Search

The environmental degradation of materials at high temperatures limits the useful life of different industrial components and hinders the development of more economical and environmentally friendly processes for the energy production. Despite the importance of this phenomena, a model to predict lifetime of materials that degrade due to high-temperature corrosion has up till now been lacking due to limitations of the computational possibilities and the complex nature of oxidation. In the present work we develop some strategies to model high-temperature corrosion in Fe-based alloys using the Calphad (Calculation of Phase Diagrams) approach. It is proposed that kinetic-based simulations for oxidation of Al and Cr can accurately represent the lifetime of the protective layers in FeCrAl and FeCr alloys at different temperatures in air. The oxide systems are in addition investigated by equilibrium calculations. The corrosion mechanisms of FeCr and FeCrAl alloys are discussed based on theoretical and experimental knowledge., QC 20220323

The major tools used in applying computational thermodynamics to various problems in materials science are briefly presented and several practical examples are given as illustrations. Solutions to industrial problems, pertaining to the processing of and microstructure development in several different materials, are shown with answers given in graphical form. Solutions to kinetic problems linked with diffusion are also treated. The last section is devoted to the problem of interfacing between thermodynamic computations and applications oriented software., QC 20220124

Pure titanium has an HCP structure and lacks mechanical properties for many industrial purposes. The BCC phase of Ti is required to make alloys with increased strength compared to pure Ti. Iron is the most potent element for stabilising the BCC phase. However, the addition of Fe to Ti causes segregation issues during solidification, which can be avoided by diffusion-driven solid-state alloying. To predict the diffusion kinetics, the interaction mobility parameters of Ti and Fe in the disordered BCC phase of Ti are necessary. In this work, these parameters are optimised based on new experimental data from Ti-Fe diffusion couples produced by the Field Assisted Sintering Technology (FAST). Diffusion couples were held at 1173K and 1273K for one hour. High-resolution Fe concentration profiles are obtained from Electron Probe Micro Analyser (EPMA). Ternary mobility interaction parameters are assessed based on binary endmembers with a DICTRA sub-module, and results are compared to earlier assessments of mobilities of the disordered BCC TiFe system., QC 20210929

Many empirical equations of the variation of the critical temperature with alloy content of the start of bainite formation in steels are available. They are often obtained by regression analysis of measured values for a large number of alloyed steels, usually with several alloying elements. However, such equations differ considerably, especially when applied to pure Fe-C alloys, which results in large differences between reported effects of individual alloying elements since they have not been based on the Fe-C system as a reference. Apparently, for the first time, an empirical equation is now derived by starting with information from Fe-C alloys and low alloy steels and then adding the effect of each alloying element separately, using information from ternary Fe-C-M alloys. Sets of information from the same alloy content but different carbon contents proved particularly useful. Lines connecting such points are regarded as B-S lines for the respective alloy content and the effect of alloying elements was evaluated from their distance from the B-S line for Fe-C alloys. Only under this condition can coefficients for alloying elements be expected to represent the physical effect of the elements. The resulting equation was tested with about 600 experimental B-S temperatures., QC 20191010

A thermodynamic-based model to predict the fraction of martensite in steels with undercooling has been developed. The model utilizes the thermodynamic driving force to describe the transformation curve and it is able to predict the fraction of athermal martensite at quenching to different temperatures for low alloy steels. The only model parameter is a linear function of the martensite start temperature (M (s)), and the model predicts that a steel with a higher M (s) has a lower difference between the martensite start and finish temperatures. When the present model is combined with a previously developed thermodynamic-based model for M (s), the model predictions of the full martensite transformation curve with undercooling are in close agreement with literature data., QC 20160926

The multicomponent composition space pertinent to the single crystal nickel-based superalloys is mapped and searched, using computational modelling. A resolution of 0.1 wt.% for the alloying elements is assumed, consistent with manufacturing practice. Databases are constructed of alloy compositions which are predicted to be of promising microstructural architecture: e.g. equal fractions of the γ and γ′ phases. These may be regarded as maps - one might term them genomes - of this class of structural alloy. By combining the databases with additional composition-dependent property models, it is demonstrated that compositions can be identified which - subject to the accuracy and limitations of the sub-models - are likely to prove optimal, e.g. on the basis of their creep resistance, density and cost. The methods circumvent the need for the traditional empirically-driven approaches to alloy design., QC 20150602

QC 20160615