特集 金属間化合物の粉末冶金と諸持性 Ｎｉ３Ｓｉ系金属間化合物の対硫酸性能に及ぼす成分組成，ＭＡ条件並びに熱処理条件の影響

Abstract

Ni3Si intermetallic compounds have an excellent corrosion resistance in sulphuricacid solution. However, it was difficult to produce these compounds because of poor ductility caused by formation of a very brittle phase. In order to suppress formation of the brittle phase, process conditions involving a mechanical alloying(MA) method have been investigated for the production of Ni3Si intermetallic compounds. First, fine Ni-Si composite powders prepared by the MA method were hot extruded. Then, Ni3Si intermetallic compounds were obtained by a particular heat treatment. Influence of Si contents, MA conditions and heat treatment conditions on the sulphuric-acid corrosion resistance of Ni3Si intermetallic compounds were investigated. As a result, the Ni3Si intermetallic compounds appeared to have a strong correlation between the sulphuric-acid corrosion resistance and the α-phase content. Moreover, an excellent corrosion resistance was obtained when the content of a -phase was less than 5 %. The recommendable manufacturing conditions are as follows: mechanically alloying for 346 ks(B/P=16) using 13.1 mass%Si- 86.9 mass%Ni powders, hot extruding at 1223K and then heat treating for more than 18 ks. Under these conditions Ni3Si intermetallic compounds with an excellent sulphuric-acid corrosion resistance, below 0.3 mm/year, were obtained.