Solubility of iron-nickel alloys in liquid aluminum

Abstract

In order to check the agreement of the alloy composition obtained with the given initial ratio of iron and nickel in the charge, selective chemical analyses were performed. The homogeneity of the specimens was investigated by electron-probe x-ray spectral microanalysis (EPMA) using the "Jeol" superprobe-733 analyzer. Deviation of the alloy compositions from the nominal did not exceed +0.5% (Table i). Therefore it was assumed in the calculations that every alloy was of the nominal composition. Metallographic analysis of microsections showed that the specimens were single phase with the exception of the 90% Fe-10% Ni alloy, in which a small amount of second phase was discovered. All of the alloys were, apparently, "y-solid solution at 700~ since the a --, T transformation of even the 10% Ni alloy is 640~ [1]. The temperature of this transformarion decreases rapidly with increasing nickel content. Since the o~ --, T transformation is diffusionless (martensitic type) it most likely went to completion in all alloys during the time required to stabilize the temperature in the measurement cell (10 rain). The experimental method is described in detail in [2]. A flux consisting mainly of alkali metal halides was used to protect the aluminum melt from oxidation, as well as for preliminary heating of the solid specimens to the required temperature. The flux was first melted in an aluminum oxide crucible of 26 mm internal diameter, and then pieces of aluminum were melted below the flux layer. When the melt had reached the desired temperature the specimen was placed in the flux so that the distance from the lower surface of the specimen to the surface of the aluminum melt was about 10 mm. Upon cessation of temperature fluctuations the rotating specimen was plunged into the liquid aluminum, held there for a given period of time, and then withdrawn and cooled in water. After this procedure most of the aluminum alloy was removed mechanically from the surface of the specimen, and the remainder by etching in a 10% NaOH or KOH solution. After removal of the solution products the specimen was washed in water and ethanol, dried, and weighed. The loss of mass by solution in liquid aluminum was determined from the weight measurements before and after the treatment. The Al-Fe-Ni alloys obtained were chemically analyzed for their iron and nickel content. The relative error in determining the elements was + 10%, on the