Study on test method of white layer microhardness in hard cutting based on chord tangent method

Abstract

White layer features including mechanical properties, wear, and corrosion resistance are closely related to the white layer hardness. It is of great value to accurately test the white layer hardness during investigations on white layer. To improve measurement accuracy of white layer microhardness, a chord tangent method is proposed and applied in the white layer hardness test in hard cutting in this work. Test accuracy analysis of white layer with different thickness is conducted according to nano-indentation hardness test. The results show that the chord tangent method is suitable for white layer hardness test with thickness over 3 μm, and the test accuracy can be above 85%. The indentation distance along the depth direction of the chord tangent method is much less than the section method, and the hardness distribution is more ideal. When the white layer thickness is 2 μm, the test error is 23.3%. When the white layer thickness increases from 3 to 12 μm, the test error decreases from 14.7 to 6.8%, especially when the white layer thickness is over 7 μm, the test error is relatively stable and stays below 8%.