Cooper, Timothy Paul
(2023)
Investigating challenges in producing adherent Boron Nitride PVD coatings for tooling and additive manufacturing applications.
PhD thesis, University of Nottingham.
Abstract
Magnetron Sputtering Physical Vapour Deposition (MS-PVD) is a process capable of depositing thin (< 10 µm) layers of myriad materials onto vacuum stable components. Boron Nitride (BN) is a ceramic with potential for use in surface coating and alloy doping due to its desirable mechanical properties. Multiple issues prevent adoption of BN as a coating material, related to its low deposition rate, low adherence, and the intensive processing required.
The work presented in this thesis investigated the deposition of BN onto powder and planar substrates, developing the knowledge of BN in Additive Manufacturing (AM) and Tooling applications.
Chapter 4 focused on developing a coating rig for depositing thin films onto powdery materials. Prior to the deposition of BN onto powder, three preliminary studies were undertaken.
Zn coatings were deposited onto Cu powder (D50: 39.4 and 7.3 µm), and Ag powder (D50: 28.7 µm) was coated with Ti. The common goal was reflectance reduction at 1070 nm, a wavelength used in Laser Powder Bed Fusion (LPBF), an AM process. Reflectivity was reduced by 38.4 % for the Cu-Zn and 25.7 % for the Ag-Ti, dependent on powder size distribution and sputtering power. This was due to different agitation, time exposed to coating flux and dependence on cohesive vs gravitational forces. Agglomeration of the Ag was exacerbated by higher power, dependent on surface moisture, lack of surface oxides, and snowballing of agglomerates. In-situ drying partially solved this issue.
316L powders were coated with Cu and BN, comparing agitation via rotation and vibration. Neither agitation was successfully deposited uniform coatings across the powder, flow mechanisms were suggested. The deposition of BN onto the 316L powder was insufficient for full analysis of ceramic deposition onto powders.
Chapter 5 focused on the development of a novel adhesion interlayer for c-BN coatings, combating high internal stresses remaining from coating, and ambient degradation, onto steel substrates at low temperatures. A single process was used with a 4 magnetron industrial coater. This interlayer consisted of a fully blended gradient Cr-CrC-C-BCN layer with BN top layer. c-BN nucleation methodology adapted from literature only formed amorphous mixed phase films (~300 nm thick BN) as identified via HRTEM, however these were stable in atmosphere for > 18 months. Significant surface coverage/homogeneity issues were present in all samples.
Chapter 6 iterated the methodology of Chapter 5, moving to a rotational coating setup for intensification of coating parameters via Closed Field Magnetron Sputtering (CFUBMS), first step investigation in coating higher numbers of components, and improved surface coverage. Varied substrate bias voltage (60-180 V), pulsing parameters and gas flows were used in the final BN layer deposition to produce different phases such as Wurtzite phase BN and Extra-Diamond phase BN. Potential mechanisms related to the ratio and energy of ion bombardment to the flux of arriving coating material were discussed. All coatings deposited with different parameter sets except one degraded in ambient conditions over time, and showed insufficient hardness for tooling applications.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Clare, Adam
Grant, David
Murray, James |
| Keywords: |
Boron Nitride; Powder substrates; Planar subtstrates; Additive manufacturing |
| Subjects: |
T Technology > TS Manufactures |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering |
| Item ID: |
76253 |
| Depositing User: |
Cooper, Timothy
|
| Date Deposited: |
30 Jul 2024 10:00 |
| Last Modified: |
30 Jul 2024 10:00 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/76253 |
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