Residual Stress Evolution during Manufacture of Aerospace Forgings

The residual stresses present through the quenching, ageing, and machining processes in sub-scale forgings of RR1000 have been measured experimentally using neutron diffraction, and the contour method. The forgings, 88.9mm in diameter, and 25.4- 50.8mm thickness, were of small enough geometry to allow neutron strain measurement in 3 directions throughout most of the bulk. The contour method was employed successfully to generate a full 2D map of the hoop stress in the as-aged and machined samples. The two experimental data sets have been shown to agree very well. Finite element modelling predictions based on an experimentally derived heat transfer coefficient (HTC) curve allowed further comparison and generated additional data. Agreement between the experimental and simulated data was found to be reasonable with some discrepancy visible in the axial direction. The water quenching process was found to generate peak stresses up to 1400MPa in the hoop and radial direction, which were relaxed by as much as 700MPa through ageing. Material removal by machining had a less significant impact in most cases, relaxing residual stress by 100-200MPa. © 2012 The Minerals, Metals, & Materials Society. All rights reserved

The effect of β grain coarsening on variant selection and texture evolution in a near-β Ti alloy

In the present study, the role of β grain coarsening on α variant selection has been investigated in the near-titanium alloy Ti–21S (Ti–15Mo–3Nb–3Al–0.21Si). The material was first thermomechanically processed in a fully β stabilised condition in order to obtain a fine β grain size before undertaking controlled β grain-coarsening heat treatments. Two different cooling regimes ensured that either all β was retained at room temperature or significant α formation was achieved during cooling with predominant nucleation from β grain boundaries. Detailed electron backscatter diffraction (EBSD) characterisation was carried out on the β quenched and slowly cooled samples in order to compare the predicted α texture based on the β texture measurements assuming no variant selection with the measured α textures. A strong correlation was found between β coarsening and level of variant selection. It was also found that the grain coarsening is driven by the predominant growth of low energy grain boundaries, which strengthen specific β texture components that are part of the 〈1 1 1〉∥ND γ fibre. Finally, it was possible to demonstrate that the strengthened β texture components promote β grain pairs with a common 〈110〉, which is known to enhance variant selection when α nucleates from β grain boundaries

Picosecond dynamics of a shock-driven displacive phase transformation in Zr

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Orientation effect on mechanical properties of commercially pure titanium at room temperature

The effect of sample orientation on the mechanical properties of commercially pure (CP) titanium plate with a transverse split basal texture was investigated at room temperature (RT) using plane strain compression (PSC). A large variation in flow stress of up to (EBSD) and calculating Schmid factors for all important slip and twinning modes. Importantly, the Schmid factors were calculated for all orientations in Euler space because there are significant variations over all orientations for the PSC stress state, unlike uniaxial compression or tension. The Schmid factor analysis and twin data for the wide variety of orientations tested enabled the conclusion to be drawn reliably that higher flow stresses were primarily due to an unfavourable orientation for prism- slip. A greater proportion of to twinning was also a major factor in the higher flow stresses. Increased strain hardening was observed in the sample orientation that showed a dramatic texture change to a more difficult orientation for further deformation as a result of dominant twinning. This indicated that reorientation hardening was the responsible mechanism