Abstract
High temperature nitridation is a common corrosion issue in the processes ranging from those containing air to those containing more specific gases, such as nitrogen or ammonia. High temperature alloys could provide good nitridation resistance, but the nitridation data of commercial alloys in nitrogen or ammonia at high temperatures, such as 871°C and above, is limited. The paper studies the high temperature nitridation resistant behaviors of six modern commercial high temperature Ni- and Co-based alloys, which include four chromia forming alloys, N06230, R30188, 625 and N06617, and two alumina forming alloys, N07214 and a recently developed NiCoCrMoAl alloy. The high temperature nitridation tests were conducted for 1,008h cycled weekly in ultra-high purity nitrogen gas at 871 and 982°C. The test results showed different nitridation resistant behaviors of the chromia and alumina forming alloys. Either chromia or alumina scales formed on these alloys to provide nitridation protection in the nitrogen atmosphere. Alumina scales exhibited excellent nitridation resistance at both temperatures, and pre-oxidation to form an alumina scale was proven to be very effective to improve nitridation resistance. Chromia scale showed less protection, particularly at 982°C. The nitridation resistant behaviors of these alloys are analyzed and discussed.
