ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, June 26–30, 2017, Charlotte, NC, USA
ceramic composites; erosion
The improvement of bulk ceramic properties through the addition of a secondary or even tertiary phase is a field of research that has been actively pursued since the mid twentieth century. This pursuit has become more relavent with the adoption of ceramic phases to protect structural components within the hotpath of gas turbines. Improving the properties of these ceramic coatings and tiles has the potential of reducing catastrophic damage events leading to an overall reduction in unplanned maintence and downtime.
To date, Several approaches have been undertaken to improve the physical properties of these ceramics including preferential microstructural grain growth and doping to develop metastable crystal phases. This paper examines the effect of whisker additions to a mechanical mixture of oxide ceramics on the erosion properties. The baseline structure is a mechanical mixture of zirconia and alumina particles in the ratio of 89.8vol% alumina to 10.2vol% partially stabalized zirconia. A ratio of 20.0vol% mullite whiskers is incorporated into the structure as a toughening agent. The mullite whiskers are grown using a molten salt method. The overall structural composition is 20.0vol% mullite whiskers, 8.2vol% partially stabilized zirconia, and 71.8vol% alumina. This whisker toughened material is compared to a baseline 89.8vol% alumina 10.2vol% zirconia ceramic.
Erosion tests were conducted using a 50 μm diameter alumina erodant with a velocity of 104 m/s. Impingement angles of 30°, 60° and 90° were examined to determine the effect of whisker additions at steeper attack angles. Despite the increased hardness, tensile strength and fracture toughness, whisker-enhanced zirconia-toughened alumina has shown similar erosion rate as non-reinforced ZTA at 30° ad 90° and much higher erostion at 60°. It can be surmised that whisker-enhanced toughening of ceramics has little positive effect on the erosion resistance of ceramics at room temperature and is potentially harmful. Microstructure analysis results are also presented within to illustrate the erosion material removal mode under different conditions.
ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy, GT2017-63736: V006T02A005–.