Synthesis of Nano-Structured Duplex and Ferritic Stainless Steel Powders by Planetary Milling: an Experimental and Simulation Study

Abstract

Nano-structured duplex and ferritic stainless steel powders were prepared by planetary milling of elemental Fe, Ni and Cr powder compositions (duplex: 69Fe-18Cr-13Ni and ferritic:82Fe-17Cr-1Ni) in a dual drive planetary mill for 10 hours. The feasibility for solid solution formation of Cr and Ni in Fe matrix were studied. The samples were collected at regular time intervals and characterized for their morphological and phase analysis using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). It has been observed that as the milling time increases crystallite size decreases and lattice strain increases. Powders were then compacted and sintered at the temperature of 1000 °C with a holding time of 1 hour. The sintered samples were again characterized for their morphological and phase change analysis using same techniques. Thermodynamic aspects of milled stainless steel powders were performed using Miedema model. The theoretical values of ?H, ?S and ?G were calculated and found to be -14.32kJ/mol, 6.93J/mol and -16.39 kJ/mol for duplex stainless steel and -2.81kJmol, 4.35Jmol and -4.11 kJ/mol for ferritic stainless steel respectively. The thermodynamic parameters were further experimentally calculated by differential scanning calorimetry (DSC) and the value of ?H was found to be -174.9 kJ/mol for duplex stainless steel and -134.2 kJ/mol for ferritic stainless steel respectively.