The role of microstructure and environments on strain localisation in high performance alloys

When: 
8 April 2019 - 4:00pm to 5:00pm
Venue: 
Ainsworth Building J17, 2nd Floor, Room 202
Photo of Prof Michael Preuss

Professor Michael Preuss
Deputy Director, Materials Performance Centre and the Nuclear Rolls-Royce University Technology Centre, University of Manchester, United Kingdom

—All Welcome —

ABSTRACT

Strain localisation is a fundamental aspect of plastic deformation in most engineering alloys due to a range of factors including low stacking fault energy, small precipitates being sheared or environmental effects such as hydrogen enhanced local plasticity or irradiation-induced dislocation channelling. During my presentation I will discuss new methodologies of quantifying slip mode specific strain localisation using a combination of grain orientation mapping, backscatter SEM imaging and high-resolution digital image correlation (HR-DIC) for 2D surface strain mapping. Slip trace determination through such correlated microscopy has been verified for Ti-alloys using side-specific TEM analysis and for Nickel-base Superalloys using electron channel contrast imaging (ECCI).

I will present three case studies where we have utilised our methodology to explore strain localisation in more detail. First, I will discuss the effect of a2 formation and microtextures in two-phase Ti-alloys on plasticity. We have been able to demonstrate that a2 precipitation will enhance strain localisation but that preference of specific slip mode (i.e. prismatic , basal  or pyramidal  slip modes) is greatly affected by the texture in the material. Next, I will show the effect of irradiation in Zr-alloys, typically used as nuclear fuel cladding, on deformation patterns, where dislocation channelling results in highly localised deformation. Here we have been able to demonstrate that irradiation-induced prismatic  do not switch off slip on those planes while overall strain patterns change very dramatically as a result of irradiation. Finally, I will discuss hydrogen enhanced local plasticity (HELP) in nickel-base Superalloys and how detailed slip trace investigations have provided new insight into hydrogen embrittlement.

BIOGRAPHY

Michael Preuss is currently Deputy Director of the Materials Performance Centre and the Nuclear Rolls-Royce University Technology Centre in Manchester.

Michael obtained his PhD from the Technical University Hamburg-Harburg, Germany on creep in two-phase titanium alloys. He joined the University of Manchester in 1999, first working in the field of friction welding nickel-base superalloys and titanium alloys. In 2003, he was appointed a Lectureship in Materials Performance and became a core member of the Materials Performance Centre. In 2010, Michael was appointed Professor of Metallurgy and is currently member of the ILL Scientific Council.

Michael's research focuses on microstructure, mechanical properties and residual stresses in high temperature materials for the aeroengine and nuclear application. The materials he is particularly interested in are zirconium alloys used to encapsulate nuclear fuel, as well as titanium alloys and nickel-base superalloys, which are used for example in aeroengines. A central aspect of his research is to develop a more physically based understanding of how these complex materials develop their microstructure during processing and the mechanisms that determine their performance.

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