ＡＩＰ法によりＴｉ‐６Ａｌ‐４Ｖ基板上に形成したＣｒ‐Ｎ膜の構造および耐溶融Ａｌ性に与える成膜時の窒素圧の影響

Abstract

A series of chromium nitride coatings with different nitrogen contents were deposited on Ti-6Al-4V substrate by the arc ion plating method using a Cr target and nitrogen as the reactive gas. At nitrogen pressures below 027Pa, the deposited coatings contained 20 to 27 at% nitrogen and mainly consisted of the Cr2N phase. Above this pressure, coatings contained more than 35 at% nitrogen and consisted of the CrN single phase. The dissolution rate of the Cr-N coating in pure molten aluminum was drastically decreased above a nitrogen content of about 35 at%, which corresponds to the transition point from Cr2N to CrN. In TEM observation, it was found that a thin (∼50nm) reactive layer confirmed to be as wruzite type AlN formed in the interface between the CrN and Al after Al immersion. It was concluded that this AlN acts as a protective layer for the molten aluminum. In heat cycle testing, formation of heat cracks was significantly suppressed when deposited on Ti-6Al-4V in comparison to deposition on conventional tool steel. This behavior agrees with the results of thermal stress calculations for both substrates.