Browsing by Author "Hadianfard, M. J."
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Item Open Access Fabrication of nanostructured medical-grade stainless steel by mechanical alloying and subsequent liquid-phase sintering(Springer, 2012-05-10) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, Mohammad; Mashhadi, S. B.; Okyay, Ali KemalThis article focuses on the microstructure of medical-grade P558 (ASTM F2581) stainless steel produced by mechanical alloying and liquid-phase sintering. Rietveld X-ray diffraction and transmission electron microscopy reflect that the mechanically alloyed stainless steel powder is a nanocrystal dispersed amorphous matrix composite.Mn-11.5 wt pct Si eutectic alloy as additive improves densification of the synthesized P558 alloy via liquid-phase sintering mechanism. X-ray mapping shows that after sintering at 1323 K (105°C) for 1 hour, a uniform distribution of dissolved Mn and Si is achieved. Moreover, the development of a nanostructured, fully austenitic stainless steel after sintering at the same temperature is realized by X-ray diffraction and transmission electron microscopy.Item Open Access Liquid-phase sintering of medical-grade P558 stainless steel using a new biocompatible eutectic additive(Elsevier, 2012-02-02) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, M.; Mashhadi, S. B.; Okyay, Ali KemalOne of the effective approaches to reduce residual pores in powder metallurgy parts is activated liquid-phase sintering process using proper additives. In this work, for the first time, a new biocompatible additive (Mn-11.5 wt.% Si, a eutectic alloy) is experimented for liquid-phase sintering of nanocrystalline/amorphous P558 stainless steel powders. It is realized that by increasing the sintering aid content and temperature, the density is effectively increased: a sharp densification progress when the sintering temperature increases from 1000 °C to 1050 °C and a slower densification rate when it exceeds 1050 °C. This preliminary study opens up the development of high-density medical-grade stainless steels produced by powder metallurgy, where suitable additives can lower sintering temperature and time, which is promising for retarding grain growth and commercial applications.Item Open Access Microstructural characterization of medical-grade stainless steel powders prepared by mechanical alloying and subsequent annealing(Elsevier, 2013) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, M.; Amini, R.; Mashhadi, S. B.; Okyay, Ali KemalThe harmful effect of nickel ions released from conventional stainless steel implants has provided a high level of motivation for the further development of nickel-free stainless steels. In this paper, the microstructure of medical-grade nickel-free stainless steel powders, with the chemical composition of ASTM F2581, is studied during mechanical alloying and subsequent annealing. Rietveld X-ray diffraction and transmission electron microscopy evaluations reflect nanocrystallization, austenitization and amorphization of the powders due to mechanical activation. It is also realized that annealing of the as-milled powder can develop a single austenitic structure with nanometric crystallite sizes, implying a considerable inherent resistance to grain growth. This study demonstrates the merit of mechanical alloying and subsequent annealing in the development of nanostructured medical-grade stainless steels.