Microstructure and mechanical properties of slowly cooled Zr_(66.4)Nb_(6.4)Cu_(10.5)Ni_(8.7)Al_(8.0) with ductile bcc phase

摘要

We report about the preparation and properties of a Be-free Zr_(66.4)Nb_(6.4)Cu_(10.5)Ni_(8.7)Al_(8.0) alloy with a glassy or a nanocrystalline matrix and ductile bcc precipitates,which were developed with the aim to improve the mechanical properties.The samples were prepared in form of rods by injection casting into a copper mold.The phase formation as well as the resulting microstructure and the mechanical properties of the different samples have been investigated upon cooling from the melt at different quenching rates.The formation of the bcc phase embedded in a glassy matrix is strongly governed by the alloy composition and the actual cooling rate during solidification,because the glass forming ability is much lower compared to Zr-based alloys containing Be.Already small reductions in cooling rate lead to precipitation of additional crystalline phases.Compression tests reveal that the in-situ glass-matrix composite undergoes work hardening and plastic deformation prior to failure.Surprisingly,also a nanocrystalline matrix leads to high elastic strain values.These features significantly improve the mechanical behavior of the composites compared to the monolithic glass.