Date: 15 Feb 2011

In Situ Observations of Ductility-Dip Cracking Mechanism in Ni-Cr-Fe Alloys

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Abstract

The ductility-dip cracking (DDC) behavior of Ni-Cr-Fe alloys has been evaluated by the use of in situ scanning electron microscopy (SEM) involving high temperature deformation. This unique approach provides information regarding the DDC phenomenon and its dependence on microstructural features such as grain boundaries and second phase precipitates. Experimental materials were prepared based on the ERNiCrFe-7 alloy (Filler Metal 52) with additions of Nb, Mo, and Hf. These additions provided a range of precipitates and gamma matrix chemical composition, which had an important effect on high temperature ductility. Evidence of grain boundary sliding (GBS), the role of precipitates, grain boundary morphology, and gamma phase composition were evaluated and related with fundamental properties governing the material deformation. The in situ observations revealed that DDC is a high temperature intergranular fracture phenomenon dominated by Rachinger-like grain boundary sliding. Finally, this new approach provided valuable information to understand material ductility at high temperature.