Thesis (M.D.S.) -- University of Adelaide, Dept. of Restorative Dentistry, 197

Weidenhofer, Robert Napier George

Adelaide Research &amp; Scholarship

-5-"5Dislocations and Stress CorrosionCracking in ASrSnR.N.G. WEIDENH0FER, B.D.S. (Adel. )A Thesis submitted for the degree of Master of Dental Surgery inDecember, 1973. The investigation was carried out in the MaterjalsScience Group, Department of Chemical Engineering of the Universityof Adelaide, in association with the Department of RestorativeDentistry of the University of Adelaide.SUMMARYTcchniques have been developcd that cnablc lattice defectsto be observed in AgrSn crysta'ls using transmission electron microscopy.The presence of dislocations and other lattice defects wìthin Ag,Sn hasbeen demonstrated and although comp'lete ana'lysis of micrographs was notundertaken, basic analys'is has shown that the dislocations and otherlattice defects run in t ifO I t 1-101 and tilOl dÍrections. A]thoughthese directions do not belong to p'lanes of a zone, there is agreementw'ith prev'ious authors who have observed twinning of A9,Sn during x-raydiffraction studies and found that the directiori of shear was IO-fi] inthe (o1o) plane.It has been conclusively demonstrated, as a secondary aim ofthe proiect, that the intermetalfic compound AgrSn, in the presence ofboth mercury and tensile stress, is susceptible to stress corrosioncracking. It is this reactjon which is probably the basis of themechanism of the reaction between dental amalgam a11oy and mercury.Scanning electron microscope study of AgrSn has confirmed thesusceptib'ifity of the alloy to stress corrosion cracking and has alsoshown that the a11oy now appears to be heterogeneous and demonstratesthe presence of grain boundary voids that explain difficultiesexperíenced in preparation of transmission electron microscopespec'imens.DECLARATIONThÍs thesis contains no material which has been acceptedfor the award of any other degree of diploma in any University and,to the best of the author's knowledge and belief, the thesis containsno material prev'iously published or wrÍtten by another person, exceptwhere due reference is made in the text.R.N. G. l^lEIDENHOFERACKNOhILEDGEMENTSThe author wishes to thank Professor D.R. Miller andDr. 0.F. Makinson, co-supervisors of the research project, for theirvaluable guidance and encouragement throughout the project, alsoDr. D.R.G. l^Jill iams and Mr. A.S. Pearce of Materials Science Groupfor continuing technical advice during the course of the project, andMr. B. Ide for his assistance in the design and preparation ofequipment and specimens used in the research project.The author also wishes to thank Amalgamated Dental(International) Co. for their generous support in the preparationand supp'ly of ingots of commercial dental amalgam a'lloy and AgrSnused in this research project.12TABLE OF CONTENTSSUMMARYDECLARATIONACKNOt^lLEDGEMENTSINTRODUCTIONDENTAL AMALGAM AND DENTAL AMALGAM ALLOY2.I Dental Amalgam2.2 Stacking Fau'lts and Dislocations ín Silver-TinAl 1 oys2.3 Stress Corrosíon CrackingEXPERIMENTAL METHODS3.1 MetallograPhY of AgrSn3.2 Transmission Electron Microscopy3.3 Stress Corrosion CrackingRESULTS AND DISCUSSION4.1 Transmission Electron Microscopy4.2 Stress Corrosion CrackíngCONCLUSIONSBIBLIOGRAPHYPage1. 12.12.t2.252.323.13.13.43.134.14.r4.35.1345l:

Dislocations and stress corrosion cracking in Ag3Sn

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Dislocations and stress corrosion cracking in Ag3Sn

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Dislocations and stress corrosion cracking in Ag3Sn

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Adelaide Research &amp; Scholarship

Adelaide Research & Scholarship