurrent vibration and thermal loading.
Abstract: Concurrent vibration and thermal loading is commonly encountered in the service life of electronic packaging, such as in automotive, airplane, military and mobile electronic devices. Solder joint r...
49 citations
Cites background from "Superplastic Behavior of the Sn-Pb ..."
...After that, microstructure will still evolve, but in a much slower pace as discussed by Kashyup and Murty [24]....
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TL;DR: In this paper, as-solidified eutectic Pb-Sn solder joints exhibit superplastic behavior in shear creep loading, and the total shear deformation of joints in stress-rupture tests performed at 65° C are found to exceed 150%.
Abstract: This paper presents experimental evidence that as-solidified eutectic Pb-Sn solder joints can exhibit superplastic behavior in shear creep loading. Stepped load creep tests of as-solidified joints show a change in the stress exponent from a high value typical of con-ventional creep at high stress and strain rate to a superplastic value near 2 at lower stress and strain rates. In addition, the change in stress exponent is accompanied by a change in the activation energy for creep from a value near that for bulk self-diffusion (20 kcal/mol) to a value near that for grain boundary diffusion (12 kcal/mol). The total shear deformation of joints in stress-rupture tests performed at 65° C are found to ex-ceed 150%. The concomitant observation that quenched solder joints creep faster than air-cooled ones is attributed to a grain, or phase, size dependence of the strain rate. The source of superplastic behavior is a fine, equiaxed microstructure. It is not yet clear whether the superplastic microstructure is present in the as-solidified joint, or develops during the early stages of plastic deformation.
36 citations
TL;DR: In this paper, a micro-mechanistic approach for modeling fatigue damage initiation due to cyclic plasticity and cyclic creep in eutectic Pb-Sn solder is presented.
Abstract: This paper presents a micro-mechanistic approach for modeling fatigue damage initiation due to cyclic plasticity and cyclic creep in eutectic Pb-Sn solder. The is- sue of damage evolution is deferred to a future paper. Fatigue damage model due to cyclic plasticity is modeled with dislocation mechanics. A conceptual framework is provided to quantify the influence of temperature on fatigue damage due to cyclic plasticity. Damage mechanics due to cyclic creep is modeled with a void nucleation model based on mi- cro-structural stress fields. Micro-structural stress states are estimated under viscoplastic phenomena like grain boundary sliding and its blocking at second phase particles, and diffusional creep relaxation. A conceptual framework is provided to quantify the creep-fa- tigue damage due to thermo-mechanical cycling.
33 citations
TL;DR: In this article, a tensile test is proposed to evaluate the thermal fatigue resistance of solder alloys, which is based on the strain rate change method to obtain the strain sensitivity index, m. The m value at zero strain related to the coarseness or fineness of solder alloy microstructure.
Abstract: A tensile test is proposed to evaluate the thermal fatigue resistance of solder alloys. The test is based on the strain rate change method to obtain the strain rate sensitivity index, m. The m value is obtained at various strains during the tensile test. The plots of m and strain where m is measured showed a linear relation; therefore, the m value at zero strain, m0, and the gradient, k, are obtained by extrapolation. The m value at zero strain related to the coarseness or fineness of solder alloy microstructure; m0 becomes lower with coarsening of the microstructure. The solder alloys with low m0 and low k have excellent thermal fatigue resistance when compared with alloys with high m0 and high k. m0 and k would be good measures to estimate the thermal fatigue properties of solder alloys; highly resistant alloys have low m0 and low k.
31 citations
References
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TL;DR: In this article, the deformation behavior of a superplastic Ti-6A1-4V alloy at 927°C has been characterized by means of constant strain-rate tensile tests up to large plastic strain.
Abstract: The deformation behavior of a superplastic Ti-6A1-4V alloy at 927°C has been characterized by means of constant strain-rate tensile tests up to large plastic strain. Significant hardening has been recorded in the course of deformation. Microstructural studies on deformed samples indicate the occurrence of simultaneous strain-rate induced grain growth, which explains nearly all of the hardening. A small amount of hardening may also be expected from grain elongation or grain clustering effects. As a result of concurrent grain growth, the strain-rate sensitivity is found to decrease with strain, thus indicating that stress-strain rate behavior determined initially may not be applicable after large amounts of plastic strain. The stressJstrain-rate data obtained from step strain-rate test for a variety of grain sizes, together with the grain growth kinetics plots, provide a means for developing a constitutive description for this material at large strains.
250 citations
TL;DR: In this paper, the shape of the log stress-log strain rate curve for the Al-33 wt pct Cu eutectic alloy was examined and the inherent grain growth of the very fine grains which occurs during deformation, and the strain dependence of m at low strains, were shown to be the causes of the familiar shape of log stresslog strain curve for Al-Cu alloy.
Abstract: The usual method of measuring the strain rate sensitive ‘m’ values of superplastic materials through differential cross-head speed is found to result in improperly definedm values;m is found to depend strongly on the strain to which the material is subjected, especially at low strains. In this connection, the shape of the log stress-log strain rate curve is examined for the Al-33 wt pct Cu eutectic alloy. The inherent grain growth of the very fine grains which occurs during deformation, and the strain dependence ofm at low strains, are shown to be the causes of the familiarS shape of the log stress-log strain rate curves for the Al-Cu alloy. At high strains (15 to 20 pct and higher) where the stress is no longer importantly strain sensitive, the log stress-log strain rate curve is a straight line of slope near 0.5. The elongation at fracture also does not go through a maximum but continues to increase slowly to the lowest strain rate examined: 10-7 per s.
138 citations
TL;DR: In this article, the microstructure of two-phase α β alloys such as Ti-6A1-4V was evaluated in terms of their fully characterized microstructures.
Abstract: The strong dependence of the superplastic behavior of metals and alloys on grain size has been demonstrated, and it is now well known that a fine grain size is normally a requirement for superplasticity. However, the microstructure of certain alloy systems such as Ti-6A1-4V cannot always be adequately characterized by a single parameter such as grain size. In two-phase α β alloys such as Ti-6A1-4V, other microstructural parameters such as volume fractions of the two phases, grain aspect ratio, grain size distribution and crystallographic texture may also influence superplasticity. For example, if “grain switching” is an important deformation mechanism in superplastic flow as suggested by Ashby and Verall, then factors such as grain aspect ratio and range of grain sizes would be expected to have an effect on superplastic behavior. In this study, these microstructural features were determined for several different heats of Ti-6Al-4V, and the corresponding superplastic properties were evaluated in terms of their fully characterized microstructure. The flow stress as a function of strain rate, strain rate sensitivity exponent (m) as a function of strain rate and total elongation on properties were found to be strongly influenced by microstructural parameters such as grain aspect ratios, grain size and grain size distribution.
104 citations
TL;DR: In this paper, the first rapid stage of precipitation of tin, β, from lead, α, is effected by the nucleation and growth of cells, each cell consists of a multiplicity of β-plates, originating from a single nucleus, interspersed in the depleted α.
94 citations