Alloy Developments and Applications

The advantageous magnetic properties of Fe-Ni-Al alloys with a suitable composition were first discovered by Mishima in 1931, which initiated the development of the Alnico alloys for applications as permanent magnet materials (see, e.g. Jelling- 

Alnico alloys are brittle and hard, they can only be machined by grinding, spark erosion, and electrochemical milling, and they resist atmospheric corrosion well up to 500 °C (Fiepke, 1990). The mechanical behavior, in particular creep, of Alnico-type, Fe-Ni- Al alloys has been studied in detail, and both Fe-rich alloys with precip- 

It is noted that presently NiAl is also considered an attractive candidate phase for other functional applications, e.g. contacts in electronic thin film devices or high voltage electrodes in electron-optical instruments (Miracle, 1993). 

It is well known that the martensitic transformation of Al-deficient NiAl (see Sec. 4.3.2) is thermoelastic and produces the shape memory effect. Consequently materials developments have been started which aim at applications as shape memory alloys (Furukawa et al., 1988 Kainuma et al., 1992b, c). The martensitic transformation temperature can be varied within a broad temperature range up to 900 °C, and thus the shape memory efftct can be produced at high temperatures which allows the development of high-temperature shape memory alloys. The problem of low room temperature ductility of NiAl has been overcome by alloying with a third element - in particular Fe - to produce a ductile second phase with an f.c.c. structure. 

Many high-temperature alloy components with insufficient resistance to corrosion in hot gases, e.g. in gas turbines, are coated with a corrosion resistant surface 

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