Distribution of alloying elements in secondary carbides of heat-resistant nickel alloys

Abstract

This paper presents the data of studies dedicated to the influence of lanthanum and the joint effect of lanthanum and nickel on the structure and properties of AlSi9Cu3 aluminum alloy in the cast state and after heat treatment. Structures and phase composition of base alloy, lanthanum-modified alloy and alloy with lanthanum and nickel addition are presented before and after thermal treatment, the essence of which is to simulate cyclic working conditions at high temperatures (it lasted for 100 hours at a temperature of 300 ± 10 ° C). The addition of lanthanum contributes to the formation of a more pronounced dendritic structure, a uniform distribution of eutectics, and certain modification of the iron-containing phases. After heat treatment, lanthanum is stored in a solid solution based on aluminum and reduces its alloying with other elements. Simultaneous addition of nickel and lanthanum results in a more coarse and non-uniform casting structure. Lanthanum in the presence of nickel goes into eutectic and ceases to be in a solid solution based on aluminum. Investigations of experimental specimens mechanical properties shows, that the addition of lanthanum to the AlSi9Cu3 alloy had a positive effect in terms of increasing the strength under elevated temperatures about300 ° C. This effect may be related to the formation of Al₃La particles with submicron sizes that are insoluble up to 640 ° C in the aluminum matrix. The simultaneous addition of nickel and lanthanum increases the amount of eutectic and complicates it. The slight mechanical properties increase about ~ 5% after selected heat treatment is explained by the homogenization of the structure and the greater dissolution of copper in aluminum solid solution. Complications of eutectics with simultaneous lanthanum and nickel alloying also stabilize mechanical properties.