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Precious Metals

Thermo-Calc can be used to predict thermophysical and phase-based properties as well as to simulate material behavior throughout the materials life cycle for precious metal alloys, also known as noble metal alloys, including Au-, Ag-, Pt-, and Pd-based alloys.

Solutions for Precious Metals

Because of their biocompatibility and high resistance to corrosion, precious metal alloys, also known as noble metal alloys, are commonly used for medical applications and jewelry. High noble alloys are most typically considered as three groups: Au-Pt, Au-Pd, and Au-Ag-Cu alloys. Pd and Pd-based materials are also increasingly being accepted as substitutes for Au in contacts for separable electronic connectors.

Handbook data typically covers only the most common alloys, and additionally does not always take into account variations in chemistry or processing conditions. Where this data is missing, Thermo-Calc can be used to generate the materials property data and make predictions of material behavior throughout the materials life cycle.

Calculate the following, based on your actual alloy chemistry:

  • Thermophysical properties, such as:
    • Specific heat, enthalpy, latent heat, density as a function of temperature, coefficients of thermal expansion, and more
    • Phase-based properties, such as:
      • Critical transformation temperatures such as solvus temperatures of precipitates, amounts and compositions of phases, solubility limits, activities, phase diagrams, and more
      • Equilibrium and non-equilibrium solidification, such as:
        • Liquidus, solidus, incipient melt temperatures, freezing range, fraction solid curves, solidification path, fraction eutectic, microsegregation, partition coefficients, latent heat, shrinkage, and more
        • Homogenization:
          • Optimal homogenization temperatures, time needed to homogenize any chemical segregation arising from solidification, and/or dissolve precipitates
          • Precipitation hardening:
            • Concurrent nucleation, growth/dissolution, coarsening of precipitate phases, volume fraction, and size distribution as a function of time

Application Examples

Thermo-Calc has many applications to precious metal alloys. Below are two such examples.

Castability of Pt-base Alloys

Castability of traditional platinum jewelry alloys can suffer if the solidification temperature range is too narrow. An additional challenge is the need to limit the alloy content to maintain the value and noble properties of the jewelry. Thermo-Calc can be used to calculate the non-equilibrium solidification behavior of such alloys and investigate the effect of composition using the included Scheil Solidification Simulation Calculator.

In this example, it is shown that the addition of Co to a Pt-Ru alloy can increase the solidification temperature range leading to improved form-filling during casting. Thermo-Calc can also be used to predict the extent of microsegregation, although in this work, Klotz et al. found no pronounced segregation of platinum for the Pt-1.5Ru3.5Co alloy (recalculated from Klotz, et al., Johnson Matthey Technol. Rev., 2015, 59, (2), 132–14).

Two plots calculated using the Scheil calculator in Thermo-Calc showing the effect of alloy content in Pt-jewelry alloys on solidification temperature range for the left plot and the segregation for the right plot.

Improving Casting Design of Platinum-Copper Alloys

Platinum-copper alloys are commonly used in jewelry making. This alloy system provides for good workability and machining characteristics. However, casting can be difficult. To improve casting design, thermophysical properties such as density, thermal expansion, and heat capacity are often needed as inputs to casting simulation software. Thermo-Calc can be used to provide such properties to investigate the influence of composition and temperature.

In this figure, Thermo-Calc was used to calculate the density of Pt-Cu alloys as a function of Cu content for two temperatures. As shown in the figure, the results correlate well with physical experimental measurements (experimental data from Mehmood, et al., Thermophysical Properties of Platinum-Copper Alloys. Metall Mater Trans A 43, 5029–5037 (2012).

A plot showing a comparison of calculated and experimentally measured density of platinum-copper alloys.

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