DILATOMETRIC ANALYSIS AND HK HARDNESS MEASUREMENT OF DIRECTIONALLY SOLIDIFIED ALZN EUTECTIC SPECIMENS

Two simple and relatively fast methods have been verified of an object ive inference of the quality of the directionality of the volume struc ture of a specimen. The above methods can thus be conveniently added t o classical metallography and image analysis. AlZn eutectic appears to be an appropriate model system due to a linear thermal expansion anis otropy of the directionally solidified specimens, which is given by th e expansion anisotropy of a directionally positioned beta-Zn phase wit h a hexagonal lattice. The thermal expansion is lowest in the growth d irection of the lamellae. The hardness is anisotropical on the surface . The HK hardness is anisotropical with respect to the position of the indentor in the structure. The hardness shows an overall increase wit h the growth rate of the specimen (i.e. with the fineness of the struc ture) and its value its always lowest, when the longer diagonal of the HK indentor is parallel with the lamellae on the cross sections of th e specimens.