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Takeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya
no journal, ,
The impact stress exfoliates a Nitride surface layer on Titanium alloy prepared in some conditions. So we prepared specimens in two different conditions, (1) 810
C, 600min and (2) 850C, 720min, and performed depth profile analysis of their surfaces with Doppler broadening measurements of positron annihilation 
-rays (DB) that is sensitive for defects by Slow Positron beams. Although the specimens (2) is harder than (1) according to the Vickers Hardness test, DB results indicated that defect layer of specimen (1) is thicker than (2). It means that the defect layer thickness was not the cause of surface hardening. Furthermore, chemical elements at the positron annihilation sites could be analyzed qualitatively by DB and the change of the composition appeared in deeper region than the defect layer. The defect layer depth does not match the depth where chemical composition changes by DB appeared. TEM and EDS observation showed different tendency from the results by DB. It is because positrons probe specific sites, and the combination of these methods will be a strong tool to investigate surface structures.
Ishimoto, Kazukiyo; Hirade, Tetsuya; Suzuki, Junichi*; Okubo, Nariaki; Suzuki, Kazuhiko*
no journal, ,
Positron annihilation lifetime measurements were performed to evaluate defects introduced by plastic deformation of SUS316 specimens. Although there was almost no long lifetime component before the deformation, a component with a lifetime of 177 picosecond gave intensity of 86% after the deformation of 40%. This lifetime corresponds to the lifetime of positrons trapped in mono vacancies. As a result of small angle neutron scattering experiments, the enhancement of scattering intensity at the plastic strain greater than about 50% where necking of the specimens was initiated, probably, indicated the formation of 
m voids. The defect size observed by the positron annihilation methods and the void size observed by the small-angle scattering method were in different scale, therefore the combination of the two methods would be useful to evaluate the microstructural changes on the way to the fracture.
Fukaya, Yuki; Entani, Shiro*; Sakai, Seiji*; Mochizuki, Izumi*; Hyodo, Toshio*; Shamoto, Shinichi
no journal, ,
no abstracts in English