<p>This work predicts multiple reheat thermal histories and resulting microstructure and hardness of wire-arc directed energy deposition (WA-DED) fabricated components through development and validation of a computational modeling framework. The framework combines a finite element analysis (FEA) process model, a calibrated dual double ellipsoid Gaussian (DDEG) heat source, a thermal history-based microstructure identification procedure, and thermal history-property relationships. The framework was demonstrated and validated through accurate predictions of measured thermal histories, characterized microstructures, and measured hardness of a single bead per layer ultrahigh-strength steel WA-DED build. It was predicted that WA-DED process generates a transient temperature field along the build height. Deposition of the final layer remelts the previously deposited layer, forming as-solidified fresh martensite in the top two layers. The layer below is supercritically reheated, forming an affected zone (HAZ) with coarse- and fine-grained fresh martensite. The fresh martensite in the top three layers has hardness of 500–530 HV<sub>0.5</sub>. The material below the three top layers is tempered by subcritical reheats. The latter generate cyclic hardness variation along the build height from 370 HV<sub>0.5</sub>, in tempered fine- and coarse-grained HAZ regions, to 450 HV<sub>0.5</sub> in tempered intercritically reheated coarse-grained HAZ regions. This work represents the first application of a calibrated DDEG heat source in a WA-DED FEA process model, thermal history-based HAZ microstructure identification, and HAZ-specific tempering response relationships, for microstructure and hardness prediction in a WA-DED fabricated build. The demonstrated computational framework provides a basis for component property optimization by predicting the distribution of microstructures and hardness as a function of WA-DED process parameters.</p>

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Computational framework for microstructure identification and hardness prediction in ultrahigh-strength steel components fabricated by wire-arc directed energy deposition

  • N. M. Vega Michalak,
  • Y. Luo,
  • M. Pacenta,
  • P. Flater,
  • B. Alexandrov

摘要

This work predicts multiple reheat thermal histories and resulting microstructure and hardness of wire-arc directed energy deposition (WA-DED) fabricated components through development and validation of a computational modeling framework. The framework combines a finite element analysis (FEA) process model, a calibrated dual double ellipsoid Gaussian (DDEG) heat source, a thermal history-based microstructure identification procedure, and thermal history-property relationships. The framework was demonstrated and validated through accurate predictions of measured thermal histories, characterized microstructures, and measured hardness of a single bead per layer ultrahigh-strength steel WA-DED build. It was predicted that WA-DED process generates a transient temperature field along the build height. Deposition of the final layer remelts the previously deposited layer, forming as-solidified fresh martensite in the top two layers. The layer below is supercritically reheated, forming an affected zone (HAZ) with coarse- and fine-grained fresh martensite. The fresh martensite in the top three layers has hardness of 500–530 HV0.5. The material below the three top layers is tempered by subcritical reheats. The latter generate cyclic hardness variation along the build height from 370 HV0.5, in tempered fine- and coarse-grained HAZ regions, to 450 HV0.5 in tempered intercritically reheated coarse-grained HAZ regions. This work represents the first application of a calibrated DDEG heat source in a WA-DED FEA process model, thermal history-based HAZ microstructure identification, and HAZ-specific tempering response relationships, for microstructure and hardness prediction in a WA-DED fabricated build. The demonstrated computational framework provides a basis for component property optimization by predicting the distribution of microstructures and hardness as a function of WA-DED process parameters.