Quantifying boundary effect of nanoparticles in metal matrix nanocomposite fabrication processes

Lightweight, high-strength Metal Matrix NanoComposites (MMNCs) are promising materials for use in automotive, aerospace, and numerous other applications. A uniform distribution of nanoparticles within the metal matrix is critical to the quality of such composites. In current MMNC fabrication processes, however, a boundary effect often occurs where the nanoparticles tend to gather around the grain boundaries of the metal matrix. To realize quality control and guide process improvement efforts, this article proposes a method for quantitatively assessing the boundary effect observed in microstructure images of MMNC samples based on the theory of spatial statistics. Two indices for quantifying the degree of boundary effect in an image, called Boundary Indices (BIs), are developed and their statistical properties are provided. The performances of the BIs are shown and compared in a numerical study. They are also applied to images from a real MMNC fabrication process to validate the effectiveness of the proposed method.