Low-Load Vickers Microindentation Hardness Testing

[mrfailure]

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

http://www.lehightesting.com

 

[Guest102023]

Vander Voort's metallography text has been my constant companion in the laboratory, and it has a good discussion on hardness testing. Hardness, for such a simple test, is the product of a lot of complex, interacting factors. Without seeing the paper I can accept that conclusion, but it would be difficult for me to conceive that there would be no mass or other effects whatsoever for all metallic materials.

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.

 

[metengr]

The link does not provide direct access to the paper unless you have membership with ASM. Can you please re-attach the paper or scan it and attach it separately?

 

[mrfailure]

Metengr,

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

http://www.lehightesting.com

 

[TVP]

ASM has made the online version of AM&P magazine freely available. This link should work:

http://www.asminternational.org/sta...oken=ce38f92fc92dba9baf010f1c2199286c197ccd49

 

[Metalhead97]

mrfailure,

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

 

[Guest102023]

TVP,
The link does not work.

 

[mrfailure]

Last night TVP's link took me to the ASM web portal on a computer that did not know I was a member. I was able to get to the article from there and confirmed it is available for free. You can get to the AM&P articles including the Vickers hardness paper by using the attached link to get to the portal, then selecting the Information Resources tab. AM&P Magazine is one of the options in the left column; you can then look in the magazines archives at the April 2012 articles.


Aaron Tanzer
www.lehightesting.com

 

[Guest102023]

Rather a crooked path but I found it, thanks.