EFFECT OF THE VANADIUM ADDITION ON THE GRAIN SIZE AND MECHANICAL PROPERTIES OF THE COPPER-ALUMINIUM-ZINC SHAPE MEMORY ALLOYS

The effects of vanadium addition on the β-grain size, pseudo-elastic and shape memory behaviour and fracture mode of the copper-aluminium-zinc shape memory alloys with different vanadium contents were investigated. It was found that the vanadium addition is very effective in reducing β-grain size. In the specimen hot-rolled and recrystallized for several ten minutes at 1073K, the maximum mean grain size was only 300 µm. When the annealing time is shorter, i.e. a few minutes, it reaches 200 µm. The minimum β-grain size 100 to 150 µm of the specimen in the recrystallized state was obtained by combination of vanadium addition and cold-rolling. The recoverable pseudo-elastic strain of the specimen having four-five grains along its thickness was found to be up to 5%, and recoverable shape memory strain up to 5.5%, both are near the mean theoretical values of polycrystalline materials. It was found that grain boundary cracking, which is usually observed in copperbase β-brass alloys and is considered to be the most undesirable failure of these alloys, was remarkably suppressed by vanadium addition