first you need to decide the substrate material, then one can suggest you the coating material for your requirement. Because the substrate properties and the interlayer properties will influence much on the selection of top coat.

I think is more a matter of the size of the raw material. On first I would say alumina, if nanostructured poder is better. But if you use other material like TiO2, TiO2/ZrO2 or (Ti,Al)N will be nice if you use nanoparticulate powders. I have seen outstanding results of (Ti,Al)N for high temperature ash valves for thermoelectric plants

First define your requirements and the way you want to manufacture your coatings using thermal spray. Metal-carbides/oxides/nitrides are normally preferred for some of the important applications on steel and other substrates. Wear resistance can also be improved through various post-processing of the coatings. Indentation, rolling contact fatigue, sliding wear, etc can be good to characterize these coatings. Also, through thickness residual stress profile also determine the wear properties.

Of course, first of all you have to decide your requirements, but, apart of good anchorage and tribological properties, another problem that we always find in my research group is the interconected porosity formation. Thermal spraying conditions will be crutial to a good coating, and far in ceramics. Have you thought using cermets too?

I think harder the coating material, greater will be wear resistance.

To start with it is true, but if the residual stress is high (e.g. say tensile at the surface), then slight amount of load will trigger the failure of the coating. You may want to read this article, http://rd.springer.com/article/10.1007/s11666-011-9680-7

before discussing all these, its better first decide the base metal on which coating has to be done.

If base metal is 7075 Al, then NiCr bond coat of around 10-15 microns thk, and top coat may be TiO2/ZrO2/Al2O3 anything will work. but if the base metal is Steel, the coating may not bond at all..

So first decide the base metal

thanks to all for suggestions. I want to know that how the brittleness and ductility of the base material affect the selection of coating material.

Cbn

Cbn posses an excellent wear resistance and is harder only next to diamond. However tell about.your.substrate there are better diffusion process, preferably boronizing which can provide excellent wear resistance

Dear Chandrasekar,

boronizing any ferrous alloy will give a minimum hardness of 1200 HV0.1, which may be twice the hardness of hardened AISI8620, this increased hardness will improve the wear resistance, However i believe a cold working tool steel may be a better option for this application. I have been working on boronizing for some time now using commercially available boronizing agent WCT B-Cote MSB.