Effect of Nb addition on microstructure evolution and nanomechanical properties of a glass-forming Ti-Zr-Si alloy

The glass-forming Ti75Zr10Si15 alloy is regarded as a potential material for implant applications due to its composition of non-toxic, biocompatible elements and some interesting mechanical properties. The effects of partial substitution of 15 at.% Ti by Nb on the microstructure and the mechanical behaviour have been investigated by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, transmission electron microscopy and nanoindentation techniques. Copper mold casting and melt-spinning methods have been applied to study the influence of the cooling rate on the properties of both alloys, Ti75Zr10Si15 and Ti60Zr10Nb15Si15. As a result of different cooling rates, significant microstructural variations from multiphase crystalline states in cast rods to nanocomposite structures in ribbons were observed. The limited glass-forming ability (GFA) of the Ti75Zr10Si15 alloy results for melt-spun ribbons mainly in nanocomposite structures with beta-type nanocrystals being embedded in a glassy matrix. Addition of Nb increases the glass-forming ability. Raising the overheating temperature of the melt prior to melt-spinning from 1923 K to 2053 K yields for both alloys a higher amorphous phase fraction. The mechanical properties were investigated using compression tests (bulk samples) and the nano-indentation technique. A decrease of hardness (H), ultimate stress and reduced Young's modulus (E-r) is observed for Ti60Zr10Nb15Si15 rods as compared to Ti75Zr10Si15 ones. This is attributed to an increase of the fraction of the beta-type phase. The melt-spun ribbons show an interesting combination of very high hardness values (H) and moderate reduced elastic modulus values (E-r). This results in comparatively very high H/E-r ratios of >0.075 which suggests these new materials for applications demanding high wear resistance. (C) 2013 Elsevier Ltd. All rights reserved.