Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)2O3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum

Ludvig Landälv,Muhammad Junaid,Ching-Lien Hsiao,Lina Rogström,Emmanuelle Göthelid,Fredrik Eriksson,Daniel Ostach,Michael Stüber,Norbert Schell,Lars Hultman,Björn Alling,Erik Ekström,Per Eklund,Jens Birch,Naureen Ghafoor,Mats Ahlgren,Harald Leiste,Jun Lu

doi:10.1557/jmr.2019.340

Abstract

The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at ∼750–800 °C, followed by decomposition of the α-Cr2O3 structure in conjunction with bcc-Cr formation, starting at ∼950 °C. The resulting coating after annealing to 1140 °C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at ∼750 °C. The resulting coating after annealing to 975 °C is a mixture of t-ZrO2 and α-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with α-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 °C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.

Highlights

Oxide ceramics such as alumina, chromia, and zirconia are important materials for cutting tool development mainly due to their high hot hardness, chemical inertness with respect to work piece material, and oxidation resistance [1]
The chemical composition of the as-deposited coating was measured in the previous study with electron probe microanalysis (EPMA) [43] and remeasured in the present work with the top-view energydispersive X-ray spectroscopy (EDX)
The close compositional agreement between EPMA and EDX strengthens the validity of the EDX analysis of the as-annealed compositions

Summary

Introduction

Oxide ceramics such as alumina, chromia, and zirconia are important materials for cutting tool development mainly due to their high hot hardness, chemical inertness with respect to work piece material, and oxidation resistance [1]. Using physical vapor deposition (PVD) techniques to deposit these coatings permits lower substrate temperatures than the traditionally used chemical vapor deposition (CVD) and possible residual stress tailoring. The goal has been to stabilize the corundum phase, a-Al2O3, at lower deposition temperatures than in CVD with the help of isostructural a-Cr2O3 [2, 3]. Stabilization of the a-Al2O3 can be done by template growth on, e.g., a-Cr2O3 [4, 6, 7] or by solid solution alloying of, e.g., a-(Al,Cr)2O3 [3, 8, 9, 10, 11, 12, 13, 14]. Another possible phase on a-Al2O3 alloying with Cr is the cubic B1-like vacancy-stabilized structured (Al,Cr)2O3 [2, 15, 16]

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