First, some apparent explanations as follow cannot explain the so great (several times) difference. A. Projected or total indent areas may differ only by factor not more than 1.5;  B.  Just more local scale as such is not the reason for the AVERAGE nano-hardness to increase by 3...4 times, this could only increase fluctuations (Inhomogeneity). This will be evident by MICRO (not nano) hardness. //////  The reason is principally different! When the stress singularity dimensions (unlike the macro or micro hardness indentor) no more cover several spacings between lattice dislocations, the response becomes essentially or almost elastic. Apparently, when visible nanoindents approach say 100 nm the "almost" becomes more relevant than "essentially", however the mentioned effect remains significant.  It is characteristic in this regard that the same AFM technique is used for both the nanohardness and local elastic properties.

When load is small, the error measurements are biggers. Also, the material behaviour is more elastic. For this reazons hardness increase when load decrease.

Hi Sujakahu

Hardness value depends how are you applying the load. If the magnitude of the load is high, the indenter (Vickers or Knoop etc.) will pierce through the outer layer(s) (contamination layer,  oxide layer, work-hardened layer, modified crystalline bulk microstructure and the crystalline bulk microstructure) of the material. If the magnitude of the applied load is less, the indenter may not pierce and the reach the bulk microstructure. Hence, for the same material the value of hardness is different for different applied load.

Hence it  is important to mention the load value as well as the dwell time while reporting the hardness value for any material.

If your material is polycrystalline, you will only hit one grain in nanoindentation and results may strongly depend on the crystal orientation.

Hi Professor Zisman,

Could you please provide some reference material to study to further understand how stress singularity without lattice dislocations affects the hardness in micro and nano scale.

Thanks,

Hi Dr. Martin,

Yes, I have investigated the size of indentation and grain size and it is true that the indentation size is smaller compared to grain size. So I am trying to figure out whether the effect of grain boundaries are the only reason for less hardness value (2.5 time) in Vickers hardness.

Hi Sunny,

I understand that the hardness value does depends on load. But how can we compare load applied in nano-indentation and Vickers test?

Thanks all for sharing your knowledge.

On elastic (dislocation-free) indentation, have a look at  DOI:10.1016/j.ijengsci.2013.04.005   DOI:10.1080/01418618208236917

DOI:10.1007/s10853-010-4326-6 and related references.

The difference in the Vicker's hardness and the nanoindentation hardness is often ascribed to size effect (i.e., the hardness reduces with increase in load). The load applied in Vicker's hardness is usually greater than that applied in nanoindentation. Because of this reason, some researchers have suggested that Vicker's hardness measure bulk hardness of materials because it will cover larger area whereas nano-hardness is a measure of surface hardness because it probe the micro structural hardness. This assertion is not always true. I have used nanoindentation to show that nano-hardness is comparable to Vicker's hardness for zirconia (See my paper attached). Also, you can get other information from the following link: http://www.sciencedirect.com/science/article/pii/S0257897204006802. 

You may consider reading this: http://www.sciencedirect.com/science/article/pii/S0921509306012822#

Thanks Sir for the additional information and references.

I can't tell you about the reasons, but here is an example for WC (tungsten carbide) where very large single crystals were measured. The influence of orientation and test load used is clear. Above approximately 2N load (HV 0.2) the measured hardness values start to become independent of load. In this case, the maximum hardness to be expected is around 25 GPa (90 degrees from the prism plane).

The difference between projected area and real area is less than 5 %. You have a difference because the volume measured by the Vicker indenter is much bigger than the volume measure by a nanoindenter! If your material is a steel, with the nanoindenter you can easily measure the hardness of each grain, while the Vicker tip will affect many grains and will give you a mean value. Also, the nanoindenter tip penetrates only 1-3 microns from the surface (depends on the model) while with the Vicker indenter you go deeper. You always have differences in the surface of steels, and other materials (oxides, structural changes due to polishing, dirt, etc etc) so the values measured by both methods could have a big difference, even for homogeneous or single-crystal materials.

Yes, there much be some differences in the hardness values measured from Vickers and nanoindentation tips. 

Reasons could be 1. Contact area, 2. Localized response in nanoindentation 3. Global response in Vickers indentation. 

For more information , go through below links. It might be helpful. 

http://onlinelibrary.wiley.com/doi/10.1002/app.43532/full

http://www.sciencedirect.com/science/article/pii/S0032386116301227

Hi

I tested nanoindentation of Inconel X-750 alloy (solution annealed (1080C/2h) and aged (1149C/2h AC+843C/24h AC+704C/20h AC)). The aged alloy would be expected to have higher hardness than the solution annealed one, because of precipitations of carbides after ageing process. But in my test, solution annealed alloy displayed higher hardness and elastic modulus, as well as less indentation depth (HIT=6GPa; HVIT=560; EIT=243GPa; E*=267Gpa for solution annealed one and HIT=4.8GPa; HVIT=449; EIT=243GPa; E*=267Gpa for aged one ). What might be the reason for this results? Any comments will be appreciated, thanks everyone.

En fait, c'est assez compliqué... As-tu pensé à faire plutôt un scratch test et mesurer la résistance à l'arrachement de la couche peut être que tu seras mieux renseigné sur le comportement de ton dépôt....

Effectivement, le scratch test st un bon moyen de caracterisation. Il renseigne beaucoup du moment qu'il donnee l'aptitude du matériau à résister à la penetration de l'indenteur en diamant ( penetration depth), et la valeur de lPd_Rd)%/Pd. Et l'émission acoustique qui donne les informations sur les charges critiques (Lc) correspondant au début de tel ou tel forme d'endomagement.(avec Rd: Residual depth).

no, not such a big difference! see our paper on „Hardness and elastic properties of Ti(CxN1-x),…“, J.Alloys Compds. 309, L5, 2000 Q.Yang et al. also on ResearchGate

no, not such a big difference! see our paper on „Hardness and elastic properties of Ti(CxN1-x),…“, J.Alloys Compds. 309, L5, 2000 Q.Yang et al. also on ResearchGate

no, not such a big difference! see our paper on „Hardness and elastic properties of Ti(CxN1-x),…“, J.Alloys Compds. 309, L5, 2000 Q.Yang et al. also on ResearchGate

no, not such a big difference! see our paper on „Hardness and elastic properties of Ti(CxN1-x),…“, J.Alloys Compds. 309, L5, 2000 Q.Yang et al. also on ResearchGate

no, not such a big difference! see our paper on „Hardness and elastic properties of Ti(CxN1-x),…“,

J.Alloys Compds. 309, L5, 2000 Q.Yang et al. also on ResearchGate