Measurement of Elastic Characteristics of Single-Crystals of a Nickel-Base Superalloy by Speckle Interferometry

Abstract

The elastic properties of single crystals of nickel-base superalloy VGM7 have been investigated by speckle interferometry. Plate-shaped specimens of different crystallographic orientations were loaded under pure shear conditions and speckle interference patterns from the deformed specimens were imaged. Numerical processing of these interference patterns allowed us to determine the values of Young’s modulus in directions [001] and [011], \({{E}_{{001}}}\) = 138 GPa and \({{E}_{{011}}}\) = 241 GPa, the basic value of Poisson’s ratio, \({{\nu }_{0}}\) = 0.39, in the coordinate system 〈001〉, as well as its minimum and maximum values, \({{\nu }_{{{\text{min}}}}}\) = −0.10 and \({{\nu }_{{{\text{max}}}}}\) = 0.69, under longitudinal loading along [101] when the specimen transversely deforms along [10\(\bar {1}\)] and [010], respectively. Using the measured values \({{E}_{{001}}}\), \({{E}_{{011}}}\), \({{\nu }_{0}}\), \({{\nu }_{{{\text{min}}}}}\), and \({{\nu }_{{{\text{max}}}}}\) the single-crystal elastic stiffnesses, \({{C}_{{11}}}\) = 264 GPa, \({{C}_{{12}}}\) = 166 GPa, and \({{C}_{{44}}}\) = 133 GPa, and the elastic compliances, \({{S}_{{11}}}\) = 7.35 TPa^–1, \({{S}_{{12}}}\) = –2.84 TPa^–1, and \({{S}_{{44}}}\) = 7.52 TPa^–1, were calculated. The applied method allows one to unambiguously determine the sign of Poisson’s ratio and, therefore, it should be recommended for studying the elastic properties of auxetic materials, for which determination of the sign of Poisson’s ratio is of great importance.