Development of nondestructive evaluation methods and prediction of effects of flaws on the fracture behavior of structural ceramics

摘要

Continuous fiber ceramic matrix composites are being developed for turbine engine components, heat exchangers, and hot-gas filters in fossil energy systems. Reliable application requires nondestructive evaluation (NDE) methods that provide data for quality assurance and inputs to life time prediction models and that aid in process development. NDE developments at Argonne have focused on methods to assess density distribution, fiber orientation (for mechanical properties), and defect detection in both SiC/SiC and A1(sub 2)O(sub 3)/A1(sub 2)O(sub 3) materials. and that also assess the chemical state at fiber/matrix interfaces. 2-D cloth lay-up and 3-D weave CVI-infiltrated SiC/SiC specimens were studied by X-ray imaging methods now under development. Microfocus X-ray computerized tomography (MXCT) methods are being developed to provide these data. Multinuclear Nuclear Magnetic Resonance spectroscopy (13C, 29Si, and 11B) is under development for quantizing B content at fiber/matrix interfaces. Magic angle spinning techniques on SiC/SiC specimens with different coating thicknesses showed that quantification of B at the Interface is achievable. NDE data are being coupled to room- and elevated-temperature fracture studies to evaluate effects of fiber orientation and fiber coating thickness on resulting flaw morphology and mechanical properties of Nicalon-fiber-reinforced SiC matrix composites. Specifically, composites with fiber cloth lay-up sequences of varying coating thicknesses were evaluated. For room-temperature mechanical evaluation, composites with carbon-fiber coating thicknesses of 0 and 0.2 (mu)m were used, while elevated-temperature studies used composites with a coating thickness of 0.4 (mu)m. Composites with uncoated fibers failed in a brittle mode, while composites with 0.2 (mu)m fiber coating showed noncatastrophic failure.