Thermodynamic modelling of Ta-based Z-phase formation from precursors MX and M2X in martensitic Z-steels

Riedlsperger, F. K. (Speaker), Erwin Povoden-Karadeniz (Contributor), Bernadette Gsellmann (Contributor), Ernst Kozeschnik (Contributor), Bernhard Sonderegger (Contributor)

Activity: Talk or presentationTalk at conference or symposiumScience to science


Z-steels are a promising, newly developed family of creep-resistant martensitic 12 % Cr-steels in the pursuit of higher operating temperatures and pressures for components of thermal power plants. They contain Ta and form the finely distributed and long-term stable Z-phase CrTaN. To simulate thermodynamic equilibrium and precipitation kinetics of such Z-steels, element Ta had to be incorporated into an existing CALPHAD steel database. For this purpose, binary and ternary systems (such as Ta-C, Ta-N and Ta-C-N, e.g.), diffusion data and atomic solubilities were combined and implemented into the database. Two (trans-)formation mechanisms of Z-phase were considered in the MatCalc precipitation kinetic simulation, namely 1.) Cr diffusing into fcc MX precursors and 2.) Ta diffusing into hcp M2X precursors. The evolution of particles in two sample alloys (ZULC, Z6) was modelled and then compared to TEM and APT data with respect to Z-phase sizes and their chemical composition, showing satisfactory agreement.
Period3 Jun 2021
Event titleInternational Conference on Processing and Manufacturing of Advanced Materials: Thermec 2021
Event typeConference
LocationVirtual, Vienna, Austria
Degree of RecognitionInternational


  • creep
  • martensitic steel
  • tantalum
  • thermodynamics
  • simulation
  • TEM

Fields of Expertise

  • Advanced Materials Science