- #1
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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 ?
Tribological problem involving a MoS2 coating
- Thread starter PerennialII
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Discussion Overview
The discussion revolves around the tribological properties of a MoS2 coating, specifically focusing on the challenge of determining its elastic modulus (Young's modulus). Participants explore various approaches to estimate this value, considering its implications in mechanical applications.
Discussion Character
- Technical explanation
- Exploratory
- Debate/contested
Main Points Raised
- One participant expresses difficulty in finding reliable elastic modulus data for MoS2 coatings.
- Another suggests that modulus data for composites containing MoS2 could be derived from known properties of the plastic-ceramic composites in which it is used, proposing a method to estimate the modulus based on volume fractions.
- A calculation yields an estimated range for the modulus of MoS2 between 100 to 130 GPa based on density and composition assumptions.
- A participant acknowledges the difficulty in obtaining mechanical property data from coating producers, noting that their experiences with MoS2 suggest an elastic modulus typically between 90 to 110 GPa, which aligns with earlier estimates.
- One participant expresses appreciation for the collaborative effort in estimating the modulus and shares insights on the failure behavior of MoS2 under tribological contact.
Areas of Agreement / Disagreement
Participants generally agree on the difficulty of obtaining precise elastic modulus values for MoS2, and while there are estimates provided, no consensus on a definitive value is reached. Multiple estimates and approaches remain under discussion.
Contextual Notes
Limitations include the reliance on assumptions regarding density and composition percentages, as well as the challenges in characterizing the hexagonal structure of MoS2, which complicates measurements.
Who May Find This Useful
This discussion may be useful for researchers and engineers working with tribological coatings, particularly those interested in the mechanical properties of MoS2 and its applications in composite materials.
- #2
Gokul43201
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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...
- #3
Gokul43201
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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)
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)
Last edited:
- #4
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Thanks for a great effort ! I searched quite a bit myself and came pretty empty handed ... I' going to 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 !
- #5
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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 
.
.- #6
tribdog
- 768
- 17
wow, I'm sort of impressed by gokul
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