3D X-ray Microprobe Investigation of Local Dislocation Densities and Elastic Strain Gradients in a NiAl-Mo Composite and Exposed Mo Micropillars as a Function of Pre-strain

Abstract

3D spatially-resolved polychromatic microdiffraction was used to nondestructively probe the depth-dependent dislocation density and elastic strain gradients in separate phases of a NiAl –Mo composite. Dislocation density and strain gradients are investigated before and after compressive strain. After plastic deformation important changes in the local stress state are found compared to the as grown composite. In as grown composites, due to the thermal expansion mismatch, the Mo phase is under compression and the NiAl phase is in tension. After compressive strain, the Mo phase is in tension and NiAl matrix is under compression. This result can be understood from the mismatch in yield strain of the composite material and from the elastic constraints during unloading. The dislocation density in both phases is found to grow with increased straining. These measurements provide quantitative dislocation information to guide recent directional solidified Mo micro-pillar testing. They also guide models of interface dynamics in composite materials.