Comprehensive list of metal alloys along with Moh's hardness scale

Question

Material property lists, such as springermaterials.com, has lists of metal alloys and their properties. Is there a similar website that lists alloys along with their Mohs scale hardness? For springermaterials I can't seem specifically find hardness values. For example, when I search "hardness" or "Moh" in the search box nothing comes up.

Answer 1

You can find Mohs hardness values for various pure metals, but it sounds like you want something more specialized: Mols hardness values for specific alloys.

That's probably harder to find. But there is an alternative: One could create a formula to convert from the types of hardness values readily availble for alloys (e.g., Vickers hardness) to Mohs. That's what I do here.

I need to add the caveat that this is just an approximation: Mohs hardness is based on a scratch test, while Vickers hardness is based on indentation, so these two scales aren't fully comparable.

To start, I made use of a table of Vickers values for the ten Mohs reference substances, found here: https://geology.com/minerals/mohs-hardness-scale.shtml

Then I plotted Mohs hardness vs. Vickers hardness:

You can see from the above plot that, because of the highly non-linear nature of the Mohs hardness scale, it would be difficult to create a good fit that includes diamond (the point at the far right). Since metals probably top out at a Mohs hardness of ~$9$, I decided we could eliminate that value, and replot. This gives a curve that would be much easier to fit:

A log-log plot nearly linearizes it, indicating it follows a power law:

This tells me I should try to fit it with a power law function. After some testing, I found that a nice fit can be obtained with a function of the form $a + b x^c$:

The above fit is:

$$\text{Mohs hardness} = -0.5853 + 0.4829 V^{0.3912}$$

where V is the Vickers hardness value.

To use it, just plug and play. For instance, the Vickers hardness of 316 stainless steel is 152. Substituting into the above, the estimated Mohs hardness of stainless steel is 5.0 (because of the problematic nature of comparing two different types of hardness scales, I wouldn't express the predicted Mohs values to anything beyond two significant figures; I included two guard digits beyond this in the above formula, to avoid round-off error).