Miscibility gap of the Fe-NiAl partial system relative to the physical properties of alloys. II. Alloys with a high Fe content

In the first part, the iron influence at low temperatures on NiAl intermeta llic compound was studied. The boundary of the miscibility gap on the NiAl intermetallic compound side of the Fe-NiAl partial system was determined. I n this second part, in order to determine the boundary at low temperatures on the Fe corner side, if is necessary to know the solubility limit of nick el and aluminium on iron. For this purpose, using the same method as in the first part, a close study of physical properties and phases occuring in a series of 32 selected allo ys was carried out. The chemical compositions of the used alloys were selec ted along a line between Fe and NiAl. For low nickel and aluminium content of the alloys, results show that a single phase alpha-Fe is present. When t he nickel and aluminium content exceeds 4.3 at. %, the physical properties and the microstructure change from a single domain to a mixture of two phas es alpha(1) and alpha(2). The microstructure of alloys consists of B2 preci pitates (alpha(2)) in alpha-Fe matrix (alpha(1)). The precipitates exhibit increasing coarseness with an increase in nickel and aluminium content. If the nickel and aluminium addition increases up to 4.3 at. %, there is a dec reased density and magnetization, a zero constant coercive force, and incre ased hardness and lattice parameter. In excess of 4.3 at % nickel and alumi nium content all these properties change. The micro-hardness, density, magnetization and coercive force increase whil e the lattice parameter decreases. These effects were attributed to the B2 precipitates. This change at 4.3 at. % of nickel and aluminium reveals the maximum solubility at low temperatures of nickel and aluminium on iron. Thi s maximum solubility clearly indicates the boundary of the miscibility gap on the iron rich region of the Fe-NiAl partial system.