# Tribological problem involving a MoS2 coating

#### PerennialII

Gold Member
I'm working on a tribological problem involving a MoS2 coating, molybdenite, but am having a problem finding a suitable value for its elastic modulus (Young's modulus). Anyone got any insight ?

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#### Gokul43201

Staff Emeritus
Gold Member
It is hard to find elastic data for oxides, sulfides, etc. Hardness numbers are easily had though. Let me look around, and see if I find anything...

#### Gokul43201

Staff Emeritus
Gold Member
Still no luck...but perhaps an idea :

MoS2 is used as a lubricating additive in certain plastics. The resultant is essentially a plastic-ceramic composite. For composites, you probably know that the modulus of the composite is a linear function of the moduli of the components weighted by their volume fractions. So, if you can find modulus data for such plastics giving the percentage of moly in it, you can calculate the modulus of MoS2 from that.

I found such data for one class of plastics (ComAlloy), but unfortunately it didn't specify percentages. Yet, from density data, I was able to guess percentages (since I know the density of MoS2). Using two different compositions, I calculated E = 110 GPa and E = 117 GPa respectively. Since these numbers are pretty close to each other, they may not be a terrible approximation.

So, my final word on this, for now is : E(MoS2) ~ 100 to 130 Gpa (or 15,000 to 19,000 ksi)

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#### PerennialII

Gold Member
Thanks for a great effort ! I searched quite a bit myself and came pretty empty handed ... I' gonna go with the value you suggested and try to verify it from a couple of coating producers ... they should have an idea, although as you said, parameters like elastic modulus can be really tough to come by for sulfides etc (and many producers etc. don't really focus on mechanical props of coatings you can actually use in e.g. mechanical analysis). And the value you get is consistent with the behavior of the coating I'm working on, I essentially have a brittle & soft MoS2 on a tool steel, and the failure behavior under tribological contact resembles spalling of kind (under relatively light contact conditions [compared to coatings like TiN, DLC etc.] huge chunks of it start to fracture off). Thanks again !

#### PerennialII

Gold Member
Wanted to give an update ... got in touch with couple of people who have actually measured the E using nanoindentation ... their experiments & experiences with MoS2 have been that its elastic modulus is typically between 90 to 110 GPa (the hexagonal structure does not really help in characterization either) ... so your estimate was really good .

#### tribdog

wow, I'm sort of impressed by gokul

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