Influence of AlN/Al nanoparticles incorporated by high shear dispersion technique on the creep resistance of Elektron21 alloy

RWTH Publications (RWTH Aachen)

Abstract

In this work, the microstructures, creep properties and strengthening mechanisms are systematically investigated in AlN/Al nanoparticle (NP) reinforced Elektron21 (El21) alloy processed by a high shear dispersion technique (HSDT). The optimum shearing speed of HSDT, optimum addition of AlN/Al NPs and the individual/synergistic roles of AlN and Al NPs on the creep resistance of El21 alloy are investigated. Since El21 alloy is a fully heat treatable alloy, the effects from the heat treatment on the creep properties of El21 and El21+1% AlN/Al are also revealed. The results show that HSDT at 3000 rpm is an effective way to incorporate the NPs in El21 alloy. The creep resistance improves by about one order of magnitude with 0.5 % AlN/Al NPs in El21 alloy. True stress exponent indicates that viscous glide of dislocation and dislocation climbing are the main mechanisms during creep. The eutectic becomes much thinner and more homogeneously distributed at the grain boundaries and inside the grains by adding AlN/Al NPs in El21 alloy. These eutectic and AlN NPs can pin the grain boundary sliding and hinder the dislocation movement, thus resulting in an improvement of the creep resistance.By comparing the creep resistance of El21 alloy and El21+x AlN/Al (x=0.25 wt. %, 0.5 wt. % and 1 wt. %) nanocomposites, it is found that 1 % AlN/Al gives the highest creep resistance in El21 alloy. The enhancement is mainly ascribed to the homogeneous and refined intermetallics on the dendritic boundaries, which can effectively inhibit dislocation movement during creep. The formation of Al2(Nd, Gd) phase with high melting point can also help to hinder dislocation movement and therefore improve the creep resistance. The individual effects from Al and AlN on the microstructures and creep resistance are investigated. The creep results show that the additions of 0.25 wt. % Al and 0.75 wt. % AlN could both increase the creep resistance of El21 alloy. A combined addition of 1 wt. % AlN/Al NPs in El21 exhibits even a higher creep resistance than separate additions of Al and AlN. It is observed that Zr preferentially nucleates on the outer layer of AlN particles instead of Al and the formation of Al-Zr phase is suppressed. True stress exponent indexes that the dominant deformation mechanism during creep is viscous glide of dislocation/dislocation climbing.The influence of heat treatment on the microstructural evolutions and creep performances in El21 and El21+1% AlN/Al nanocomposites are discussed. It is found that T6 treatment is beneficial for improving the creep resistance of El21 alloy, but it is ineffective to enhance to creep resistance of El21+1% AlN/Al. This is attributed to the diminished precipitate strengthening effect in El21+1% AlN/Al (T6) by the additional formation of acicular Al2(Nd, Gd) precipitates. The decreased amount of intermetallics on the dendritic boundaries also results in the reduction of creep resistance in El21+1% AlN/Al (T6). Moreover, it is revealed that El21+1% AlN/Al and El21+1% AlN/Al (T6) exhibit longer duration at secondary regions than that of NP-free El21. This is due to the formation of particulate/acicular Al2(Nd, Gd) precipitates, which have a high melting point and could render higher thermal stabilities during creep.

Authors 1

1. Hong Sun Yang corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen