Dear Farooq

Both Hv and HK are almost the same, but I would recommend HV test in a comparison to HK test, because the former test has more loading capacity for the tool steel.

Hello Farooq Ahmad,

For measurement of hard coating on plasma nitride H13 tool steel, micro and macro measurement with HV can be used.

With micro HV0.05, the hardness of the superficial phases in the structure and the change of hardness in depth can be determined, and with the macro HV1 it is possible to evaluate the average distribution of the float on the surface after plasma nitrided treatment.

.

Respected,

Prof.Dr. Khaled j. Habib  . 

and  

Prof. Dr.Emil Hristov Yankov  

Thank you very much for your valuable suggestions

Dear Mr. Ahmad,

For the nitrided materials, you should measure the hardness values on the top surface and cross-section. For the proper surface hardness value determination, you should have in mind the thickness of the surface compound layer and its roughness. Then you should choose a load value so that the penetration depth does not exceed 1/10 of the compound layer thickness. In that way, you will measure a true hardness value of the compound layer.

In the cross-sections, loads of 50 N or 100 N are usually used. It is better to make the indents in chess-game order in depth. The distance between the indents could be 10 - 20 μm. The effective case thickness of the underlying diffusion layer could be calculated as the case hardness values reaches the substrate hardness and 50 HV is added.

Wish You good luck in the research!

Best regards,

Maria

Thanks Dear, Maria

Actually i want to measure hardness of AlCrON coating on nitruded H13. 

There is variation of hardness at each point due due micro partical and pith on the coated surface. I measured from both HV and Hk . I am not sure which one is best?

Best Regards

Ahmad

Dear Mr. Ahmed,

Hardness of thin ceramic coatings is usually measured either by using Vickers or Berkovich indenter. Low loads between 5 and 50 mN should be applied in order to keep penetration depth lower from 1/10 of coating thickness. For the same load, penetration depth is larger for Berkovich indenter. If we compare Vickers and Knoop indenters, then for the same load Vickers indenter penetrates deeper. However, Vickers indenter is less sensitive on surface finish. Best results with Knoop indenter are obtained on polished surfaces.

My suggestion would be to use Vickers indenter with low load to keep indentation depth bellow 1/10 of coating thickness. However, you should keep in mind that indentation depth should be higher than 200 nm in order to avoid indentation size effect.

Kind regards, Aleksandar

Dear Mr Aleksander Miletic,

I am very thankful to you for your guidance. 

Thank you so much. 

Regards, Ahmad 

Dear Mr. Ahmad, 

Other than advises above, you may also refer to few published and well-known journal paper/book. These paper and book are fundamental and useful to hardness measurement of coating. I have list down few paper below.

Holmberg, K., H. Ronkainen, et al. (2000). "Tribology of thin coatings." Ceramics International 26(7): 787-795.

Oliver, W. C. and G. M. Pharr (2004). "Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology." Journal of Materials Research 19(01): 3-20.

Oliver, W. C. and G. M. Pharr (1992). "An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments." Journal of Materials Research 7(06): 1564-1583.

Li, H. and J. J. Vlassak (2009). "Determining the elastic modulus and hardness of an ultra-thin film on a substrate using nanoindentation." Journal of Materials Research 24(03): 1114-1126.

Respected Dear PC siow,

Thank you very much for your valuable sugeations.

Regards Ahmad

Generally, to investigate the mechanical properties of hard coating we can use both HV and Hk techniques. If hard coating thickness is low (about 200-400 nm) then you must use Vk indenter with low load.