Nondestructive Inspection of High Performance Ceramics

Two ceramic materials, a hot-pressed silicon nitride and a siliconized silicon carbide, were manufactured with seeded particulates to evaluate the effectiveness of existing nondestructive test practices at AMMRC for defect detection in ceramics and to evaluate the effect of inclusions upon material strength. The types of seeded defects were of greater and lower density relative to the matrix materials and ranged in size from approximately 0.1 mm to 0.6 mm. The nondestructive methods used in the investigation were ultrasonics, radiography, eddy current and penetrant. Bend bar specimens were cut from the seeded regions of the billets and tested at 25°C, 1093°C and 1371°C. Fracture origins were examined by optical and electron microscopy and by microprobe to correlate the nature of the fracture initiating defects with the nondestructively detected defects. This permitted a ranking of defect detection sensitivity and defect effect upon strength