Hardness Conversion

[kc77]

Hi all,

I am wondering anybody knows how to convert the hardness in HRB scale to R15Y scale? I have browse through the hardness conversion table in this forum and only found the correlation between HRB and R15T.

Thanks and Regards,
kc77

[Gordon]

Hi kc77

You will not find conversions or equivalents for values between HRB and HR15Y scales. This simple due to the fact that the scales don't overlap. HR15Y scale is for very soft materials for which the HRB scale is not suitable or capable of testing with any accuracy.

[kc77]

Hi kc77

You will not find conversions or equivalents for values between HRB and HR15Y scales. This simple due to the fact that the scales don't overlap. HR15Y scale is for very soft materials for which the HRB scale is not suitable or capable of testing with any accuracy.

This leads to the next question. For hardness measurement on Metco 450 Powder (Nickel Aluminium), should it be measured using HRB or R15Y?

Thanks and Regards,
kc77

[LEN WOOD]

Nickel Aluminium 95/5 bond coat (SM 450 NS, Amdry 956, etc) is measured using HRB and the typical acceptence range is 60-80.

Cheers

GlenB

[Gordon]

Hi kc77

Hi kc77

You will not find conversions or equivalents for values between HRB and HR15Y scales. This simple due to the fact that the scales don't overlap. HR15Y scale is for very soft materials for which the HRB scale is not suitable or capable of testing with any accuracy.

This leads to the next question. For hardness measurement on Metco 450 Powder (Nickel Aluminium), should it be measured using HRB or R15Y?

Thanks and Regards,
kc77

Nickel Aluminium 95/5 bond coat (SM 450 NS, Amdry 956, etc) is measured using HRB and the typical acceptence range is 60-80.

Cheers

GlenB

Which type of Metco 450 coating?

Abradable Metco 450 coatings depending on parameter set need HR15T, HR15W and HR15Y (Rockwell superficial) scales.

Your normal 450 coatings could be measured with HRB, but you would need coating thickness around 2 mm or more to get accurate reading. If your coatings are for bond coats, I don't really see a need to hardness test, unless customer specification insists. Testing coatings only 100 -150 micrometres thick would require micro-hardness testing, All Rockwell methods are not suitable at this thickness. For thicker coatings I would suggest Rockwell superficial T scales.

[Gordon]

Reference to this thread may be important hardness-testing-methods-and-conversion

[LEN WOOD]

Hi Gordon,
Obviously it depends on what you are spraying and what specs you are working to.

I was referring to Plasma sprayed 450NS - Does anyone still spray 450NS Abradables?

We always test the bond coats on the shop floor as a basic conformance test the sprayer can do to satisfy that all is well with his setup and process. This additional (non-lab) sample is sprayed to 0.020" so that a reliable hardness result can obtained on an Avery superficial tester. Obviously the lab processes the other samples and tensile bond bars are run monthly to satisfy all bond strength specification expectations.

I should also add that we perform many repairs where we build up worn locations with 450NS and finish off with 73 F-NS. The 450NS thickness is engineered to facilitate, accommodate and compensate the top coat and its thickness limitation.

I realise this post has way more info than is required but I think that the reason and scenarios should be substantiated.
Cheers
GlenB

[Gordon]

Hi GlenB

Some good points and your procedures sound good to me

If your coatings are for bond coats, I don't really see a need to hardness test, unless customer specification insists.

I should really have made it it clear in this statement , that I was meaning testing of actual bond coats (typically 0.004-0.006" thick) and not thicker coatings or used as a process/operator proving/qualification test.

Metco 450 technical bulletin quotes macrohardness of 80 HRB for typical macrohardness for plasma sprayed coatings. My point being that HRB is not a very practical test for this coating, in most cases you would choose to use a superficial scale. Converting HRB to another scale will only be approximate using tables, but then I think the technical bulletin is only indicating a typical value as a posed to rigid specification.

Does anyone still spray 450NS Abradables?

To be honest I don't know. Have not come across it in recent times, but it was certainly used many moons ago.