Large enhancement of yield stress of metals by surface etching in ultra-high vacuum

Abstract

Recently, it has been revealed from a variety of experiments that mechanical properties of metallic materials are strongly dependent on the surface conditions of specimens and on the test environments as well. All these experimental results clearly indicate that in order to get any intrinsic mechanical properties of them it is necessary to control the specimen surface state and the testing atmosphere in an ideal manner as much as possible. For this purpose the authors have constructed a new apparatus suitable for measuring mechanical properties of metals and alloys. It is concluded that yield stresses of bulk metals are sensitive to the existence of thin oxide or oxide-like films on the surface. The intrinsic yield stresses of most metals are probably higher than the reported values which have been obtained by a conventional mechanical test in air using the specimens coated with some oxide films.