| CHEN Sainan,DONG Zhihong,BAO Zebin.Effect of Combining Hollow Cathode Discharge with Rare Earth Oxide on Microstructure and Properties of Plasma Nitrided Ti6Al4V Alloy[J],53(5):78-84, 107 |
| Effect of Combining Hollow Cathode Discharge with Rare Earth Oxide on Microstructure and Properties of Plasma Nitrided Ti6Al4V Alloy |
| Received:March 06, 2023 Revised:May 11, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.05.008 |
| KeyWord:plasma nitriding hollow cathode discharge rare earth oxide Ti6Al4V wear nitrided layer |
| Author | Institution |
| CHEN Sainan |
Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China;School of Materials Science and Engineering, University of Science and Technology of China, Hefei , China |
| DONG Zhihong |
Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China |
| BAO Zebin |
Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China |
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| Abstract: |
| The work aims to improve the wear and corrosion resistance of Ti6Al4V alloy and explore the effect of auxiliary means used in plasma nitriding on the microstructure and properties of nitrided layer. Hollow cathode discharge (HCD) and rare earth (Y2O3 nanoparticle) were introduced to assist the plasma nitriding of Ti6Al4V alloy at 720 ℃ for 4 h. Three different sets of plasma nitriding conditions were selected, namely conventional plasma nitriding (PN), plasma nitriding with HCD (PN with HCD) and plasma nitriding with HCD and Y2O3 (PN with HCD and Y2O3). The hardness, wear and corrosion properties of the alloy were tested by microhardness tester, reciprocal linear sliding tester and electrochemistry station. The microstructure and phase composition were analyzed by means of optical microscopy, scanning electron microscopy and X-ray diffraction. Under the condition of plasma nitriding with HCD and Y2O3, the nitrided layer with a thickness of about 126 μm was formed on the Ti6Al4V alloy surface, which was 3.1 and 2.4 times thicker than that obtained by conventional plasma nitriding and plasma nitriding with HCD respectively. The content of TiN in the compound layer increased significantly, resulting in an increase in the surface hardness of the nitriding layer to 1 067.9HV0.05, which was 26.7% and 8.5% higher than those of the other two sets respectively. The overall hardness of the nitriding layer was obviously increased, but the hardness gradient was reduced. The friction coefficient of Ti6Al4V alloy decreased from 0.4 under the conventional plasma nitriding condition to 0.2, and the corrosion resistance of the alloy in 3.5wt.% NaCl solution was improved. HCD is a special glow discharge phenomenon that occurs mainly inside a cavity-like cathode and can produce high-density plasma. The use of appropriate HCD for plasma nitriding can increase the nitrogen potential and accelerate the nitriding process. When HCD is combined with Y2O3, the catalytic effect of rare earth elements in plasma nitriding is introduced and can be superimposed with the catalytic effect of HCD. As a rare earth element, yttrium has a special electronic structure and high activity. The yttrium atom can combine with the active nitrogen atoms in the plasma to generate rare earth nitride that promotes the adsorption of nitrogen on the alloy surface and the penetration of nitrogen into the alloy. At the same time, the large atomic radius of yttrium atom leads to the lattice distortion and accelerates the diffusion of nitrogen inside the alloy. In this study, Y2O3 particles are used as the rare earth source. The yttrium elements (atoms or ions) can be released by the bombardment of high-energy particles generated by HCD. In the high-density plasma region of the hollow cathode, the interaction between yttrium elements and active nitrogen atoms is easier, and the catalytic effect of rare earth is enhanced. It is known from the above results that the combination of HCD with Y2O3 is an effective method to substantially increase the nitrogen potential and promote the diffusion of nitrogen into the Ti6Al4V alloy during the plasma nitriding. In this case, the wear and corrosion resistance of the Ti6Al4V alloy can be improved. |
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