FORMATION OF A LaCrO3 PARTICLE DISPERSED ALLOY LAYER AS A MEANS FOR IMPROVING OXIDATION RESISTANCE

Abstract

At elevated temperature, perovskite structure LaCrO 3 is electron conductive and resistant to oxidation. A method to form a LaCrO 3 particle dispersed alloy layer by laser irradiation was developed. The method consists of (i) the formation of precursor films, LaOHCrO 4 n H 2 O, on metals by cathodic deposition from chromate solutions containing La(III) ions, (ii) heat treatment of the precursor films, and (iii) the simultaneous conversion of the precursor films to LaCrO 3 particles and the formation of the LaCrO 3 dispersed layer by CO 2 laser irradiation. The Type 430 and 304 stainless steels treated in this manner showed marked improvement in oxidation resistance, though a high yield of perfectly treated specimen has not been achieved, mainly due to technical problems. One Type 430 steel specimen showed only 5.8 g/m 2 of mass gain after 24.5 h oxidation at 1000°C in 0.20 atm H 2 O - air: this mass gain was caused by the formation of an oxide nodule on a corner and the other parts of the specimen showed no accelerated oxidation. A Type 304 steel specimen showed no spalling after 10 cycles of oxidation in air for 60 min at 1100°C and cooling to room temperature, and the final mass gain was 3.2 g/m 2 . Further development of the method is in progress.