Institute for Microstructural and Mechanical Process Engineering (IMMPETUS)

IMMPETUS - Institute for Microstructural and Mechanical Process Engineering: The University of Sheffield (http://immpetus.shef.ac.uk/imm/) is a multi-disciplinary research centre established in May 1996 to study thermomechanical processing of metals, to model the microstructural and nanostructural processes taking place, and to develop improved planning and control of related industrial processes.  IMMPETUS is based within three host Departments: Engineering Materials, Mechanical Engineering and Automatic Control and Systems Engineering.   Across the three Departments it involves some fifty people: academic and research staff, research students, an administrator, a computer programmer and three technicians.  Just over half these people are based in the Department of Engineering Materials.

In August 2002 we began work funded by the second major five-year research grant from EPSRC, an award of £3.91 million. This grant exceeded its predecessor of £2.75M and provides clear recognition by our peers and the Research Council of the high quality research carried out in IMMPETUS. The new grant supports over a dozen specific projects in: internal state variables as a function of process conditions, composition and segregation effects; the effect of strain history and local strain conditions on microstructure evolution in single and multi-phase alloys; tool-workpiece interface behaviour; oxide scale formation, descaling and surface quality for ferrous and non-ferrous metals; semi-physical modelling of microstructure and texture; metal design using evolutionary computing; model-based control and management of experimental processes; process modelling; hybrid modelling. The grant also permits 10% of the research staff time to be assigned to innovative projects as they emerge.

The new arbitrary strain path machine (ASPII).
The new arbitrary strain path machine (ASPII).

The new arbitrary strain path machine (ASPII) [Fig. 1] arrived at the end of July and provides a unique, world class facility. Built by Servotest Systems Ltd, from design specifications by Brad Wynne and John Beynon, this machine significantly expands our capabilities to investigate microstructure evolution under complex non-linear thermomechanical conditions which are often observed in industrial hot metal working operations. Like the original in-house built ASP, ASPII is capable of either sequential or concurrent torsion/reverse torsion and tension/compression with the added advantage of enhanced and comparable deformation rates in both deformation axes. This gives us the ability to test the whole spectrum of strain path angle changes, i.e. from 0 to 180°, at strain rates close to those experienced in actual industrial processes [Fig. 2]. Furthermore, the machine is capable of "playing back" a totally arbitrary strain path history from a finite element simulation giving us the possibility of fast tracking the development of new process routes without the need for costly plant trials. This facility adds to an already impressive range of state-of-the-art high temperature deformation equipment, including the Thermomechanical Compression (TMC) such that we now have one of the world´s leading hot working simulation laboratories.

The microgrid technique to show strain distributions
The microgrid technique to show strain distributions within deformed samples. a) The grid as applied, b) sliding at the grain boundary and heterogeneous strain within a grain (c).

The new field emission gun SEM with electron backscatter diffraction (FEGSEM/EBSD) has already allowed us to determine the microscopic texture of materials that we could not hitherto analyse. The world beating resolution, coupled with the fastest acquisition times available means that sample regions of up to a cm can be examined, with a resolution of sub 100 nm. For example, Fig. 3 shows a selection from a 5mm scan of partially recrystallised sample, but which shows the microband structure (i.e. the dominant dislocation walls).
It is the combination of techniques which provides the step changes in our understanding of microstructural evolution. For example, the combination of strain path, with EBSD to determine texture, grain shape, recrystallised fraction etc, and the microgrid technque to determine local strain evolution is a remarkably powerful approach.

The 2003 Colloquium was held on 29th and 30th April at Halifax Hall and was widely regarded as the most successful in the series. 26 external delegates attended on top of the 39 internal delegates. The high standards of both research quality and presentation were commented on by both EPSRC and several of our overseas delegates.

We pass on our best wishes to a number of IMMPETUS members who have moved on. One of our key roles is to train post graduate and post doctoral researchers so that they can realise their full potential in their chosen career. IMMPETUS now has an outstanding record in placing its members in high responsibility careers and last year was no exception. For example, Dr Sumitesh Das has returned to India to take up position as Technologist in the Automation Division in Tata Steel. Dr Xuehua Xu has joined NAMTEC. Dr Qiang Zhu was originally seconded to Holset Engineering, but they liked him so much that they have taken him on with a permanent contract. Dr Raphael Mercado-Solis has returned to Mexico and taken up research position at Universidad Autónoma de Nuevo León. Dr Mikhail Trull has been employed by Corus, Swinden Technology Centre.

We have seen some important changes to the Industrial Steering Committee, which is chaired by Dr Brian Smith of Corus plc. Since IMMPETUS sees the ISC as a key aspect of formulating our strategy, we were keen to see as wide a range of representation as possible. We have welcomed new members Dr G Honeyman of Sheffield Forgemasters Engineering and Dr P Morgan of Corus Engineering Steels. Following the changes within Alcan, we have welcomed Dr R Honeyman as a representative of Alcan Technology and Management AG, but are delighted that we have able to retain Dr R Ricks, who now represents the Innoval Technology Centre.

Details of all IMMPETUS activities are given in a separate Annual Report (available from Vanessa Dalton, v.m.dalton@sheffield.ac.uk).

IMMPETUS web page.

4.23mm EBSD scan
4.23mm EBSD scan showing the texture components in a partially recrystallised sample (colour coded, for example red is brass, green is goss). The deformation substructure is resolvable.