Effect of Strain Rate and Loading Direction on the Mechanical Properties of Ni-Cr-Al Superalloy Foam Fabricated by Powder Alloying Method

Abstract

The powder-alloyed metallic sheet foam manufacturing process has the advantage of being able to control pore shape, size, and distribution more easily and homogeneously than conventional foam manufacturing processes. The effects of strain rate and tensile direction on the mechanical properties of Ni-Cr-Al superalloy foam fabricated by powder alloying method were investigated. As a result of structural characteristics obtained by X-ray tomography and scanning electron microscopy, average pore sizes were measured to be 2762.4 μm (normal direction), 2709.1 μm (rolling direction, RD), and 2518.4 μm (transverse direction, TD) respectively. The γ-Ni matrix and γ’-Ni3Al (which was evenly distributed in the strut) were identified as the main constituent phases of the Ni-Cr-Al foam used in this study. Tensile tests were conducted with strain rates of 10<sup>−2</sup> ~ 10<sup>−4</sup> s<sup>−1</sup> along the rolling and transverse directions. The results showed that the tensile strength in the RD direction was 1.84~2.01 MPa, and in the TD direction was 1.2~1.27 MPa. The elongation in the TD direction was higher (30~36%) than in the RD direction (17~22%). It is noteworthy that the effect of quasi-static strain rate on the tensile strength and elongation was negligible. However, the loading direction was found to change mechanical properties significantly. This study also discussed the deformation behavior of the Ni-Cr-Al superalloy foam through observations of the fracture surface, and realtime observations during tensile tests in different directions.