Microstructure Evolution and Phase Transformations

Microstructure Evolution and Phase Transformations

Materials microstructure evolution lies at the very essence of understanding the relations between process parameters, properties and performance.  Understanding the (un)intentional phase transformations in materials form the basis for materials modelling activities.

Generic research activities involve development and refinement of microscopy, diffraction and spectroscopy techniques to obtain detailed information of the microstructure of advanced materials on various length scales. Tomography and 3D reconstruction of series of 2D images allow detailed examination of materials, particularly in combination with 3D spectroscopy and crystallography (3D EDS and 3D EBSD). Cutting edge techniques as Ion/electron channelling contrast imaging (ICCI/ECCI) is exploited with other microscopy, spectroscopy and diffraction techniques for analysis.

Microstructure evolution and estimation of life expectancy of materials for high temperature applications is a successful industry-academia collaboration and has received scientific and industrial attention. Projects address the development of stronger creep resistant 12%Cr martensitic steels. This requires understanding of microstructure formation and evolution during heat treatment and creep. Microstructure characterization and modelling of microstructure evolution serve as tools for alloy design and heat treatment optimization.

Computer modelling of phase transformations is largely based on thermal and chemical influences, while mechanical influences are largely omitted. The importance of the role of stresses on phase transformations in thermochemical surface engineering and high temperature materials is currently investigated. Martensitic transformation in iron-based advanced materials are perhaps the most studied phase transformations. Our research concentrates on thermally activated (or isothermal) martensite formation, which is considered an anomaly. Our research has demonstrated that this is a common feature at low temperatures.

Fundamental studies and advanced modelling of the relation between strength, work-hardening and formability and the evolution of the microstructure of metals and alloys during plastic deformation are pursued by macroscopic mechanical testing, post mortem electron microscopy of the deformation-induced microstructures and, particularly, in-situ monitoring of the evolution of the microstructure inside individual grains during different loading conditions by means of large scale facilities.

1 APRIL 2020