Papers by Author: Masayuki Kudoh

Abstract: Titanium surface was covered with thin layers of titanium monocarbo-nitride, Ti(C,N) and nitrogen-rich a-titanium, after a titanium specimen was heat-treated at a temperature between 1388 and 1573 K in a graphite cup in an atmosphere of pure nitrogen. The total thickness of those layers increased in accordance with the parabolic law when both temperature and time of the heat treatment increased. The parabolic rate constants was described as k = 4.83 × 10-6 exp (-178000/RT)m2/s using Arrhenius’ equation. Vickers hardness of the Ti(C, N) layer remained at approximately 2000 but that of the a-titanium layer gradually decreased from 1500 to 500, as the distance from the surface increased. The carbo-nitridetreated titanium exhibited excellent resistances in wear and corrosion compared with those of pure titanium.

Abstract: When a surface of a titanium disk was melted in an atmosphere of pure nitrogen using a 3D Micro Welder which was designed by the present authors, the surface was nitrided to a depth of 90 to 260μm depending on the arc current of 6 to 24 A. The concentration of nitrogen in the nitrided layer was approximately 50 mol% at the surface, and the concentration decreased as the distance from the surface increased. A TiN layer was formed at the surface, and beneath the TiN layer, a dual phase layer of TiN and α-Ti was formed. Vickers hardness was approximately 1800 in the TiN layer and it varied from 900 to 200 in the dual phase layer as the distance from the surface increased.

Abstract: TiC particle dispersed FeAl intermetallic alloys have been combustion synthesized from mixtures of titanium, carbon, aluminum and iron powders. When the powder mixture was heated in an argon atmosphere to approximately 900 K, an abrupt increase in temperature was observed, which indicates that the combustion synthesis reaction occurred in the powder mixture. The combustion-synthesized alloys consisted of an FeAl matrix phase with homogeneously dispersed fine TiC particles. As the concentrations of titanium and carbon of the powder mixture increased, the volume fraction and average diameter of the TiC particles increased, and Vickers hardness of the sample also increased.