Plasma nitriding and plasma nitrocarburizing of electroplated hard chromium to increase the wear and the corrosion properties

摘要

We have investigated the effect of plasma nitriding and plasma nitrocarburizing on the microstructure and properties of electroplated chromium. Plasma nitriding and plasma nitrocarburizing are applied to 15-100μm thick electroplated hard chromium coatings to increase both the wear and the corrosion resistance. The properties of the plasma-modified hard chromium layers are characterized by measuring the wear resistance with a Taber wear tester and the corrosion resistance with a salt spray fogtest. Cyclic voltammetry is performed in a standard electrochemical cell using a 0.5 M H{sub}2SO{sub}4 solution acidified to pH 0.3. The compound layer after plasma nitriding consists of CrN and Cr{sub}2N with a maximum hardness of about 1100 HK{sub}0.01. After plasma nitrocarburizing, Cr{sub}3C{sub}2 and Cr{sub}7C{sub}3 are formed. After plasma nitrocarburizing, the maximum hardness is increased up to 2200 HK{sub}0.01. The wear rate is reduced as compared to an untreated chromium layer. The exposure timein the salt spray fog, before corrosion products are visible can be increased by a factor of 5. The improvement in wear and corrosion resistance after plasma nitriding and plasma nitrocarburizing is discussed considering microstructural changes of thetreated layer.