Tailoring the Properties of Novel Sintered Materials

One of the main challenges in the field of Materials Science and Engineering is to find a way to tailor the properties of engineering materials by properly adjusting their chemical composition and processing route (the so called Materials Science Paradigm). This applies in particular to the Powder Metallurgy (PM) production route, in which metallic powders are pressed into the desired shape and then consolidated by sintering at elevated temperatures (but below the melting point of the main constituent). The PM route allows a more efficient use of energy and raw material, and a minimization of greenhouse emissions. But there is one important characteristic of the PM route that is still not fully exploited: the possibility to provide materials with unique microstructures and properties. This project is grounded on the use of masteralloys (MA): a powder containing a combination of alloying elements that is mixed in small amounts with the main constituent (iron powder) to improve PM-steel properties. The composition of this MA powder can be specifically designed to form controlled quantities of a liquid that enhances the physical phenomena occurring during sintering and can thus improve significantly the final properties. The project is based on the hypotheses that: 1) the combined introduction of alloying elements can be used to take advantage of the synergistic effects, and 2) through the design of the liquid properties it is possible to obtain microstructures with defined heterogeneity that give rise to tailored properties. In this project, a design methodology based on the use of computational software tools will be used to design liquid-forming masteralloy compositions and to model the thermodynamic and kinetic properties of these liquids. The predictions will be first validated with macroscopic experiments (wetting and infiltration tests), and afterwards on PM components. The idea is to be able to predict and control the complex phenomena occurring during liquid phase sintering, by first understanding the underlying liquid/solid/gas interactions. As liquid phases with different characteristics will be designed, it will be possible to evaluate their different effects on the sintering process and thus find a link with the final mechanical performance of the PM-steel. The innovations of this project lay on: 1) the bottom-up approach of the design (from theoretical models to final PM products), 2) the study of a significant number of liquids with different properties and 3) the use of advanced characterization techniques to understand complex phenomena such as the inter-diffusion of elements between solid-liquid and the influence of the chemical reactions with the surrounding atmosphere. Thus, this will be the first study in which computational software tools are directly applied to tailor the mechanical properties of engineering steels produced with PM routes.

One of the main challenges in the field of Materials Science and Engineering is to find a way to tailor the properties of engineering materials by properly adjusting their chemical composition and processing route (the so called Materials Science Paradigm). This applies in particular to the Powder Metallurgy (PM) production route, in which metallic powders are pressed into the desired shape and then consolidated by sintering at elevated temperatures (but below the melting point of the main constituent). The PM route allows a more efficient use of energy and raw material, and a minimization of greenhouse emissions. But there is one important characteristic of the PM route that is still not fully exploited: the possibility to provide materials with unique microstructures and properties. This project is grounded on the use of masteralloys (MA): a powder containing a combination of alloying elements that is mixed in small amounts with the main constituent (iron powder) to improve PM-steel properties. The composition of this MA powder can be specifically designed to form controlled quantities of a liquid that enhances the physical phenomena occurring during sintering and can thus improve significantly the final properties. The project is based on the hypotheses that: 1) the combined introduction of alloying elements can be used to take advantage of the synergistic effects, and 2) through the design of the liquid properties it is possible to obtain microstructures with defined heterogeneity that give rise to tailored properties. A design methodology based on the use of computational software tools was used to design liquid-forming masteralloy compositions and to model the thermodynamic and kinetic properties of these liquids. The predictions were validated with macroscopic experiments based on wetting and infiltration tests. The results show how critical is the composition of the liquid phase for the wetting and infiltration behaviour of the liquids on metallic substrates, and points out that Si and C content play a key role in this sense. The project could not be completed, but the results obtained set the basis for further studies. Future work should be aimed to link the properties that can be modelled -using computational tools- with the final properties of the materials Due to the particular characteristics of the PM production process it is possible to obtained materials with unique microstructures and properties. Furthermore with the methods proposed and developed within this project, such unique properties could be tailored in order to produce advanced materials for future challenging applications. Through the design of liquid phases with different characteristics it is possible to evaluate their different effects on the sintering process and thus find a link with the final mechanical performance of the PM-steel. The innovations of this project-idea lay on: 1) the bottom-up approach of the design (from theoretical models to final PM products), 2) the study of a significant number of liquids with different properties and 3) the use of advanced characterization techniques to understand complex phenomena such as the inter-diffusion of elements between solid-liquid and the influence of the chemical reactions with the surrounding atmosphere. Thus, this would be the first study in which computational software tools are directly applied to tailor the mechanical properties of engineering steels produced with PM routes.