J. F. Smith

A viable tin-lead solder substitute: Sn-Ag-Cu

Rising concern over the use of lead in industry provides a driving force for the development of improved lead-free industrial materials. Therefore, a new lead-free base solder alloy Sn-4.7Agl.7Cu (wt.%) has been developed upon which a family of lead-free solders can be based. This solder alloy exhibits a ternary eutectic reaction at 216.8 ± 1°C (L ↠ η+ ϕ + β-Sn; η = Cu6Sn5, θ = Ag3Sn). Preliminary tests of solderability demonstrate intermetallic phase formation on model solder joint interfaces and good wettability in a fluxed condition suggest technological viability and motivates much more extensive study of this solder alloy.

Angular dependence of ultrasonic wave propagation in a stressed, orthorhombic continuum: Theory and application to the measurement of stress and texture

A theory for ultrasonic wave propagation in a symmetry plane of a biaxially stressed, orthorhombic continuum is presented. Since many of the material parameters which appear in the analysis are unknown, in particular the third‐order elastic constants of polycrystalline metals, emphasis is placed on the angular dependence of the velocities. An expansion to first order in stress‐induced anisotropy and to second order in textural anisotropy reveals terms with twofold, fourfold, and sixfold symmetry. Scenarios are proposed for using various properties of this symmetry to deduce the difference in magnitude and directions of the principal stresses independent of textural anisotropy and the textural anisotropy independent of the stresses. Experimental results are presented for the cases of aluminum, 304 stainless steel, and copper.

Relative anisotropies of plane waves and guided modes in thin orthorhombic plates: implication for texture characterization

Abstract The angular dependences of the long wavelength velocities of S0 and SH0 modes of orthorhombic (orthotropic) plates are compared to those of the velocities of corresponding plane waves. To first order in the anisotropy, many of the phenomena are as expected. The absolute velocities and anisotropy of the SH0 plate modes are identical to those for plane SH waves and the absolute velocities of the S0 modes propagating along symmetry axes are reduced from the longitudinal plane wave velocities by an amount explained by the change from the plane strain to the plane stress condition. However, for certain classes of materials such as metal polycrystals, the anisotropy of the S0 mode can be substantially different from that of the longitudinal plane waves. This effect is explained through an expansion of the crystallite orientation distribution function in terms of generalized spherical harmonics. Implications of the results for the ultrasonic measurement of preferred grain orientation (texture) in polycrystals is indicated.

A comparison of ultrasonic and X-ray determinations of texture in thin Cu and Al plates

Ultrasonic techniques for determining the orientation distribution coefficients (ODC’s), which define the preferred orientation of polycrystals, are discussed. The theory is reviewed for thin plates of cubic crystallites for which the texture information is deduced from the velocity anisotropy of guided modes. Experimental ultrasonic and X-ray predictions of the ODC’s of up to an order of 4 are compared for plates of commercially pure electrolytic tough pitch (ETP) copper and aluminum. ForW420 andW440 in both samples andW400 in copper, the predictions agree to |ΔW|∼10-3. However, considerably greater differences are reported for the predictions ofW400 in aluminum. Interpretation of these comparisons is assisted by a detailed error analysis for the ultrasonic technique and reference to a number of other recent comparisons of ultrasonic and neutron or X-ray predictions of ODC’s Possible applications of the ultrasonic technique during the production and forming of metal sheet are indicated.

Texture monitoring in aluminium alloys: a comparison of ultrasonic and neutron diffraction measurement

Abstract Theories have been developed by several authors to calculate velocities of bulk, guided and surface waves in polycrystalline aggregates of cubic metals. These theories can be used to predict the effect of texture on ultrasonic velocity in rolled aluminium and steel sheet, provided that the effects of dislocations, second-phase particles, inclusions, etc. can be ignored. The theories predict that ultrasonic velocities will will be influenced by three orientation distribution coefficients (ODCs). The ODCs are quantitative measures of the texture in the material; in general, more than three ODC are required to completely characterize texture. Neutron diffraction pole figures can also be used to obtain the ODCs. Neutron diffraction measurements of ODC can be compared against ultrasonic values to obtain an independent check on the validity of the ultrasonic theories. In this work, the texture of thin sheets of a commercial grade aluminium alloy was measured with both ultrasonics and neutron diffraction. Several ultrasonic techniques were employed, using bulk, guided and surface waves. Both piezoelectric and electromagnetic-acoustic transducers (EMATs) were used. Quantitative measurements of texture made with different ultrasonic techniques were in good agreement. These ultrasonic measurements also agreed with neutron diffraction measurements, indicating that the dominant features of the effect of texture on wave propagation have been modelled with sufficient accuracy. The extension of the ultrasonic technique to on-line (production) monitoring of texture is considered. In particular, it appears that EMATs are the transducer of choice for on-line texture measurement of rolled sheet, since they are non-contacting.

Microstructure‐independent acoustoelastic measurement of stress

Measurements are reported of the velocities of horizontally polarized shear waves (fundamental mode) propagating in the plane of aluminum plates under tensile loads applied parallel to the rolling direction. In agreement with the predictions of previous theories, the applied stress is found to be predicted by the expression 2C(ΔV/V), where C is the appropriate second‐order shear elastic constant and ΔV/V is the fractional difference in velocities of waves propagating parallel and perpendicular to the load. The data show that, whereas the individual velocities are strongly influenced by microstructure, the stress prediction based on their difference is not. Included are results illustrating the effects of preferred grain orientation and plastic deformation.

Laser-flash calorimetry III. Heat capacity of vanadium from 80 to 1000 K

Abstract The heat capacity of vanadium has been measured by laser-flash calorimetry in the temperature region from 80 to 1000 K. The results are compared with available low- and high-temperature heat capacities, and revised thermodynamic values of vanadium are given. No heat-capacity anomaly has been found in the pure vanadium sample over the temperature range investigated, while a small heat-capacity discontinuity, less than 1.2 J · K −1 · mol −1 , has been observed at 220 to 230 K on the same sample but electropolished before measurement. This anomaly disappeared after annealing at 1000 K in vacuo for 1 h and is attributable to the introduction of a small amount of hydrogen during electropolishing.

Absolute Determination of Stress in Textured Materials

The continuum theory of elastic wave propagation in deformed, anisotropic solids is reviewed with emphasis on those features which might be used to distinguish between stress induced changes in ultrasonic velocity and changes due to material anisotropy, such as would be produced by preferred grain orientation in a polycrystalline metal As noted by previous authors, one such feature is the difference in velocity of two shear waves, whose directions of propagation and polarization have been interchanged. In particular, when these directions fall along the symmetry axes of a rolled plate (assuming orthorhombic symmetry) and these are also the directions of principal stress, then the theory predicts that ρ(V 12 2 −V 21 2 ) = T1−T2 where ρ is the density, Vij is the velocity of a shear wave propagating along the i-axis and polarized along the j-axis, and Ti is a principal stress component. In addition to being independent of the degree of texture, this relationship has the advantage that no microstructurally dependent acoustoelastic coefficient is involved. The applicability of this prediction of continuum theory to heterogeneous engineering materials such as metal polycrystals is discussed using previously reported stress dependencies of ultrasonic velocities, and new experiments to answer some remaining questions are described. A possible configuration for using the effect to measure the value of a uniform stress in a plate of unknown texture is proposed.

The Use of Ultrasonics for Texture Monitoring in Aluminum Alloys

Many alloys of common metals (such as aluminum and steel) are polycrystalline aggregates having preferred orientation (texture) of the single crystals making up the aggregate. Texture often affects mechanical properties, such as response of material to deep drawing which occurs in the manufacture of aluminum cans.

Inference of Crystallite Orientation Distribution Function from the Velocity of Ultrasonic Plate Modes

Techniques have recently been reported for the ultrasonic measurement of stress.1–3 In these, the effects of texture are suppressed by comparing the velocity of two shear waves whose directions of propagation and polarization have been interchanged. Here, an alternate goal is described. It is desired to enhance, rather than suppress, the textural effects so that the preferred orientation of crystallites can be determined.