Title

Relative contributions of secondary and tertiary γ′ precipitates to intergranular crack growth resistance in IN100 alloy

Document Type

Conference Proceeding

Date of Original Version

12-1-2012

Abstract

This paper examines the role of secondary and tertiary γ′ on intergranular crack growth rate in P/M IN 100. A series of different heat treatments were carried out on the as received material to vary the γ′ statistics (size and volume fraction) through control of the different features of the heat treatment cycle. Dwell fatigue crack growth experiments have been performed on as received as well as heat treated specimens at 650°C and 700°C in air with dwell time loading cycles. Results on the as-received material show that the intergranular crack growth rate while temperature dependent, is independent of the hold time period. For the modified microstructures tested at 650°C, the dwell crack growth rate is shown to be sensitive to γ′ variations. Considering that the yield strength of the continuum is a function of γ′ statistics, the role of γ′ on intergranular cracking was illustrated by correlating the crack growth rate and the continuum yield strength. This inverse relationship is examined numerically by modelling the grain boundary fracture path as an interface surrounded by near and far field continuum regions represented by viscoplastic flow formulations. Results of the model show that an increase in the continuum yield strength is accompanied by a lower viscous strain, resulting in higher constraint on the grain boundary sliding and thus, a decrease in the crack growth rate. This observation was further examined by calculating the individual components of yield strength associated with tertiary and secondary γ′ precipitates. These components were correlated with the crack growth rate, showing higher sensitivity to the tertiary γ′ precipitate hardening effects.

Publication Title

Proceedings of the International Symposium on Superalloys

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