Detailed Microstructure and the Influence of Post-Treatment on CVD TiAlN Wear Resistant Coatings
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Materials engineering (MPAEM), MSc
Publicerad
2023
Författare
Mead, Monica Audrey
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The deposition of TiAlN by chemical vapour deposition (CVD) for the application
as wear-resistant coatings for cutting tools has been the subject of research interest
for numerous years, yet a comprehensive understanding of its growth mechanism and
intricate microstructural characteristics remains incomplete. Furthermore, although
the positive effect of blast-treatment on the stress state of wear-resistant coatings
has received attention in scientific studies, there remains a relative sparsity of research
investigating its influence on the microstructure. In this work, the detailed
microstructure of nano-lamellar low-pressure CVD TiAlN coatings on cemented carbide
substrates and the influence of post-treatment on the microstructure was investigated
by scanning electron microscopy (SEM), scanning transmission electron
microscopy (STEM) and transmission Kikuchi diffraction (TKD). SEM imaging revealed
two distinct types of surface morphologies corresponding to specific grain
orientations unveiled by TKD on thin foil cross-sections. As previously shown [1],
pyramidal surface morphology is connected to growth in a <111> direction, additionally,
a ridge-like surface morphology was connected to growth along <110>
directions. Both growth directions enable fast growth with low-energy {100} facets.
Furthermore, truncation of pyramidal and ridge-like surface morphologies was observed.
A growth mechanism was proposed aiming to explain the characteristics
of the truncated grain morphology. Here, strongly facetted surfaces emerging on
the truncated grains increase the surface reaction kinetics, leading to an increased
Al/Ti-ratio in the core region of the grain compared to its sides with large {100}
facets. Blast-treatment of the TiAlN coatings with corundum particles led to plastic
deformation up to a few hundred nanometres in depth. Impact jet wear introduced
a high defect density and crack or void formation beneath the surface. Plastic deformation
of the near-surface region of the coating led to the bending or disappearance
of the Ti- and Al-rich lamellae typical in TiAlN coatings prepared by CVD and a
continuous lattice rotation in three dimensions. The available data indicates that
grains which have grown along one of their <110> directions exhibit a more pronounced
lattice rotation when compared to grains that have grown along a <111>
direction.
Beskrivning
Ämne/nyckelord
TiAlN , LPCVD , lamella , SEM , STEM , TKD , film growth , texture , blasting , plastic deformation