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We have observed ‘‘giant magnetoresistance’’ in short-period Cu/Co-Ni-Cu alloy superlattices electrodeposited from a single electrolyte under potentiostatic control. The superlattices were grown on polycrystalline Cu substrates which were removed before transport measurements were made. Room-temperature magnetoresistances of over 15% in applied magnetic fields of up to 8 kOe were observed in superlattices having Cu layer thicknesses of less than 10 Å.

This paper describes the oxidation behaviour of two technologically important nickel based superalloys, RR3000 and CMSX-4, used extensively in gas turbine blade applications. Oxidation tests were conducted in air at 1100uC for equal and extended periods of time, up to 100 h to compare the superalloys characteristic properties. The morphology of oxide growth in the test samples was investigated using metallography, SEM, EDX, X-ray diffraction (XRD) and Cr 3z photoluminescence spectroscopy. The results indicated that irrespective of the duration of exposure, alloy RR3000 develops a much thicker oxide scale than alloy CMSX-4. Examination of cross-sections revealed that the scale grown on the alloy RR3000 is porous and has a three layered structure consisting of an outer layer of (Ni,Co)O; a sublayer of CrTaO 4 rich oxide with different spinels; and an inner layer of a-Al 2 O 3 . By contrast, the scale that forms on alloy CMSX-4 is compact and consists of two layers. The upper layer is primarily composed of spinels (Ni,Co)Al 2 O 4 and (Ni,Cr) 2 O 4 , and the inner layer of a-Al 2 O 3 . Residual stress measurements using luminescence spectroscopy point to a weak adhesion of the oxide scale to the substrate for alloy RR3000 and a strong adhesion for alloy CMSX-4.

In this study, the evolution of sigma-phase development in a 2205 duplex steel was studied following thermal ageing in the temperature range 750-850°C for periods up to 100 h. A suite of materials analysis techniques including combined electron backscatter diffraction-energy-dispersive X-ray imaging and magnetic force microscopy are used to quantify the change in volume fraction of the phases. The experimental results for each ageing condition are compared with the results from other ageing experiments and the predictions from the computer modelling. They show good correlation for the amount of sigma phase formed under a range of ageing conditions (and thus varying quantities of sigma phase). EBSD measurements showed no preferential orientation relationships relative to the parent ferrite for the nucleation of sigma phase, implying that the minimisation of boundary misorientation energy is not significant in determining sigma-phase nucleation sites. The results are discussed with respect to the experimentally measured properties of sigma phase and the kinetics of the precipitation process.