Microstructural investigation of CVD TiAlN, TiN and WN coatings
Doctoral thesis, 2021

High speed machining of workpiece materials puts extreme thermal and pressure loads onto the cutting tool inserts, which thus must possess both high hardness and good toughness. Nowadays, most cutting tools are made of cemented carbide substrates that are coated with wear-resistant coatings. Chemical vapour deposition (CVD) is a widely used industrial method for producing the wear-resistant coatings, and has advantages like conformal coverage of irregular shapes and high purity of the deposited materials. However, CVD is a complex process and the coating growth is therefore not fully understood.

This thesis focuses on examining topics of relevance to increase the understanding of hard nitride coatings synthesized by CVD. The main research methods are analytical transmission and scanning electron microscopy (TEM and SEM), with complementary X-ray diffraction (XRD), atom probe tomography (APT) and simulations. Three types of CVD coatings were studied in this work: TiAlN coatings, TiN coatings and WN coatings.

The work on TiAlN coatings: (i) First, the growth facets and texture were revealed. (ii) Second, an effect of precursor gas flow on the growth of the coating was studied, including the correlation between the formation of a nanolamella structure and the rotating precursor gas supply, and a microstructural inhomogeneity relevant to the varying gas environment. (iii) In addition, the full chemical composition of the TiAlN coating was studied via APT and electron microscopy. (iv) Finally, an intra-grain misorientation that forms in TiAlN during the CVD growth, and the formation of relevant dislocations, was studied. The work on TiN coatings: (i) The microstructure of the CVD TiN coatings deposited on a CoCrFeNi multi-principal elemental alloy (MPEA) substrate was studied, and (ii) the etching effect of the corrosive gas environment on the MPEA substrate was evaluated. The work on WN coatings: The microstructure and grain morphology of WN deposited on a (0001) sapphire substrate, especially the influence of deposition temperature on the microstructures, were studied.

In conclusion, the results presented in this thesis provide insights into the detailed microstructures of TiAlN, TiN and WN coatings, which will increase the understanding of the growth mechanisms for these CVD coatings.

EBSD

CVD

TiAlN

coating growth

TiN

APT

WN

XEDS

SEM

TEM

PJ lecture hall at the Department of Physics, Chalmers University of technology
Opponent: Prof. Magnus Odén from Linköping University, Sweden

Author

Ren Qiu

Chalmers, Physics, Microstructure Physics

CVD TiAlN coatings with tunable nanolamella architectures

Surface and Coatings Technology,; Vol. 413(2021)

Journal article

Ren Qiu, Hisham Aboulfadl, Olof Bäcke, Dirk Stiens, Hans-Olof Andrén, Mats Halvarsson, Atom probe tomography investigation of 3D nanoscale compositional variations in CVD TiAlN nanolamella coatings

Ren Qiu, Olof Bäcke, Dirk Stiens, Hans-Olof Andrén, Mats Halvarsson, Grain rotation during growth of CVD TiAlN

Chemical vapor deposition of TiN on a CoCrFeNi multi-principal element alloy substrate

Surface and Coatings Technology,; Vol. 393(2020)

Journal article

Johan G. Hulkko, Katalin Böőr, Ren Qiu, Olof Bäcke, Mats Boman, Mats Halvarsson, Erik Lindahl, Kinetics of the low-pressure chemical vapour deposited tungsten nitride process using tungsten hexafluoride and ammonia precursors

Developing new cutting tool materials with better performance enables machining of workpiece materials with higher production efficiency. To withstand the extreme thermal loads and pressure generated during metal machining, cutting tool materials need to maintain both high hardness and toughness (especially at high temperatures). Cutting tool inserts are commonly made of cemented carbide (WC and Co), which has a high hardness and fracture toughness. In order to obtain an even higher hardness of the cutting tools, thin (~10 μm) wear-resistant coatings made of hard ceramic materials are deposited onto the cemented carbide inserts using chemical vapour deposition (CVD). However, the CVD reactions are very complex, and detailed investigations of the microstructure of these types of coatings are needed to fully understand their properties and growth mechanisms.

The aim of this work is to generate new knowledge about growth of hard, wear-resistant CVD coatings through systematic microstructural studies, using various state-of-the-art materials analysis method, such as X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and electron backscattered diffraction (EBSD). This work studies microstructures of different CVD coatings, including titanium nitride (TiN), titanium aluminium nitride (TiAlN) and tungsten nitride (WN). For the TiN coating, which was deposited on a CoCrFeNi multi-principle elemental alloy (MPEA) substrate, the etching effect of the corrosive CVD gas environment on the substrate was studied. For the WN coatings, the variation of microstructures at different deposition conditions was studied. For the TiAlN coatings, the influence of precursors gas flow on an internal microscopic nanolamella structure and microstructural inhomogeneities was revealed. The 3D nanoscale compositional variation in the CVD TiAlN was also studied. In addition, a grain rotation phenomenon during the growth of CVD TiAlN, associated to internal dislocation structures, was revealed. It is hoped that the results presented in this thesis could help the design and synthesis of new and better CVD coatings in the future.

Ren Qiu

Gothenburg, Sweden, August 2021

CVD 2.0 - En ny generation av hårda beläggningar

Swedish Foundation for Strategic Research (SSF) (RMA15-0048), 2016-05-01 -- 2021-06-30.

Driving Forces

Sustainable development

Subject Categories

Materials Engineering

Ceramics

Roots

Basic sciences

Infrastructure

Chalmers Materials Analysis Laboratory

Areas of Advance

Materials Science

ISBN

978-91-7905-542-4

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5009

Publisher

Chalmers University of Technology

PJ lecture hall at the Department of Physics, Chalmers University of technology

Online

Opponent: Prof. Magnus Odén from Linköping University, Sweden

More information

Latest update

8/27/2021