Baek-Hee Lee

Microstructure and magnetic properties of nanosized Fe-Co alloy powders synthesized by mechanochemical and mechanical alloying process

Abstract An optimum route to synthesize nanosized Fe–Co alloy powder with enhanced magnetic properties was investigated. Two methods of mechanical alloying (MA) and mechanochemical alloying (MCA) for developing a nanosized alloy powder were compared on the basis of the resulting microstructural characteristics and magnetic properties. The alloy powder, synthesized by MCA process with ball milling and hydrogen reduction using Fe2O3 and Co3O4 powders, showed ordered BCC structure with the grain size of 40 nm. Also, this powder exhibited low coercivity of 43 Oe and good permeability compared with MA powder. Enhanced magnetic properties of the MCA powder were explained by the formation of ordered structure and relaxation of internal strain.

XPS study of bioactive graded layer in Ti-In-Nb-Ta alloy prepared by alkali and heat treatments

Ti and Ti-based alloys have been widely used for the biomedical applications due to their superiorities of biocompatibility, mechanical properties and corrosion resistance. However, there has been the limiting factor for these metals to show the low affinity to the living bone. Most of commercially used Ti alloys have harmful alloying elements such as Al, V, etc. The purposes of this study are design of new Ti alloy having the good mechanical properties and corrosion resistivity without harmful alloying elements and to improve the bone-bonding ability between Ti-based alloy and living bone through the chemically activated process (alkali treatment) and thermally activated one (heat treatment). Mechanical properties of the Ti-In-Nb-Ta alloy were observed by tensile test (Instron model 8511). Corrosion potential and corrosion rate were investigated using a Potentiostate machine (EG&G, Princeton Applied Model 273, Boston, USA) with saline solution (9% NaCl) without dissolved oxygen at 37 degrees C. After alkali and heat treatments, the effects of the pre-treatments on the bonding property were evaluated by in vitro test. In this study, the surface changing behavior, which is apatite formation, of newly designed Ti-In-Nb-Ta alloy without harmful alloying elements was investigated through analyzing its surface by using X-ray photoelectron spectroscopy after surface activation treatments (alkali and heat treatments) and after subsequent soaking in the simulated body fluid.

The enhancement of tensile strength and elongation in two phase (NiAl + Ni3Al) intermetallics of Zr-doped Ni-20Al-27.5Fe (at.%) alloys

Abstract Microstructure and tensile properties in the nickel intermetallics, Ni–20Al–27.5Fe and Ni–20Al–27.5Fe–1Ti (at.%), were investigated in order to understand the effect of zirconium addition. It was found that the addition of zirconium causes formation of a thin layer along the phase boundary of NiAl and Ni3Al. The thin layer was identified as an ordered fcc phase with 6.9 A in lattice parameter. The compressive deformation caused by hot extrusion results in fine precipitates and a mixture of subgrains within the matrix phase in zirconium-doped alloy. Additional zirconium gives significant improvement in the room and high temperature fracture strength and strain. The extruded zirconium-doped alloy exhibited a high tensile elongation of above 10%, and also a relatively high tensile strength of 1350 Mpa at room temperature, keeping it as high as 600 Mpa at 700°C.

Effect of Grain Size on Nanostructured Fe-20 wt.%Si Alloy Powders Produced by High-energy ball milling

The structural and magnetic properties of nanostructued alloy powders were investigated. Commercial alloy powders (Hoeganaes Co., USA) with purities were used to fabricate the nanostructure Fe-Si alloy powders through a high-energy ball milling process. The alloy powders were fabricated at 400 rpm for 50 h, resulting in an average grain size of 16 nm. The nanostructured powder was characterized by fcc and hcp phases and exhibited a minimum coercivity of approximately 50 Oe.