Fracture strength characterization of protective intermetallic coatings on AZ91E Mg alloys using FIB-machined microcantilever bending technique

The fracture strength of β-Mg17Al12and τ-Mg32(Al, Zn)49intermetallic coatings on AZ91E Mg alloy was investigated using a nanoindentation-based microcantilever bending technique. A set of micrometer-sized cantilevers with varying dimensions were machined using focused ion beam milling. A nanoindenter was then used to apply an increasing bending load until each cantilever fractured. The corresponding linear-elastic finite element models were created to simulate the deflection of the cantilevers and the fracture strength σmwas derived from the models. The results showed that the fracture occurred at the root of the cantilever where the tensile stresses were highest; the average fracture strengths of the β-Mg17Al12and τ-Mg32(Al, Zn)49phases were 1.76 and 1.05 GPa, respectively. The potential sources of error are also discussed.