Yasuko Takuma

Optical Properties of Au-Pt and Au-Pt-In Alloys

The effects of platinum addition to gold and indium addition to a gold-platinum alloy on their optical properties were investigated using a computer-controlled spectrophotometer. Spectral reflectance data from a polished sample for the incident CIE standard illuminant D65 was collected as a function of the wavelength at 10 nm intervals from 360 to 740 nm. Three coordinates,L* (lightness),a* (red-green),b* (yellow-blue), in the CIE 1976L*a*b* colour space, were determined to quantify the colour of experimental binary Au-Pt and ternary Au-Pt-In alloys. p ]The pronounced step near 520 nm (approximately 2.4 eV) in the spectral reflectance-wavelength curve for pure gold, which is responsible for the rich yellow colour of gold, became less pronounced with the addition of platinum. The decoloring effect of platinum was found to be due to this phenomenon. The addition of indium of up to ca 4 at% to a Au-10 at% Pt alloy increased both chromaticity indices, ie,a* andb* values, giving a gold tinge to the alloy: this effect was brought about by both the slight increase in reflectance in the long-wavelength range and the slight decrease in reflectance in the short-wavelength range of the visible spectrum.

Fractal dimension of grain boundary in CuAu alloys refined by platinum addition

Irregularity of the grain boundaries in CuAu alloys refined by platinum addition was estimated by fractal analysis. The fractal dimension increased with decreasing the grain size, which introduced by platinum addition. The grain refinement produced more complexity in microstructure.

Two types of checkerboard-like microstructures in Au–Cu–Pd ternary alloys

Abstract The phase transformation process in Au–Cu–Pd ternary alloys with the compositions within or near the two-phase region (Au 3 Cu+AuCu I) was studied by means of transmission electron microscopy and hardness testing. Two types of characteristic checkerboard-like microstructures were observed: (1) the coexistence of the Au 3 Cu and AuCu I ordered phases, and (2) the coexistence of the AuCu I ordered phase and disordered phase with face-centered cubic structure. Different age-hardening behaviors were recognized: The high hardness value in the former was maintained for prolonged aging periods, and that produced in the latter was maintained to a certain period followed by over-aging.

Partial phase diagram for the AuCu–Zn pseudobinary system

Abstract Zinc addition to AuCu was found to have significant effects on the structural change of AuCu. A partial phase diagram for the AuCu–Zn pseudobinary system was constructed based on electrical resistivity measurements and X-ray diffraction study. The addition of Zn to AuCu stabilized the AuCu II superstructure and extremely enlarged the AuCu II single-phase region in the Au–Cu–Zn system. The order–disorder transition temperature was slightly lowered with the addition of Zn to AuCu but the AuCu II↔AuCu I transition temperature was greatly lowered. The antiphase domain size of the AuCu II superstructure markedly decreased with increasing Zn content. The lattice parameter a decreased and c increased with Zn addition, thus the axial ratio, c / a , considerably increased.

CHARACTERISTIC MICROSTRUCTURES ASSOCIATED WITH ORDER-DISORDER TRANSITION IN Au-Cu-Pd TERNARY ALLOYS

Department of Dental Materials Engineering, Faculty of Dentistry,Kyushu University, Fukuoka 812-8582, Japan(Received February 24, 2000)(Accepted in revised form March 28, 2000)Keywords: Transmission electron microscopy; Gold alloy; OrderingIntroductionBinary Au-Cu alloys undergo order-disorder transition in some compositional regions. At lowertemperatures, they form a cubic L1

Coherent phase diagram of Au-Cu-Pd ternary system near and within the two-phase region of Au3Cu and AuCu I ordered phases

Abstract Phase identification and analysis of microstructural configuration were done by transmission electron microscopy to determine the coherent phase diagram of the Au–Cu–Pd ternary system near and within the two-phase region of the Au 3 Cu and AuCu I phases. Six distinguishable regions were found in the present experimental phase diagram: a single-phase region of the disordered solid solution, α; a single-phase region of the Au 3 Cu ordered phase; a single-phase region of the AuCu I ordered phase; a region of the coexisting Au 3 Cu and AuCu I ordered phases; a region of the coexisting Au 3 Cu and α phases; and a region of the coexisting AuCu I and α phases.

Martensite transformation in Au3Zn alloy

Abstract Martensite transformation in a Au 3 Zn alloy was estimated by electrical resistivity measurements, X-ray diffraction and high-temperature optical microscopy. Au 3 Zn[R 1 ] structure was confirmed at room temperature. Repeated heating and cooling accompanied a reproducible change due to the surface relief. The reverse martensite transformation proceeded in two stages.

Effects of indium addition to CuAu alloy on phase transformation behaviors

The effects of indium addition to CuAu on the alloy phase transformation behavior were investigated by hardness tests, electrical resistivity measurements, X-ray diffraction and transmission electron microscopy. These established that indium additions lower the critical temperature and stabilize the CuAu II phase at room temperature. Formation of the long period ordered phase produces an age-hardening; although this age-hardening is retarded, the degree of hardening is comparable to that in CuAu. It was noted that the axial ratio increases and the antiphase domain size decreases.

Phase transformation behavior in a multipurpose dental casting gold alloy during continuous heating.

Phase transformation in a multipurpose dental casting gold alloy during continuous heating was studied by electrical resistivity measurements, hardness tests, X-ray diffraction and scanning and transmission electron microscopy. The behavior can be explained by the following reaction sequences in the nodule: α1(FCC) + α2 (L12) → α1(fcc) + α2(L12) + β(L10), where fcc is face centred cubic. A discontinuous precipitation with very fine nodules contributed to the hardening and the growth produced the softening. This multipurpose gold alloy is characterized by the introduction of a PtZn ordered phase with L10 structure instead of a CuAu I phase.

Quantitative analysis of unreacted hemihydrate in set dental stone by adiabatic calorimetry

The unreacted hemihydrate in set dental stone was estimated quantitatively by means of specific heat measurements. With decreases in the water-to-powder ratio (W/P), increases were observed in the amount of unreacted hemihydrate in the set mass. These increases were marked in set stone with a W/P ratio less than 0.25. Furthermore, the amount of unreacted hemihydrate was higher in the interior of the dental stone than in the set surface. It is very difficult to attain a complete reaction, even with higher W/P ratios such as 0.8 in the dental mixing procedure.