Study on microstructures, wear resistance and corrosion resistance of laser cladding-ion nitriding composite modified layer

Key words:  laser cladding  ion nitriding  rare-earth permeation  wear resistance  corrosion resistance

Abstract:

In order to solve the problems of low nitriding speed, shallow nitriding layer, large cross-section hardness gradient and high brittleness of conventional nitriding technology, and further improving the wear and corrosion resistance, the Cr-Ni-Ti-La laser cladding-ion nitriding composite modified layer was prepared on the surface of N80 steel substrate. The microstructures, wear resistance and corrosion resistance on the laser cladding-ion nitriding composite modified sample and the nitrided sample without cladding were studied by the optical microscope, X-ray diffractometer, hardness tester, friction and wear tester and electrochemical workstation for comparison. The results show that the microstructures of the cladding layer before and after nitriding are basically the same and the hardness is much higher than that of the N80 steel substrate, and this treatment enhances the strength support of the nitriding layer and improves the hardness gradient of the sample section. The presence of the cladding layer promotes the ionic nitriding and significantly increases the nitriding speed and thickness of the nitriding layer. Compared with the nitrided sample without cladding, the surface hardness of the composite modified sample is further increased, the friction coefficient, wear scar depth and wear weight loss are significantly reduced, and the wear resistance is improved. In salt solution, the self-corrosion current density is about half of that of the nitrided sample without cladding; in acid solution, the difference of self-corrosion current density between the two cases is about 100 times. The corrosion resistance of the laser cladding-ion nitriding composite modified sample is significantly increased.