Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges

A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.

Research highlights
► Surface strains measured using nanogauge were compared to the texture obtained by EBSD.
► Statistics of the principal strain discern the grains according to the Schmid factor.
► Strain hotspots were localized near a triple junction of alloy 600 under tensile loading.
► Asymetrical profile of the GB strains is a criterion for surface cracking initiation.