Compressive properties of lotus-type porous stainless steel
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Lotus-type porous stainless steel (SUS304L), possessing cylindrical pores aligned in one direction, was fabricated by means of a continuous zone melting technique under a pressurized hydrogen/helium atmosphere. Compression tests were carried out on the resultant lotus stainless steel not only in the directions parallel and perpendicular to the elongated-pore direction but also in other directions to reveal its anisotropic compressive behavior. The macroscopic deformation modes depend on porosity and the angle between the elongated-pore direction and compression direction, which is a unique characteristic resulting from its anisotropic porous structure. The yield stress in the pore direction decreases almost linearly with increasing porosity, while that in the perpendicular direction decreases more rapidly. The yield stress in the direction of from the elongated-pore direction decreases monotonically with increase in . The yield behavior of lotus stainless steel was described using micromechanical mean-field theory.
I. INTRODUCTION
Over past the few decades, porous and foamed metals have been the focus of great interest due to their special features that include low density, high surface area, and sound absorption, etc.1,2 However, conventional porous metals, fabricated by sintering or foaming, etc., possess pores of spherical or irregular shape.3–5 As a result, the strength of the porous metals is quite low due to stress concentration around the pores, and their poor mechanical strength has been a long-standing obstacle to their wider use. To overcome this problem, lotus-type porous metals have been fabricated by unidirectional solidification in pressurized gas.6,7 The pores of these lotus metals are cylindrical and aligned in one direction; this pore structure differs completely from that of conventional porous metals. Thus, the mechanical properties of lotustype porous metals are superior to those of conventional porous metals.8–11 Recently, Ikeda et al.12 have successfully fabricated lotus-type porous stainless steel by using a continuous zone melting technique.8 Stainless steel is an important structural material in many fields. It is expected that lotus stainless steel, which has additional features, will prove to be a useful material. For practical use, it is first essential to clarify its mechanical properties.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0016 J. Mater. Res., Vol. 21, No. 1, Jan 2006
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Simone and Gibson13 performed tensile tests on lotustype porous copper in the direction parallel to the longitudinal axis of the pores (hereafter, this direction is referred to as the “pore direction”). However, a systematic investigation could not be carried out because of the data scattering that originates from nonhomogeneous pore distribution. Hyun et al.9 also studied the mechanical properties of lotus-type porous copper and showed that the tensile strength is anisotropic; i.e., it depen
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