Temperature and chemistry-dependent thermophysical properties play an important role in finite element modeling (FEM) simulations. For example, thermal and fluid flow solvers, commonly used to model processes like casting, welding, and additive manufacturing processes, rely on temperature dependent properties, such as density, viscosity, surface tension, and thermal conductivity. Ma et al (2015) identified specific heat, thermal conductivity, and density as three of the top six critical variables for affecting peak temperature sensitivity when modeling a laser powder bed fusion process.

Handbooks are a common source of data, but these typically do not have temperature-dependent data for industrial alloys. Furthermore, data does not exist for novel materials, and handbooks do not capture the differences due to heat-to-heat variations in chemistry of a given alloy. It can be costly and time consuming to measure such data experimentally, but with Thermo-Calc you can calculate these properties as a function of material chemistry and temperature. These can then be used as inputs to FEM codes, resulting in more accurate predictions.

To assess the sensitivity to temperature-dependent values, Smith et al (2016) compared the effect of using handbook values for 316L for a constant specific heat and latent heat measured over a narrow solidus-liquidus temperature range with CALPHAD generated data and found that it had over a 500K difference in peak melt pool temperature and two times difference in the size of the melt pool.

Variation in composition, for example across a chemistry specification, can also be captured and understood, as discussed in our blog post How to Use Sensitivity Calculations to Evaluate the Effect of Composition Variation on Critical Phase Transformation Temperatures.

In Figure 1 below, the room temperature thermal conductivity has been calculated across the Alloy 718 chemistry range and is shown as a histogram. Note the roughly 10% variation in thermal conductivity. These calculations are all for valid chemistries that fall into the alloy 718 specification range. Engineers can use this to specify tighter or custom chemistry specification ranges, or to simply calculate new properties and re-validate FEM models when new heats of material are acquired.