07-28-2009, 07:35 AM
One of the questions that come up in Industrial non-specification application is the testing of hardness. I have read the information on the this site, as well as books, and researched some, but still have few questions on how best to explain to a customer.
Is there any guideline for determining when a material should be tested using Microhardness vs Macro Hardness testing. In our experience, microhardness testing, with low force, is not a common test equipment in general industry, hence customers are not familiar.
How best to explain to customers about when, where how to microhardness test thermal spray coatings?
Thanks much, by the way we are all safe here after the terrible bombing in the Ritz Hotel in Jakarta (i was in the hotel in a seminar 24 hours prior to the bomb, lucky)
07-28-2009, 11:52 AM (This post was last modified: 07-28-2009 12:24 PM by LEN WOOD.)
|RE: Hardness Testing
It's really a question of relevant levels of testing, analysis and examination to the application and industry. A 'horses for courses' approach. You wouldn't Dyno test a Model T or scrutinise it to the same degree as an F1 car.
Samples prepared for Micro Hardness testing are also ready for metallurgical examination for integrity. Superior, higher performance and more consistent coatings can be achieved/sustained with higher levels of testing and examination. Greater scrutiny and testing inevitably facilitates a better coating which has to be the customer's greatest desire. Obviously the processing costs are higher but a substandard coating is a waste of money and a false economy.
Macro Hardness testing is superficial and the very basic requirement. It is fraught with more bogus results than Micro Hardness testing.
There is however still some coatings that can only be macro hardness tested
You were fortunate in Jakarta. Not a local lad then? Indonesia is such a beautifully exotic and diverse country. It has changed since I was last there. Bali was one of my favourite places especially with Komodo Island and its wonders just down the road.
I forget how many times I nearly blew up while in the Middle East, particularly when working with Northerners!
08-08-2009, 05:16 PM
|RE: Hardness Testing
Glad to hear you are still with us. Very worrying when you think you are lucky not to be in the wrong place at the wrong time.
Quote:Is there any guideline for determining when a material should be tested using Microhardness vs Macro Hardness testingOther than when dictated by specification/customer requirement - The best hardness test method to a large extent will depend on type of coating and thickness. Micro-hardness testing in some circumstances may be the only viable way, like on thin coatings. Usually, micro-hardness testing is done on the coating cross-section and involves metallographic sample preparation. So usually metallography and micro-hardness analysis go hand in hand on the same test sample.
Quote:In our experience, microhardness testing, with low force, is not a common test equipment in general industry, hence customers are not familiarYes, probably because they don't have a metallurgy laboratory where this test is most commonly employed.
Quote:How best to explain to customers about when, where how to microhardness test thermal spray coatings?
Not really an easy one to answer, but her goes:
Depends if using as a quality control or coating development tool. I assume as quality control.
First, hardness testing is really about proving process, rather than proving actual finish product. So to a large extent, whether to test or not, frequency etc will depend on confidence levels in the coating process. There are a few coatings (high end carbide, ceramic and abradable coatings) which tend to be very sensitive to process conditions/ powder batch quality and do really require hardness testing for setting process parameters and subsequent quality monitoring. Many coatings are not this sensitive and are not (needed ?) routinely tested, though again this is very dependent on process/equipment quality (servicing, calibration, operators etc...) Process is key - the greater the process consistency - higher confidence - lower the testing frequency. Some coatings hardness is not an issue as long as other requirements are met.
Micro-hardness testing is relatively costly, time consuming and requires trained/skill people, so economics raises it ugly head here.
Micro-hardness testing is not really an alternative to macro-hardness testing. Very often when cross-sectional micro-hardness is called for, macro-hardness tests are also required. The results are not always directly comparable as they are measuring different aspects of the coating properties.
Hope that helps in conjunction with GlenB's comments.
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