Stoichiometric intermetallic compounds have always been touted for their attractive chemical, physical, electrical, magnetic and mechanical properties, but few practical uses have materialized because they are brittle at room temperature. Here we report on a large family of fully ordered, stoichiometric binary rare-earth intermetallic compounds with high ductility at room temperature. Although conventional wisdom calls for special conditions, such as non-stoichiometry, metastable disorder or doping to achieve some ductility in intermetallic compounds at room temperature, none of these is required in these unique B2 rare-earth compounds. Ab initio calculations of YAg, YCu and NiAl crystal defect energies support the observed deformation modes of these intermetallics.

Ultrasonic velocity is widely used in the investigation of material properties. In cases where thickness of the test piece is not precisely known or varies spatially, it is desirable to determine the wave velocity and the sample thickness in the same ultrasonic measurements. For tests in an immersion tank or using squirters, both wave velocity and the specimen thickness may be deduced from the time of flight of several ultrasonic pulses. In this paper four different configurations of pulse echo and through transmission are described for the ‘‘simultaneous’’ velocity and thickness determination. The method is then applied to investigate the porosity content in graphite/polyimide and graphite/epoxy composite laminates. Good results were obtained for both the wave velocity and the part thickness, and a clear correlation between velocity and void content is demonstrated.

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