A. Iwaniak

Characterization of Thermal Properties of Micro-Sized Ceramic Powders for APS Deposition of Ceramic Layers

The paper presents test results concerning characteristics of the selected thermal properties of ceramic powders based on rare earth zirconates with a pyrochlore structure of RE2Zr2O7 type, intended for thermal spraying of TBCs. Gadolinium, lanthanum, samarium and neodymium based powders were tested. The scope of the tests encompassed thermal diffusivity analysis of the powders in a compressed pellets form within temperature range 25-1500°C, and also tests of specific heat and thermal expansion coefficient within similar temperature range. Standard powder of 8YSZ type on the basis of zirconium oxide modified with yttrium oxide was used as a reference material. Specific heat measurements of the powders showed that the highest values within the entire test temperature range were obtained for the standard YSZ type powder. In the case of new type of powders, the results obtained are very similar and only slightly lower in comparison with YSZ powder. The lowest values were obtained for the samarium based powder (temperature range corresponding to operating temperature). Character of the curves obtained do not show course of strong reactions connected with phase changes. Dilatometric tests of materials made it possible to determine thermal expansion coefficient. Mean coefficient values are included within the range from 5.5 x 106mm/°C to 10.0 x 106mm/°C. The highest mean value of thermal expansion coefficient was obtained for Nd2Zr2O7 powder and the lowest one for La2Zr2O7 powder. The lowest thermal diffusivity value at room temperature was shown by Nd2Zr2O7 powder, and the highest one by 8YSZ powder (0.215 mm2/s).

Erosion Resistance of the ZnAl22Cu3 Alloy

The aim of this study was to determine the effect of soaking on the erosion resistance of ZnAl22Cu3 alloy. The following samples were examined: as-cast, soaked at 185 °C and after solutionizing at a temperature of 385 °C. The scope of the examination included: Brinell hardness test, test of resistance to erosion and the examination of the surface of the samples after erosion tests. The examination showed a high resistance to erosion of ZnAl22Cu3 alloy. Heat treatment had no significant effect on the erosion resistance of the tested alloy. A significant impact on erosion resistance exerted the abrasive incidence angle. Consumption was greater when the angle of incidence was lower.

Characterization of Microstructure and Properties of Plasma Sprayed Ceramic Coatings on AZ91 Magnesium Alloy

The paper presents the microstructure test results of carbide layers with bond coat obtained on the magnesium alloy with WC/Co – NiCr – AZ91D type thermal spraying method. Layers were sprayed with the APS method on the sandblasted surfaces of approx. 5 mm thick elements manufactured with high pressure die casting (HPDC). The standard process parameters were used for the powders sprayed. The scope of the tests included characteristics of the AZ91D alloy top surface after HPDC process and after sandblasting. The stereometric analysis of surface was performed by using the laser profilometer. The top surface geometric parameters were determined and presented in the form of numbers and topographic maps. Both surfaces were subject to SEM analysis by using the Hitachi S3400N microscope and chemical composition analysis in micro areas (EDX analysis by using the Noran System Six software) to determine presence of impurities and other type of artefacts on the alloy surface before plasma spraying. The alloy surfaces were also subject to detailed tests after spraying process (on lateral micro-sections) to determine the influence of the spraying process on the substrate quality and consequently layer adhesion. Phase composition assessment of the NiCr 80/20 type bond coat and carbide layers WC/10Co and WC/8Co was also performed. Further tests referred to top surface morphology of both carbide layers and chemical composition assessment in micro areas.