Materials used in the industrial process are exposed to wide range of thermomechanical conditions during processing, fabrication and service. Depending upon these thermal cycles, both equilibrium and nonequilibrium microstructure evolution may occur in these materials. Since microstructure controls the mechanical properties, there is a need to predict these microstructure evolutions as a function of processing and servicing history. To address this critical need, computational thermodynamic and kinetic models have been applied and the results have been evaluated with experimental characterization. In this talk, two applications including alloy design for ethylene cracking tubes and laser surface processing will be highlighted.

Ethylene cracking tubes operate under very high carbon activity, reduced oxygen activity and at high temperatures. The material to be used in the tubes, therefore, must resist embrittlement due to carbide formation while maintaining the strength and the protective oxide coating. Thermodynamic calculations showed a critical balance between aluminum and chromium concentrations in the alloy for maintaining oxide coatings. The conditions that may lead to carbon diffusion and precipitation of carbides in the sub-surface regions of the tube were described with diffusion controlled growth models.

Laser surface alloying (LSA) is used to modify the surface properties of metals by localized melting and solidification and also by distributing hard particles such as carbides, borides, nitrides and other intermetallic phases. In this research, the dissolution and re-precipitation of carbides was modeled using thermodynamic and kinetic models. The model was applied to evaluate reactive-gas shielding LSA method for a mixture of martensitic stainless steel powders mixed with titanium carbide powders.

Although, above work has shown methodologies to describe microstructure evolution for industrial materials, there exist numerous challenges including measurement and dissemination of reliable thermodynamic and kinetic data under conditions that is far from equilibrium conditions.