Influence of heat treatment on stress–strain behaviour and lattice parameters of Sn–In alloy

Abstract

Sn based alloys have important industrial applications specially as pewters and soldering materials. One of these alloys, Sn–5·2 wt-%In alloy, is designed to be examined in the present work. The differential thermal analysis of this alloy gives a melting temperature value of 493 K. An empirical equation that can be used to determine the melting temperature of some Sn–In alloys is derived. Two different heat treated groups of samples, slowly cooled and quenched, are prepared. The phases present in these two groups of samples are determined from their X-ray diffraction patterns. The isothermal tensile stress–strain tests of all samples are reported at temperatures between 343 and 403 K. The changes of the work hardening parameters and also of the lattice parameters of the β-Sn phase with the deformation temperature are discussed. The values of the activation energy characterise a dislocation fracture mechanism.     

On the validity of Rayleigh–Gans–Debye type approximations in red blood cell size determination

The validity of the Rayleigh-Gans-Debye (RGD) approximation for the size determination of a soft prolate spheroidal scatterer has been examined. Calculations have been carried out for the volume range 30–100 µm³ and for aspect ratios ranging from 1.1 to 4.0. Particular attention has been paid to size determination of a red blood cell (RBC) in a flow cytometric arrangement. The applicability of the RGD approximation has been compared with its two modified forms and also with the WKB approximation.     

Effect of grain size on strain rate sensitivity of cryomilled Al–Mg alloy

Al–Mg alloy powder was cryomilled to achieve a nanocrystalline (NC) structure having an average grain size of 50 nm with high thermal stability, and then consolidated by quasi-isostatic forging. The consolidation resulted in a bulk material with ultrafine grains of about 250 nm, and the material exhibited enhanced strength compared to conventionally processed Al–Mg alloy. The hardness of as-cryomilled powder, the forged ultrafine-grained (UFG) material, and the conventional coarse-grained (CG) alloy were measured by nanoindentation using various loading rates, and the results were compared with strain rate sensitivity (SRS) from uniaxial compression tests. Negative SRS was observed in the cryomilled NC powder and the forged UFG material, while the conventional alloy was relatively insensitive to strain rate. The dependence on loading rate was stronger in the NC powders than in the UFG material.     

Effect of strain on the I–V characteristics of discontinuous silver films and determination of their gauge factor

Three films (A, B and C) of discontinuous silver films whose mass thicknesses (d _m ) are 6, 12 and 18 Å, respectively were deposited onto Corning 7059 glass substrates at ambient temperature using a thermal evaporation technique. The increase in dc resistance (R _dc ), in air, with time (time-ageing) was monitored till short-term stability was achieved. The effect of strain on the I–V characteristics of discontinuous silver films and determination of their gauge factor (v) was studied and it was found that; (1) a deviation from linearity is observed at higher voltages (>60 V) and at particular voltage, the electric current increases as d _m increases (2) R _dc increases as the tensional strain (?) increases and the dependence of fractional change of resistance on ε is linear with no hysteresis (3) v decreases as d _m increases and the high values of ν for these films candidates them to be miniature strain sensors. The data of this work are discussed on the ground that the thermally activated tunneling is the mechanism responsible for the electrical conduction in discontinuous silver films.     

Chemical mechanism of precipitate formation and pH effect on the morphology and thermochemical co-precipitation of W–Cu nanocomposite powders

W–25%Cu composite powder was produced via thermochemical procedure. Copper nitrate and sodium tungstate salts were used as Cu and W containing precursors, respectively. Aqueous solutions of these salts were reacted under several different pH conditions. It was found that the products of all stages involving Cu₂WO₄(OH)₂ and CuWO₄·2H₂O as raw precipitates, CuWO_4−x, CuO, and WO₃ as calcined powders, and W–Cu reduced composite powders possessed similar compositions in different pH conditions. But changing the reaction pH in the range of 3–13 was found to markedly influence the microstructure of the products. At low and medium pH precipitates were in the form of large monolithic agglomerates while in high pH smaller cotton like agglomerates were formed. At low and medium pH conditions simple ion replacement was found to be dominant mechanism of precipitation while in high pH Cu(NH₃)₄²⁺ complex ion was formed and ligand exchange was the dominant mechanism of precipitation.     

Effects of strain rate and temperature on the stress–strain response of solder alloys

To ensure reliable design of soldered interconnections as electronic devices become smaller, requires greater knowledge and understanding of the relevant mechanical behavior of solder alloys than are presently available. The present paper reports the findings of an investigation into the monotonic tensile properties of bulk samples of three solder alloys; a lead–tin eutectic and two lead-free solders (tin–3.5 copper and a tin–3.5 silver alloy). Temperatures between–10 and 75°C and strain rates between 10^–1 and 10^–3 s^–1 have been studied. Both temperature and strain rate may have a substantial effect on strength, producing changes well in excess of 100%. Strength is reduced by lowering strain rate and increasing temperature, and Sn–37 Pb is usually most sensitive to the latter. Expressions for strain and strain rate hardening have been developed. The Sn–0.5 Cu alloy is usually the weakest and most ductile. Sn–37 Pb is strongest at room temperature but with increasing temperature and lower strain rates it becomes inferior to Sn–3.5 Ag. Ductility changes with temperature and strain rate for all three alloys are generally small with inconsistent trends. The role of such data in stress analysis and modeling is considered and the paramount importance of employing data for conditions appropriate to service, is emphasized.     

Effects of strain and strain aging on fracture toughness of C–Mn weld metal

Abstract

Specimens of both as-deposited and fine-grained, reheated, manual metal arc C–Mn weld metal have been subjected to various strain and static strain-aging treatments in an attempt to simulate the thermomechanical cycles imposed upon the root region of a multipass weld as subsequent passes are made. The toughness was then measured, as a function of severity of treatment, using a crack opening displacement test. The strain aging treatments are found to lower markedly the cleavage resistance of the as-deposited and reheated microstructures. Non-metallic inclusions within the crack-tip plastic zone are found to be active as cleavage initiation sites in both types of microstructure. While the general shift in toughness can be explained by considering the changes in flow properties brought about by the various treatments, the observed variations in size and distance from the crack tip of the initiating inclusions are thought to be responsible for the associated experimental scatter.

MST/157     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Influence of strain and strain rate on microstructural evolution during superplasticity of Mg–Al–Zn sheet

Strain-induced abnormal grain growth was observed along the gage length during high-temperature uniaxial tensile testing of rolled Mg–Al–Zn (AZ31) sheet. Effective strain and strain rates in biaxial forming of AZ31 sheets also affected the nature of grain growth in the formed sheet. For the uniaxial testing done at 400 °C and a strain rate of 10^?1 s^?1, abnormal grain growth was prevalent in the gage sections that experienced true strain values between 0.2 and 1.0. Biaxial forming of AZ31 at 5 × 10^?2 s^?1 and 400 °C also exhibited abnormal grain growth at the cross sections which experienced a true strain of 1.7. Uniaxially tested sample at 400 °C and a strain rate of 10^?3 s^?1, however, showed no abnormal grain growth in the gage sections which experienced true local strain values ranging from 1.0 to 2.3. The normalized flow stress versus temperature and grain size compensated strain rate plot showed that the deformation kinetics of the current AZ31 alloy was similar to that reported in the literature for AZ31 alloys. Orientation image microscopy (OIM) was used to study the texture evolution, grain size, and grain boundary misorientation during uniaxial and biaxial forming. Influence of deformation parameters, namely strain rate, strain, and temperature on grain growth and refinement were discussed with the help of OIM results.     

Investigation of the effect of composition on microhardness and determination of thermo-physical properties in the Zn–Cu alloys

Zinc–copper of (99.99%) high purity alloys were directionally solidified upward with different compositions, C_o, Zn–(0.7,1.5, 2.4 and 7.37) wt.% Cu under two different solidification conditions (G = 3.85 K/mm, V = 0.0083 mm/s and G = 8.70 K/mm, V = 0.436 mm/s) using a Bridgman type directional solidification apparatus. The measurements of microhardness of directionally solidified samples were made by using a microhardness test device. The dependence of microhardness (HV) on composition was analyzed. According to these results, it has been found that the values of HV increase with the increasing Cu content (C_o). Variation of electrical resistivity (ρ) and electrical conductivity (σ) with the temperature were also measured by using a standard d.c. four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (Cp) of the Zn–Cu alloys were determined from heating curve during the transformation from solid to liquid phase by using differential scanning calorimeter (DSC).     

Effect of composition on critical (cold working) strain and recrystallised grain size of dilute Al–Fe alloys

Abstract

Low strain cold deformation and annealing techniques have been applied to establish the effects of composition and heat treatment variables on the recrystallisation behaviour of Al–Fe alloys. The parameters controlling the critical strain required to initiate recrystallisation and the grain size produced by subsequent recrystallisation annealing have been established to be the volume fraction of secondary phases, the eutectic colony size in both as cast and processed material, matrix composition, the initial grain size preceding final cold deformation, the amount of deformation before annealing, and the final annealing temperature. The results derived from the application of the strain annealing test showed that increasing the volume fraction of secondary precipitate phases, the homogenisation and final annealing temperatures, or the eutectic colony size, decreases the critical strain and increases the maximum grain size produced after annealing, but increasing the initial grain size has opposite effects on these parameters.

MST/1348     

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al₂O₃ hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10^?3 s^?1 using a conventional load frame to 1720 s^?1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.     

Architecturally modified Al–DRA composites: the effect of size and shape of the DRA rods on fracture behavior

Architectural modification of aluminum matrix composites is considered as an efficient method to improve fracture toughness. Al–DRA (Al–Al/SiC/20_p) composites were fabricated via “powder extrusion–casting–ingot extrusion” route with structures similar to that of reinforced concrete, so that DRA rods were surrounded by unreinforced aluminum. The effects of variation in shape, size, and number of DRA rods on fracture behavior of Al–DRA composites were investigated. Composites containing DRA rods with hexagonal cross-section exhibited higher resistance to crack initiation and growth, in comparison to those containing circular rods. In the case of hexagonal rods, increasing the number of rods (reducing the rods’ cross-section surface) led to further enhancement of fracture toughness. Fracture surface observations of all samples revealed the existence of desirable cohesion between rods and the surrounding matrix. The remained sharp and unblunted corners of hexagonal DRA rods caused stress concentration and microcrack formation upon loading. Hence, plastic deformation constraint of aluminum ligament between rods was alleviated, which, in turn, led to further energy consumption during the fracture process.     

Comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials

This paper presents the results of a comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials using the discrete element method. The study used the Particle Flow Code (PFC) to simulate biaxial compression tests in granular materials. To study the effects of rolling resistance, a user-defined rolling resistance model was implemented in PFC. A series of parametric studies was performed to investigate the effects of different levels of rolling resistance on the stress–strain response and the emergence and development of shear bands in granular materials. The PFC models were also tested under a range of macro-mechanical parameters and boundary conditions. It is shown that rolling resistance affects the elastic, shear strength and dilation response of granular materials, and new relationships between rolling resistance and macroscopic elasticity, shear strength and dilation parameters are presented. It is also concluded that the rolling resistance has significant effects on the orientation, thickness and the timing of the occurrence of shear bands. The results reinforce prior conclusions by Oda et al. (Mech Mater 1:269–283, 1982) on the importance of rolling resistance in promoting shear band formation in granular materials. It is shown that increased rolling resistance results in the development of columns of particles in granular materials during strain hardening process. The buckling of these columns of particles in narrow zones then leads to the development of shear bands. High gradients of particle rotation and large voids are produced within the shear band as a result of the buckling of the columns.     

Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

Temperature and strain rate effect on tensile properties of 9Cr–1·8W–0·5Mo–VNb steel

Abstract

Tensile tests have been carried out on 9Cr–1·8W–0·5Mo–VNb steel (grade 92) over wide ranges of temperature (300–923 K) and strain rate (3×10^?3–3×10^?5 s^?1). The tensile strength of the steel decreased slowly with temperature at relatively lower temperature range, whereas rapidly in the higher temperature range with a plateau in the intermediate temperature range. The decrease in strain rate decreased the tensile strength of the steel both at lower and higher temperature ranges. Elongation to fracture and reduction in area increased with increase in temperatures and decrease in strain rate at higher temperature regime with a plateau in the intermediate temperature regime. The ductile mode of tensile failure has been observed in the investigated temperatures and strain rates. The plateau in the variation of tensile strength with temperature, the negative strain rate sensitivity of tensile strength and minimum in ductility of the steel in the intermediate temperature range are considered as a consequence of dynamic strain ageing. The rapid decrease in tensile strengths and increase in ductility at high temperatures have been attributed to the dynamic recovery.     

Effect of freeze–thaw cycles on the stress–strain curves of unconfined and confined concrete

An experimental research was performed on the complete compressive stress–strain relationship for unconfined and confined concrete after exposure to freeze–thaw cycles. For the unconfined concrete, tests were carried out on three series of prisms specimens (100 mm × 100 mm × 300 mm) with water/cement ratio of 0.60, 0.54 and 0.48 respectively. While for confined concrete, two series of tied columns (150 mm × 150 mm × 450 mm prisms) with confinement index of 0.317 and 0.145 were prepared. Analytical models for the stress–strain relationship of frozen-thawed unconfined and confined concrete were empirically developed respectively. Through the regression analysis, formulations for the main parameters were established, including the compressive strength, peak strain and elastic modulus. Compared with the available experimental data, the proposed models were shown to be applicable to concrete after different numbers of freeze–thaw cycles.     

X-ray diffraction and Mössbauer spectrometry studies of the mechanically alloyed Fe–6P–1.7C powders

Nanostructured Fe–6P–1.7C powders were obtained by mechanical alloying in a planetary ball mill. Morphological, microstructural and structural changes during the milling process were followed by scanning electron microscopy, X-ray diffraction and ⁵⁷Fe Mössbauer spectrometry. The crystallite size refinement to the nanometer scale (5–8) nm is accompanied by an increase in the internal strain. The nanocrystalline structure distortion is evidenced by the lattice parameter changes of the milling products. The hexagonal Fe₂P phosphide is formed within 6 h of milling, while the tetragonal Fe₃P and orthorhombic Fe₃C phases appear after 12 h of milling. A mixture of Fe₃P phosphide, Fe₃C carbide and α-Fe(C, P) solid solution is obtained on further milling time.     

Influence of shear bond strength on compressive strength and stress–strain characteristics of masonry

The paper is focused on shear bond strength–masonry compressive strength relationships and the influence of bond strength on stress–strain characteristics of masonry using soil–cement blocks and cement–lime mortar. Methods of enhancing shear bond strength of masonry couplets without altering the strength and modulus of masonry unit and the mortar are discussed in detail. Application of surface coatings and manipulation of surface texture of the masonry unit resulted in 3–4 times increase in shear bond strength. After adopting various bond enhancing techniques masonry prism strength and stress–strain relations were obtained for the three cases of masonry unit modulus to mortar modulus ratio of one, less than one and greater than one. Major conclusions of this extensive experimental study are: (1) when the masonry unit modulus is less than that of the mortar, masonry compressive strength increases as the bond strength increases and the relationship between masonry compressive strength and the bond strength is linear and (2) shear bond strength influences modulus of masonry depending upon relative stiffness of the masonry unit and mortar.