CORROSION PROPERTIES OF MATERIALS-CONTINUED NICKEL AND ITS ALLOYS

摘要

Nickel and its alloys resist corrosion in many environments better than almost any other group of alloys but they are very expensive. Generally, they are selected only when a cheaper alternative cannot be found. Nickel has good resistance to corrosion in normal atmospheres up to 800 deg C, in non oxidising acids, in natural fresh waters and in hot and cold caustic alkalies. Alloying with elements such as copper, chromium and molybdenum will further improve the corrosion resistance. Nickel and its alloys are considered immune to SCC except in some environments such as halides in the percent range at high temperatures. Nickel and its alloys are not resistant to strongly oxidising solutions such as nitric acid and ammonia and they are attacked and embrittled by sulphur-bearing gases at elevated temperatures. There is no Australian Standard that specifically covers nickel and its alloys. It is generally referred to in terms of trade names, with those of the Inco Company (e.g. Monel, Inconel, Incoloy and Nimonic) being the most common. Table 7-8 lists some common nickel alloys using their trade name, their compositions and major uses.