The effects of isothermal deformation and annealing on the microstructure of nickel-aluminum-bronze in relation to the friction stir process

Abstract

The FSP of Nickel Aluminum Bronze is a novel approach to enhance the microstructural properties of the material through a shear deformation process. This thesis examines the effect on microstructure of isothermal annealing and quenching of as-cast Nickel Aluminum Bronze and, furthermore, reports on investigation of the effects of isothermal hot rolling on microstructure of this material. Quantitative analysis of the microstructure constituents shows that heating to about 800oC results in the formation of beta by reversion of the eutectoid constituent alpha + kappaiii. Further heating in the range of 800- 1000oC results in an approximately linear decrease in the volume fraction of primary alpha and a corresponding increase in the volume fraction of beta transformation products. Isothermal rolling of NAB over this same temperature interval results in deformation of both phases and an elongated, banded distribution of alpha and beta transformation products in the middle of this interval. This suggests that local peak temperature in the stir zone of material that has been subjected to FSP may be estimated by microstructure analysis. The yield and ultimate strengths of NAB are increased and ductility is also increased when rolled material is compared to as-cast NAB. However, strength and hardness appear to be independent of prior rolling temperature.