Nucleation Process of Voids Studied by Positron Lifetime Spectroscopy

Research Project

Project/Area Number	60550459
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	Physical properties of metals
Research Institution	Kyoto University
Principal Investigator	SHIRAI Yasuharu (1986) Faculty of Engineering, Kyoto University, Instructor, 工学部, 助手 (20154354) 古川弘三京都大学, 工学部, 助教授
Co-Investigator(Kenkyū-buntansha)	NAKAMURA Fujinobu Faculty of Engineering, Kyoto University, Instructor, 工学部, 助手 (00026212)
Project Period (FY)	1985 – 1986
Project Status	Completed (Fiscal Year 1986)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1986: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1985: ¥1,300,000 (Direct Cost: ¥1,300,000)
Keywords	Void / Hydrogen / Aluminium / Positron / 空孔
Research Abstract	In order to clarify the void formation mechanism by hydrogen in aluminium, positron lifetime study has been performed on pure Al, and on dilute Al-Mg, Al-Si and Al-Ag alloys. The main results are summarized as follows. 1. Hydrogen were introduced into pure Al(99.9999%) specimens by four different methods (1)quenching from hydrogen atmosphere,(2)quenching into hydrochloric acid,(3)glow discharge in hygrogen gas after quenching into brine and (4)electrolysis after quenching into brine. In all cases void formation were observed during subsequent isochronal annealing. 2. It has been found that the hydrogen introduction before or during quenching is much more effective than after quenching on void formation. Furthermore, in the case of hydrogen charge arter quenching, the ratio of the void formation to faulted dislocation fromation increases with decreasing quenching temperature. These results strongly suggest that hydrogen has the effect on void nucleation only at the very early stage in vacancy clustering. 3. With the aid of computer simulations of vacancy kinetics during quenching, a nucleation model for the secondary defects is proposed: Without a hydrogen atom trivacancies and tetravacancies are attended with great atomic relaxations and grow into faulted dislocation loops. On the other hand, with hydrogen atoms trivacancies and tetravacancies cannot have the relaxed configulations and act as void nuclei. 4. No indication of void formation has been observed for dilute Al-Mg,Al-Si and Al-Ag alloys hydrogen charged. This result indicates that these solute atoms trap hydrogen and inhibit the nucleation of voids mentioned above. 5. It has been found that the density of voids formed in 5N Al is always lower than that in 6N Al. This clearly shows that even such a small amount of impurities as 10ppm suppress the void formation by hydrogen.