• D D Upadhyaya

      Articles written in Bulletin of Materials Science

    • Positron annihilation in Zr-0·5 Nb alloy

      D D Upadhyaya R V Muraleedharan

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      The measurement of coincidence counting rate at the peak of the angular correlation curve shows a considerable difference between the recovery behaviour of cold-worked Zr-0·5 Nb alloy from that reported for pure zirconium. This difference in behaviour illustrates the point-defect activity during the course of isochronal annealing in this alloy. The recovery spectrum can be understood in terms of the vacancy-solute entrapment upto about 250°C. In the next stage the release and clustering effects of vacancies are indicated prior to their elimination. The study thus demonstrates the effect of alloying element on the defect mobility and associated point defect interactions in Zr.

    • Alumina ceramics by sol-gel technique

      S Ramanathan R Bhat D D Upadhyaya S K Roy

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      The processing of alumina ceramics using the sol-gel technique was investigated. Alumina sols were prepared by precipitation-peptization of aluminium hydroxide obtained from aluminium nitrate and aluminium oxyhydroxide obtained from aluminium isopropoxide. Sols cast on Teflon substrate were gelled by controlled dehydration at near-ambient temperature. Gels were converted to ceramics through processes of drying, calcination and sintering in the temperature range 773–1473 K. Ceramics derived from both the sols retained a porosity of 35–45% even after sintering at 1273 K. However, at 1473 K densification was drastically enhanced and bodies could be sintered to about 90–93% of theoretical density (TD) and was accompanied by theϑ-to-α transformation. The progress of the reactions occurring at various stages of the process was studied using pycnometry, TG-DSC, XRD, SEM, MIP and TEM techniques.

    • Studies on high temperature deformation behaviour of 3Y-TZP ceramics

      D D Upadhyaya S K Roy G K Dey S Banerjee

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      The present work reports the results on the deformation behaviour of ZrO2-3 mol% Y2O3 (3Y-TZP) ceramics which were prepared by pressureless sintering at 1400°C. Dense, cylindrical samples were subjected to uniaxial compression tests under a constant stress of 15 MPa in the temperature range of 1200–1400°C. The ceramics exhibit considerable ductility, attaining over 60% true strain without any edge cracking. Microstructural changes due to interaction of grain boundary viscous phase with the ultrafine and equiaxed grains were analyzed by transmission electron microscopy. Results show the grain boundary sliding accompanied by a diffusion accommodation process as the predominant deformation mechanism in these ceramics.

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