C-308 Tribological Coatings
This tutorial is intended for design engineers, materials scientists, and coatings developers who have a need to specify and develop coatings for tribological applications (i.e., those in which wear must be reduced or prevented and/or friction minimized). The coatings also may need to have corrosion-resistant properties to operate in arduous conditions. The tutorial begins with a description of the mechanics of wear and discusses the problems of selecting coatings for optimal tribological performance. An overview of the main processes for producing tribological coatings is given, emphasizing vacuum deposition methods. Tribological test methods also are over-viewed, including tests for adhesion and mechanical properties. Coatings developed for enhanced tribological properties are described, and information is provided on some applications for these coatings.
- Wear mechanisms and theories (adhesion, abrasion, erosion, fatigue, corrosion, etc.)
- Tribological and mechanical test methods (e.g., pin on disc, abrasive wheel, scratch adhesion, microhardness, etc.)
- Coating processes and selection
- Benefits of ceramic coatings by PVD methods
- Information on tribological coatings (e.g., metal nitrides, carbides, oxides, superlattices, multilayers, nanocomposites, DLC, etc., plus hybrid and duplex processes)
- Applications information (e.g., metal cutting and forming, molding, bearings, pumps, auto parts, etc.)
Understanding the effect of the deposition process is very important for producing high quality tribological films, and this understanding starts with how vacuum plasma processes work. Plasma process fundamentals are presented to give the student a better understanding of the effects of the process parameters on the generation of the sputtered or evaporated species and how the energy of these vaporized species plays an important role in the nucleation and growth of the deposited films. Important vacuum tribological coating processes such as triode electron beam evaporation, sputtering, reactive sputtering, and cathodic arc deposition are reviewed in detail, and similarities and differences in the processes are discussed with the goal of giving the student a better understanding of where to use one process over another. All successful tribological coating processes today use ion-assisted deposition (IAD), and how IAD works with the different deposition techniques is reviewed.
Once a tribological coating is deposited, it is important to be able to determine that a good coating has been produced. Common characterization tests for hardness and adhesion are presented, and the advantages and disadvantages are discussed. For example, the scratch adhesion test is routinely used to test the adhesion of a hard coating on a hard substrate. However one must be aware that the results from this test depend on many factors such as coating thickness and hardness, substrate hardness, and the condition of the test instrument. There are many tests for measuring the wear resistance of the coatings such as the pin-on-disc or abrasive wheel tests, and the pros and cons of these different tests are reviewed.
Common tribological coatings in use today are metal nitrides, carbides, oxides, and diamond like carbon (DLC) films. These different coatings can be deposited as single layer films, or they can be deposited as multi-layer or superlattice coatings. DLC films cover a wide variety of coatings that are carbon based, but which may include the incorporation of hydrogen or nitrogen to enhance their properties. Coatings can also be produced as nanocomposite compound films. These can be carbon-based or may (for example) contain ceramic/ceramic, ceramic/metal or metal/metal combinations. The use of nano-layered and nanocomposite coatings allows the mechanical properties to be tailored to optimize both hardness (H) and elastic modulus (E)- to obtain a high H/E ratio, and thereby ensure that the coating can accommodate substrate deformations without yielding.
Depositing a coating is thus only part of the solution for a well performing tribological coating. How the coating interacts with the substrate is an important part of the equation, and how the substrate supports the coating is equally important. Surface engineering where both the coating and the substrate are designed to work together to provide an enhanced performance that neither is capable of producing by itself is the basic building block for a successful tribological coating.
Many tribological coatings applications are discussed to give the student an awareness of the many successful applications for the different coatings. Coatings for metal cutting and forming, molding, bearings, pumps, and automotive parts are but a few of the successful applications in production today.Instructor: Allan Matthews, The University of Manchester - United Kingdom
Allan Matthews is a Fellow of the Royal Academy of Engineering and is Professor of Surface Engineering and Tribology in the School of Materials at the University of Manchester, UK. He is also Director of the BP-sponsored International Centre for Advanced Materials (ICAM). He spent his early career in the aerospace industry and carried out research into ion plating processes at the University of Salford before moving to the University of Hull, where he built up the Research Centre in Surface Engineering as Director for over 20 years. He moved the Centre to the University of Sheffield in 2003 and then to Manchester in 2016. His group researches plasma assisted processes, mostly for tribological coatings and diffusion treatments. He is Editor-in-Chief of the Elsevier journal Surface and Coatings Technology, a former member of the SVC Board of Directors and a former Chair of the British Vacuum Council and the AVS Advanced Surface Engineering Division Executive Committee.
This course is currently available via:
On Location Education Program