Band 99, Heft 11

A model has been developed that links the viscosities of silicate melts to their thermodynamic properties. Over the past several years, through critical evaluation of all available thermodynamic and phase equilibrium data, we have developed a quantitative thermodynamic description of multicomponent silicate melts using the Modified Quasichemical Model for short-range ordering. The local structure of the liquid, in terms of the bridging behavior of oxygen, calculated using our thermodynamic model allows us to characterize the structure of the liquid semi-quantitatively using the concepts of Q-species and connectivity of Q-species. The viscosity is modeled by optimizing viscosity parameters that are related to the structure of the liquid. The viscosity of pure liquid silica is modeled using four model parameters and every other unary liquid is modeled using two. The viscosity of all binary liquids is reproduced within experimental accuracy by optimizing one or at most two binary viscosity parameters for each system. In the present article the equations for the viscosity model are derived and analyses for the experimentally well-established systems CaO – SiO 2 MgO – SiO 2 , NaO 0.5 – SiO 2 , KO 0.5 – SiO 2 and AlO 1.5 – SiO 2 are presented. This is the first step in the development of a predictive model for the viscosity of multicomponent silicate melts that will be presented in part II.

Our recently developed model to describe the viscosity of binary silicate melts is extended to describe and predict the viscosities of multicomponent silicate melts. The viscosity of multicomponent melts containing no AlO 1.5 is modeled to vary linearly as a function of the mole fractions of the basic oxides at constant SiO 2 mole fraction. Systems containing AlO 1.5 show a more or less pronounced viscosity maximum close to the charge compensating composition. This maximum is caused by some of the Al 3+ taking on the same structural role as Si 4+ , thereby participating in the formation of the silica network. The network-forming Al 3+ must remain associated with either one Na + , or two Al 3+ ions must remain associated with one Mg 2+ or Ca 2+ , in order to assure charge neutrality. To take this into account we introduce the associates NaAlO 2 , CaAl 2 O 4 and MgAl 2 O 4 that correspond to charge compensated network-forming Al 3+ . The Gibbs energy of formation of these associates determines the amount of Al 3+ that takes on the network-forming role. We assume the effect on viscosity of network-forming Al 3+ to be the same as Si 4+ and optimize the Gibbs energies of the associates to reproduce the experimental viscosity data. Viscosities in ternary silicate systems without AlO 1.5 are quantitatively predicted with no additional ternary model parameters. Ternary systems MeO x – SiO 2 – AlO 1.5 are modeled with only two temperature-independent ternary parameters per system. The model not only reproduces the magnitude of the observed viscosity maximum, but also its complex shape, asymmetry and temperature dependence.

When an equilibrium state contains degenerate phases, the number of independent phases must be considered in applying Gibbs' Phase Rule. This number can be derived from the rank of the matrix containing the coefficients of the Gibbs – Duhem equations. This provides a quantitative determination of the degrees of freedom even under such conditions of degeneracy.

The thermodynamic properties of liquid Ag – Sn – In alloys were determined using solid oxide galvanic cells with zirconia electrolyte. The following galvanic cells were employed: Re + kanthal, Ag x – In y – Sn (1− x−y ),(In 2 O 3 ) s.s //ZrO 2 + (Y 2 O 3 )//NiO, Ni, Pt(I) in the temperature range from 973 to 1273 K, and in the range of indium mole fraction from 0.3 to 0.8. This limitation was imposed by the side reaction between tin in the liquid alloy and solid In 2 O 3 . It was also found that the liquid is in equilibrium with the solid solution of oxides. Calorimetric measurements of the heat of mixing were also carried out at constant temperature 1003 K and along one isopleth with X Ag /X Sn = 1/1. The thermodynamic properties of the liquid phase were described by the Redlich – Kister – Muggianu formula and the phase relations in the ternary system were calculated. The results of calculations were compared with the experimental data which are available from different literature sources.

This study focuses on the microstructure formation in two Al – Cu – Ag alloys with near-eutectic composition on either side of the α(Al)/θ-Al 2 Cu groove. The alloys solidified equiaxially with two different cooling rates for each composition of alloy. The primary phases formed are α(Al) or θ-Al 2 Cu, but univariant and invariant eutectic reactions are common. In hypoeutectic samples macrosegregation of the α(Al) phase occurred. The univariant α(Al)/θ-Al 2 Cu eutectic in these samples is formed by coupled two-phase structures. The univariant eutectic in the samples, which exhibit primary θ-Al 2 Cu, grew partially competitively due to the α(Al) single phase instability. It is suggested that the difference in solubility of the segregating element Ag in α(Al) and θ-Al 2 Cu phases and processing parameters such as cooling rates determine the resulting microstructure.

Polycrystalline L1 2 -type Ni 3 (Si,Ti), Ni 3 Al and Co 3 Ti alloys prepared through thermomechanical processing from arc-melted ingots were successfully cold-rolled to thin foils with a thickness of less than 200 m. The cold-rolling with over 90 % reduction in thickness was possible without providing intermediate annealing. The cold-rolled foils showed high tensile strength (∼2 GPa) at room temperature although no plastic elongation was observed. The tensile strength of the annealed foils generally decreased acquiring a certain level of fracture strain. Room temperature fracture strain increased with increasing annealing temperature, and reached to 30 – 40 % by a high temperature annealing at 1173 K. Among three kinds of intermetallic alloys, the Ni 3 (Si, Ti) foil annealed around at 900 K exhibited an extremely high tensile strength and yield strength (over 2 GPa) with a reasonable fracture strain. Also, it was found that the fully-recrystallized Ni 3 (Si, Ti) and Co 3 Ti foils showed a strength anomaly at intermediate testing temperature. The observed tensile properties, especially tensile strength at low temperature as well as at high temperature for the present L1 2 intermetallic foils, were found to be superior to those for the conventional alloys such as nickel based alloys and stainless steels.

The present research identifies manufacturing factors that influence the metastable constituent in mottled Nihard cast irons. These irons constitute the roll shells of duplex work rolls processed by centrifugal casting. The research methodology employed a saturated design of experiments program with 7 factors, 8 experiments and a resolution of III. An increase from 6 to 10 kg/T of inoculated FeB enhanced metastable solidification by increasing the amount of ledeburite and the amount of cementite. Similarly, decreasing the Si content from 1.1 – 1.2 to 0.9 – 1.0 wt.% increased the amount of ledeburite and cementite. Finally, the use of casting machines without isolating sleeves increased the roll barrel hardness in the as-cast condition and after tempering.

X-ray diffraction peak profiles obtained from 18Ni lath martensite were analyzed in accordance with the modified Williamson – Hall and modified Warren – Averbach methodologies, aided by supplemental optical and transmission electron microscopy. After instrumental broadening removal, structural peak broadenings were determined for diffraction lines. Consequently, a log-normal size distribution with a mean size of about 156 nm was determined, corresponding reasonably to the lath width illustrated by means of transmission electron microscopy. Further, a dislocation density of 0.723 × 10 16 m – 2 along with a near equal proportion of edge and screw dislocations were identified. Determination of the dislocation arrangement parameter revealed a weak dipole and thus, weak screening action of dislocation strain fields.

Interfacial reactions and mechanical properties between the Cu and Pb-free solders, Sn-3.0Ag-0.5Cu and Sn-58Bi with addition of 0.1 to 1.0 wt.% Pb are investigated in this study. Two kinds of intermetallic compounds, scallop-shaped Cu 6 Sn 5 and plane layered Cu 3 Sn phases, were found in both Sn-3.0Ag-0.5Cu + Pb/Cu and Sn-58Bi + Pb/Cu couples. The intermetallic compound thickness increased with longer reaction times, higher reaction temperatures and greater Pb contents. The Cu 6 Sn 5 phase was the thicker intermetallic compound in the Sn-3.0Ag-0.5Cu + Pb/Cu couple. However, in the Sn-58Bi + Pb/Cu system, the Cu 3 Sn phase is the thicker intermetallic compound. Experimental results indicate that the higher Pb concentration in Sn-3.0Ag-0.5Cu or Sn-58Bi solders reduces the alloy liquidus temperature and increases the thickness of the intermetallic compound. Thicker intermetallic compounds reduce the mechanical strength of the solder joint.

Fibre reinforced ceramic components are most efficiently produced by the braiding technique. Since the braiding angle can be adjusted during the preform fabrication process in a wide range as required by the loading situation of the composite, the evaluation and prediction of the elastic properties as a function of variable braiding angles is of high importance. Based on the classical laminate theory an inverse method for the determination of the elastic properties of an equivalent unidirectional ply is elaborated and applied to predict the effect of variable braiding angles. Orthogonal and non-orthogonal braided carbon/carbon composites were tested under in-plane tensile and shear loading in order to validate the analytical concept. A very good correlation between theoretical and experimental results was obtained.

Low cost titanium alloy compacts were produced via the powder metallurgy approach through the hydride – dehydride process and hot consolidation (hot pressing and hot isostatic pressing). The conditions of the reversible hydride – dehydride process were determined by X-ray and scanning electron microscopy characterisation of powders. Powders were consolidated both above and below the β transformation temperature. The morphology of the microstructure, and the presence of open and closed pores, as well as residual particles of hydrides and oxides have a direct influence on the mechanical properties of compacts (tensile properties and impact toughness).

In this paper, the effects of Sn and Hf additions on microstructures and room temperature mechanical properties of Nb-20Ti-5Cr-3Al-18Si alloy were investigated. The Sn addition has no significant effect on the microstructure of the alloy. Sn is preferentially partitioned in (Nb, Ti)ss rather than (Nb, Ti) 5 Si 3 . The addition of Sn decreases the solubility of Cr in (Nb, Ti)ss. The addition of Hf causes coarsening of the eutectic structure of (Nb, Ti)ss and (Nb, Ti) 5 Si 3 and the formation of the Hf-rich γ(Nb, Ti) 5 Si 3 along phase boundaries. With the addition of Sn the strength of the alloy decreases, while its ductility increases slightly. The Hf addition simultaneously improves strength and ductility of the alloy. The relationships between composition, microstructure and properties are discussed.

The model proposed by Speer et al. to calculate the constrained carbon equilibrium is expanded to include any number of substitutional solutes and coded with the MatLab and Thermo-Calc programs. This model is used to evaluate the effect of Al, Cr, Cu, Mn, Mo, Ni and Si solutes on the final austenite carbon concentration of ternary Fe – X – C alloys. Comparison is also made with the carbon concentration measured experimentally in some Transformation Induced Plasticity steels.

In this study, the hardfacing behavior of Cr – Ni stainless steel was studied by depositing of Stellite 1, Stellite 6, and Stellite 12 superalloys on Cr – Ni stainless steel specimens using electric arc welding and tungsten inert gas welding. The cobalt base alloys were hardfaced on stainless steel plates as a single layer. The samples taken from the hardfaced materials were studied by optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness measurements. The hardness and wear resistance values of the layer obtained after the hardfacing processes are satisfactory and the process seem to be suitable for application.

Taguchi' design of experiment method and statistical F-test were used to optimize design of tuning forks for use in Qualcomm ® mobile station modem (MSM)-3000 TM series central processing unit chips of code division multiple access, personal communication system, and global system for mobile communication systems. Design parameters for motional capacitance C 1 was further optimized after much trial and error so that as-fabricated resonance frequency values of a tuning fork blank remain almost the same prior to final frequency adjustment plating of the mounted crystals, regardless of packaging pressure change from ambient to designated 6 × 10 – 5 Torr. Finite element method modeling was used in conjunction with Taguchi' design of experiment method and, after much trial and error, this enabled selection of essential design parameters to effectively manufacture tuning fork test samples using photolithography with subsequent photoresist spray coating. The tuning fork test samples thus fabricated were characterized and analyzed using Taguchi' method and statistical F-test to evaluate sensitivity of motional capacitance C 1 and as-fabricated resonance frequency for various design parameters at ambient to designated packaging pressure of 6 × 10 – 5 Torr. Motional capacitance C 1 is most sensitive to tine width and tine surface electrode width. Unlike as-fabricated resonance frequency values, motional capacitance values do change with vacuum level of the package. However, tine width asymmetry, electrode thickness and tine tip electrode thickness could be freely adjusted for crystal impedance level without affecting resonance frequency and motional capacitance value. Other design parameters could be adjusted to best suit the manufacturing process.