LIGHTer Academy & LIGHTer PhD Network Seminar

Welcome to our next joint LIGHTer Academy & PhD Network Seminars! This time we are pleased to invite Dr. William Hearn and Dr. Mattias Gärdsback. 
 
Dr. William Hearn, Chalmers: Development of Structural Steels for Powder Bed Fusion - Laser Beam 
Dr. Hearn is also a LIGHTer PhD Network alumnus

Abstract
Despite the importance of structural steels in traditional manufacturing, they have yet to be developed for powder bed fusion - laser beam (PBF-LB) as their high carbon content makes them susceptible to cracking. The objective of this thesis was to develop structural steels for PBF-LB by determining the impact of various process parameters on part quality, microstructure and mechanical properties. Results found that it was possible to robustly produce these alloys with PBF-LB. Additionally, the properties would meet or exceed those of conventionally produced alloys indicating the strong suitability of these alloys for PBF-LB.     
 
 

Dr. Mattias Gärdsback, Alleima AB: Microstructure and flow stress modeling of nickel-based superalloys during hot working and heat treatments at Alleima 
Dr. Gärdsback is also an industry researcher affiliated to LIGHTer Academy

Abstract
Nickel-based superalloys offer very good high temperature strength, creep resistance and remarkable corrosion resistance at both high temperature and tough environments. Applications are in e.g.: aerospace, power generation, marine, nuclear reactor and chemical industries. 
Alleima produces seamless tubes, bars, hollow bars (and limited amounts of strip) made of nickel-based alloys. Because the demand of these products increases rapidly, Alleima is increasing both the portfolio of grades and dimensions and the volumes. This increases the demands on both the manufacturing equipment and on the production rate, which makes better and more advanced models necessary. The manufacturing involves complex thermo-mechanical processing involving hot working and heat treatments.  
Hardening and softening mechanisms are important both to set the microstructure, properties and performance of the final material and to know the flow stress during hot working. Hardening mechanisms are deformation hardening (all alloys), solution hardening (e.g. alloy 625) and precipitation hardening (e.g. alloys 718 and 925). Softening, either by recrystallization or recovery after deformation hardening, or by solution annealing, after precipitation hardening, are required to reduce forces and torques during hot working. Knowledge of softening rates are required to minimize time in annealing furnaces or increase rolling rates (i.e. decrease time for recovery/recrystallization between passes). 
Alleima has therefore participated in projects to develop flow stress, recovery and recrystallization models (during hot working) by Lars-Erik Lindgren and precipitation models (during age hardening) by Martin Fisk and Greta Lindwall. In Lighter, the focus has been on Alloy 718 because models existed and much literature is available, but Alleima are equally or more interested in other nickel-based alloys. In this presentation, we present our general modeling needs for nickel-based superalloys with focus and greater details on the projects in Lighter. 
 

Link to the seminar: https://chalmers.zoom.us/j/61244615538
Password: LIGHTer