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• High cycle fatigue strains mapped by nanoscale resolution digital image correlation. • Fine bands of deformation in lamellar γ-TiAl alloy formed ∼50 nm from interfaces. • Unlike monotonic loading, high cycle fatigue strains remain highly localised. • Strain gradients develop along slip bands, increasing in magnitude with cycling. Microcompression testpieces of a lamellar γ-TiAl alloy were high cycle fatigued up to 105 cycles at stress ratios of 0.5–0.7, to maximum stresses above and below the yield stress. The localised deformation was studied by nano-scale digital image correlation strain mapping of a Pt patterned side-face of the pillars. With crystal orientation mapping, the fatigue deformation lines were found to locate at the γ/γ and γ/α 2 lamellar interfaces. The deformation lines were closely spaced slip lines in transmission electron imaging. Gradients of shear strain developed along the deformation lines, increasing in magnitude as cycling progressed. Extensive transverse twinning also occurred. [ABSTRACT FROM AUTHOR]

• Nanoscale digital image correlation (HR-DIC) strain mapping of HCF up to 670 °C. • Microplasticity mainly in softmode colonies: parallel to lamellae, near interfaces. • Poor strain transfer across colony boundaries at both temperatures. • At 25 °C, maximum stress influenced the slip band count more than did the cycle count. Microplasticity in a lamellar TiAl alloy upon high cycle tensile fatigue was measured by high resolution digital image correlation strain mapping at several stress and cycle increments, at 25 °C and 670 °C, for two lamellar thicknesses. Plastic deformation occurred primarily in soft-mode colonies at both temperatures, operating by slip parallel to the lamellae, and near lamellar interfaces. Plastic strains generally decreased to zero by the colony boundary; strain transfer across such boundaries was rare at both temperatures. At 25 °C, the maximum applied stress influenced the number of slip bands more so than did the number of loading cycles. [ABSTRACT FROM AUTHOR]