Cobalt rich phase formation in metastable Cu–Co alloys by means of melt spinning

Abstract

Metastable CO_xCU_100?x alloys with extended cobalt solubility (5≤x≤20), which can not be obtained by equilibrium methods, were prepared by melt spinning. The separation of the cobalt rich phase upon heating was monitored by X-ray diffraction and calorimetric measurements. The volume fraction of cobalt rich particles can not be determined using X-ray diffraction if the cobalt rich particle size is below a critical value. The separation of the cobalt rich phase seems to be a three step process including nucleation, growth, and coarsening. The non-isothermal kinetics of nucleation and growth of the cobalt rich phase were analysed in terms of a modified Kissinger model. The heat release during phase separation is closely related to the amount of cobalt dissolved in the copper matrix.

MST/3258     

Photoconduction of rapidly quenched films in the PbOTiO2 system

The PbOTiO₂ films were prepared by a rapid quenching technique using a twin-roller type equipment. The quenched films containing from 10 to 30 mol% TiO₂ precipitated tetragonal PbO solid solution as single phase. The PbTiO₃ crystal precipitated from the melt of equimolar composition of PbO and TiO₂ had a denser structure and a lower tetragonality compared to that obtained by solid phase reaction. In the films containing 60 mol% TiO₂ or above, the formation of amorphous phase was predominant. Crystalline films, as well as PbTiO₃ film, showed photoconductivity.     

TEM observation of icosahedral,new crystalline and glassy phases in rapidly quenched CdCu alloys

TEM study of microstructures observed in rapidly solidified CuCd alloys in the compositional range between 37.2 to 60.5 at% Cd demonstrates for the first time:

• 1.1. The formation of an icosahedral CuCd quasicrystalline phase;
• 2.2. The existence of a tetragonal CdCu phase first identified by x-ray diffraction by Dey and Quader as the Cd₃Cu₄ phase.
• 3.3. The existence of a new CuCd cubic fcc phase with a giant unit cell of a ≅ 3.25 nm, close to the Cd₃Cu₄ composition.
• 4.4. Formation of Cu-37.2 at% Cd metallic glass.
• 5.5. The possibility of forming giant unit cell crystalline structures from the melt and by solid-state precipitation during the limited times of rapid quenching.

     

The effect of quenching on the martensitic transformation in ß1 phase of Au-Cd alloys

The effect of quenching on the martensitic transformation mechanism in ₁ Au-Cd alloys has been investigated by measurements of the electrical resistivity and X-ray diffraction. In the case of the Au-47.5 at%Cd alloy, the ₂-martensite is the characteristic product under quenching conditions, but it always exists with the equilibrium ₂-martensite phase. Consequently, the _{1 2} and ₂transformations occur simultaneously during the heating and cooling cycles. The corresponding resistivity behaviour is very complicated and extremely sensitive to thermal treatments such as quenching temperature and thermal cycling. On the other hand, in the case of the Au-49.0 at%Cd alloy, only the _{1 2} transformation occurs even when quenched, and the transformation is unaffected structurally by quenching. A distinct resistivity anomaly, which is considered to be due to the disappearance of quenched-in vacancies, is observed in quenched alloys. Some important characteristics of this anomaly are determined. In particular, the quenching effect disappears when the specimen is heated above the temperature at which the resisitivity anomaly begins. This result suggests that the quenched-in vacancies play an essential role in the martensitic transformation process under quenching conditions.     

Ion-nitriding behaviour of Fe-Ti alloys in theα-phase region

The ion-nitriding behaviour of four iron alloys containing between 0.11 and 1.48 wt% titanium was investigated in the-phase region to discuss kinetics of the growth of the nitriding layer. The ion-nitriding experiments have been made at 823 K. Two nitriding layers were observed: a thin surface layer which mainly consists of Fe₄N; an internal nitriding layer beneath the surface layer, where the nitride formed was found to be TiN. The growth of the internal nitriding layer is controlled by a diffusion process of nitrogen in the matrix metal. The apparent diffusion coefficient of nitrogen in the nitriding layer, evaluated using the rate equation proposed for internal oxidation, increases linearly with the volume fraction of titanium nitride. Furthermore, by excluding the effect of the titanium nitride from the apparent diffusion coefficient, the diffusion coefficient of nitrogen in-iron was calculated, being in good agreement with that reported so far. In addition, the increase in hardness in the internal nitriding layer has been discussed.     

Structure and stability of rapidly quenched Al86Cr14−x Fe x alloys

The structural and thermal properties of melt spun Al₈₆Cr_14–x Fe _x , alloys have been investigated using X-ray diffraction, transmission electron microscopy, electron diffraction and differential thermal analysis. Electron diffraction patterns indicate that all alloys contain quasicrystalline nodules with icosahedral symmetry in a matrix of f cc aluminium. Microscopically the alloys fall into two categories; those with x 6 and those withx > 6. The first class alloys shows large (>1m) icosahedral crystallites with well defined dendritic crystallite growth and sharp quasicrystalline X-ray diffraction peaks. The latter alloys show quasicrystalline crystallites which are predominantly much smaller as well as considerably broadened X-ray diffraction peaks. Thermal analysis measurements indicate that the activation energy for crystallization in these alloys is about 1.5 eV.     

The intracellular phase in rapidly solidified lloys based on the AlFe system

The nature of the second phase formed in rapidly solidified AlFe alloys has been determined. For those alloys studied exhibiting micro-cellular morphologies, the second phase is T′. The alloy Al-6.8Fe-2Mo-1.1V, in the melt-spun condition, exhibits a different microstructure, consisting of a uniform and extremely fine distribution of second phase particles. These particles possess the icosahedral structure, identical to that observed in rapidly solidified AlMn alloys. The mechanism of formation of these second phase particles is thought to involve the formation of an amorphous material following the nucleation of primary α-Al; this amorphous material is thought to be crystallized as a result of recalescence.     

The role of silicon in the formation of the (Al5Cu6Mg2) σ phase in Al-Cu-Mg alloys

The role of silicon in the precipitation of the phase (Al₅Cu₆Mg₂) has been investigated through comparative studies on Al-3.63Cu-1.67Mg (wt%) and Al-3.63Cu-1.67Mg-0.5Si alloys. Both alloys were extensively examined after solution treating at 525°C for 2.5 h followed by ageing at 265°C for times up to 650 h. Limited studies were also undertaken on both alloys after ageing at 200 and 305°C. Precipitation of was observed in Al-3.62%Cu-1.66%Mg-0.5%Si for all ageing conditions studied but was absent in Si-free Al-3.62%Cu-1.66%Mg. In addition, S and phases were observed in both alloys. The volume fraction of phase in the Si containing alloy was substantially reduced by a pre-age stretch followed by ageing for 24 h at 265°C with S being the dominant precipitate type. The volume fraction of phase in the Si containing alloy was lower after ageing 24 h at 200°C than after 24 h at 265 and 305°C. Peak hardness was higher for the Si free alloy on ageing at 200 and 265°C, but the Si free alloy softened more rapidly, reflecting the more rapid coarsening kinetics of S compared with .     

The nature of the transition atH c2 in low-κ type II lead-indium superconducting alloys

The anomalous magnetic and calorimetric properties atH _c2, which we reported for a lead-indium sample, are in agreement with the prediction of a bulk first-order phase transition from recent theories for critical κ superconductors \(\kappa \approx 1/\sqrt 2 \) . Other experimentalists, however, explain this behavior as an effect of the superconducting surface sheath. In an attempt to clarify the issue, magnetization and specific heat measurements are reported here on two samples with nominal concentrations of 1.9 and 1.4 at % indium in lead. The latter is type I above 6 K (T _c =7.12 K). It is shown that surface effects are relevant for the effect reported previously. However, after empirical surface treatments have been applied to eliminate or at least minimize such effects, most of the results for the sample, which fulfills the theoretical requirements, are in agreement with theoretical predictions of Fischer, Usadel, and Jacobs. A bulk first-order transition atH _c2 is thus, nevertheless, likely to occur for strong-coupling type II superconductors with critical κ values.     

The composition of the gas phase over liquid lithium at 1600–6000 K in view of existence of atoms and metastable self-associates

Methods of thermodynamic simulation in view of existence of lithium atoms (Li₁), condensed and volatile Li₂–Li₅ self-associates, Li ₁ ⁺ , Li ₂ ⁺ , and Li ₃ ⁺ ions, and e-gas are used to calculate partial pressures of components of the gas phase over liquid lithium in the 1600–6000 K temperature range and the thermal characteristics of the system at 1600 and 6000 K.     

The activation of 〈c + a〉 non-basal slip in Magnesium alloys

The activation of 〈c + a〉 non-basal slip system can help to improving the mechanical properties of Magnesium alloys. The activation conditions of 〈c + a〉 non-basal slip system in Mg alloys are reviewed, such as the addition of lithium elements, increasing temperatures, and regions of stress concentration, and so on. Moreover, the article summarizes our results from the work on Mg alloys using equal channel angle pressing with back pressure, and points out that 〈c + a〉 non-basal slip systems also become active much easier under hydrostatic pressure, which will help to open new window to explore the basic physics of the activation of non-basal slip.     

Experimental investigation of phase equilibria in the Cu–Ni–Zr system

Phase equilibria in the Cu–Ni–Zr ternary system have been measured through alloy sampling combined with diffusion couple approach. According to the phase relations identified with electron probe microanalysis and X-ray diffraction techniques, isothermal sections at both 1073 and 1293 K were constructed. It is evident that remarkable ternary solubility occurs in almost all binary intermetallic phases at both temperatures. The formerly reported ternary compounds T1 (Cu_20–40Ni_40–60Zr₂₀) and T2 (Cu_20–25Ni_60–65Zr₁₅) were not verified in this work. No other ternary compound was detected. In addition, continuous dissolution between Cu₁₀Zr₇ and Ni₁₀Zr₇ at 1073 K was observed.