A Gold-Based Bulk-Solidifying Amorphous Alloy for Jewelry — Comparison with a Palladium-Based Amorphous Alloy

Abstract

The gold alloys are used in jewelry for their aesthetic appearance and inertia to the environment. In jewelry a hardness superior to 300 HV is desirable to facilitate the final machining and reduce the wear of the final product. The maximum hardness that can be obtained with the standard 18 carats gold (Au75-Ag12.5-Cu12.5 (wt%)) through a combination of heat treatment and cold working is about 290 HV. Gold-based bulk metallic glasses (BMGs) are an alternative as they present unique properties in comparison with crystalline counterparts, especially easy thermoplastic processing combined with a high hardness. Pd-base BMGs are another solution, due also to their attractive features.An Au49Cu26.9Si16.3Ag5.5Pd2.3 (% at.) and a Pd40Cu30Ni10P20 (% at.) bulk metallic glasses were fabricated by a copper mould suction casting technique in an argon atmosphere. In the as-cast state hardness, shear modulus and hardness are high (HV0.3= 360 and 530 in the Au-and Pd-base BMGs, respectively). Various heat treatments have been performed to modify the microstructural state. Formation of crystalline particles induces an increase of both shear modulus and hardness but a drastic decrease in toughness and therefore this formation should be absolutely avoided during casting or thermo processing.

Top-view analysis of ultrafast differential scanning calorimetry data

“…例如, 激光加工 [13] [14] . Au基非晶合金是一种理想的替代 材料 [15] , 得益于其非晶态原子结构, Au基非晶合 金的硬度高, 是18克拉晶态合金的1.2 -2.4倍 [16] .…”

“…一些Au-Ag-Pd-Cu-Si系列的合金成分具有较高 的玻璃形成能力, 可以在维持18克拉金含量的同 时, 通过对其合金熔体的快速冷却制成5 mm直径 的非晶态圆柱 [15,17,18] . 与Au基晶态合金容易形成 原电池而受腐蚀不同, Au基非晶合金的无晶界结 构特征使其具有抗腐蚀性 [19] .…”