Rapid growth of single crystals in the solid state utilizing a massive transformation

Abstract

A method is described for rapidly growing single crystals in the solid state, utilizing the massive transformation. The technique involves moving a necked specimen through a thermal gradient and it has been shown to be successful in alloys of the Ag-Al system near 24.5 at. % Al. Single crystals of the hcpζ phase have been grown from the b c cβ phase at rates between 0.01 and 1.2 cm sec⁻¹. X-ray observations indicate the development of misorientations and a substructure with increasing crystal growth velocity. Metallographic observations on numerous crystals demonstrate that the occurrence of single crystal growth is closely related to the relationship between the undercooling at the transformation interface and the interface velocity. Favourable conditions require that the velocity of the transformation interface be near the maximum value possible under the imposed thermal conditions. Success in growing a single crystal decreases with increasing undercooling and no crystals could be grown when the undercooling exceeded about 20°C. Solid state crystal growth utilizing the massive transformation has many features in common with crystal growth resulting from undercooled liquids.