Effect of local crystallographic texture on near-surface residual stress variation in machined titanium
Akshay Mundayadan Chandroth, Nikhil Prabhu, Martin Diehl, Marc Seefeldt, Joris Everaerts
Abstract
Machining of metals causes near-surface plastic deformation, inducing residual stresses that can significantly impact a component's performance. Since most metals are polycrystals these stresses are multiscale in nature. Most studies on machining-induced residual stresses focus on the macroscale, even though microscale stresses, which are more challenging to measure, can deviate significantly from the macroscale average. In this study, microscale residual stresses in annealed Ti-6Al-4V subjected to abrasive wheel cutting are quantified experimentally for the first time. Titanium is of particular interest for this study due to its strong crystallographic anisotropy and the presence of clusters of grains with similar orientation known as microtextured regions (MTRs). Via Focused Ion Beam - Digital Image Correlation ring-core measurements, it is shown that microscale residual stresses are present in the range of ±200 MPa prior to cutting. After cutting, in-plane near-surface residual stresses are found to be more compressive to depths of approximately 20 μm. Cutting also induces out-of-plane near-surface residual stresses, with large dispersion in both tension and compression. The sign of out-of-plane residual stresses is found to correlate with the MTR’s average elastic modulus. Crystal plasticity simulations confirm that elastic anisotropy affects residual stress development due to elastic recovery. Furthermore, lower compressive stress levels during loading combined with a higher elastic recovery promotes the formation of detrimental tensile residual stress in grains, particularly in those oriented for easy basal slip. Overall, this study illustrates the importance of investigating microscale residual stress variation in polycrystalline metals after machining, particularly for highly anisotropic metals. • Machining induces multiscale residual stresses in polycrystalline metals. • Microscale stress variation was quantified for the first time in cut Ti-6Al-4V. • Microscale residual stresses deviate significantly from the macroscale average. • The observed scatter is shown to correlate with underlying microtextured regions. • Degree of scatter depends on the elastoplastic anisotropy of the machined metal.