The oxidation behaviour of NiAl-I. Phase transformations in the alumina scale during oxidation of NiAl and NiAl-Cr alloys

A re-assessment of the ternary system Al-Cr-Ni following Dupin's thesis work using a single Gibbs energy function for the γ and γ' phases is presented taking into account new experimental liquidus temperatures. The disordered bcc A2 and ordered B2 phases are also modelled with a single equation. The existence of vacancies as defects in this structure is described. The other phases are modelled as substitutional solutions, or as stoichiometric or non-stroichiometric binary compounds. The present assessment is limited to the sub-system AlNi-Cr-Ni where no ternary phase exists. The parameters describing the Gibbs energy of all the assessed phases are given. Extensive comparisons between calculation and experimental data are presented.

Thermodynamic re-assessment of the ternary system Al-Cr-Ni

The diffusion rates of chromium, vanadium, and hafnium in α- and γ-Fe have been determined by radiotracer techniques. The results are (in sq cm sec−1): α-Fe γ-Fe ChromiumD = 8.52 exp (−59,900/RT)D = 10.80 exp(−69,700/RT) VanadiumD = 3.92 exp (−57,600/RT)D = 0.25 exp (−63,100/RT) HafniumD = 1.31 exp (−69,300/RT)D = 3600 exp (−97,300/RT) The differences in diffusion rates are discussed in terms of the compressibility of the diffusing atom. Diffusion of chromium in γ-Fe was also measured by a microprobe analysis technique. The result is:D = 4.08 exp (−68,500/RT) Comparison is made between diffusion analysis by tracer techniques and by electron probe microanalysis.

Solute diffusion in alpha- and gamma-iron

Oxidation behaviour of NiAl—II. Cavity formation beneath the oxide scale on NiAl of different stoichiometries

Vacuum-purified niobium crystals of various orientations have been tested in tension and compression, mainly at room temperature and 158 °K The observed slip planes were almost always of the {101}

Deformation properties of niobium single crystals

An isothermal section of the Ni-Cr-Al system at 1423 K has been investigated using Knudsen cell mass spectrometry to determine the activities of nickel, chromium and aluminium. These data provide independent measurements, i.e. without the need for integration, of all of the components, both in the binary and ternary systems. The data on the binaries are mutually consistent, as can be seen by the comparisons given between the experimental results and values obtained by integration.

Thermodynamics of Ni-Cr-Al alloys

The temperature and enthalpy changes of the h.c.p.-to-b.c.c. transformation in several Ti-Zr-Hf alloys have been measured using an adiabatic calorimeter. A comparatively smooth variation of the entropy of transformation with composition is noted for Ti-Zr, Ti-Hf and the ternary alloys. The difference between the enthalpies of formation of the alloys in the two crystallographic forms can be deduced from the results and the values are consistent with the form of the phase diagrams.

The α → β transformation in the Ti-Zr system and the influence of additions of up to 50 at.% Hf

The yield point behaviour of niobium containing varying quantities of oxygen has been investigated. Oxygen raises the yield stress at 293°K and 77°K. Twinning is observed in zone-melted niobium at 77° K but this is inhibited by oxygen additions.

The effect of oxygen on the mechanical properties of zone-refined niobium

The physical properties of niobium, tantalum, molybdenum and tungsten are reviewed in relation to the properties of the other elements of groups IVa, Va and VIa of the periodic table. Zone-refined specimens of niobium and tantalum have been prepared and resistivity, magnetic susceptibility and thermal e.m.f. measurements made in the temperature range 10°–295°K.

The physical properties of niobium, tantalum, molybdenum, and tungsten

The interdiffusion of niobium and molybdenum has been studied over the temperature range 1400°–2375°C. Values obtained for Q the activation energy for interdiffusion (95.4 kcal mole −1 ) and D 0 the frequency factor (1.5 cm 2 sec −1 ) are close to those previously reported for self-diffusion in niobium and molybdenum.

The interdiffusion of niobium and molybdenum

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