Role of matrix microstructure in the ultrasonic characterization of fiber-reinforced metal matrix composites

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Role of matrix microstructure in the ultrasonic characterization of fiber-reinforced metal matrix composites S. Krishnamurthy USAF Materials Directorate, Wright Laboratory, WL/MLLM/UES, Wright-Patterson AFB, Ohio 45433–7817

T. E. Matikas and P. Karpur USAF Materials Directorate, Wright Laboratory, WL/MLLP/UDRI, Wright-Patterson AFB, Ohio 45433–7817 (Received 14 March 1996; accepted 1 November 1996)

This work deals with the application of ultrasonic nondestructive evaluation for characterizing fiber-reinforced metal matrix composites. The method involved the use of a recently developed technique in which the fiber reinforcement acts as a reflector to incident ultrasonic shear waves. Single fiber and multifiber, single ply composites consisting of SiC fibers in several titanium alloy matrices were investigated. The ultrasonic images obtained were correlated with the results of metallographic characterization of the composites. The results showed that the ultrasonic response of the metal matrix composites is significantly influenced by the microstructure of the matrix through which the incident wave traverses. The general effects of matrix on ultrasonic wave propagation are reviewed, and the ultrasonic signals obtained from various SiC fiber-reinforced titanium alloy composites are discussed in terms of the scattering effects of matrix microstructure.

I. INTRODUCTION

There are numerous studies dealing with the application of nondestructive evaluation (NDE) techniques for investigating fiber-reinforced metal matrix composites (MMC’s). In particular, ultrasonic NDE techniques have been used in the past for determining the distribution of reinforcements and detecting macroscopic defects such as ply delaminations and nonuniform fiber spacing, arising from either missing fibers or displacement of fibers during fabrication of composite panels.1,2 Recent work has demonstrated that ultrasonic NDE is an equally valuable technique for detecting microscopic defects arising during the processing of continuously reinforced MMC’s, and that it can be reliably used to minimize the number of iterations required for optimization of the consolidation process.3 Further, it has also been shown that ultrasonic NDE can serve as a powerful tool for studying important damage evolution phenomena in fiber-reinforced MMC’s, including fiber fracture and fiber/matrix interfacial debonding.4,5 However, when ultrasonic waves are used to evaluate a composite with a polycrystalline matrix, the waves propagating in the matrix will be scattered by the grains, and the ultrasonic evaluation of the material will be affected by the resulting noise. Therefore, the objective of the present work is to study the influence of matrix alloy microstructure on ultrasonic wave propagation and its effects in evaluating 754

http://journals.cambridge.org

J. Mater. Res., Vol. 12, No. 3, Mar 1997

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the aforementioned damage evolution phenomena in MMC’s. The role of grain boundaries is of particular

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