Effects of gas flow on detailed microstructure inhomogeneities in LPCVD TiAlN nanolamella coatings
Journal article, 2020

Depositing homogeneous TiAlN coatings with a high Al content on cutting tool inserts is a challenging task. In this work, high-Al cubic Ti1-xAlxN coatings (average x = 0.8) with periodic Ti(Al)N (x = 0.5) and Al(Ti)N (x = 0.9) nanolamellae structure were synthesized by low pressure chemical vapour deposition (LPCVD) with different gas flow velocities, and the detailed microstructure was investigated by electron microscopy and simulations. Using a high gas flow rate, the columnar TiAlN grains with regular periodic nanolamella structures disappeared, the coating became enriched in Ti and hexagonal AlN (h-AlN) formed in the coating. The high Ti content is suggested to be caused by the high gas flow rate that increases the mass transport of the reactants. However, this does not influence the Al-deposition much as it is mainly limited by the surface kinetics due to the relatively low deposition temperature. Density functional theory (DFT) modelling and electron microscopy showed that h-AlN tends to form on the Ti(Al)N phase with a specific crystallographic orientation relationship. The Ti enrichment due to high gas flow rate promotes the formation of h-AlN, which therefore deteriorates the nanolamella structure and causes the disappearance of the columnar TiAlN grains. Thus, by designing the CVD process conditions to avoid too high gas flow rates, homogenous TiAlN coatings with high Al content and nanolamella structures can be deposited, which should yield superior cutting performance.

DFT

TiAlN

CVD

Transmission electron microscopy

EBSD

Author

Ren Qiu

Chalmers, Physics, Microstructure Physics

Axel Forslund

Royal Institute of Technology (KTH)

Olof Bäcke

Chalmers, Physics, Microstructure Physics

Anand Harihara Subramonia Iyer

Chalmers, Physics, Microstructure Physics

Mohammad Sattari

Chalmers, Physics, Microstructure Physics

Wiebke Janssen

Walter AG

Thorsten Manns

Walter AG

Johannes Kümmel

Walter AG

A. Ruban

Royal Institute of Technology (KTH)

Dirk Stiens

Walter AG

Hans-Olof Andrén

Chalmers, Physics, Microstructure Physics

Mats Halvarsson

Chalmers, Physics, Microstructure Physics

Materialia

25891529 (eISSN)

Vol. 9 100546

CVD 2.0 - En ny generation av hårda beläggningar

Swedish Foundation for Strategic Research (SSF), 2016-05-01 -- 2021-06-30.

Subject Categories

Inorganic Chemistry

Manufacturing, Surface and Joining Technology

Other Materials Engineering

Infrastructure

Chalmers Materials Analysis Laboratory

DOI

10.1016/j.mtla.2019.100546

More information

Latest update

8/28/2020