Plastic Deformation Behavior of Mg-Y Alloy Single Crystals Observed Using In Situ Brinell Indentation

Abstract

A newly established in situ Brinell indentation technique was conducted to investigate the plastic deformation behavior of pure Mg and Mg-Y alloy single crystals under complex stress conditions. The deformation morphology on the upper surfaces of the specimen around the indent could not be sufficiently observed using the previously reported in situ indentation methods with an optically transparent indenter due to the refraction of rays at the indenter/air interface. In this study, the gap between the indenter and the specimen surface is filled with immersion liquids such as silicone oil and kerosene. This technique enables observation of the specimen surface during indentation. Application of the in situ Brinell indentation to pure Mg and Mg-Y alloy single crystals revealed that the shape of the indents is not circular but elliptical, even during loading. The aspect ratio of the indents decreases with increasing Y content. Moreover, the occurrence of plastic deformation around the indents and beneath the indenter could be observed during the loading and unloading processes using the in situ Brinell indentation method.

Fig. 2 In situ images of (a) pure Mg, (b) Mg-1.3 at% Y and (c) Mg-2.3 at% Y single crystals during loading process (n_r/n_i = 0.85). (d) In situ image processed to measure the major and the minor diameters of the indent on pure Mg single crystal under a load of 9.8 N.