ZHAO Lihua;WU Lijun;HUANG Qizhong;YANG Qiaoqin 1)(Material Research and Test Center,Hunan University,Changsha,China)2)(Powder Metallurgy Research Institute,Center-South University of Technology,Changsha,China)3)(Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Chinese Academy of Science,Shenyang,China)Manuscript received 18 April 1995