Hi Vishy

to the Surface Engineering Forum.
Could you let us know what the issues are with the coatings?
Checking the actual coating as per the original qualification/production testing (which would have been applied to test coupons) would require destructive testing. The >1050 HV hardness value probably would have been from cross-sectional micro-hardness test usually HV/0.3. Some times 'macro' surface hardness is done as well on test pieces with suitable coating thickness (>250 - 300 um typically needed for this coating) using Superficial Rockwell HR-15N. These hardness tests applied to the surface of a working coating should really be considered as destructive. If you have an area of coating away from the working area, then this may be feasible. The use of non-marking portable hardness testing devices could be tried, but the problem then is correlating the results with the standard methods. Even relating a surface HV/0.3 with cross-section HV/0.3 hardness value could be problematic.
Generally, these coatings will suffer detrimentally low hardness values only if the coating is sub-standard with regard to density and inter-particle bonding. This may well show itself in poor finishing capability of the coating. Coatings with a relative low hardness value, but retaining good density and bonding very often will out perform the same coating with higher hardness value. This really should tell you that hardness is only one of many indicators to coating quality/performance, so avoid judging coating on this one criteria alone.
Unfortunately, there is not much non-destructive testing that can be done, particularly with regard to direct correlation to qualification tests. I would consider may be lightly polishing a small area for metallographic examination using a potable microscope.
Quote:Being such high hardness is it possible / necessary to maintain a minimum hardness differential between the mating parts if both are TC coated.
The two WC-10%Co-4%Cr coatings should really have the same properties. One coating having a different hardness to the other would indicate one coating being sub-standard quality.
Quote:I believe that the bend test is now a redundant and futile procedure.
Hi GlenB
Yes, bend tests do appear to be a thing of the past. People do not like test results with no numerical value
I still believe that bend tests can be very useful and informative if applied in the right manner.