High-Resolution Electron Microscopy Study of Phase Transformations in Dental Alloys

本研究的最终目的是根据设计原则定制新型牙科合金，该设计原则是通过阐明力学，电化学，生物学因素与合金晶体微观结构特征之间的相关性而构建的，因为这些因素在很大程度上受固体界面如晶界，堆垛层错，孪晶界和反相畴界的控制。以下是研究项目的具体描述。(1)结合理论结果和已有的实验数据，建立了AuCu-Ag和（Ag_<0.5>Cu_<0.5>）_x-Au_2<1-x>截面的相干相图。(2)AuCu-Ag赝二元合金中长周期反相畴界结构的高分辨电镜观察。（3）AuCu-3at的孪晶界结构特征。%Ag合金。(4)时效硬化机制和相转变的高分辨电子显微镜研究 ...更多信息 商业牙科金合金中的ns。（1）在AuCu-Ag赝二元系中发现了三种不同的相变模式，即：(i)AuCu有序化是由FCC结构（_0相）的无序固溶体引起的。结果表明，AuCu-3at合金中形成了_0无序相和AuCu Ⅱ有序相共存的温度区、AuCu Ⅱ有序相的单相区、AuCu Ⅰ和AuCu Ⅱ两种有序相共存的温度区和AuCu Ⅰ的单相区。%Ag合金在653 K的临界温度下进行有序化，（ii）有序化和两相分解的双重机制是由时效引起的，在一个组成区域之间的可扩展性差距和调幅lucus。在该组成范围内，相变由成核和生长过程控制，即，(a)（B）两个无序相和一个有序相共存区，_1+ _2+AuCu II，（c）一个有序相和一个无序相共存区，AuCu II + _2，（d）两个有序相和一个无序相共存区，AuCu I + AuCu II + _2，（e）有序相和无序相AuCu I +2共存区;（iii）失稳区内部组成区老化产生有序化和失稳分解的双重机制。在该组成范围内的相变过程的速率高于位于可渗透性间隙和旋节线之间的组成范围。虽然时效引起的显微组织的差异是最重要和最令人感兴趣的，但相变的温度和成分依赖性还没有被精确地确定。(2)用高分辨电子显微镜观察了AuCu-3at.%中长周期反相畴界的结构、不同相之间的界面结构特征和wtin畴界Ag、AuCu-6at.% Ag、AuCl 1 -9at.%和AuCu-14 at.%银合金，在不同的温度和时间老化。由时效引起的显微组织根据合金中的银含量而彼此相当不同，即，在能隙外的成分范围内，AuCu有序化完全由无序固溶体引起，在能隙与旋节线之间的成分范围内，相变由成核和生长机制控制，在旋节线内的成分范围内，AuCu有序化与旋节线分解同时发生。在AuCu-9at.%合金的高分辨电子显微镜照片中发现了由AuCu Ⅱ有序相和富银的无序FCC_2相组成的特征镶嵌结构Ag合金在614 K时效100 ks。(3)在测定Au-Cu-Ag三元系共格相图的系统研究过程中，必须确定与AuCu Ⅱ长周期超结构共存的无序FCC相，这是相规则所期望的。用高分辨电子显微镜观察了AuCu-3at.%合金中的无序FCC相和AuCu Ⅱ相Ag合金在643 K时效100 ks。结果发现，在孪晶板的尖端附近形成三角形区域。三角形区域显示出相当大的弹性应变，从原子构型的几何特征可以认为是无序的FCC相。(4)商业牙科用金合金Au-5 wt.%的淬火硬化特性Pt-3wt.% Pd-6wt.% Ag-15wt.% Cu-3wt.%通过电阻测量、硬度测试、X射线衍射和电子显微镜等手段对镀层进行了研究。在较低的时效温度下，硬化是由于AuCu I型有序结构的成核，其特征在于有序片晶的缓慢生长速率。在较高的温度下时效形成了一个交替的粗糙AuCu I有序的血小板相互交叉。在此温度范围内，在AuCu I有序片晶和周围基体之间的界面处没有观察到应变场。少

The eventual purpose of the present research project was the tailoring of new type dental alloys based on designing principle which was constructed with elucidating the correlationship between mechanical, electrochemical, biological factors and microstructural features of the alloy crystal, because these factors were governed greatly by solid interface such as grain boundaries, stacking faults, twin boundaries, and antiphase domain boundaries. The followings were concrete descriptions of the research project. (1) Construction of the coherent phase diagram of AuCu-Ag and (Ag_<0.5> Cu_<0.5>)_x-Au_<1-x> sections combining a theoretical results and available experimental data. (2) High-resolution electron microscopic observations of the long period antiphase domain boundary structure in AuCu-Ag pseudobinary alloys. (3)Structural features of twin boundary in AuCu-3at. %Ag alloy. (4) High-resolution electron microscopic study of age-hardening mechanisms and the associated phade transformatio … More ns in commercial dental gold alloys. Works done were as follows: (1) Three distinguishable mode of phase transformations were found in the AuCu-Ag pseudobinary system, i.e., (i) the AuCu ordering was brought about solely from disordered solid solution of FCC in structure ( _0 phase) at a composition region of outside of the miscibility gap. It was found that a temperature region of coexistence of the _0 disordered and AuCu II ordered phases, a single phase region of AuCu II ordered phase, a region of coexistence of two ordered phases AuCu i and AuCu II, and a single phase region of AuCu I were formed in aucu-3at. %Ag alloy under the critical temperature for ordering at 653K, (ii) dual mechanism of ordering and two-phase decomposition was induced by ageing in a composition region between the miscibility gap and a spinodal lucus. The phase transformations were governed by a nucleation and growth process in this composition range, i.e., (a) a two-phase decomposition region containing copper-rich FCC _1 and silver-rich FCC _2 phases, (b) a coexisting region of two disordered phases and an ordered phase, _1+ _2+AuCu II, (c) a coexisting region of an ordered phase and a disordered phase, AuCu II + _2, (d) coexisting region of two ordered phases and a disordered phase, AuCu I + AuCu II + _2, and (e) a coexisting region of an ordered phase and a disordered phase, AuCu I + _2, and (iii) dual mechanism of ordering and the spinodal decomposition was generated by ageing in a composition region of inside of the spinodal lucus. A rate of the process of the phase transformation was higher in this composition range than in a composition range located between the miscibility gap and the spinodal lucus. Phases coexisting were essentially analogous to this range except for differences in microstructures.Although the differences in microstructures induced by ageing were the most inportant and great interest, the temperatures and composition dependence of the phase changes have not been determined exactly yet. (2) High-resoultion electron microscopic observations were performed to clarify a configuration of the long period antiphase domain boundary, structural characteristics of interfaces between different phases, and wtin boundary in AuCu-3at.%Ag, AuCu-6at.%Ag, AuC1-9at.% and AuCu-14at.%Ag alloys which were aged at various temperatures and periods. The microstructure induced by ageing was quite different from each other depending on silver content in the alloys, i.e., the AuCu ordering was brought about solely from disordered solid soulution in a composition range of outside of the miscibilith gap, the phase transformation was governed by a nucleation and growth mechanism in a composition range between the miscibility gap and a spinodal lucus and the AuCu ordering was concurrent with the spinodal decomposition in a composition range of inside of the spinodal lucus. The characteristic mosaic structure which cosisted of the AuCu II ordered phase and a silver-rich disordered FCC _2 phase was found in high-resolution electron micrographs obtained from the AuCu-9at.%Ag alloy aged at 614K for 100ks. (3) During the course of a systematic study to determine the coherent phase diagrams of Au-Cu-Ag ternary system, it was necessary to identify a disordered FCC phase coexisting with the AuCu II long period superstructure, as was expected from the phase rule. High-resolution electronmicroscopy was employed to distinct the disordered FCC phase and the AuCu II phase in th AuCu-3at.%Ag alloy aged at 643K for 100ks. It was found that a triangle shaped area was formed in the vicinity of the tip of the twin platelets. The triangle shaped area showed a considerable amount of ealstic strain and was thought to be the disordered FCC phase from geometric features of atomic configurations. (4) Age-hardening characteristics of a commercial dental gold alloy, Au-5wt.%Pt-3wt.%Pd-6wt.%Ag-15wt.%Cu-3wt.%Zn, were studied by means of resistometric measurements, hardness tests, X-ray diffraction and electron microscopy. At lower ageing temperatures the hardening was due to the nucleation of the AuCu I type ordered structure and was characterized by a slow growth rate of the ordered platelets. An alternating coarse AuCu I ordered platelets abutted on each other was formed by ageing at higher temperatures. No strain field was observed at the interfaces between the AuCu I ordered platelets and the surrounding matrix in this temperature range. Less