Abstract
Gold-Silver-Palladium alloy is generally considered softened by rapid heating or cooling such as by laser irradiation. We therefore investigated the hardening mechanism for base materials of Gold-Silver-Palladium alloy, Ag-Pd-Cu alloy and Ag-Pd-Cu-Zn alloy, which do not contain gold, using laser irradiation, and obtained the following results.
1) The surface hardness of 45 wt% Ag-25Pd-30Cu alloy, among the Ag-Pd-Cu alloys, was 264.0 HV after laser irradiation, 66.8% harder than that after casting. Based on the results of X-ray diffraction, the hardening mechanism of the alloy by laser irradiation was a phase transformation from α2 (Ag-rich) to α1 (Cu-rich).
2) The surface hardness of 36.0 wt% Ag-31.5Pd-22.5Cu-10.0Zn alloy, among Ag-Pd-Cu-Zn alloys, was 334.5 HV after laser irradiation, 70.9% harder than that after casting. EPMA at the site hardened by laser irradiation and the same site after additional heating in stain-free electric furnace, revealed a great difference between atomic distributions at the two sites. The hardening mechanism of the alloy by irradiation was found to be strain induced by changing solid solution limits.
