X-Ray Diffraction (XRD) profile of pure equal channel angular pressing (ECAP)-annealing nickel samples has been thoroughly investigated for studying the material structures changes that imply to the mechanical behavior. Nickel-based material can be used for several applications such as biomaterial, gear, and some part of the instrument at nuclear facilities, which require high-grade standard material properties. ECAP is one kind of severe plastic deformation (SPD) techniques to obtain excellent mechanical properties without adding another element. However, the ECAP process generates metastable structures due to some mismatch structure and inhomogeneous stress within the material. This problem can usually be resolved by annealing after the ECAP process. In this article, pure Nickel was processed by ECAP at 423 K for two passes. The post-ECAP annealed will be carried out at the temperature range from 298 K until 1373 K. The microhardness test results indicate that the ECAP process increases the microhardness significantly, which remains stable after annealing until 773 K. At higher annealing temperature, the mechanical properties will drop suddenly and reach the microhardness value of pure pre-ECAP Nickel. This behavior could be explained clearly by the XRD data analysis result, which shows similar behavior structure changes. XRD data initially show peak shifting to lower 2θ value, which indicates an expansion to a higher lattice parameter, then at the higher annealing temperature, the diffraction peaks split gradually. This peak splitting could be indexed as pure pre-ECAP Ni peaks, which could be related to the drop of the microhardness value.

Microstructure and corrosion behaviour of ultrafine-grained pure magnesium by severe plastic deformation has been investigated in term on initial deformation process as a biodegradable material. Equal channel angular pressing (ECAP) has been chosen as severe plastic deformation which can be introduced into the material without changing the material geometry. The ECAP process was carried out at 523 K. The microstructure was characterized by scanning electron microscope which is equipped by electron backscatter diffraction, and the corrosion behaviour was investigated by electrochemical test. The ECAP processed sample show that the deformation structures has sub boundaries in one pass and a high fraction of high angle grain boundary due to high misorientation in the grain boundaries. The corrosion behaviour exhibited that ECAP processed sample has a lower corrosion rate than that as-annealed sample due to deformed structure.

ELECTROCHEMISTRY STUDY ON THE RELATIONSHIP BETWEEN GRAIN BOUNDARY STATE AND CORROSION BEHAVIOR OF ULTRAFINE GRAINED IRON CHROMIUM ALLOY. Research on stainless steel corrosion resistance continues to grow today. This reality cannot be separated from the needs of stainless steels in various fields, one of which is bio-implant. In this research, the effect of grain size on the corrosion behavior of iron-chromium (Fe-Cr) alloy was investigated. Coarse grain Fe-Cr alloy was first processed with equal channel angular pressing (ECAP) for eight cycles to obtain ultrafine grain structure. The coarse and ultrafine grain samples then were then tested using XRD, SEM-EBSD, and the pitting corrosion properties tested using potentiodynamic polarization method in NaCl 1 M solution. The result of XRD dan SEM-EBSD shows that the initial sample is truly has a coarse grain structure, while ECAP produces an ultrafine grain structure. Corrosion test results showed that the ultrafine grain sample had better pitting corrosion resistance compared to the coarse grain sample. This behavior is related to the rate of passivation that depends on non-equilibrium grain boundaries, which can be easily observed in the ultrafine grain structure. Based on these results, it can be concluded that the ultrafine grain Fe-Cr alloy has a better corrosion resistance compared to the coarse grain.

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