Various nitrides, such as chromium nitride and titanium nitride, find
extensive use in cutting tools, micromechanical devices, and medical implants due
to their exceptional physical, mechanical, and chemical properties. These coatings
exhibit superior hardness compared to high-speed steel and cemented carbide
along with notable protective capabilities against corrosion and wear. These
coatings have been successfully used to enhance the properties of cemented
carbide and steel tools while safeguarding their surfaces. By adjusting deposition
parameters like N2 gas pressure, the properties of PVD coatings can be tailored to
effectively withstand specific dominant wear modes during machining. The study
investigates and demonstrates that CrN coatings can be specifically engineered to
have distinct mechanical and tribological properties by adjusting the N2 gas
pressure, which enhances machining performance in cases where BUE formation
occurs. A comprehensive coating characterization was conducted for each CrN
coating studied. Wear performance assessments of the various CrN-coated WC
tools were carried out during dry finish turning of SS 304. Additionally, high temperature coating characterization was performed for the best-performing in house deposited coating (nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and
a commercial coating, up to 450°C. The results highlighted the influence of N2 gas
pressure on the structural, mechanical, and tribological properties of CrN coatings.
The findings indicate that coatings with a comparatively low H/E ratio (while
maintaining higher elastic modulus values), low roughness, moderate residual stress, high plasticity index, and high toughness exhibited superior performance
when machining sticky materials and in high-temperature applications prone to
adhesive wear and built-up edge (BUE) formation. Furthermore, high-temperature
studies confirmed that the in-house coating retained a low H/E ratio, high plasticity
index, high toughness, and low roughness, without compromising the hardness or
elastic modulus values. In contrast, the commercial coating failed to retain its
properties at higher temperatures. These high-temperature studies provide
valuable insights for selecting CrN coatings tailored for machining materials that
tend to adhere to the cutting tool and for high-temperature applications. / Dissertation / Master of Applied Science (MASc) / Coating properties such as hardness, residual stress, adhesive behaviour,
elastic modulus, and roughness significantly affect tool performance and wear
patterns, besides machining parameters and conditions. This research focuses on
CrN coatings deposited by PVD cathodic arc deposition, adjusting the N2 gas
pressure while keeping bias voltage constant. The research investigates and
illustrates that CrN coatings can be specifically tailored (by adjusting the N2 gas
pressure) to possess unique mechanical, and tribological properties that
ameliorate machining performance in scenarios involving BUE formation. Three
CrN coatings were deposited using the PVD technique by varying the N2 gas
pressure. A thorough coating characterization was conducted for each of three in house deposited coatings and one commercially available coating. The wear
behaviour of different CrN-coated WC tools was evaluated during dry finish turning
of SS 304 to identify the best-performing coating. Lastly, high-temperature coating
characterization was performed up to 450 ˚C for one in-house deposited coating
(nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and one commercial coating.
The results showed that a coating that has low H/E ratio (without compromising
elastic modulus), high plasticity index, high toughness, moderate residual stress
and low roughness effectively minimizes issues related to sticking and BUE
formation and retains coating properties at high temperatures.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29109 |
| Date | January 2023 |
| Creators | Akter, Shahana |
| Contributors | Veldhuis, Dr. Stephen C, Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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