Diffusion couples as a mean for studying phase transformations in Fe-Ni alloys

• Grant number: 11/06628-6
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2011
• End date: December 31, 2012
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Helio Goldenstein
• Grantee: Arthur Seiji Nishikawa
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Phase transformations in metals normally involve nucleation and growth of new phases from pre-existing ones, with simultaneous and gradual chemical and structural modifications in the pre-existing phases. On the other hand, the morphology and distribution of the resulting phases influence drastically several properties of metals. Thus, it is extremely important to know and understand phase transformations in order to attain a full comprehension of the properties of materials. This project aims at using diffusion couples for the identification of morphological and kinetic transitions in the products of austenite decomposition. Diffusion couples are samples specifically crafted for obtaining a sample with a gradient in the content of a substitutional solute, as proposed by Hutchinson et al. Diffusion couples will be made from hot forged plates of Fe-5%Ni and Fe-10%Ni, by hot cladding. Samples will be treated at 1350°C for 48 hours to aloe the formation of the compositional gradient. After that, the samples will be cold rolled to extend the diffusion field and carburized to different carbon contents. Carburized samples will be submitted to austenitization and isolthermal hold in temperatures at which austenite decomposition takes place. Transitions in morphology and reaction kinetics are expected to be observed along the Ni gradient. The samples will be characterized using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). (AU)