CVD TiAlN coatings with tunable nanolamella architectures

Ren Qiu,Olof Bäcke,Dirk Stiens,Wiebke Janssen,Johannes Kümmel,Thorsten Manns,Hans-Olof Andrén,Mats Halvarsson

doi:10.1016/j.surfcoat.2021.127076

Ren Qiu, Olof Bäcke + Show 6 more

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https://doi.org/10.1016/j.surfcoat.2021.127076

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Abstract

In this work, Ti1-xAlxN (TiAlN) coatings were synthesized by low pressure chemical vapour deposition (LPCVD), and the influence of a rotational precursor gas supply on the coating microstructure was studied. The microstructure of the TiAlN coatings were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and electron backscattered diffraction (EBSD). It is shown that a rotational precursor gas supply induces an oscillatory surface reaction, which causes a nanolamella architecture. When the gas beam directly hits the sample, the local gas flow velocity is high, which increases the deposition rate of Ti and a Ti(Al)N lamella is formed. When the gas beam rotates away, the local gas velocity is low, so the deposition rate of Ti decreases, and an Al(Ti)N lamella is formed. As this is repeated a periodic nanolamella architecture is formed. The nanolamellae grow epitaxially on three {001} facets of the 111 textured grains, which leads to a pyramidal surface morphology. Without gas supply rotation, a high Al content cubic phase was still obtained, but no nanolamella was formed. This indicates that Ti-rich lamellae are not necessary to stabilize an Al-rich cubic TiAlN phase. In addition, spinodal decomposition is not likely to be the driving force behind the nanolamella formation in LPCVD TiAlN, as this would also have happened in the sample without a rotational gas supply. Finally, the nanolamella periodicity is found to be tunable via controlling the rotation speed of the precursor supply relative to the coating growth rate.

Highlights

High-speed metal machining generates extreme pressures and ther mal loads, which put high requirements on cutting tool materials, and requires both extraordinary hardness and fracture toughness [1]
In a previous work [7] we studied the influence of the gas flow rate on the microstructure in an low pressure chemical vapour deposition (LPCVD) TiAlN coating
We have shown that TiAlN coatings with or without nanolamella architecture can be deposited via LPCVD onto the cemented carbide cutting tool inserts pre-coated with a thin TiN layer

Summary

Introduction

High-speed metal machining generates extreme pressures and ther mal loads, which put high requirements on cutting tool materials, and requires both extraordinary hardness and fracture toughness [1]. Ti1-xAlxN (TiAlN) with rock-salt (B1) crystal structure exhibits outstanding mechanical properties and good chemical and thermal stabilities, and is a material that is widely used in the cutting tool industry [2,3]. TiAlN with a high Al content (x~0.8 in Ti1-xAlxN) has been synthesized by low pressure chemical vapour deposition (LPCVD), reaching levels of Al at present not possible with PVD without formation of considerable amounts of AlN with hexagonal structure [2,3,6,7,8,9,10,11,12,13]. Good thermal stability and hot hardness for high Al content LPCVD TiAlN coatings have been reported, which indicates a promising application of this type of coatings for the cutting tool industry [6,7]

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