WANG Ruikun SUN Lihong LI Dongpei YING Qiming T.Takeyama General Research Institute for Non-Ferrous Metals,Beijing,China [Originally published in ACTA METALL SIN (CHINESE EDN) 24 (5) 1988 pp B353—B358,received 6 May 1987;in revised form 6 February 1988] T.Takeyama is an emeritus professor of HOKKAIDO University,Japan,and now is a technical adviser of GRINFM