Blade wear

One of the phenomenon that brings a component not to be useful for its purpose, even if it's not broken, is wear, that means "lost" of material consequent to the continuous sliding between two surfaces. Wear has consequences both on industrial field, and on personal usage of consumers, such as for example razor blades.
TESTING PROCEDURE

Visual examination
The material of the blades is classified as martensitic stainless steel, of the kind X46Cr13 (UNI EN 10088).

Scanning electron microscope examination
A new blade is shown in photo 1 and 2, on cutting edge: near the border there is a darker layer, that means the presence of a coating, moreover the profile is linear, without any defects.
Micrographs 3 and 4, are those made on the first blade of the used razor. Color is uniform, and it means probably the detachment of the coating, and shows an irregular profile.
Map in photo 5 shows the distribution of the elements on the blade, with a C-Nb rich layer on the edge of the surface.
Metallographic examination
The metallographic structure of base material is typical of a ferritic stainless steel (photo 6).

Micrografia / Micrograph             : 6                                      
Attacco / Etching                      : Acqua Regia                                    
Ingrandimenti / Magnification      : 800X                                     
Campione / Sample                   : NEW BLADE                                     
Posizione / Position                   : Core                                    
Sezione / Section                      : Transversa
The metallographic structure of cutting parti s typical of a martensitic stainless steel (photo 7).

Micrografia / Micrograph               : 7                                      
Attacco / Etching                        : Acqua Regia                                    
Ingrandimenti / Magnification        : 2000X                                   
Campione / Sample                     : NEW BLADE                                  
Posizione / Position                      : Core                                  
Sezione / Section                         :Transversal
On the new blade surface, there is a wear resisting coating 0,5 µm thick (photo 8) while on the used blade surface, a lot of irregularities are present, but not layer had been detected. (photo 9).
Hardness
As shown in table n.2 hardness values of the two blades are similar, both in the base material and in the cutting surface.

Tabella N°2
  Lametta
Nuova supporto
Lametta
usata supporto
Lametta nuova
Lama
Lametta
Usata
Lama
HV0,2 232 232 627 612

Discussion
On cutting edge of new blade there is a coating of NbC, obtained by a process of chemical depositino and characterized by a high hardness and wear resistance.

With the usage, the coating comes off and deterioration of the blade take place, in this way the profile becomes irregular.

Conclusions
The loss off performance of a razor blade  is due to a wear phenomenon localized on the niobium carbide layer, but also on base material.

Probably this problem is not a customers', but above all it is important for the constructor, that surely looks for a low cost, related to good service and lasting, that obviously must not even be too long.
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