Estimation of crack initiation and growth of hard coating by uniaxial tensile test and rotating cross-cylinders wear/friction test

Abstract

Cold forming has required considerably superior hard coating on a die to manufacture net-shaped products. Especially, under poor lubrication conditions or a dry condition, the hard coating is indispensable for the success of manufacturing. Accordingly, the die has required the superior hard coating to prevent adhesion, reduce friction, and control wear. Recently, it has been also necessary to improve die life and product qualities under severe tribological conditions. However, the comprehension of damage such as cracking, flaking, and galling is insufficient for metal forming. This study focuses on initiation and growth of cracking in the hard coating. Assuming the hard coating is subjected to tensile stress, nominal stress, or frictional shear stress, the performances of typical four hard coatings are investigated by two tests. One is a uniaxial tensile test, and another is a rotating cross-cylinders wear and friction test. These tests are applied to estimate the mechanical performance of hard coatings: CrN, TiN, VC, and CrAlN. After the two test and analyses with detail observation, the CrAlN coating collectively exhibits the highest anti-cracking property of the tested four hard coatings.

Keywords

• cold forming
• hard coating
• wear
• crack
• strain