High-throughput nanoindentation mapping of cast IN718 nickel-based superalloys: influence of the Nb concentration

TL;DR

This study uses high-throughput nanoindentation to analyze how Nb segregation affects local mechanical properties in cast Inconel 718, revealing correlations between Nb content, hardness, and grain orientation.

Contribution

It provides a detailed correlative analysis of local mechanical properties, chemical composition, and crystallography in cast IN718, highlighting the influence of Nb segregation and temper conditions.

Findings

Nanohardness correlates strongly with local Nb content and temper.

Elastic moduli are unaffected by chemical composition but depend on grain orientation.

Nb segregation varies significantly within dendrite structures.

Abstract

A high-throughput correlative study of the local mechanical properties, chemical composition and crystallographic orientation has been carried out in selected areas of cast Inconel 718 specimens subjected to three different tempers. The specimens showed a strong Nb segregation at the scale of the dendrite arms, with local Nb contents that varied between 2 wt.% in the core of the dendrite arms to 8 wt.% in the interdendritic regions and 25 wt.% within the second phase particles (MC carbides, Laves phases and {\delta} phase needles). The nanohardness was found to correlate strongly with the local Nb content and the temper condition. On the contrary, the indentation elastic moduli were not influenced by the local chemical composition or temper condition, but directly correlated with the crystallographic grain orientation, due to the high elastic anisotropy of nickel alloys.