Synthesis and Characterization of Nano-Y2O3 Dispersed Zr-Fe Alloys by Mechanical Alloying and Pulse Plasma Sintering

Abstract

45.0Zr-30Fe-10Cr-5Cu-5.0Ni-5.0Ti (alloy A), 44.0Zr-30Fe-10Cr-5Cu-5.0Ni-5.0Ti-1.0Y2O3 (alloy B), 45.0Zr-25Fe-10Cr-10Cu-5.0Ni-5.0Ti (alloy C) and 44.0Zr-25Fe-10Cr-10Cu-5.0Ni-5.0Ti- 1.0Y2O3 (alloy D) alloys (all in wt %) by solid state mechanical alloying route and consolidation the milled powder by pulse plasma sintering [1] (PPS) at 1173 K (900°C), 1223 K (950°C) and 1273 K (1000°C) using 75 MPa uniaxial pressure applied for 5 min and 70 kA pulse current at 3 Hz pulse frequency. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM) and energy dispersive spectroscopy (EDS). Mechanical properties including hardness, compressive strength, Young’s modulus and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The density of the alloys increases with increasing sintering temperature and shows maximum at 1000C temperature. Similar kind of trends has been found in hardness measurements. The maximum hardness found in alloy C sintered at 1000C (9.5 GPa) and minimum in alloy A sintered at 900C (4.5 GPa). Besides superior mechanical strength, the novelty of these alloys lie in the unique microstructure comprising uniform distribution of either nanomertic (100 nm) oxide (Y2O3) particles Zr- Fe matrix useful for grain boundary pinning and creep resistance. Fig. 1 shows the microstructure of alloy A sintered at 1000C by PPS method predicts multimodal grain structure with larger grain size of 5m to smaller grain size of 300nm. This also evident that there is very less porosity (0.25 %) of the sample sintered at higher sintering temperature.