Pb-Sn Eutectic Alloy Research Articles

Axial strain variation due to torsional deformation of a superplastic Pb-Sn eutectic alloy

Resultats d'essais de torsion effectues sur des materiaux superplastiques. Experiences sur des barreaux en alliage eutectiques (38,1% Pb, 61,9% Sn). Comparaison avec les resultats sur Pb pur et Sn pur

Interphase Boundary Diffusion in Eutectic Alloys

AbstractTurnbull and co-workers have shown that the noble metals Cu, Ag, and Au diffuse into single crystals of Pb and Sn by an interstitialcy mechanism with measured diffusion coefficients of ∼10−6cm2s−1. These experiments have been extended to study the diffusion rates of the noble metals along the interphase boundaries of single crystal of Pb-Sn eutectic alloys and to measure the diffusion coefficient of silver along the interphase boundaries of Ag-Cu eutectic single crystals.The measured interphase boundary diffusion coefficients of the noble metals in the Pb-Sn single crystals are extremely high, being 2.6 × 10−3cm2s−1for Cu and ∼10−4cm2s−1for Ag and Au at room temperature. These results again imply an interstitialcy mechanism of diffusion at the interphase boundaries. In contrast, the diffusion coefficient of Ag110in a Ag-Cu eutectic single crystal worked out to be ∼8×10−9cm2s−1at 500°C, two orders of magnitude lower than the value obtained by Turnbull and Hoffman for self-diffusion along low-angle (8∼10°) boundaries in silver.

Determination of the equivalent stress versus equivalent strain rate behaviour of superplastic alloys in biaxial stress systems

Experimental work was conducted to determine the stress versus strain rate behaviour of superplastic PbSn eutectic alloy under uniaxial and biaxial tensile stress systems. Uniaxial tensile tests (at constant cross-head speed and constant load) were performed in the strain rate range 0.001–1.0 min −1. Bulge tests of superplastic PbSn thin sheets in circular, rectangular and elliptical die apertures were carried out using a constant hydrostatic pressure. The geometry of these dies provided different degrees of stress biaxiality ranging from 1.0 (circular die) to 0.5 (long rectangular die). By properly selecting the pressures inducing the bulging, the stress versus strain rate behaviour was evaluated over a strain rate range 0.001–5.0 min −1 at two strain levels of 0.12 and 0.4. The data obtained from both uniaxial and biaxial tests were correlated reasonably well using the concepts of equivalent stress and equivalent strain rate.

The influence of prestrain on ductility in the superplastic Pb-Sn eutectic alloy

Experiments were conducted to investigate the effect of prestraining on the ductility of the superplastic Pb-62 wt % Sn eutectic alloy at room temperature. It is shown that prestraining at a fast strain rate in region III leads to a decrease in the elongation to failure on subsequent testing at a slower rate in region II. This decrease is due to the development of strain inhomogeneities during the prestrain. There is a further decrease in elongation if a holding time is inserted between the prestrain in region III and the subsequent testing in region II. It is shown also that prestraining at a slow strain rate leads to a sharp increase in the elongation to failure on subsequent testing at a fast strain rate. The reasons for these trends are discussed with reference to the occurrence of grain growth and the uniformity of strain.

Evaluation of microstructural instability during the differential strain rate test of a superplastic alloy

Stress (σ)-strain rate (\(\dot \varepsilon \)) data of banded and elongated grain microstructures of the Pb-Sn eutectic alloy were analysed over 298 to 443 K to evaluate microstructural instability during differential strain rate tests in the superplastic region. With reference to a stable equiaxed microstructure exhibiting uniqueσ-\(\dot \varepsilon \) relation, banded structure is more susceptible to strain hardening while the elongated grain microstructure exhibits either strain softening or strain hardening depending on the test temperature. This flow behaviour is considered in terms of a change in grain size, represented by the cube root of the grain volume. Activation energy for grain growth calculated from the differential strain rate test data indicates that the activation energy depends on strain rate and type of microstructure.

Observations of grain boundary sliding during superplastic deformation

Flat test specimens of a 10-micron grain size Al-33 pct Cu alloy were deformed in air over a range of strains at 450 °C (723 K) and at 10-5 strain per second, and examined by SEM. Direct observations and measurements were also made in a SEM during superplastic deformation of a 5-micron Pb-Sn eutectic alloy at room temperature at a strain rate of about 10-5 s-1. Extensive grain boundary sliding was noted. Microcreep curves were obtained between initially adjacent grains and showed that deformation is cyclical in nature and varies by several orders of magnitude locally from point to point. Many surface grains are observed to change neighbors many times, to undergo some rotation and tilt, to show little change in size or shape, and yet to avoid intergranular cracking. Superplastic deformation is a highly heterogeneous process, not unlike that observed in the creep of conventional types of alloys at elevated temperatures, but differing in the extent of plastic deformation free of intergranular cracking, combined with extensive recovery in the form of boundary migration.

Mode of solidification and strength properties for lead‐tin binary system

AbstractTensile strength and ductility of unidirectionally and randomly solidified Sn, Pb and Sn–Pb eutectic alloy are determined. Appreciable increase in the ductility from random to directional growth has been observed in case of Sn, Pb and Pb–Sn eutectic. Improvement in tensile strengths of pure metals and their eutectic composite by 15–20% and 15%, respectively, was evident in case of directionally solidified to randomly grown samples. The increase in tensile strength of the eutectic was 2–2.5 times to the strength of the pure metals. Tensile strength of directionally solidified Pb–Sn eutectic studied at different rates of solidification for constant temperature gradient was lower at higher and at lower rates of solidification than the value at medium rates of solidification.

Fracture of a tin-lead eutectic alloy in Region III of superplastic flow

With the aid of scanning electron microscopy, cavitation and fracture behaviour in the Sn-Pb eutectic alloy, whose reduction in area of cross-section before failure is close to 100%, has been investigated in Region III of superplastic flow (where both the elongationto-fracture and the strain-rate sensitivity index decrease with increasing strain rate). It has been demonstrated that, although it decreases, grain-boundary sliding persists in this range as the strain rate is increased. At all strain rates the final failure was due to tearing by plastic flow of the inter-cavity ligaments, but the interlinkage of cavities along the graininterphase boundaries decreased with increasing strain rate. The features of cavitation and fracture did not differ much from an earlier study on a pseudo-single phase copper alloy, although copper alloys usually fail non-ideally, i.e., a large area of cross-section is present at fracture.

Surface contours in the axi-symmetric upsetting of solid cylinders

Surface flow contours during the axi-symmetric upsetting of aluminium, Sn-Pb eutectic alloy and Plasticine have been studied as a function of the extent of deformation, frictional condition and height-to-diameter ratio. The roughness of the end faces after upsetting has also been measured. The results have been explained in terms of the changes in the frictional condition, the strain-rate sensitivity and the local strain rate and it is concluded (a) that cold upsetting of a material of negligible strain-rate sensitivity gives rise to a parabolically-shaped barrel, (b) that hot upsetting the Sn-Pb alloy specimens of height-to-diameter ratio 1.5 results in a linear increase in diameter from the top to the bottom of specimens, due to a linear decrease in strain rate in the same direction, (c) that hot compression of Plasticine specimens and Sn-Pb alloy specimens of height-to-diameter ratio 2.0 leads to complex shape changes which cannot be predicted using the present knowledge concerning the upsetting of strain-rate sensitive materials and (d) that the greater increase in roughness following significant compression of the end faces of lubricated specimens, compared with that observed for unlubricated specimens, is due to enhanced surface metal flow with a decrease in frictional constraints.

On the uniqueness of stress-strain rate relation for superplastic flow of the Pb-Sn eutectic

The uniqueness of stress-strain rate relation in superplastic deformation of the Pb-Sn eutectic alloy for different grain sizes and test temperatures has been explored after subjecting the deformation processed alloy to a standard tensile prestrain. About 30 pct elongation at 421 K was found to eliminate the mechanical and microstructural instabilities that are characteristic of the as-worked material. After this prestraining, the flow stress was uniquely dependent on strain rate for a given grain size and test temperature, irrespective of the cross head speed, the path through which a particular strain rate is achieved, or the strain.

Experimental constitutive relations for the high temperature deformation of a PbSn eutectic alloy

The high temperature steady state deformation behaviour of PbSn eutectic alloy was investigated over wide ranges of grain size (9.7 – 32.0 μm), temperature (298 – 443 K) and strain rate (10 −7 – 10 −2 s −1), after stability of microstructure and strength had been achieved through prior tensile deformation. The σ-ϵ plots for these materials consisted of regions II and III. In region II the strain rate sensitivity index m is 0.6 ± 0.1 and the grain size exponent p is 3.34 ± 0.23. The activation energy Q in region II was found to depend on temperature with Q = 44.7 ± 1.1 kJ mol −1 below about 408 K and Q = 81.1 ± 3.9 kJ mol −1 above this temperature. These experimental parameters do not agree with any of the superplasticity models that have been proposed to date. However, in region III the parameters m = 0.09 ± 0.01, p = 1.00 ± 0.72 and Q = 100.0 ± 8.8 kJ mol −1 observed are in better agreement with the recovery creep model of Gifkins.

Extrusion of rate-sensitive materials using a viscoplastic constitutive equation and the finite element method

The flow of a rate sensitive material in a forming process in general and an extrusion process in particular has been analysed by using a constitutive equation in the form where such a material is treated as a viscous, non-Newtonian incompressible fluid flow. The discretized form of the flow equation is obtained using the principle of virtual work and the finite element technique. Velocities and pressures are used as primary variables in the formulation. The method which is presently applied to the axisymmetric steady state extrusion of rate sensitive materials can readily be extended to unsteady problems. The two rate-sensitive materials choosen are an aluminium having a definite yield stress and a Pb-Sn eutectic alloy having no detectable yield limit. The results of the present analysis are compared with available experimental values or with that obtained by other methods and in general good agreement is found to exist.

Melt spinning of crystalline alloys

Abstract : This paper describes the effect of melt-spinning process parameters such as orifice diameter, ejection pressure, and wheel speed, in determining the ribbon dimensions of Pb-Sn eutectic and low content A1 alloys. Rapid solidification techniques have been studied ever since the early experiments of Duwez et al. In recent years, the melt-spinning process (sometimes known as chill block casting) has been of particular interest because of the possibility of manufacturing iron-based amorphous alloys for magnetic applications. Liebermann and Graham and Kavesh have discussed the effect of melt spinning process parameters on the dimensions of melt-spun ribbons of amorphous Fe(40)Ni(40)B(20). This note describes the results of an investigation into the effect of melt spinning process parameters on the ribbon dimensions of two other materials, namely Pb-Sn eutectic and AL containing small quantities of Fe and Mn. The main objective was to determine whether the conclusions of Liebermann and Graham and Kavesh can be applied over a wide range of materials. Thus, Pb-Sn and AL-(Fe,Mn) were chosen because they have very different melting points from Fe(40)Ni(40)B(20), and because they solidify in a crystalline rather than amorphous form.

Superplasticity in splat-quenched PbSn eutectic

PbSn eutectic alloy tapes were prepared by melt spinning over a wide range of solidification conditions. In all cases the rapid solidification produced a microstructure consisting of equiaxed lead-rich and tin-rich grains, approximately 4 μm in size. This microstructure could result from a divorced eutectic solidification process or more probably from post-solidification coarsening. Under tensile loading the melt-spun PbSn eutectic tapes exhibited superplastic deformation with large failure strains, a sigmoidal variation of the logarithm of flow stress with the logarithm of flow strain, a strain rate sensitivity of 0.42 and an activation energy for superplastic flow of 54 kJ mol −1.

Superplastic behavior of PbSn eutectic alloy

The superplastic behavior of PbSn eutectic alloy was investigated for grain sizes from 2.2 to 6.1 μm over a range of temperatures from 298 to 373 K and with strain rates from 10 −7 to about 10 −2 s −1. The results showed that the stress-strain rate relation can be divided into two distinct regions: (a) at strain rates lower than approximately 10 −3 or 10 −4 s −1 the stress exponent was 2.4, the inverse grain size dependence exponent was 1.6 and the true activation energy was 10.5 kcal mol −1; (b) at higher strain rates the stress exponent was 5.7, the strain rate was independent of grain size and the true activation energy was 20.8 kcal mol −1. At low strain rates an apparently distinct region characterized by a stress exponent equal to unity was observed when datum points were taken at strains between 0.2% and 3.5%. When datum points were taken at strains larger than 5% this region was not observed.

Deformation of PbSn eutectic alloys at relatively high strain rates

The steady-state stresses of lead-tin eutectic alloy (Pb-62Sn) samples of mean phase diameter from 5.5 to 9.9 μm were measured over a range of temperatures from 0° to 160°C and strain rates from 2.66 × 10 −5 to 1.33 × 10 −2 s −1. The alloy exhibited both conventional and superplastic deformation over this range of experimental variables. The data were consistent with the assumption that the two deformation behaviors occur simultaneously via independent mechanisms. The data may be represented by the dimensionless constitutive relation γ ∗ = 900(τ ∗) 1.96(d ∗ −1.8 exp(−11,500/RT) + (1.3 × 10 15)(τ ∗) 7.1 exp(−19,400/RT) , where the first term on the right gives the rate of superplastic deformation and the second term gives the rate of conventional deformation.

The morphology and crystallography of directionally solidified Pb-Sn eutectic alloys : Verhoeven, J.D., Mourer, D.P., and Gibson, E.D. Mettalurgical Transactions Vol 8A (August 1977) pp 1239–1247

The morphology and crystallography of directionally solidified Pb-Sn eutectic alloys : Verhoeven, J.D., Mourer, D.P., and Gibson, E.D. Mettalurgical Transactions Vol 8A (August 1977) pp 1239–1247

The morphology and crystallography of directionally solidified pb-sn eutectic alloys

Directional solidification of Pb-Sn eutectic alloys at high temperature gradients has shown that two distinct eutectic morphologies occur, a regular lamellar structure and a wavy lamellar structure, termed degenerate. An electron channelling technique was used to characterize the crystallography of the two morphologies. The degenerate grains grow in advance of the regular grains and are the preferred growth morphologies in spite of the fact that coarsening experiments revealed that the degenerate grains possessed a higher lamellar interface energy. This result conflicts with the Zener model of eutectic growth. A possible rationalization of this conflict based on the anisotropy of thermal conductivity in Sn is presented.

On the spiral growth of Pb-Sn eutectic alloys

Directionally solidified Pb-Sn eutectic alloys have been observed to display four different crystallographic relationships. The present study determined that only one of these crystallographies exhibits the spiral growth phenomenon. The rate of spiralling was shown to increase strongly with solidification rate; its dependence upon temperature gradient was not reproducible, but it was found that the spiral rate did not decrease with increasing gradient as previous investigators had postulated.

鋼板の軟ろう接せん断強度に関する研究

This paper presents some experimental data concerning the relation between the shearing strength and roughness of base metal (mild steel) surface soldered with Pb-Sn eutectic alloy. The specimens used in this experiment were made according to the configuration of JIS Z3192, and had the same shape as designed by F.M. Miller and R.L. Peaslee.To make various degrees of roughness on the base metal, the specimens were finished by means of abrasive paper (60, 120, 240, 400 and 600 mesh) polishing, milling cutting or WA 60 and WA 80 wheel grinding. The soldering operation of these specimens was conducted using a 0.3kW resistance solder bath, and the joint clearance of each specimen was adjusted at the cementing fixture. To obtain the tensile-shearing strength of these specimens, a 50tons tensile testing machine was used in this experiment. The results were as follows:(1) As regards to the relation between the shearing strength of soldered joint and the roughness of soldering surface of base metal, it was clear that the shearing strength of a soldered specimen having a small roughness value was greater than that of the one having a large roughness value.(2) The maximum shearing strength for the soldered specimens was obtained at the joint clearance of about 0.2∼0.3mm.(3) It was clear that the shearing strength of a specimen having a long brazed joint length was lower than that of the one having a short soldered joint length.(4) Most of the specimens fractured at the weak part near by the interface of the soldered joint which had a different composition than the original Pb-Sn eutectic composition, but no specimen ruptured in the base metal.