The assessment of growth kinetics in the intermetallic layers of Al-AlxNiy-Ni laminate composites

M Azimi,M Shamanian,L A I Kestens,M R Toroghinejad

doi:10.1088/1742-6596/1270/1/012026

Abstract

Ni aluminides have technologically attracted much attention as oxidation protective layers on Ni-superalloys for high-temperature and harsh environments applications as well as for reinforcements in metal-matrix composites. Among the Ni aluminides, the AlNi compound exhibits the best combination of oxidation-protective characteristics and hardness; thus there is a progressive demand to produce it particularly through convenient in-situ fabrication processes. Therefore, the evaluation of growth kinetics in AlxNiy layers is of crucial importance in determining an optimum compound formation process. To this purpose, Al-Ni intermetallic laminate composites were produced through cold roll bonding and subsequent annealing of aluminum and nickel sheets. The microstructure of the intermetallic layers was investigated in order to specify the controlling mechanisms and subsequently the growth model of the different phases. The Al3Ni layer was kinetically the first to appear but started to decompose at the expense of the AlNi compound when the direct source of Al disappeared for the reactive diffusion couples. The Al3Ni layer growth was initially controlled by bulk diffusion, but then at T≥525°C was modified as a function of competition between formation and consumption, whereas the AlNi growth was governed strongly by the interfacial reaction. The time dependence of the growth rate revealed different behaviors of linear and parabolic kinetics. The overall assessment revealed a bulk diffusion-controlled growth for all of the intermetallic layers. Arrhenius parameters could be derived for the Al3Ni layer, while it was impossible for the AlNi phase because the formation of this layer was caused by a mixture of diffusion mechanism.

Highlights

Between nickel aluminides, the AlNi intermetallic phase exhibits the best combination of oxidationprotective characteristics and hardness, which provokes a great interest in Al-AlNi-Ni composites
According to Michaelsen and Barmak [3] the growth of Al3Ni phase indicates a parabolic dependence on the annealing time, whereas Jung et al [4] have reported that the growth kinetics of Al3Ni phase does not obey the parabolic law
A more detailed examination of the formation mechanism of intermetallic phases is of crucial importance to better control the processing of these materials and the aim of this work is to investigate the formation mechanisms and growth kinetics of intermetallic phases in the Al-Ni diffusion couple fabricated by the roll bonding process

Summary

Introduction

The AlNi intermetallic phase exhibits the best combination of oxidationprotective characteristics and hardness, which provokes a great interest in Al-AlNi-Ni composites. There are some inconsistencies in the data on the growth kinetics of intermetallic phases. According to Michaelsen and Barmak [3] the growth of Al3Ni phase indicates a parabolic dependence on the annealing time, whereas Jung et al [4] have reported that the growth kinetics of Al3Ni phase does not obey the parabolic law.

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