Precipitation hardening of Cu-4Ti-1Cd alloy

Precipitation hardening of Cu-4Ti-1Cd alloy has been studied using hardness measurements and transmission electron microscopy. This alloy exhibited hardness of 238 Hv in solution treated (ST) condition and attained peak hardness of 318 Hv after ageing at 450°C for 40 h. Electrical conductivity of Cu-4Ti-1Cd alloy increased from 5.7 %IACS (International Annealed Copper standard) in ST condition to 8.9 %IACS on ageing at 450°C for 16 h. This alloy exhibited markedly higher yield strength (751 MPa in the peak-aged condition) compared to Cu-4.5Ti alloy but the increase in UTS due to cadmium addition was less significant. The higher yield strength of ternary alloy in peak aged condition is due to the solid solution strengthening of cadmium as well as the presence of -Cu₄Ti precipitate. On over-ageing the alloy showed a decrease in hardness as a result of formation of equilibrium precipitate, -Cu₃Ti. Optical microscopy reveals single phase with equiaxed grains in solution treated condition. A coherent, metastable phase -Cu₄Ti is responsible for high strength and hardness in peak aged condition. The over-ageing in this alloy shows the formation of cellular structure at the grain boundaries of the matrix phase.     

Codeposition of Metallic Components in the Growth of Thin PbTe?Ga? Films on Si Substrates

In depositing thin PbTeGa films onto Si and SiO₂/Si substrates by the hot-wall method, Pb_{1 – x} Ga _x melts were used as Ga vapor sources in combination with separate Pb and Te vapor sources. The vaporization of Pb_{1 – x} Ga _x (0.15 x 0.95) melts was studied between 1000 and 1300 K in the reaction chamber of the deposition unit. Using electron probe x-ray microanalysis, all the deposited films were shown to contain Ga. Pb_{1 – x} Ga _x melts were also used as separate Pb and Ga vapor sources.     

The stress dependence of superconducting parameters in pure In and Sn and in α-phase In-Sn alloys

We have measured the length change due to the transition from the super-conducting to the normal state in pure In and Sn and in In-Sn alloys. The measurements were made on single-crystal specimens. The alloys had Sn content ranging from zero to 12 at %. Crystals parallel and perpendicular to the tetragonal axis were grown at each alloy content. We find that the relative length changes l/l are very sensitive to alloy content. From l/l we have calculated the stress derivatives H _c/ and T _c / and we find that T _c / changes from +59 to –92 mK/bar for stress along the tetragonal axis, and from –9 to 46 mK/kbar for stress perpendicular to the tetragonal axis. We suggest that these large changes are due to Fermi surface topology changes upon increasing the Sn content in In.     

Phase equilibria in the Ag4SSe-ZnTe system

The Ag₄SSe-ZnTe phase diagram has been determined on the basis of X-ray diffraction, differential thermal and metallographic analyses, as well as microhardness and density data. It has been divided into two subdiagrams of eutectic type by an intermediate A-phase with most probable composition of 2Ag₄SSe.ZnTe. The unit-cell parameters of the low-temperature -2Ag₄SSe·ZnTe modification have been determined (a=3.330 , b=3.010 , c=2.895 , =95.04°, =107.83°, =92.62°). It has been supposed that in the ZnTe-rich part a second intermediate B-phase with a composition of Ag₄SSe·2ZnTe is formed, which is stable in the range of 320÷500 °C.     

Crystalline structure and dielectric properties of Ba(Ti1−y Ce y )O3

Crystalline structure, microstructure and dielectric properties for Ba(Ti_1–y Ce _y )O₃ (0 y 0.5) ceramics have been studied. Dense ceramics with the relative density higher than 95% and grain size of 0.7–1.5 m have been obtained. The limit of the solid solubility is determined as y = 0.3 by the X-ray diffraction, SEM, and dielectric properties measurements. The crystalline symmetry is tetragonal for the sample with y = 0.02 and cubic for y 0.06 at room temperature, and the unit cell increases with increasing Ce content in the solid solution range. Correspondingly, the dielectric response exhibits three dielectric peaks for y = 0.02, and one pinched dielectric peak with ferroelectric relaxor behavior for y 0.06.     

Excess energy in quenchedβ-Cu-Zn-Al alloys: relation to the martensitic transformation

The disorder-induced excess energy,L , of a-Cu_1– x)(ZnAl) _x (0.30 x 0.35) alloy, which shows a martensitic transformation at low temperature, after quenching from different initial temperatures,T _i, is calculated. Ordering-energi-es for the different nearest and next-nearest neighbour atom pairs, obtained by fitting mean field expressions of order-disorder critical temperatures to experimental data, are used. The excess energy is related to the changes of the latent heat of the martensitic transformation,L, observed just after quenching from T_i. It was found that the shift in latent heat correlates linearly with the calculated excess energy of the-phase. Calorimetric measurements justify the results.     

Low-temperature synthesis of binary cuprates from hydroxide precursor

Binary cuprates of Sr₂CuO₃₊ and SrCuO₂ have been synthesized at low temperatures below 500 °C under various values of partial oxygen-pressure by thermal decomposition of hydroxide precursors, Sr₂Cu(OH)₆ and SrCu(OH)₄, respectively. The tetragonal Sr₂CuO₃₊ ( 0.3) is obtained by the heat-treatment at 400 ° C and 0.2 atm. The value of appears to be independent of and unchangeable. On the other hand, the orthorhombic Sr₂CuO₃₊ ( 0) is obtained by the heat-treatment at 400 °C in flowing gas of N₂. For 0 < < 0.2 atm, a mixture of the tetragonal and orthorhombic phases is obtained. The orthorhombic SrCuO₂ is obtained by the heat-treatment at 500 ° C in flowing gas of N₂, although the tetragonal SrCuO₂, namely, the so-called infinite-layer compound is not obtained.     

Reversible colour change in Cu-Al-Ni alloy ribbon associated with phase transformation

The colour change behaviour and its relation to phase transformation of Cu-14 wt% Al-4 wt% Ni alloy ribbon produced by the twin-roller type melt-quenching method were investigated by spectral reflectivity and X-ray diffraction, respectively. This ribbon turns copper-coloured around room temperature on quenching it from a temperature above 1020 K, and turns gold-coloured on ageing it between 670 and 970 K. By repeating these heat treatments, either of the two colours can be acquired interchangeably. The spectral reflectivity also changes with respect to the colour change. The copper-coloured alloy shows a DO₃ structure which is the ₁, phase. The gold-coloured alloy shows a mixed phase of ₂ (cubic, Cu₉Al₄ compound), and (fcc, Cu-Al-Ni solid solution) and/or ₁ which is a martensite of the ₁ phase having a (1 21) twinning structure. Therefore, the colour change between copper and gold is due to the solid-state phase transformation between ₁ and ₂ + ( and/or ₁) on heat treatment.     

Microstructural and chemical stability of Y-ZrO2 reinforced β″-alumina in molten sodium sulfide and sulfur

The stability of -alumina reinforced with 10 vol% of tetragonal partially stabilized 3 mol% Y₂O₃-ZrO₂ (3Y-ZrO₂) and with 10 vol% of cubic 8 mol% Y₂O₃-ZrO₂ (8Y-ZrO₂) in molten sulfur or molten Na₂S₄ has been examined using scanning electron microscopy (SEM) X-ray diffraction (XRD) and electron probe microanalysis (EPMA) both before and after immersion at 350 °C. Tetragonal partially stabilized 3 mol % Y₂O₃-ZrO₂ was destabilized when reinforced into -alumina and immersed in molten Na₂S₄. Destabilization without incorporation into -alumina or using molten S as the immersion medium was minor. EPMA analyses indicated that the presence of -alumina enhanced zirconia destabilization in that -alumina can react with the molten corrodants to form corrosion products which are known corrosion agents for the leaching of Y₂O₃ from partially stabilized 3Y-ZrO₂. From XRD analyses, changing from partially stabilized 3Y-ZrO₂ to cubic 8Y-ZrO₂ in the composite increased resistance against phase destabilization. EPMA analyses revealed that the depletion was almost halted for cubic 8Y-ZrO₂ suggesting that the change in the zirconia phase used had reduced the chemical reactivity between Y₂O₃ and the corrodants. In order to avoid depletion destabilization of zirconia in -alumina, corrosion resistance can be increased by reducing chemical reactivity by using fully stabilizing zirconia. In addition, partially stabilized tetragonal zirconia may still be considered for use if a less reactive stabilizer such as CeO₂ is used.     

Phase relation in titanium-aluminide alloy — an X-ray study

Results of X-ray diffraction studies on titanium aluminides stabilized by niobium, vanadium and molybdenum are reported to establish a phase relation in the Ti-25Al-10Nb-3V-1Mo at% (Ti-25-10-3-1) alloy. It is shown that the composition of the phases probably deviated slightly from ideal stoichiometry Ti₃Al for ₂ and Ti₂AlNb for -type; its partial ordering in of the -phase type and the phase relation is 64% -type and 36% ₂ phase.     

The constitution of the Ni-Al-Ru system

The constitution of the Ni-Al-Ru system has been investigated in the range 0 to 50 at% Al. Isothermal sections at 1523 and 1273 K have been determined using microstructural observations, electron probe microanalysis and X-ray diffraction. The phases present were: nickel-based solid solution (); (based on Ni₃Al); solid solutions based on NiAl and RuAl, respectively (designated ₁ and ₂), and ruthenium-based solid solution (Ru). The maximum solubility of Ru in was 5 at%. ₁, and ₂ show extensive range of solubilities, namely up to 20at% Ru in ₁ and up to 25 to 35 at% Ni in ₂. Three-phase equilibrium between , ₂ and (Ru) existed at 1523 and 1273 K. Also at 1523 K, three-phase equilibria existed between , and ₁ and ,₁ and ₂, while at 1273 K, the equilibria were between , ₁,₂ and , , ₂ indicating the occurrence of a reaction +₁, +₂ at a temperature between 1523 and 1273 K. Liquidus features have been deduced from data on as-solidified structures. Lattice parameter data and hardnesses are also reported.     

Microstructural characterization of γ-TiAl base alloy by electron probe x-ray microanalysis and electron backscatter diffraction

Electron backscatter diffraction (EBSD) and electron probe x-ray microanalysis (EPMA) in combination with x-ray diffraction (XRD) were applied for phase identification of the ternary precipitates and accompanying phases in Ti-49.6Al-1.9Fe alloy after heat treatment at 1400°C followed by furnace cooling. The heat treatment resulted in formation of the duplex structure consisting of equiaxed grains of the phase (AuCu type) and lamellae of the and ₂ (Ni₃Sn type). The ternary ₂ (Mn₂₃Th₆ type) phase, containing 21–22 at. % Fe, was revealed on the grain boundaries of the -matrix and lamellae, and is accompanied by ₂ precipitates. Different morphologies of the ₂ + ₂ colonies were found to differ in chemical composition, coarse particles being depleted in titanium, and the fine particles enriched in it. The combination of EPMA and EBSD in scanning electron microscopy proved to be very effective in local phase identification of specimens with fine multiphase structure.     

The modulated structure formed by isothermal ageing in ZrO2-5.2 mol % Y2O3 alloy

The modulated structure produced by isothermal ageing of ZrO₂-5.2 mol % Y₂O₃ alloy was examined mainly by electron microscopy. It was found that the modulated structure was formed at ageing temperatures between 1400 and 1600° C, but not at 1700° C. The structure is developed by spinodal decomposition, which produces compositional fluctuation in the elastically soft 111 direction in cubic zirconia. The hardness increase caused by the development of modulated structure during ageing is larger than the hardening by precipitation of tetragonal phase in the cubic matrix.Graduate Student, Tohoku Univerisy, Sendai, Japan.     

Effect of scandium on the decomposition of aluminium-zinc alloys

The effect of scandium on the hardness, structure and heat evolution of an aluminium-40% zinc alloy was investigated. It was found that contrary to its action in other aluminium-based alloys, scandium does not raise the maximum hardness during an ageing treatment. This may be explained by insufficient scandium redissolution at the rather low temperature necessary for achieving a solid solution of zinc in aluminium. Differential scanning calorimetry studies show a similar heat evolution in both alloys upon linear heating, starting with the reversion of modulated structures. An exothermal effect appears only in the scandium-bearing alloy due to increased heterogeneous precipitation of _r, and on Al₃Sc particles. Above 200 °C, the dissolution of the _r and phases starts, followed by the monotectoid reaction.     

X-ray Diffraction Study of an Inhomogeneous Langasite (La3Ga5SiO14) Crystal

A Czochralski-grown langasite, La₃Ga₅SiO₁₄ (La₃Ga₄(GaSi)O₁₄), crystal was studied by x-ray diffraction. The crystal was found to consist of two isostructural solid solutions, except in the center of the tail end. The solid solutions differ in the Ga and Si occupancies on the (Ga,Si) site: Ga > Si in solid solution I, and Si > Ga in solid solution II. The composition of I (center of the tail end) is La₃Ga₄(Ga_1.14Si_0.86(4))O_{13.840.16(11)}. The composition of II, which coexists with I in the peripheral part of the tail end, is (La_2.950.05)Ga₄(Ga_0.84Si_1.16(6))O₁₄.     

Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

We have measured the nuclear specific heat C_n and nuclear susceptibility _n of In nuclei (I=9/2, =5.5 _n) in the cubic intermetallic compound AuIn₂ (Korringa constant =0.11 Ksec) in the normal conducting state at 30K10mK and 2mTB115 mT. Our data show a positive nuclear Weiss temperature =+ 43 K and that the In nuclei undergo a nuclear ferromagnetic transition at T_c=35 K. The In nuclei experience an internal field of about 10 mT (obtained from C_n at T>T_c ). The nuclear ordering temperature T_c and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction S(T_c)/S_max=8.6% and critical enthalpy E=0.28 RT_c are in reasonable agreement with the measured ordering temperature T_c,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time calculated from the real and imaginary parts of _n is 10 msec at T>50 K, but drops to <1msec at T_c.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T _nuclear =T _electron .     

The crystallization of the amorphous alloy Fe40Ni40P14B6

The isothermal transformation behaviour of the metallic glass Fe₄₀Ni₄₀P₁₄B₆ between 320 and 400° C is described. Crystallization occurs by a eutectic mechanism to form Fe-Ni austenite and a body-centred tetragonal phase which is isomorphous with Fe₃P and Ni₃P. The eutectic crystals have a barrel shape such that the c-axis of the tetragonal phase is parallel to the barrel axis. The orientation relationship between the two phases is 1 1 0T 1 1 0 and 0 0 1T 1 1 2. The austenite phase contains (1 1 1) twins.     

Phase decomposition in extruded Zn-Al based alloy

Ageing characteristics of an extruded eutectoid Zn-Al based alloy were investigated using X-ray diffraction and scanning electron microscopy techniques. The extruded alloy consisted of Al rich phase and Zn rich _E and phases. The original cast eutectoid Zn-Al alloy was extruded at 250 °C. Both supersaturated _s and _s phase decomposed during extrusion and appeared as fine and coarse lamellar structures. The _E and phases particles formed in the original interdendritic region. It was found that two Zn rich phases _E and decomposed sequentially during ageing at 170, 140 °C. The decomposition of the _E phase occurred as a discontinuous precipitation in the early stage of ageing and the decomposition of the phase took place in a four phase transformation: + T + in the prolonged ageing. Two typical morphologies of the decomposition of the Zn rich phases _E and were distinctive in back-scattered scanning electron microscopy.     

The athermal α → ω transformation in Zr-2 at% Nb alloy

The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT ₀ ,T ₀ ,T ₀ and the correspondingM _s ,M _s andT _s start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data.     

Coexistence of Cubic and Tetragonal Structures in Yttria-Stabilized Zirconia Nanoparticles

Experimental evidence is presented for the coexistence of cubic and tetragonal phases in yttria partially stabilized zirconia nanoparticles (centaurs).