Comparative Study of Nano-Tio2/Y2O3 Dispersed Zirconium Based Alloys by Mechanical Alloying and Conventional Sintering

Abstract

mechanical properties, excellent corrosion resistance and very low thermal neutron cross section. These alloys have high thermal conductivity and less thermal expansion coefficient than stainless steel which is necessary for elevated temperatures dimensional stability. Moreover, elevated temperature yield strength, creep and corrosion resistance of zirconium alloys can be increased by dispersion of nano-oxides. Compared to high temperature conventional melting method, preparation of zirconium based alloys by mechanical alloying followed by low temperature fast consolidation process is better in producing ultra-fine final structure and in improving strength properties. The present study deals with the synthesis and mechanical property investigation of 1.0-2.0 wt.% nano-TiO2/Y2O3 dispersed Zr based alloy with nominal composition of 45.0Zr-30.0Fe-20.0Ni-5.0Mo (alloy A), 44.0Zr-30.0Fe-20.0Ni-5.0Mo-1.0(TiO2/Y2O3) (alloy B) and 44.0Zr-30.0Fe-20.0Ni-4.0Mo-2.0(TiO2/Y2O3) (alloy C), synthesized by mechanical alloying (MA) followed by conventional sintering. In order to examine the microstructure, morphology and blending homogeneity the alloyed powders were subjected to X-ray diffraction (XRD), microscopic characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Recrystallization behaviour of the final milled powder was studied by DSC. The average grain size of the as milled powder after 10 h of milling was 10-15 nm. The calculated activation energy of the base alloy A was 310 K J/mol. Consolidation of the milled powder was done by 0.998GPa uniaxial pressing and conventional sintering at 1673K (1400oC). Finally, comparative study of the Zr-alloys (dispersed with TiO2/Y2O3) was made in terms of hardness and wear properties. With increasing dispersoid content the hardness and wear properties increase. The maximum hardness observed for alloy C (with Y2O3dispersion) was 6.2GPA whereas with TiO2 dispersion it was 7.0GPa. In line of this, the alloys with TiO2 dispersion showed better wear properties than Y2O3 dispersion.