Stable strengthening of 990-gold

Abstract

The addition of 1wt% titanium to gold was found to substantially harden the precious metal and enhance its wear resistance, which makes it attractive for jewellery applications. The enhanced hardening is due to the formation of fine AU4Ti precipitates under the appropriate thermo-mechanical treatments. It has been shown that another hardening mechanism can be induced in wire having a diameter of less than lOO/lm, which is stable to heating in air up to 200°C. These observations are consistent with the formation of a network of titanium oxide inclusions up to lOO/lm below the free surface, which has been reported elsewhere. New results have indicated that thin foil of Au-lTi, which has been subjected to similar thermo-mechanical processing, exhibits similar properties to those of fine wire of this material. Potential uses for the fine wire and foil are described.Age-hardened gold containing 1% Ti (990-gold) represents one of the most significant new jewellery alloys developed in the last 25 years (1). The fact that gold with up to 1% base metal content qualifies as '24 carat gold jewellery' in much of the Far East has provided the opportunity to choose an addition which substantially enhances the mechanical resilience of gold. Following a systematic study of additives which could be used to precipitation-harden gold at the 1wt% level, titanium was identified as the optimum element for this purpose, on both alloy constitution criteria and experimental findings.The addition of titanium to gold satisfies two important criteria for achieving optimum precipitation hardening.

Mechanical, thermal, and chemical analyses of the binary system Au-Ti in the development of a dental alloy

“…This discontinuity is attributed to a solid state reaction taking place between 400 and 500°C, because in this temperature range, hardening of the alloy with 1 wt % (≈4 atom %) Ti can be performed. 15,16 The solid state reaction must be attributable to an additional formation of the intermetallic phase TiAu 4 . As a result, the thermal expansion of the alloys decreases slightly.…”

“…Although the solid solution is weak, precipitations of the intermetallic phase hardens the alloy. 15 An alloy with 1 wt % (≈4 atom %) of Ti is already used in jewelry 16 and has been proposed for bonding wires in electronic applications. 15,17,18 Melting of the alloy for the casting procedure can be performed with induction melting in a crucible of graphite, zirconia, or alumina under argon or helium atmosphere.…”

“…16,19,20 The alloy is hardenable up to 170 HV5 with a thermal treatment at 500°C for 1 h. 16 This hardness and therefore the yield strength would not be sufficient for long-span bridges. With a thermal treatment at 400°C for about 30 h a hardness of 200 HV5 is obtainable, 15 but for a dental laboratory this long-term heat treatment is not practical. To get higher mechanical strength, more Ti must be added.…”

Controlled biological and biomimetic systems for landmine detection

“…Biosensors come in a large variety of sizes and shapes, and the can monitor changes in environment conditions, detect and measure concentrations of specific bacteria or hazardous chemicals, measure acidity levels (pH), etc. (Jacobson, 1996). There are many different ways to combine chemistry, physics, information and biology with suitable transducers that can lead to develop variety of biosensors supporting an unlimited number of applications.…”

Doped and low-alloyed gold bonding wires

“…Work hardening is therefore increased by solid solution hardening and grain refining effects, leading to much higher strengthening levels and also to increased recrystallization temperatures (22). Precipitation hardening, which gives stronger effects than those of the doping elements discussed above, can be obtained, for example by titanium (23,24). However, this approach is not yet commonly used because it is generated mainly by alloying elements that increase the corrosion risk and often give ball hardnesses which are too high.…”