Grain Boundary Sliding Phenomenon and Its Effect on High Temperature Ductility of Ni-Base Alloys

Abstract

The structural materials phase transformations and failure mechanisms have been under scrutiny for many years. However, the advent of new and more powerful techniques is always making possible to address unsolved problems. Nowadays, the implementation of sophisticated in-situ electron microscopy tests is providing new insights in several fields of chemistry, physics, and materials science by allowing direct observation of a wide variety of phenomena at submicron and even atomic scale. These experiments may involve controlled temperature and atmospheres, mechanical loading, magnetic and/or electric field among other conditions that are imposed to the sample while its response or evolution is studied. An in-situ high temperature deformation experiment was developed and adapted within the vacuum chamber of a scanning electron microscope (SEM). This setup was used to study the grain boundary sliding (GBS) mechanism and its effect on the high temperature cracking phenomenon known as ductility-dip cracking (DDC). The Ni-base filler metals AWS A5.14, ERNiCrFe-7 and ERNiCr-3, which correspond to alloys 690 and 600, respectively, were studied within the temperature range between 700 and 1000 °C. Analysis of the recorded digital videos that registered the high temperature deformation made possible differentiating and quantifying, with submicron resolution, two different components of GBS. The designated pure-GBS and deformation-GBS components were described and quantified. In addition, the GBS relationship with the material high temperature ductility and the DDC failure mechanism was established.