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A COMPREHENSIVE INVESTIGATION ON A PECULIAR DEFECT IN WURTZITE GaN FILM

S.Q.Wang1 , 2) and H.Q.Ye1) 1) Laboratory of Atomic Imaging of Solids , Institute of Metal Research , The Chinese Academy of Sciences , Shenyang 110015 , China 2)Department of Materials Science and Metallurgy , University of Cambridge , Cambridge CB2 3QZ , UK

金属学报(英文版)

Apeculiar crystal defect was observed by experiment of high resolution electron microscopy( HREM) .It wasidentifiedtoformed bytwothreading dislocationsand asegmentof(11 20) domain boundary. An atomicstructure model was proposed for the anomalous defect. Theresultofthe weak beam experimentofelectron microscopeaffirmedthesuggested model.Thestructuralpropertiesofseveral GaN(11 2 0) domain boundaries werestudied by Molec ular Dynamicscalculations. Thetheoreticalresultsshowedthatthelike atom bonding domain boundary, whichcomposesthe main partofthe peculiar defect, has much higher formationenergy than itcounterpartof unlike atom bonding domain boundary. Theoutcome providesanotherevidenceforthesuggested model.

关键词: HREM , null , null , null , null

IN SITU TEM STUDY ON THE R-PHASE TRANSFORMATION IN TiNi ALLOY

CHEN Qing , WU Xingfang and C. J. Humphreys(Department of Materials Physics , University of Science and Technology Beijing , Beijing 100083 , China)(Department of Materials Science and Metallurgy , University of Cambridge , Cambridge CBZ 3QZ , U. K.)Manuscript received 30 November 1995 , in revised form 17 April 1995

金属学报(英文版)

The R-phase transformation process in selected TiNi alloys has been studied in great detail by using in situ TEM technique. The R-phase transformation was found to be a reversible thermoelastic displacive transformation with a nucleation and growth process. The R-phase nucleates at the precipitate/matrix interface in aged specimens and grows by moving the coherent R/matrix interfaces. The stress field of Ti3Ni4 precipitates plays a much more important role in the formation of the R-phase than dislocations in aged TiNi alloy. The microstructure of the R-phase has also been studied.

关键词: : R-phase transformation; TiNi alloy; in situ TEM

ENHANCED PASSIVITY OF GUILLOTINED ALUMINIUM IN Na_2SiO_3 SOLUTION BY GEL FORMATION

C. Liu and G.T. Burstein (Department of MateriaIs Science and Metallurgy , University of Cambridge , Pembroke Street , Cambridge CB2 3QZ , United Kingdom)

金属学报(英文版)

The passivity of guillotined aluminium electrode is enhanced in alkaline electrolytes by SiO32-. It is proposed that the formation of a complete aluminosilicate gel is responsible for this phenomenon. Dissolution of the metal proceeds via the existing film and the dissolution product reacts with SiO_3~2- ions to form the gel. Under galvanostatic polarisation, significant amount of the gel is formed when the applied anodic i > 10mA cm-2. This gel layer can then be transformed into barrier-type of oxide film, thus contributing to the initial stage of the high voltage anodisation.

关键词: passivity , null , null , null , null