Matthew Thomas

Mapping microstructure inhomogeneity using electron backscatter diffraction in 316L stainless steel subjected to hot plane strain compression tests

Abstract The microstructure inhomogeneity in 316L stainless steel subjected to hot plane strain compression tests has been assessed using electron backscatter diffraction (EBSD). Two variables were investigated: the effect of strain rate and the effect of friction at the tool/specimen interface. Tests were performed isothermally at 950°C at nominal equivalent tensile strain rates of 0·01 and 1 s−1. Low and high friction conditions have been simulated by applying both a glass based lubricant and a boron nitride spray respectively. Results suggest that friction causes a variation in microstructure from the surface to the midplane of the deformed specimen. Several methods used to quantify and represent this inhomogeneity are presented in the present paper. Electron backscatter diffraction measurement issues are discussed. A grain size mapping method using a two-dimensional moving average has been developed to overcome the difficulties associated with the visualisation of measurement results over large areas on EBSD maps. It has proved to be a powerful tool for the spatial statistics of large quantity data obtained by EBSD.

Titanium alloy developments for aeroengine fan systems

Abstract Recent research relating to two α+β processed titanium alloys, designed for specific employment in aeroengine fan disc and aerofoil components, is described. Timetal 575 (Ti575) and Timetal 639 (Ti639) are both novel compositions that provide relatively high strength compared to Ti–6Al–4V. Static and cyclic behaviour of the two developmental alloys were evaluated at room temperature. A dwell fatigue assessment of Ti575 is reported, while the effects of unidirectional rolling and associated evolution of microtexture were studied for Ti639.

Titanium Alloy Developments For Future Fan Disc Applications – The Fatigue Response of “Alloy 104”

Alloy 104 is a novel high strength, α+β titanium alloy primarily aimed at aero-engine fan disc applications. Two microstructural variants of Alloy 104 have been assessed. Room temperature tensile strength and elongation have been investigated alongside a more detailed study of low and high cycle fatigue behaviour. The alloy clearly demonstrated an improved fatigue resistance in both microstructural conditions, whilst maintaining forgeability and a comparable density to Ti-6Al-4V. Furthermore, the alloy has been subjected to a load regime with a hold period at peak loads and proven to be insensitive to dwell fatigue.

The Effect of Aluminium on Deformation and Twinning in Alpha Titanium: The 45° Case

The deformation behaviour of binary Ti-Al model alloys has been observed in respect to nucleation, propagation and growth of twins, specifically the interaction of slip and {1 0 -1 2} tensile twins. The area fraction of twins increases by trend from Ti-0Al to Ti-4Al but significantly reduces to Ti-6Al. The lattice strain evolution during compression was measured using in-situ neutron diffraction and decreases from Ti-0Al to Ti-4Al but increases to Ti-6Al. The twin activity in hcp Ti behaves as expected from fcc materials until 4 wt.% Al concentration, but it is believed that short or long range ordering reduces the twin activity in Ti-6Al.