Surface World May 2018 Surface World May 2018 - Page 14

new high technology coating process in the market place and lack of appreciation of the benefits that can be achieved from thin PVD layers when compared to traditional low technology thicker spray or electroplating technologies. HVM supply chains must acquire the confidence on; performance of such coatings over months or years (by contrast, most coated cutting tools have lifetimes under continuous operation measured in 10s of minutes or a few hours); coating adhesion to their particular substrate materials and more generally have confidence on coating reproducibility, particularly thickness and composition. Addressing these prerequisites through the introduction of significantly enhanced quality assurance (QA), enabled through real-time process monitoring and control, could provide HVM companies access to new coating functionalities for product enhancement. Such improvements in process control and QA would give designers and engineers absolute confidence that PVD coatings can be safely included at the component design stage knowing that suppliers operate in a similar quality space to others in the HVM chain, rather than being seen as an emergency fall back when things go wrong. Coatings deposited by Physical Vapour Deposition (PVD) offer many advantages for product innovation including: extreme hardness and chemical stability providing excellent wear resistance; low friction; excellent adhesion; and direct application to finished products with no further finishing required. However, although PVD-deposited hard coatings are known to provide many tens or hundreds of percent improvement in the performance of cutting and forming tools used in HVM, they are often disregarded by the HVM supply chain for enhancing product performance. There are a number of reasons for this, including limited knowledge of this relatively 12 It is the contention of an Innovate UK supported joint project between Ionbond UK Ltd (IB) and the National HIPIMS Technology Centre at Sheffield Hallam Univeristy (SHU) that this advance in QA can be achieved through the application of a single process technology, Optical Emission Spectrometry (OES), to provide real-time monitoring and automatic control of all stages of the coating process – evacuation, in-chamber cleaning, and coating deposition - together with condition monitoring of the coating equipment. The team is using the ability of plasmas to excite all process and contaminant species and cause them to emit characteristic light thus providing a non- intrusive monitoring technique. An auxiliary plasma produced within an Optix instrument, produced by Gencoa ltd., is used to monitor the pump down cycle, whilst the process plasma is used to monitor the deposition steps. Developing and proving the method requires the project team to identify suitable optical emission lines to: 1. monitor the progress of chamber evacuation and provide a reliable end-point indicator; 2. monitor the progress of in-chamber substrate cleaning and signal that surfaces are sufficiently clean to ensure optimum coating adhesion; 3. control the composition of the coating plasma, and hence the composition of the deposited coating; 4. monitor the deposition rate and final thickness of the coating by measuring the flux of depositing particles produced by the cathodes; 5. controlling the crystallographic texture of the coating by measuring the composition of the depositing pl