Papers by Author: Tara Chandra

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Authors: M. Ahmadian, M. Reid, Rian Dippenaar, Tara Chandra, David Wexler, Andrzej Calka
Abstract: The densification behavior of WC composites based on iron aluminide binder was investigated using laser scanning confocal mi¬croscopy (LSCM). Doped Fe60Al40 alloys with boron levels ranging from 0 to 0.1 wt% were used as the aluminide binders. The aluminide binders were prepared using controlled atmosphere ring grinding and then blended with WC powder. The composite powder compacted in an alumina crucible and held in a platinum holder in the confocal microscope. The temperature increased from ambient temperature up to 1500 °C under high purity argon. The presence of boron was found to facilitate compaction of the composites and improve the wetting between WC and FeAl binder during liquid phase sintering. Increasing the amount of boron in the binder resulted in the melting of binder at lower temperature and increasing of the compacting of the intermetallic tungsten carbide composites.
Authors: Tara Chandra, Jose María Cabrera, Jose Manuel Prado
Authors: M. Ahmadian, Tara Chandra, David Wexler, Andrzej Calka
Abstract: The effect of boron on the WC morphology and on the grain size of binders in sub micron WC composites containing Fe60Al40 and Ni3Al binders was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composites were prepared under uniaxial hot pressing of milled powder samples at 1500 °C in inert argon atmosphere. Doped aluminides with boron levels ranging from 0 to 0.1 wt% were used as the binders. It was found that the microstructural characteristics of boron doped aluminide WC composites were similar to those of hot pressed WC-Co and commercial grade WC-10wt%Co (H10F) hardmetals. The contiguity of WC particles (WC/WC contact) and the grain sizes of aluminides decreased and the extent of faceting of tungsten carbide increased in the aluminide tungsten carbide composites in presence of boron.
Authors: Mihail Ionescu, Bryce Richards, Keith McIntosh, R. Siegele, E. Stelcer, D.D. Cohen, Tara Chandra
Abstract: Thin SiN film deposited on Si by plasma enhanced chemical vapour deposition (PECVD) is used for surface passivation of Si. During the PECVD process Hydrogen is incorporated into the SiN film, and the passivation properties of the resulting SiNx:H layers play an important role in enhancing the energy conversion efficiency of solar cells. It is believed that the Hydrogen present in SiNx:H is responsible for this enhancement, and therefore its concentration in the passivating layer is an important parameter. The Hydrogen composition and its depth profile in thin SiNx:H films of 20nm to 200nm was measured by elastic recoil detection analysis (ERDA), using a 1.7MeV He+ ion beam of (1x2)mm2, generated by a high stability 2MV Tandetron ion beam accelerator. Simultaneously, Rutherford backscattering (RBS) spectra were recorded for each sample. The results show that the Hydrogen concentration in the SiNx:H layers is dependent of the deposition conditions. Also, Hydrogen was found to be homogenously distributed across the SiNx:H layer thickness, and the SiNx:H/Si interfaces were well defined.
Authors: S.W. Huang, S. Burgess, L. Németh Wehrmann, D. Nolan, Tara Chandra
Abstract: Insulated rail joint assemblies provide electrical insulation between two sections of rail for signalling purposes. In this work, rail steel was successfully bonded to PSZ ceramic using an active brazing technique. In order to increase the wettability of the PSZ ceramics, titanium coating was deposited on the ceramic surface using a filtered arc deposition system. A filler metal called BVAg-18 (60%Ag-30%Cu-10%Sn) was used and the joining was performed at a temperature of 750 °C. Bonding between partially stabilised zirconia and rail steel with BVAg-18 filler metal was not achieved using a standard brazing method. Bonding did occur with the BVAg-18 filler metal using the advanced brazing technique of active metal brazing, with best results obtained using a brazing temperature of 750oC and a dwell time of 10 minutes. The microstructure of the coating and joint interface were characterised by XRD, SEM and EDS.
Authors: M. Ahmadian, David Wexler, Andrzej Calka, Tara Chandra
Authors: M.J. Franklin, S.W. Huang, Tara Chandra, A. Kiet Tieu
Abstract: This research is part of a larger project to investigate the wear and friction of the centre bearing of a rail freight truck. Existing centre bearing surfaces include flame hardened AISI 1030 steel and AISI 1053 cast steel top centres mating against un-greased and/or greased Hadfield steel centre bowl liners, and polyethylene centre bowl liners. The wear life of the unlubricated steels against Hadfield steel is short, greasing the bearings is costly, and industry reports some failures of polyethylene centre bowl liners due to excessive plastic flow and cracking of the rim wall.
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