Browsing by Author "Reed, R. C"

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    Interdiffusion in the face-centred cubic phase of the Ni–Re, Ni–Ta and Ni–W systems between 900 and 1300 C
    (Elsevier, 2000-04-15) Karunaratne, M. S. A; Carter, P; Reed, R. C
    In order to deduce the temperature and composition dependence of the interdiffusion coefficient in the nickel-rich end of the Ni–Re, Ni–Ta and Ni–W systems, a number of diffusion couples have been fabricated and heat treated at temperatures between 900°C and 1300°C. The concentration profiles so-obtained have been determined using an electron microprobe. Subsequently, values of the interdiffusion coefficients were determined using a modified form of the Boltzmann–Matano analysis, and these are presented. Only a very weak concentration dependence of the interdiffusion coefficients was found. The results are compared with the very limited data which are available in the literature.
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    Interdiffusion of the platinum-group metals in nickel at elevated temperatures
    (Pergamon, 2003-06-11) Reed, R. C; Karunaratne, M. S. A
    Rates of interdiffusion of the platinum group metals Ir, Pd, Pt, Rh and Ru with nominally pure nickel have been characterised. Interdiffusion coefficients are estimated by analysing the measured diffusion profiles. In the composition range studied (no greater than 10 wt.% of the platinum group metal), the interdiffusion coefficients display little concentration dependence, but the values can differ by an order of magnitude. In order to rationalise the dependence of the interdiffusion coefficient on atomic number, the data are compared with values for other elements which are already in the literature. A systematic trend is observed: elements furthest from the centre of the period display the largest values and elements at the centre the smallest. It appears therefore that the magnitude of the interdiffusion coefficient correlates strongly with the atomic radius of the interdiffusing transition metal species. Our results suggest the existence of a binding energy between the vacancies and the impurity species. We believe that the interdiffusion data are of considerable use to those designing new and novel grades of superalloy for high temperature applications.
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    Topologically close packed phases in an experimental rhenium-containing single crystal superalloy
    (TMS, 2000) Rae, C. M. F; Karunaratne, M. S. A; Small, C. J; Broomfield, R. W; Jones, C. N; Reed, R. C
    The kinetics, morphology and composition of the formation of TCP phases in an experimental alloy containing no tungsten is studied. At high temperature P phase forms after 20 h, whereas below 950°C the phases p and R occur. At lower temperatures a polycrystalline form of cr phase is observed which is meta-stable but acts as a nucleation site for the other phases. The phase occurrence and compositions are compared with a thermodynamic model using a rhenium-containing database, and reasonable agreement is found for the P, R and cs phases. However the model underestimates the stability of the p phase.