Determination of the elastic constants of metal-matrix composites by a laser ultrasound technique

Abstract The longitudinal and transverse ultrasonic wave velocities of a series of as-cast short-Al 2 O 3 -fiber-reinforced SAE321 matrix composites (Al 2 O 3f /SAE321) and SiC-particle-reinforced ZA-27 matrix composites (SiCp/ZA-27) in the as-cast conditions were measured by a laser ultrasound technique. The experimental results showed that the wave velocities in two composites varied with the volume fraction, f , and the size of the ceramic reinforcements within the metal matrix. The interfacial structures and metallurgical defects of the composite played an important role in the variation of ultrasonic wave velocities. The effective elastic constants of the composites, including Young's modulus, E , the shear modulus, G, Poisson's ratio, ν , and the Lame coefficient, λ , were calculated by using the values of the velocities and the mass densities of composites according to the elastic theory of solids. As expected, the Young's modulus and shear modulus of as-cast Al 2 O 3f /SAE321 composites monotonically increased with increasing volume fraction of the reinforcement. The elastic constants of SiCp/ZA-27 composite with a volume fraction of 0.05 in the as-cast conditions were essentially larger than that of the monolithic alloy and tended to increase with the particle size. However, property deterioration was observed when the particle volume fraction was above this level. It is believed that a thin layer of oxidation inclusions and microvoids at the interface observed by transmission electron microscopy (TEM) as well as metallurgical defects (SiC particle segregation, shrinkage pores and gas-blows) by scanning electron microscopy (SEM) may be responsible for the property degradation.