Bordoni peak formation as a result of a martensitic transformation

THE indium-thallium alloys in the composition range 16–31 atom% TI undergo a martensitic phase transformation from the higher temperature f.c.c. form to the lower temperature f.c.t. modification1,2—a transformation which is well suited to ultrasonic studies. Here we report ultrasonic attenuation measurements, which have revealed the development of an internal friction peak which results from the passage of 27 atom% TI alloy single crystals through the phase transition (which occurs at 127 ± 2 K for this composition3). The general behaviour of this peak strongly suggests a relaxation type of effect similar to that first observed by Bordoni in copper4. Such peaks are either absent or negligibly small in well annealed metals; but they are produced by plastic deformation and are considered to arise from thermally activated processes involving dislocations5. We can therefore expect that any dislocations which are formed as a result of the martensitic transition would give rise to such a peak, and that it could be detected ultrasonically, provided that the investigated ranges of ultrasound frequency and temperature are appropriate to the activation energy involved.