Effect of High Frequency Power Supply and Active Screen Plasma Nitriding on the Adhesion of Surface Nano-sized TC4 Titanium Alloy Nitriding Layer

High frequency power supply and active screen technology can alleviate the negative factors such as arc striking, edge effect and hollow cathode effect during traditional direct current (DC) power supply nitriding, but the evaluation of adhesion needs to be studied. The work aims to evaluate the effect of high frequency power supply on the adhesion of surface shot peening nano TC4 titanium alloy nitriding layer, and further explore the effect of nitriding parameter optimization on the adhesion of nitriding layer based on the combination of high frequency power supply and active screen technology. Based on the optimization results of the high frequency power supply and active screen parameters in the early stage of the research group, samples of DC power supply under –500 ℃-20 h-300 Pa nitriding and high frequency power supply under –500 ℃-20 h-200 Pa nitriding with similar nitriding layer thickness (to eliminate the effect of thickness difference on the adhesion of the nitriding layer) were selected to analyze the structure, morphology and adhesion respectively by X-ray diffraction (XRD), scanning electron microscopy (SEM) and scratch experiments. On the basis of high frequency power supply, the optimized parameters of the active screen (high frequency power supply under –500 ℃-20 h-200 Pa-400 V bias voltages) and the nitrided samples before the optimization of the active screen (high frequency power supply under –500 ℃-20 h-300 Pa-1 100 V bias voltages) were selected to compare structure, morphology, and adhesion. According to the scratch adhesion test results, the acoustic signal of the high frequency power supply nitriding layer was stable, and the scratches did not peel off. The load values (5.1 N and 5.2 N) of the frictional force signal of the nitriding layer in the original nitriding sample and the shot peening nitriding sample increased sharply compared to the load values of the nitriding sample corresponding to the DC power supply (starting from the initial loading). Under the combination of high frequency power supply and active screen technology, it was found that the thickness of TiN and Ti2N layers of the original nitriding sample and the shot peening nitriding sample before optimization respectively was 0.4 μm/0.1 μm and 0.5 μm/0.1 μm. After optimization, the thickness of TiN and Ti2N layers of the original nitriding sample and the shot peening nitriding sample was 1.5 μm/2.0 μm and 1.6 μm/3.7 μm. After optimization of nitriding, the thickness of the nitriding layer increased significantly. The sound signal of the scratch test was more stable, without obvious abrupt changes, and the load values (7.5 N and 11.5 N) of the frictional force signal of the nitriding layer of the original nitriding sample and the shot peening nitriding sample after the optimization of the active screen increased significantly compared to the corresponding load values (3.8 N and 4.9 N) of the sample before the optimization. The use of high frequency power supply successfully inhibited the arc phenomenon in the nitriding process of traditional DC power supply, alleviated the thermal stress accumulation in the nitriding layer, improved the surface properties of the nitriding layer, and improved the load bearing capacity and adhesion of the nitriding layer. Under the combined process of high frequency power supply and active screen, the nitriding dynamic conditions of the optimized nitriding sample are better (the nitrogen diffusion effect is more significant), and the nitriding layer thickness, especially the Ti2N layer thickness, increases significantly, which improves the performance of the nitrogen diffusion layer in the matrix. At the same time, the increase of Ti2N thickness can slow down the sudden change of the composition and properties of the TiN layer and the matrix, so as to improve the adhesion between the nitriding layer and the matrix. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.