Heterogeneous strain evolution in representative polycrystalline MAX phases

Abstract

• Strain fields in MAX phases are analyzed for the first time using DIC. • Field evolution characteristics show heterogeneous character, irrespective of strain-rate. • Strain heterogeneity is quantified using point-wise strain analysis. • Analysis of strain fields confirm the role of inherent meso-structure comprised of hard and soft grain clusters. MAX phases are a class of ternary compounds, known to exhibit combined properties of both ceramics and metals. This class of materials has a low symmetry crystal structure (hexagonal close packed), which facilitates limited slip, thereby causing deformation to proceed via unconventional ductile modes, such as kink band formations at the nano-scale. In this paper, a detailed analysis of the strain evolution in two MAX phases (Ti 2 AlC and Ti 3 SiC 2 ) is presented using the full-field, non-contact technique of Digital Image Correlation (DIC). Strain measurements are performed using 2D DIC to capture localized features of deformation and a validation of the method is also provided using a 3D DIC technique. The results show that beyond a certain stress level, heterogeneous strain fields are present, the underlying origins of which can be related to lower length scales. The analysis presented here reveals a meso-structure comprising of hard and soft grain clusters, which contribute towards heterogeneous strain fields at the macro-scale.