The effects of the point defects on precipitation in NiAlFe alloys

Abstract

The high thermal conductivity, high melting point and low density of NiAl alloys compared to Ni-based superalloys make attractive materials for high temperature structural applications. The lack of high temperature strength, however, has been one of the barriers which limits the use of NiAl alloys. The use of these alloys in structures will be severely hampered, unless this problem can be overcome. Consequently, a large amount of effort has been devoted to the improvement of the various measures of high temperature strength, e.g., precipitation strengthening. In order to obtain better understanding of the effects of iron on the properties of NiAl, a systematic study of its effects on both physical and mechanical properties of NiAl has ben undertaken. Of specific interest are the correlation of point defects (thermal vacancies, constitutional vacancies and anti-site atoms) and Fe precipitates and the variation of the concentration of point defects along with iron content, substitution scheme (for Ni, for Al and for both Ni and Al) and temperature. The effects of vacancies on Fe precipitation in NiAlFe have been studied by using magnetic susceptibility measurements and transmission electron microscopy.