Influence Of The Microstructure On The Critical Angle Of Attack Of Various Materials

A goniometric microscope has been modified to evaluate the forces brought into play during the scratching of materials by a single point. Knowing these forces, it is possible to calculate a pseudo-coefficient of friction which varies with the angle of attack. These variations allow us to determine the region of transition and the critical angle of attack of the material investigated. Critical angles of attack for pure metals looked equal and explain the linear relationship between the resistance to abrasion and hardness. However, in the case of steel, the angle of attack decreases as the hardness increases, explaining the sigmoid curve of the resistance to abrasion of these materials. Ductility seems to play no significant role in this reduction in the critical angle of attack. In contrast, the strain hardening coefficient could be responsible for this variation, if the material has to attain a critical deformation state before forming a chip. The deformation needed would be attained more easily by a hard steel than by a softer one.