FATIGUE CHARACTERIZATION OF A MELT-INFILTRATED WOVEN HI-NIC-S/BN/SIC CERAMIC MATRIX COMPOSITE (CMC) USING A UNIQUE COMBUSTION 'TEST FACILITY

摘要

A melt-infiltrated woven SiC/SiC Ceramic Matrix Composite (CMC) reinforced by BN inteface coated Hi-Nicalon type S SiC fiber (MI woven Hi-Nic-S/BN/SiC) was tested under tension-tension fatigue condition using the capabilities provided by a unique burner rig facility at Air Force Institute of Technology (AFIT) which simulated both the load and combustion condition of hot-section components of gas turbine engines such as turbine blades and vanes. A set of fatigue tests performed using the burner rig (stress ratio, R = 0.05 and frequency = 1 Hz) provided S-N data and fracture surfaces, which were analyzed for the role and effects of oxidation on the failure and damage mechanisms. These test results were then compared with those obtained from fatigue tests (R = 0.05 and 1 Hz) in a standard furnace under laboaratory air environement. Fatigue life in the combustion condition was lower by an order of magnitude in comparison to that under the laboratory condition across the range of applied stress. This suggested that the burner rig condition was more damaging to the woven MI Hi-Nic-S/BN/SiC CMC. The observed difference in fatigue strength is attributed to the thermal gradient stress and increased rate of oxidation due to a high moisture level in the burner rig test condition.