Ceramic coating is provided on the metal to improve its wear resistance. There are many ceramic materials are available and seems not easy to choose best one which can fulfill our requirement. What criteria should we use to select the best material?
In real machines, materials are almost always exposed to the complex effects of various factors. For example, abrasive wear in combination with wet corrosion; variable mechanical loads in combination with dry friction or contact friction plus thermal shock combined with oxidation at high temperature. There can be a lot of such variations and they all require different properties from coatings.
For the above reason, it is simply not possible for a single coating to meet all the requirements at the same time.
For example, WC-Co and WC-Co-Cr coatings are characterized by very high resistance to abrasive wear and wear in friction pairs, but are unsuitable for operation at elevated temperatures and under conditions of high variable mechanical loads on the substrate. In turn, Cr3C2-NiCr coatings are cheaper and better than WC-Co coatings withstand elevated temperatures, but are less resistant to wet corrosion and have higher friction coefficients in friction pairs. Hard chromium coatings are cheap, suitable for application to complex surfaces, but have relatively weak mechanical properties and low corrosion resistance due to the grid of microcracks. All pure ceramic coatings (Al2O3, Cr2O3, YSZ, TiO2 and other), although in themselves and very resistant to corrosion, are characterized by the presence of a grid of microcracks, which makes them mechanically weak and permeable. And so on...
In general, it is much more difficult to find a coating resistant to high temperatures and various types of corrosion than coatings resistant only against abrasive wear (I am just working on such corrosion-resistant coatings).
By the way, very often clients incorrectly estimate the load on coatings and choose coatings that are unsuitable for their specific tasks.
Depending on the requirements and loading conditions either cemented carbides such as WC-Co or oxides such as chromia or titania toughened chromia are used.
Compared to WC-Co the chromia coatings are much cheaper and equally hard, moreover they are not vulnerable to oxidation at higher application temperature.
They will work quite well under purely abrasive conditions.
However they are very brittle (bending of the substrate may lead to spallation) WC-Co coating or other cermets are much more ductile due to the metal binder.
In real machines, materials are almost always exposed to the complex effects of various factors. For example, abrasive wear in combination with wet corrosion; variable mechanical loads in combination with dry friction or contact friction plus thermal shock combined with oxidation at high temperature. There can be a lot of such variations and they all require different properties from coatings.
For the above reason, it is simply not possible for a single coating to meet all the requirements at the same time.
For example, WC-Co and WC-Co-Cr coatings are characterized by very high resistance to abrasive wear and wear in friction pairs, but are unsuitable for operation at elevated temperatures and under conditions of high variable mechanical loads on the substrate. In turn, Cr3C2-NiCr coatings are cheaper and better than WC-Co coatings withstand elevated temperatures, but are less resistant to wet corrosion and have higher friction coefficients in friction pairs. Hard chromium coatings are cheap, suitable for application to complex surfaces, but have relatively weak mechanical properties and low corrosion resistance due to the grid of microcracks. All pure ceramic coatings (Al2O3, Cr2O3, YSZ, TiO2 and other), although in themselves and very resistant to corrosion, are characterized by the presence of a grid of microcracks, which makes them mechanically weak and permeable. And so on...
In general, it is much more difficult to find a coating resistant to high temperatures and various types of corrosion than coatings resistant only against abrasive wear (I am just working on such corrosion-resistant coatings).
By the way, very often clients incorrectly estimate the load on coatings and choose coatings that are unsuitable for their specific tasks.
Best wear resistant is Alumina , may be you need intermidiant layer of Titanium Nitride
It is dependent on your application and the method you want to deposit ceramic material. In APS methods, There are common defects such as non-bounded interface between layers, poor contact between splats, pores and cracks that not only effect on physical properties but also reduce mechanical properties,As all the ceramic material have good wear resistance, you must control APS parameters to reduce mentioned defects or improve your coating properties (by producing composite coating.)
It depends on your precise application, i.e. enhancing wear properties may impair other properties such as corrosion or toughness; To produce ceramic coatings through thermal spray processes, plasma spray methods (APS, VPS, and LPPS) due to their higher temperature are recommended. However WC and Cr2O3 plasma spray coatings are among the most used ones for wear applications. To have a dense coating Vacuum Plasma Spray (VPS) process is your best choice.
The cutting edge of the research recommending WC/metallic materials of nano-scale carbides and low ratio of metallic binder (less than 15%).
SiC/SiO2 reinforced Cr2O3 ceramic coatings may gives you results as per your requirements. However, brittleness of ceramic coating will be an issue, so you have to mix another ceramic phase to deduce coatings brittleness to improve wear resistance.
As you have not specified the type of wear. So, I am recommending you something about abrasive wear only.Likewise you can search any category and application for specific wear type.
WC-Co-Cr is commonly used material that is used to combat the abrasive wear.
If you are dealing with some specific application and wear as well, then you need to read papers like:
A critical review of the tribocorrosion of cemented and thermal sprayed tungsten carbide
October 2017Tribology International 119
DOI: 10.1016/j.triboint.2017.10.006
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