A Study for Low Carat Gold Alloys with Age-hardenability at Intraoral Temperature

金合金是牙科治疗中最有用的材料之一。所要求的强度是热处理时效硬化的应用，硬化是由具有L1_0结构的有序相的形成控制的。然而，出现了一个严重的问题。由于L1_0在晶体结构上不同于基质相（fcc），因此，本研究的目的是阐明使用具有相同结构的L1_2相（fcc）的可能性。作为L1_2结构，选择Cu_3Au和CuAu_3。用高频感应炉真空熔炼制备了四种二元合金和六种三元合金。固溶处理后，采用两种模式，即非等温和等温退火。通过电阻率测量、硬度测试、X射线衍射和透射电子显微镜研究了该合金的时效硬化行为。主要结果如下：（1）单纯的L1_2相很难获得合适的强度。需要部分引入L1_0相（CuAu I）以获得所需的强度。(2)时效硬化是由于在Au_3Cu有序基体中形成CuAu I有序相所致。(3)在等温时效过程中，晶粒内部发生了从无序相到平衡相（L1_0 + L1_2）的三种类型的相变。这种差异可以用自由能来解释。

Gold alloys are one of the most useful materials in dental treatment. The required strength is an application of heat treatment wife age4iardening,The hardening is controlled by the formation of ordered phase with L1_0 structure. However, there appears one serious problem of the. deformation on prosthetics, because the L1_0 is different from the matrix phase (fcc) in crystal structure. The purpose of the present study is to clarify the possibility for use of L1_2 phase (fcc) having the same structure. As an L1_2 structure, Cu_3Au and CuAu_3 were selected. Four binary and six ternary alloys were prepared by vacuum-melting in a high-frequency induction furnace. After the solution treatment, two modes were employed, namely anisothermal and isothermal annealings. Th age-hardening behaviors were examined by electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy. The main results were as follows ;(1) It is difficult for only L1_2 phase to obtain appropriate strength for dental prosthetics. Partial introduction of the L1_0 phase (CuAu I) is demanded for the required strength.(2) Remarkable age-hardening was due to the formation of the CuAu I ordered phase in the Au_3Cu ordered matrix.(3) Three types of phase transformation in the grain interior from the disordered phase to the equilibrium phases (L1_0 + L1_2) were detected during the isothermal aging. The difference can be interpreted in terms of the free energy.