Institut Jean Lamour, Nancy, Francija

The Solidification Group at Institut Jean Lamour is hiring a PhD student to work on the crossroads of Materials science, Thermal science and Fluid dynamics.

BACKGROUND

Future aircraft must offer reduced environmental impact, reduced operating and maintenance cost, and more comfort for passengers. One of the ways to achieve this is an increase of the thrust-to-weight ratio of aircraft engines. In low-pressure turbine blades of turbofan engines, traditionally used nickel-based superalloys are being replaced by two times lighter titanium aluminides (gamma-TiAl). The fatigue strength of metallic materials depends on the size, the morphology and the chemical composition of the crystalline microstructures. These parameters are largely determined by the solidification process during casting. Since TiAl alloys are highly reactive, centrifugal casting is used. Solidification in this process depends substantially on the strong artificial-gravity forces. To advance knowledge in this emerging technology, the ESA project GRADECET investigates the gravity dependence of solidification structures in TiAl alloys. The main questions are the transition between columnar and equiaxed microstructures, the texture evolution and the segregation of chemical elements. A series of experiments are being performed in different gravity conditions: microgravity (close to 0 g) in sounding rockets, terrestrial gravity on the ground and hypergravity (up to 20 g) in ESA's large diameter centrifuge. The experiments are supported by dedicated modeling ranging from the microstructure to the casting-process scale, all converging to a multiscale representation of structure formation.

OBJECTIVE

This PhD is part of the GRADECET project and is funded by ESA. The objective of the PhD is to build and validate multiscale modeling tools that will be able to simulate the effects of gravity on the formation of microstructures and segregations in TiAl alloys at the process scale. Once established, the models will be used to simulate the GRADECET experiments and support the experimental characterizations. The PhD project will interact closely with a parallel experimental PhD project, which is funded by SNECMA.

The process-scale models that will be employed are based on CFD finite-volume modeling of the macroscopic phenomena (multiphase fluid dynamics, heat and mass transfer) fully coupled with models of the microscopic phenomena (nucleation of solid grains, solidification of columnar and equiaxed grain structures). In order to provide a full picture of the physics, a combination of two complementary CFD models will be used:

• SOLID, the most sophisticated industrial-scale model of solidification today, will be adapted for the application to centrifugal casting of TiAl and will cover the full complexity of the physics in 2D. 
• A new, somewhat simpler model that will cover the 3D aspects of the physics will be developed on the OpenFOAM platform. 

A detailed description of the project and of the requirements for applicants is available at: http://www.cfd-online.com/Jobs/showjob.php?record_id=12990

SCIENTIFIC SUPERVISORS

Hervé Combeau, Professor at Ecole des Mines de Nancy

Miha Založnik, Associate Scientist CNRS

CONTACT

Dr. Miha Založnik, miha.zaloznik@univ-lorraine.fr