Study On Laser-Nitrding Compound Modification Of TA2

In this paper, in order to improve the wear resistance of TA2, the two surface modification methods of laser gas nitriding and laser phase transformation - nitriding nitriding were carried out on the TA2. The stereo microscope,optical microscope, scanning electron microscopy, transmission electron microscope, X-ray diffraction and electron probe analysis were adopted to analyze the surface morphology, microstructure and phase composition of two surface modification layers. The microhardness and uniformity of the hardness of two surface modification layers were measured by the microhardness tester. The corrosion resistance of two surface modification layers were analysed by M283 potentiostat, and M352 and analyse software. The wear resistance of laser gas nitrided layer was tested by MMU-5G type tribometer.TiN is formed on the surface of TA2, which serves as a reinforcing phase after a laser gas nitriding. It was made up of nitrided layer, HAZ and the base metal after the laser gas nitriding treatment. The nitrided layer mainly consists of TiN andα'-Ti which has a uniform hardness with a thickness of 30μm. The heat affected zone is mainly composed of needleα'-Ti. Laser gas nitriding improved the uniform and localized corrosion resistance of the TA2.After laser phase transformation hardening, the substrate hardness was improved, and the organization changed from the originalα-Ti to the needle-like martensite. At the same time, a large number of dislocations and other defects were produced. Phase transformation hardening layer is divided into three parts: the first is entirely martensitic transformation region; and the second is not entirely martensitic region; and the third is buttα-Ti region. After the laser phase transformation hardening - nitriding treatment, the result shows that the nitrided layer, which is about 50~60μm thickness and in which white layer mainly composed of nitride is about 4μm thickness, is formed in the surface layer of TA2 under 430℃. Surface hardness of nitrided layer increases to about HV0.01700, and the corrosion resistance increases to 1.5 times of the substrate. Nitrided layer is divided into three regions: the first is the white layer region that includes theδphase andεequal; the second is the nitrogen atom diffusion layer region which contains large amounts ofαphase martensite; and the third region only experiences the martensitic transformation. The thickness of nitriding layer increases with the temperature. When the gas nitriding temperature is up to 730℃, the nitrided layer ,in which the white layer increases to about 10μm, increases to 100~120μm, the surface hardness increases to more than HV0.011000, and the corrosion resistance increases up to 3 times of the substrate.