Volume 92, Issue 5

By the example of large strain cold worked Al, two new methods (electron back scatter diffraction and synchrotron X-ray peak profile analysis) are introduced which are well capable to monitor the characteristics of the deformation structure on a microstructural level. While the first method has been proved to properly describe the sizes of newly forming subgrains and their misorientations, the second one allows for measuring the local densities of dislocations, their arrangements and the local long range internal stresses. The results show that during large strain cold working new high angle grain boundaries are formed which exhibit markedly higher local dislocation densities and a much lower level of local internal stresses compared with those of the original dislocation cell walls from which they appear to develop.

The electrochemical metal dissolution of 100Cr6 steel in sodium chloride solution, applying high electrolyte flow rates and high current densities, has been studied with a view to the influence of material heterogeneities such as carbide segregation lines in the steel matrix. It was shown that the presence of such segregations is responsible for the formation of troughs on the specimen surface during electrochemical dissolution. A mechanism for trough formation was proposed. A dedicated heat treatment applied to the 100Cr6 steel eliminated the carbide segregation lines and established a soft annealed, fine-grained microstructure containing globular carbides. Subsequent electrochemical dissolution did not show any development of surface irregularities as troughs.^

To manufacture a high quality cold welded Al/Cu electrical transition joint, it is essential to understand the relationship between bond strength, bond morphology, and electrical resistivity of the bimetal. The samples of Al and Cu bimetal were produced by a cold roll pressure welding process. The different strengths of the metallic bond between Al and Cu strips were achieved by the different reductions in thickness. The peeling force per unit length of bond and the resistivity of the samples were measured. The threshold reduction in thickness to start the metallic bond between the Al and Cu strips was characterized. The dependence of bond strengths of different samples on the morphology of the interface was discussed. The effect of short time annealing on the relaxation of the clipping stress at the interface and the bond strength was assessed. The resistivity and bond strength have a similar trend as a function of the thickness reduction. Based on these results a calibrated diagram was established for a nondestructive evaluation of the bond soundness by an electrical resistivity test.

An accelerated crucible rotation (ACR) technique was applied to the Bridgman (B) directional solidification of Al–Cu hypoeutectic and eutectic alloys. For Al–4.5 % Cu hypoeutectic alloys. The development of dendrites was prevented and the cellular spacing was reduced by forced convection in the ACR-B process. For the Al–CuAl 2 eutectic alloy, maximum rotation rates of 100, 200, 300 and 400 rpm were adopted, and the growth rate R was varied between 5 and 60 lm/s. The results show that the periodic structure related to the crucible rotation periods occurs when the Reynold's number Re > 500, and that the average eutectic spacing decreases with the increase of Re . It is found that the convection increases the temperature gradient in front of the liquid/solid interface and reduces the depth of the concave interface, depending on Re and R . The convection also changes the solute distribution around the tips of the cells or dendrites or in front of the eutectic growth interface, and therefore influences the growth morphologies in the ACR-B process.

The B2–B19 one-stage and B2–B19–B19′ two-stage phase transformations have been observed in Ti 51 Pd 30 Ni 19 alloy under different heat treatment conditions. Differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy were used to ascertain the phase transformations. The B2–B19 transformation can be obtained by solution treatment followed by furnace cooling, while the B2–B19–B19′ transformation can be realized by solution treatment with subsequently quenching. Annealing treatment at lower temperature does not change the nature of the phase transformations. It is found that elastic softening occurs in the B2–B19 one-stage phase transformation, while a discontinuous modulus variation in the B2–B19–B19′ two-stage transformation.

Using the diffusion couple and electron probe microanalysis techniques, the phase boundaries of the solid phase of the Ni-Hf system have been determined at 1123 and 1173 K. The intermediate compound NiHf 2 is found to have a limited range of homogeneity. The Ni-Hf system is reassessed by means of the CALPHAD technique. A set of parameters consistent with most of the experimental data on both phase diagram and thermodynamic properties is obtained. The crystallization temperature T x and the glass forming range have been predicted based on the obtained thermodynamic description, and the result is consistent with available experimental information.

Optimized descriptions of the phase diagram and thermodynamic properties of the Pr–Al system have been obtained from experimental thermodynamic and phase diagram data by means of the computer program THERMOCALC based on the least squares method, using models for the Gibbs energy of individual phases. The system contains six intermetallic compounds. The calculated standard enthalpies of formation of Pr 3 Al, Pr 2 Al, PrAl, PrAl 2 , PrAL 3 , Pr 3 Al 11 are: –25.4, –33.5, –44.0, –54.9, –47.5, and –42.3 kJ/mol, respectively. A consistent set of thermodynamic parameters was derived. Optimized and experimental data are in good agreement.

The results of a complex investigation on the phase equilibria and thermodynamic properties of the system Tl–In–Te, obtained using differential thermal analysis, X-ray phase analysis, and electro motive force (EMF) measurement are presented. A projection of the liquidus surface, an isothermal section at 300 K, and a series of vertical sections [Tl(Tl 2 Te)–InTe, TlInTe 2 –Tl(In, Te, Tl 5 Te 3 )] of the phase diagram are obtained. The types and coordinates of the nonvariant equilibria are determined. It was established that in this system two intermediate phases of variable composition (c and e) based on the ternary compounds TlInTe 2 and Tl 3 InTe 2 are formed. Wide regions of homogeneity based on the binary compounds Tl 2 Te, Tl 5 Te 3 , TlTe, InTe, and In 2 Te 3 were also detected. Based on the results obtained by EMF measurements, using concentration galvanic cells, the relative partial molar values for thallium and the standard integral thermodynamic functions of the formation for the ternary compounds and solid solutions were derived.

The excess enthalpies of liquid alloys in the ternary system In–Bi–Te were determined in a heat flow calorimeter for five sections In y Bi 1 – y Te with y = 0.2, 0.4, 0.5, 0.6, and 0.8 at 1173 K, for the section In 0.5 Bi 0.5–Te at 1073 K and 973 K. Calorimetric measurements were also performed in the system Sb–Bi–Te for the section Sb 0.5 Bi 0.5 –Te at 1173, 1073 and 973 K. The excess enthalpies of the binary and ternary liquid alloys were adapted with the association model using the Lukas program. Ternary interactions were taken into account for the analytical description of both systems. The enthalpy surface of the systems is characterized by a trough of minima stretching from Bi 2 Te 3 to In 2 Te 3 , or Sb 2 Te 3 , respectively. The numerical values of the exothermic enthalpies decrease with increasing temperature by dissociation of associates. The decrease is small in the system In–Bi–Te and larger in the system Sb–Bi–Te.

Binary phase diagrams of small particle systems, which consist of a liquid phase with pure solid phases, have been evaluated from the information on the Gibbs energy in the bulk and the surface tension of the liquid phase. As the size of the particle decreases, the melting point of the pure component decreases and the liquid phase region is enlarged. These changes of the phase relations with the size of the particle are dependent upon the composition dependence of the surface tension of the liquid phase.

Using the test data of extra low interstitial (ELI) grade titanium alloy Ti–6Al– 4V (wt.%) with microstructural observations, studies are made to examine the flow localization concepts as well as the simplified metallurgical stability criterion for delineating the regions of flow instabilities in the processing maps. The optimum hot working conditions for the material are suggested.

High-temperature constant-stress creep tests of a single-phase Cu–30 mass% Zn alloy revealed an anomalous type of creep curve. The strain rate increased with increasing strain at the beginning of the 3rd creep, attained a peak value at the end of the 3rd creep and decreased again during newly discovered 4th creep stage. The shape of the creep curve depends on stress, temperature and grain size; in particular, during the tertiary creep, the fine-grained specimens showed a sudden peak without rupturing and a sudden decrease of the strain rate in the quaternary creep. Specimens with a grain diameter of 12 μm were creep-tested under various stresses at 723 K. The dislocation density increased rapidly at the 1st and 4th stages. The 4th creep stage can be explained as the result of the sudden increasing work-hardening.

Differential scanning calorimetry (DSC), powder diffraction and high-resolution X-ray diffraction (XRD), and transmission electron microscopy (TEM) investigations have been performed on melt-quenched amorphous Ni–P alloys with compositions of 18 to 22 at.% P. The calorimetric results revealed different crystallization routes during linear heating below, at and above the eutectic point (19 at.% P) but with the same general transformation scheme as reported previously for electrodeposited and electroless Ni–P amorphous alloys. The composition dependence of the activation energy of the crystallization and the heats evolved during the structural transformations were determined from DSC measurements. The average grain size was derived from XRD line broadening and inportant imformation on the crystallization products and their microstructure could be revealed also from the TEM studies. All these findings will have special significance when analysing the results of isothermal annealing experiments to be described in a forthcoming paper.

In this work the lattice parameters of the hexagonal close-packed (hcp)ε phase have been investigated as a function of the composition, using an X-ray technique. With the present results, reliable trends in the composition dependence of the axes a and c are established, which are significantly simpler than those suggested by early measurements. In addition, new extrapolations to 0 at.% Mn are performed, which are compared with other indirect information on the hcp phase of Fe at room temperature and atmospheric pressure. Finally, by combining the present measurements on the hcp phase with those on the face-centred cubic (fcc) phase reported in the first paper of this series, a detailed analysis is made of the changes in the interatomic distances as well as the relative volume change associated with the fcc → hcp martensitic transformation. According to the present results such volume change is essentially independent of the Mn content, which should be interesting in modelling the energetics of the fcc → hcp transformation.

In spannungskontrollierten Wechselverformungsversuchen konnte ein Einfluss dynamischer Reckalterung auf das zyklische Verformungsverhalten nachgewiesen werden. Im Temperaturbereich dynamischer Reckalterung erreicht der Ermüdungsfestigkeitsexponent maximale Werte. Ein Maximum des Ermüdungsfestigkeitsexponenten korreliert mit einem relativen Maximum der Bruchlastspielzahl. Sowohl die freie Versetzungsdichte als auch die Härte nehmen im Temperaturbereich maximaler dynamischer Reckalterung maximale Werte an.

Negative photoresist photolithography was found superior to previously used positive photoresist photolithography to etch array of quartz tuning forks for use in Qualcomm ® mobile station modem (MSM), 3000™ central processing unit (CPU), chips of code division multiple access (CDMA), personal communication system (PCS), and global system for mobile communication (GSM) units. Optimum processing condition was devised for reproducible precision etching of Z-cut quartz wafer into array of tuning forks. Tuning fork pattern was transferred via ordinary photolithographical chromium/quartz glass template using a standard single-sided aligner and subsequent negative photoresist development. A tightly adhering and pinhole-free 600/2000 Å chromium/gold mask is coated over the developed photoresist pattern which was subsequently stripped in acetone. This procedure was repeated on the backside of the wafer. With protective metallization area of tuning fork geometry thus formed, etching through quartz wafer was done at 80 °C in a ± 1.5 °C controlled bath containing concentrated solution of ammonium bifluoride to remove unwanted area of the quartz wafer. The quality of quartz wafer surface finish after quartz etching depended primarily on the surface finish of quartz wafer prior to etching and the quality of quartz crystals used. At 80 °C, selective etching of 100 μm quartz wafer could be effected within 90 min. Reproducible precision selective etching method has thus been established and enables mass production of miniature tuning fork resonators with electrode patterns on them photolithographically.