The Influence of Porosity on the Statistical Amplitude Distribution of Backscattered Ultrasonic Pulses in Reactive Cast Metal–Matrix Composites

In this work, we study the influence of the local porosity in isotropic reactive cast particulate reinforced metal–matrix composites on the statistical amplitude distribution of backscattered broadband pulses of longitudinal ultrasonic waves. A special laser optoacoustic transducer is employed for this purpose, which makes it possible to achieve laser excitation and piezoelectric detection of ultrasound by one-side access to a sample or product. Two series of in-situ reactive cast aluminum–matrix composites were studied: reinforced solely with the Al₃Ti intermetallic particles (volumetric contents 0.04–0.115) and with combination of Al₃Ti and synthetic diamond nanoparticles (volumetric content 0.002). The last accelerate reactive synthesis of Al₃Ti particles and lead to modification of their shape and sizes. For both series of composites, the amplitude distribution of backscattered ultrasonic pulses has been approximated with the Gaussian probability distribution applicable for statistics of large number of independent random variables. The empirical dependence of the half-width of this distribution on the local porosity in composites of two series has been fitted by the same function close to the linear one regardless the size and content of reinforcing particles. This functional relationship can be used for quantitative evaluation of the local porosity of the composite material both at its manufacturing stage and during service of composite parts and products.