This CD-Laboratory is active since 1st of May 2017 under the leadership of Prof. Maria Cecilia Poletti. The Laboratory comprises 4 Modules focused on the optimization of thermomechanical processes for high-performance materials.
We work together with processing industries
to answer technological questions with a scientific approach.
Our research is motivated by the complex microstructural evolution occurring during industrial thermomechanical processes. We aim to explain and model the microstructure evolution of non-ferrous materials during thermomechanical processing routes. These models will allow to design and process materials with high performance during service.
Nickel-based superalloys are high-performance materials characterized by their creep resistance and good mechanical properties at high temperatures. Despite the large amount of works in the literature, the creep mechanisms and the microstructure evolution were never correlated in depth. Therefore, here we aim at finding a correlation between the precipitation state and the dislocation density obtained from the industrial process with the creep performance of the IN718. We characterized the creep resistance and microstructure evolution of IN718 after different heat treatment routes. We developed a model to correlate the creep strain with the microstructure. It was demonstrated that the main influencing microstructural aspects on the material´s creep resistance were the initial dislocation density and the initial grain size. To a lower extent, the precipitation state of the alloy also played a role.
In addition, the hot deformation behaviour of a IN718 alloy without precipitates was characterized and phenomenologically modelled to stablish correlations with a standard IN718 alloy. It was concluded that the mechanisms that produce microstructural changes during hot deformation such as dynamic recrystallization and modification of twin boundaries occur similarly for the alloy with and without precipitates.
This module has been closed at the end of 2020.
The thermomechanical processing of titanium alloys consists of many steps of hot deformation, annealing and cooling applied to modify the properties and microstructures of the alloys. In the literature there are physical and phenomenological models to describe the correlation of processing parameters with stresses, and in the best cases, with the microstructure. However, it is challenging to reproduce or predict the microstructure that develops along the whole processing chain at the different parts of an industrial workpiece. Therefore, we characterize and model the microstructure evolution as a function of processing parameters such as temperature, strain, strain rate and time. The models consider the role of SRV, DRV, CDRX, dynamic globularisation of the α-phase and load transfer. We validate the models experimentally for Ti5553, Ti17 and Ti64. The models can be used to predict the microstructural evolution considering different starting microstructures and processing conditions and are implemented in FEM for accounting local microstructures.
Aluminium cast alloys have been developed to keep their strength when using in combustion engines. The strength is obtained by solution heat treatment, water quenching and subsequently artificial ageing. During artificial ageing, the internal stresses produced during quenching are partially relaxed. However, the correlation of the relaxed stresses, the ageing temperatures and the precipitation modification was never done before. Therefore, we firstly characterized and modelled the relaxation and ageing behaviours of a cast AlSi7Cu0.5Mg alloy to explain the microstructural changes during all the heat treatments. Moreover, some parameters affecting the precipitation kinetics were identified. We proved that the stress relaxation occurs due to the gliding and annihilation of dislocations during the ageing process, and that the internal stresses produced during the quenching processes cannot be totally relaxed during ageing.
In the second part of this project, we focused on the development of aluminium cast alloys with higher Cu and Si contents. The increment on Cu should increase the strength, but decrease the corrosion resistance. For this purpose, we try to identify the mechanisms leading to the corrosion in this material, correlated to the amount and nature of primary and secondary intermetallic phases.
The thermomechanical processing of aluminium wrought alloys consists of many steps of hot deformation and heat treatments that modify the properties and microstructures of the alloys. Furthermore, large grains can develop due to accelerated grain growth or due to abnormal grain growth due to a combination of the presence of intermetallic phases and the temperature, local deformations and velocities of deformation. However, it is challenging to control the processing parameters to obtain homogeneous grain sizes. We here investigate the influence of the initial microstructure and process parameters in the grain size evolution of AA6082 aluminium alloy exposed to direct extrusion, impact extrusion and hot forging. We aim at developing mesoscale models that account heterogeneous deformation within the workpiece, to predict the formation of undesired large grains. Furthermore, based on the understanding on the underlying metallurgic phenomena, we will propose new processing routes to reduce the grain sizes in finished components.
High entropy alloys have been developed in the last decades. Although promising high mechanical properties, the processing of these materials at large scale is not well established. We deformed some AlCrFeCoNi alloys using the Gleeble 3800 thermomechanical simulator with different deformation paths. The already developed unified model for hot deformation is being expanded and modified to describe the phenomena that occur during the hot compression of these alloys. We aim at producing different initial microstructures to improve strength and ductility. Par
Transient Liquid Phase Bonding was applied to Nickel based materials with the aim of producing strong intermetallic phases using low temperature melting Aluminium. This work is done in collaboration with Prof. Dr. Silvana Sommadossi at Universidad Nacional del Comahue, in Argentina.
Dr. Friedrich Krumphals moved to the industry at the end of 2019. The PhD candidates Kasyhap Pradeep (Module 1) and René Wang (Module 3) are finalizing their thesis. Ricardo Buzolin (Module 2) got his Dr. techn. title with distinction in March 2021 with his thesis entitled “Microstructure Design of Titanium Alloys via Thermomechanical Treatments”. Carolina Gonzales, student of Universidad Nacional del Comahue, completed her master work and obtained her master’s degree with distinction in July 2021.
In the new period, the group is composed by Franz Ferraz (PhD student), Esmaeil Shahryari (master student), and Emilia Guntsche (master student) for Module 2; Stefan Fortmüller (PhD Student) for Module 3 and Talina Terrazas (PhD Student) for the new Module 4. Ricardo Buzolin continues to work as deputy of the CD-Laboratory and as a post-doc covering the topics of unifying the description of and elaborating a unified model for plastic deformation related to forming, stress relaxation and creep. During this period, Marlene Eichlseder (master student) for Module 3 successfully defended her thesis entitled “Influence of Cu content on the corrosion behaviour of AlSiMgCuX alloys”.