Talk:Superhard material

message: Are these materials with Vickers < 40GPa like B4C called superhard? The article is inconsistent about this.149.156.90.26 (talk) 09:11, 21 December 2011 (UTC)

message: According to Rhenium diboride: "Although ReB2 is harder than diamond along certain directions," and "The resulting material is hard enough to scratch diamond."
but according to this page: "Only nano-diamond and aggregated diamond nanorods have been proven to be harder than diamond."
Sooooo, which one is the right one?
David  —Preceding unsigned comment added by 89.173.55.39 (talk) 22:25, 10 December 2008 (UTC)
replies: text: This is not my area of expertise, but the way I understand it is they only claim a material is harder than diamond if it is harder in all directions. Wizard191 (talk) 01:55, 11 December 2008 (UTC)
thread_title:  What about Rhenium diboride? 

message: This article claims
"Only aggregated diamond nanorods, which is a nanocrystalline form of diamond, is harder than diamond."
From the Lonsdaleite article:
"Lonsdaleite is simulated to be 58% harder than diamond and to resist indentation pressures of 152 GPa, whereas diamond would break at 97 GPa."
Are these in contradiction?  —Preceding unsigned comment added by Dstahlke (talk • contribs) 17:02, 29 September 2009 (UTC)
replies: text: No. Theoretical predictions (in materials science) are not to be trusted until experimentally proven :-) Materialscientist (talk) 22:54, 29 September 2009 (UTC)
thread_title:  Lonsdaleite 

message: *Beta carbon nitride, if it could be synthesized, is predicted to be harder than diamond.
According to the article Beta carbon nitride, it has been synthesized, if only on a nano scale. --ἀνυπόδητος (talk) 17:22, 26 December 2010 (UTC)
thread_title:  Beta carbon nitride 

message: Hydrogen-free amorphous carbon coatings (or hydrogen-free "DLC") are measured up to 70 GPa hardness by nanoindentation and should qualify for "superhardness".   — Preceding unsigned comment added by 153.96.236.16 (talk) 07:08, 20 June 2014 (UTC)
thread_title:  Hydrogen-free amorphous carbon 

message: *"A superhard material has high shear modulus, high bulk modulus and does not deform plastically"
->Misleading and likely erroneous. If a superhard material (other than diamond) does not deform plastically, what the explains the permanent indent left behind on indenting superhard materials?
It is true, however, that plastic deformation alone is inadequate to explain the indentation pattern in some materials (microcracking, deformation of the indenter tip).
*"Measuring the mechanical hardness of materials changed to using a nanoindenter (usually made of diamond) and evaluating bulk moduli, and the Brinell, Rockwell, Knoop and Vickers scales have been developed"
->Misleading and historically incorrect. The Brinell, Rockwell and Vickers tests were developed as microhardness test methods and preceded nanoindentation by many decades. 
*"The hardness of a material is directly related to its incompressibility, elasticity and resistance to change in shape"
->Confusing. The hardness of a typical material is only related to number 3, i.e. resistance to **permanent** change in shape (plasticity). 
In fact, the elastic modulus has no effect on indentation hardness because only the recovered indent is used for measurements (e.g. in the Vickers test). 
->There is also a statement about estimating hardness from Bulk modulus. This seems absurd and anachronistic, as bulk modulus is an elastic property and depends only on 
the lattice structure, as opposed to hardness / plasticity, which is intimately linked to the defect structure. In metals, the distinction between the two has been known
since 1930, at least, if not earlier. 
Anyway, I could go on, but I'll stop here. Either the superhardness folk have very different notions of what hardness is, or this section needs a rewrite. 
If it is the former, the article could be improved by highlighting the contrast between ideas of hardness for typical materials and superhard materials.
Commutator (talk) 00:47, 25 March 2013 (UTC)
replies: text: The whole article was rewritten by JBean65 in one-two edits in December 2010. This was certainly an improvement, but it was far from perfect. You're welcome to help further. Materialscientist (talk) 01:14, 25 March 2013 (UTC)
thread_title:  The "definition and mechanics of hardness" section contains a number of misleading / confusing statements 

message: The table says diamond has a Vickers hardness of 115GPa. My question is where did they get that value from?? There is no reference for it and what they should do is cite the source for each value next to it instead of having them at the top of the table. You don't know which is for which otherwise!  — Preceding unsigned comment added by 124.191.131.95 (talk) 09:08, 31 May 2016 (UTC)
replies: text: I've added values and refs from one of the two sources, but the values differ for two materials. - Rod57 (talk) 14:38, 25 October 2021 (UTC)
thread_title:  Vickers Hardness Test results? 

message: :Diamond is the hardest known material to date, with a Vickers hardness in the range of 70–150 GPa.
:One common form of a nanostructured material is aggregated diamond nanorods, which is harder than bulk diamond and is currently the hardest (~150 GPa) material known.[56]
The source [56] says: "ultrahard fullerite (that hardness exceeds diamond)". Thus I will rephrase to "Diamond is the hardest known natural material".--Eheran (talk) 07:23, 21 October 2020 (UTC)
thread_title:  Contradicting statements in the article 

message: Can we add bulk modulus and shear modulus to the small hardness table in Definitions, since the text says they are important. Could add an extra column for notes eg Poisson ratio ? - Rod57 (talk) 14:20, 25 October 2021 (UTC)
replies: text: Started with bulk modulus. - Rod57 (talk) 16:48, 25 October 2021 (UTC)
thread_title:  Can we add bulk modulus and shear modulus to the small hardness table in Definitions 

message: I’m reading about how Graphene is harder than diamond. Has this been considered for inclusion in this article? 2A00:23C6:B195:C801:D4B3:C363:913C:1663 (talk) 09:55, 21 December 2023 (UTC)
thread_title:  Isn’t Graphene harder?