Low-Load Vickers Microindentation Hardness Testing
Low-Load Vickers Microindentation Hardness Testing
(OP)
In a recent thread we discussed differences in measured Vickers microhardness when using different loads despite the basis of the procedure as-published that there should be no difference. The April 2012 issue of Advanced Materials & Processes has a good paper by George Vander Voort and Ryan Fowler which addresses this very issue. I have attached the link to it. The upshot of the research is that perceived differences obtained at 100g loads and below are attributable to poor optics, and not differences in material or load. They found the perceived differences disappeared (at least for them) when using higher magnification objectives (i.e. higher than the 40X objective found on many indenters) and better lighting for measurement at low loads.
Aaron Tanzer
www.lehightesting.com





RE: Low-Load Vickers Microindentation Hardness Testing
I have almost completely abandoned doing hardness conversions of any kind, even with disclaimers attached. Many laboratories do it far too casually. For me, microhardness (I know that term is now obsolete) is most useful for measuring differences within a non-homogeneous structure, such as welds.
RE: Low-Load Vickers Microindentation Hardness Testing
RE: Low-Load Vickers Microindentation Hardness Testing
I thought that might happen. Unfortunately, it is copyrighted material so I am afraid I cannot attach a copy without getting in trouble. The paper is not on George Vander Voort's website but you may have luck through Struers.
Sorry about that.
Aaron Tanzer
www.lehightesting.com
RE: Low-Load Vickers Microindentation Hardness Testing
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RE: Low-Load Vickers Microindentation Hardness Testing
At low loads (2-10g), the effect of elastic recovery becomes more pronounced than at higher loads. This will give an 'artificially harder' reading. This is especially more true for Knoop tests because of the shallower indentation. As far as errors in measurement, you don't necessarily need to use optical methods to measure the indent. I've actually used an SEM to measure a 2g indent for my PhD research.
metalhead
RE: Low-Load Vickers Microindentation Hardness Testing
The link does not work.
RE: Low-Load Vickers Microindentation Hardness Testing
Aaron Tanzer
www.lehightesting.com
RE: Low-Load Vickers Microindentation Hardness Testing