Papers by Author: Asma Salman

Abstract: The study involves a special class of composites called interpenetrating phase composites (IPCs). The Ti(Al,O)/Al2O3 composite was produced using high energy mechanical milling of a mixture of TiO2 and Al followed by a high temperature self-propagating reaction. Characteristics of the feedstock powder were improved by treating it with an organic binder. The feedstock powder was thermally sprayed on to a substrate using high velocity oxygen fuel (HVOF) and air plasma spraying methods. The spraying methods resulted in coatings with significantly different microstructures. Compared with plasma sprayed coating, the coating produced by a HVOF spraying method showed a much finer and densely packed microstructure.

Abstract: Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite coatings have a potential to reduce dissolution and aluminium soldering tendency of H13 tool steel used in the aluminium processing industry. The thermal shock resistance of H13 tool steel coated with Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite powders sprayed using a high velocity oxygen fuel (HVOF) technique was studied. The thermal shock behaviour of the composite coatings was investigated by subjecting the coated coupons to a number of cycles, each cycle consisting of a holding time of 30 seconds in molten aluminium at 700 ± 10 °C followed by quenching into water. The surfaces of the coupons were examined for Al soldering and an evaluation of surface spallation. Any cracks found in the coatings were studied to explain their thermal shock behaviour. The results of this study showed that both Ti(Al,O)/Al2O3 and TiAl(O)/Al2O3 composite coatings on H13 tool steel have good thermal shock resistance with a thermal shock life between 300 to 400 cycles. The composite coatings and fracture surfaces were analyzed using scanning electron microscopy.

Abstract: Thermal spray deposition has been widely used as a coating process for applying thin protective layers to the need-to-protect materials, or substrates. Recent technological developments in thermal spray processing, particularly cold gas spraying (CGS) and supersonic plasma spraying (S-PS), have enabled some emerging applications for making structural components. This paper reports on the results of our recent attempts to obtain thick TiAl coatings using three coating techniques: atmospheric plasma spraying (APS), S-PS and CGS. We successfully achieved a 3 mm thick coating using both APS and S-PS techniques, but failed in cold spray. A significant phase change was observed of the powder particles experienced during both APS and S-PS processes. Nevertheless, a considerable quantity of titanium oxides was observed in the APS coating.

Abstract: A feedstock of Ti(Al,O)-Al2O3 composite powders was produced by high energy milling of a mixture of Al and TiO2 powders followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxygen-fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)-Al2O3 composite coatings. The performance of the coatings was assessed in terms of thermal fatigue behaviour and reaction with molten aluminium (soldering). The composite powders and coatings were characterised using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses characteristics and potential applications of the composite coatings.