Lateral gradients of phases, residual stress and hardness in a laser heated Ti _0.52Al _0.48N coating on hard metal

Abstract

The influence of a local thermal treatment on the properties of Ti–Al–N coatings is not understood. In the present work, a Ti _0.52Al _0.48N coating on a WC–Co substrate was heated with a diode laser up to 900 °C for 30 s and radially symmetric lateral gradients of phases, residual stress and hardness were characterized ex- situ using position-resolved synchrotron X-ray diffraction, Raman spectroscopy, transmission electron microscopy and nanoindentation. The results reveal (i) a residual stress relaxation at the edge of the irradiated area and (ii) a compressive stress increase of few GPa in the irradiated area center due to the Ti–Al–N decomposition, in particular due to the formation of small wurtzite (w) AlN domains. The coating hardness increased from 35 to 47 GPa towards the center of the heated spot. In the underlying heated substrate, a residual stress change from about − 200 to 500 MPa down to a depth of 6 μm is observed. Complementary, in- situ high-temperature X-ray diffraction analysis of stresses in a homogeneously heated Ti _0.52Al _0.48N coating on a WC–Co substrate was performed in the range of 25–1003 °C. The in- situ experiment revealed the origin of the observed thermally-activated residual stress oscillation across the laser heated spot. Finally, it is demonstrated that the coupling of laser heating to produce lateral thermal gradients and position-resolved experimental techniques opens the possibility to perform fast screening of structure–property relationships in complex materials.

Highlights

► In- situ characterization of the stress evolution in Ti–Al–N at high temperatures. ► Position-resolved hardness and stress characterization across the laser heated spot. ► High resolution transmission electron microscopy from laser treated coating areas. ► Combination of scanning techniques to reveal local structure–property relationships.