Constitution of AuSn–Pb–Sn partial ternary system

Abstract

Thermal analysis, metallography, and electron-probe microanalysis have been used to corroborate one of the conflicting constitutions of the AuSn–Pb–Sn partial ternary system. The phase equilibria consist of two ternary transition reactions at 13–0Au, 48–0Pb, 39–0Sn at.-%, 275°C and 8–5Au, 28–0Pb, 63–5Sn at.-%, 210°C, and a ternary eutectic at 3–5Au, 20–0Pb, 76–5Sn at.-%, 177°C. The solubility of Pb in the ternary system is substantial and between 275 and 177°C the system can dissolve up to 4 at.-% Au and 27 at.-%Sn. The maximum width of the AuSn primary phase field in the partial AuSn–Pb–Sn system is approximately 3 at.-%. and that of Sn approximately 2 at.-%.

MST/82     

Constitution of Ti–Al–Ru system

Abstract

The constitution of the Ti–Al–Ru system has been studied in detail. Metallography, X-ray diffraction, electron microscopy, and X-ray spectroscopy have been used to establish the phase diagram between 17 and 37 at.-%Al and 1 and 29 at.-%Ru in the temperature range 1250–770°C. Ternary isothermal sections within the range of investigation and selected phase composition data are presented and phase relationships are discussed. Results show only a small solubility (< 1at.-%) of ruthenium in Ti₃Al and TiAl which are involved in equilibria with a ternary intermetallic compound.

MST/963     

Phase morphology of Pb–Sn–Cd ternary eutectic

Abstract

A method for viewing the detailed solid/liquid interface morphology of metallic eutectic systems has been developed. It is based on an apparatus designed to allow the unidirectional solidification of metallic samples having low thermal mass at considerably lower, and more stable, growth rates than have previously been possible with conventional equipment. As a result, high resolution quench interfaces can be produced which in quality rival those of transparent organic analogue systems. Application of this technique to the solid/liquid interface of the Pb–Sn–Cd ternary eutectic has revealed a number of new facts. It was discovered that the Cd phase forms a facet plane coplanar with its basal plane and with the Pb/Cd lamellar habit plane. Qualitative observations of the differing behaviour of the Pb and Sn phases in contact with the Cd facet plane allowed the magnitudes of the three solid/solid interfacial free energies to be compared and a mechanism for the formation and stabilization of the ABCBA lamellar structure to be postulated.

MST/352     

Calculated ternary diagram of Ti–Al–Si system

Abstract

The phase equilibria between β (body centred cubic, bcc), α (hexagonal closed packed, hcp), Ti₃ Al–α ₂ (hcp), and Ti₅ Si₃ (hcp) in the Ti–Al–Si system have been investigated in the temperature range 700–1200°C. Isothermal sections of the ternary phase diagram have been assessed employing thermodynamic software, which uses the compound energy model to describe the phases mathematically. Available experimental phase equilibria results on the Ti–Al–Si system were used to calculate missing binary and ternary interaction parameters and assess isothermal phase diagrams. Extrapolations in the resulting tie triangles indicate the existence of three eutectoid reactions in the Ti rich corner of the ternary diagram: β → α + Ti₅ Si₃ , α → α ₂ + Ti₅ Si₃ , and β → α ₂ + Ti₅ Si₃ . Additionally, extrapolations in the β + α₂ + α tie triangle observed at 1100°C indicate that two possibilities arise to represent a peritectoid reaction involving α, β, and α ₂phases: β + α₂ → α and β + α → α₂ , depending on the alloy composition and the effect of temperature on the solubitlity of Si in the α phase.     

Diffusion controlled reactions in Au/Pb–Sn solder system

Abstract

The microstructures resulting from the reaction between gold and Pb–Sn solder at temperatures of 80, 125, 140, and 160°C have been studied in the scanning electron microscope and measurements have been made of the reaction kinetics. In the initial stages, the growth rate of the layers of Au–Sn intermetal1ic product was found to be proportional to t^1/2 with an activation energy of (0·84±0·02) eV. At longer times, the growth rate fell below the t^1/2 dependence. This was thought to be owing to a restriction in the supply of gold to the reaction.

MST/1599a     

Formation of microstructure during solidification of Bi–Pb–Sn ternary eutectic

Abstract

To investigate the nature of the Bi–Pb–Sn ternary eutectic, specimens were solidified unidirectionally at very low speeds and quenched to form a representative solid/liquid interface for subsequent study. Specimens made using the generally accepted composition, as reported by Ho et al., did not form all three solid phases from the start of freezing. Specimens produced using the composition reported by Sakurai, i.e., 54 wt-%Bi, 28 wt-%Pb, and 18 wt-%Sn, did give all three phases from the beginning of freezing, indicating that it is the correct eutectic composition. It was found that this eutectic is of the faceted (Bi) non-faceted (X phase) non-faceted (Sn) type. Under the freezing conditions used, a double binary microstructure was formed, with one component consisting of Sn fibres in the X phase and the other of a Bi–Sn complex regular microstructure. While the occurrence of a double binary microstructure was predicted by C. S. Smith for a lamellar ternary eutectic, the current observation shows that it can also occur in a system with one fibrous phase.     

Tie line compositions of ternary Cu–Ag–Au alloys within miscibility gap

Abstract

Tie line coordinates of ternary Cu–Ag–Au alloys in the solid immiscible region of the equilibrium phase diagram were determined experimentally by electron probe microanalysis. The two solid phases were analysed in samples which had been thermally treated from the as–cast condition to coarsen the phases. Tie line coordinates were also calculated theoretically using a thermodynamic model which is an extension of the regular solution model. The theoretical calculations agree well with the experimental analysis of the copper–rich phase as well as with a corrected analysis of the silver–rich phase. The necessity for the correction was attributed to the thermal coarsening treatment of the samples.

MST/191     

Thermodynamic assessment of Co–Al–W system and solidification of Co-enriched ternary alloys

Based on the assessed three constituent binary systems and reported phase diagram data, the Co–Al–W ternary system was thermodynamically optimized by using CALculation PHAse Diagram (CALPHAD) method. The newly reported ternary phase γ′ was described with a two sublattice model, (Co,Al,W)_0.75:(Co,Al,W)_0.25, while liquid Fcc, Hcp(Co), and Bcc(W) were treated as substitutional solution phases. In order to describe the ternary solubility in the binary phases Co₇W₆ and CoAl, the models (Al,Co,W)₇W₂(Al,Co,W)₄ and (Al,Co,W)_0.5(Al,Co,W)_0.5(Va)₃ were, respectively, adopted. The rest 11 phases in the ternary systems were simply treated as stoichiometric compounds because their homogeneous ranges are small and can be neglected. A set of self-consistent parameters were obtained, which reasonably reproduced the phase relationship in Co-enriched corner. Finally, to confirm the reliability of the present assessment,the so-called Scheil–Gulliver model was used to simulate the solidification processes of three typical Co-based alloys. It was shown that the as-cast microstructures of the three ingots were well explained or predicted.     

Microstructures formed by directional solidification of two ternary eutectic alloys of Bi–Cd–In system

Abstract

Microstructures of the two ternary eutectic alloys of the Bi–Cd–In system were studied using slow unidirectional solidification, followed by quenching to form a representative solid/liquid interface for subsequent observation. The eutectic reactions were found to take the form L?BiIn+BiIn₂+Cd at 77.5°C and L?BiIn₂+_?+Cd at 61.5°C. The 77.5°C eutectic was observed to be of the faceted (BiIn)–faceted (Cd)–non-faceted (BiIn₂) type, while all three phases of the 61.5°C eutectic showed faceting. The BiIn and BiIn₂ phases of the 77.5°C eutectic formed a quasiregular microstructure with the Cd phase growing relatively independently. The phases of the 61.5°C eutectic tended to form a lamellar microstructure with a BiIn₂–?–Cd–_?–BiIn₂ phase sequence. Both eutectics were observed to obey the usual phase spacing law, λ²R=constant, where λ is the phase spacing and R is the growth rate.     

Constitution of Ni3Al–Ni3Mo–Ni3W section of Ni–Al–Mo–W system

Abstract

The isothermal section of the Ni–Al–Mo–W system has been studied at 75 at.-%Ni at temperatures of 1523 and 1273 K. Constitutional data have been determined using electron probe microanalysis, X-ray diffraction, and microscopical examination. The alloys studied lay in the range 12·5–15 at.-%Al, 2·5–7·5 at.-%Mo, and 2·5–7·5 at.-% W. The phases present at 1523 K were γ, γ′, and α (based on the Mo–W continuous series of solid solutions); at 1273 K, NiMo(δ′) was also encountered. The γ/γ′ mismatch values lay in the range ?0·03 to ?0·75%. In the as-solidified state, the alloys consisted predominantly of γ-phase containing γ′-precipitates formed in the solid state.

MST/462     

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

A thin film combinatorial library deposited by co-sputtering of Hf, Nb and Ta was employed to characterise fundamental properties of the Hf-Nb-Ta system. Compositional mappings of microstructure and crystallography revealed similarities in alloy evolution. Distinct lattice distortion was observed upon addition of hexagonal Hf, leading to amorphisation of alloys containing more than 32 at.% Hf and less than 27 and 41 at.% Nb and Ta, respectively. Volta potential and open circuit potential mappings indicated minimal values for the highest Hf concentration. Localised anodisation of the library by scanning droplet cell microscopy revealed valve metal behaviour. Oxide formation factors above 2 nm V^?1 were identified in compositional zones with high amounts of Nb and Ta. Fitting of electrochemical impedance spectroscopy data allowed electrical permittivity and resistivity of mixed oxides to be mapped. Their compositional behaviours were attributed to characteristics of the parent metal alloys and particularities of the pure oxides. Mott–Schottky analysis suggested n-type semiconductor properties for all Hf–Nb–Ta oxides studied. Donor density and flat-band potential were mapped compositionally, and their variations were found to be related mainly to the Nb amount. Synergetic effects were identified in mappings of Hf-Nb-Ta parent metals and their anodic oxides.     

Direct observation of ternary solid state transformation in Bi–Cd–In alloy system

Abstract

Cast or solution treated specimens of a Bi–9·0Cd–26·7In (wt-%) alloy were observed to form a fine, three phase microstructure on aging at room temperature, replacing a single phase formed at a higher temperature. The three phases resulting from this solid state reaction were found to grow with a lamellar morphology into the high temperature phase, with a growth rate of 0·5–1·0 μm h^-1 at room temperature. The equilibrium temperature for the transformation was found to be ～25°C. Using a Hitachi S-4500 field emission SEM, the phase transformation was followed in progress at magnifications of 3000 and 10 000 times. It was noted that a volume change was associated with the transformation. It was concluded that the transformation is of the ternary eutectoid type.     

Phase transformations in the ternary Ag–Ga–Sb system

Phase diagram of the Ag–Ga–Sb ternary system was extrapolated using calculation of phase diagrams (CALPHAD) method. Phase transition temperatures of the alloys with compositions along three vertical sections with constant molar ratios Ga/Sb = 1, Ag/Ga = 1 and Ag/Sb = 1 were measured using differential scanning calorimetry (DSC). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) was used for identification of phases in equilibrated samples. Experimental results were compared with thermodynamic prediction.     

Interdiffusion studies in bulk Au–Ti system

The performance of the contacts, where Au/Ti layers are used in the metallization scheme, largely depends on the product phases grown by interdiffusion at the interface. It is found that four intermetallic compounds grow with narrow homogeneity range and wavy interfaces in the interdiffusion zone. The presence of wavy interfaces is the indication of high anisotropy in diffusion of the product phases. This also reflects in the deviation of parabolic growth from the average. Further, we have determined the relevant diffusion parameters, such as interdiffusion coefficient in the penetrated region of the end members and integrated diffusion coefficients of the intermetallic compounds.     

Formation region of monophase with cubic spinel-type oxides in Mn–Co–Ni ternary system

This study was performed to find the composition area of cubic spinel-type monophase oxides composed of the Mn–Co–Ni ternary system. Starting materials were prepared by mixing Mn, Co, and Ni nitrates then evaporating to dryness. Each starting oxide was fired at 700, 800, 900, 1000, and 1100 °C in air. The regions of cubic spinel monophase (CSM) were confirmed to spread with decreasing firing temperatures. The region of CSM at 1000 °C was seen near the line connecting the points of Mn : Co : Ni = 2 : 4 : 0 and 4.5 : 0 : 1.5. The area at 800 °C spread toward Co and Ni, as compared to the results at 1000 °C. In the region containing more Mn above the area of CSM at 800 °C, the phase had tetragonal spinel or -Mn₂O₃ besides cubic spinel structure. Below this area, the phase contained rock-salt-type crystal besides cubic spinel structure. This tendency at 1000 °C was the same as that at 800 °C.     

Formation of microstructure resulting from quasi-peritectic reactions during freezing of Bi–Pb–Sn and Cu–Ni–Sn ternary alloys

Abstract

The quasi-peritectic reaction, frequently observed in ternary alloy systems, takes the form L + α?β + γ, where L indicates the liquid phase, and α, β and γ indicate solid phases. The formation of microstructure resulting from the kinetics of this reaction is considered from a theoretical point of view and compared with experimental observations of microstructures formed by quasi-peritectic reactions in two ternary alloy systems, Bi–Pb–Sn and Cu–Ni–Sn. Based on these considerations, an explanation is proposed for experimental observations previously reported in literature concerning phase transformations from the liquid in multicomponent ferrous alloys.