离子渗ZrN与喷丸复合对TC4合金疲劳行为的影响

In order to improve the wear and fatigue resistance of titanium alloy, a plasma alloying technique was applied to treat TC4 alloy with zirconium followed by nitrogen, and the gradient metallurgical zirconium nitride (ZrN) layer was fabricated. The surface metallurgical layer was then treated by shot peening. The microstructure, chemical composition and microhardness profile of the modified surface layer were then evaluated by scanning electron microscope, X-ray diffraction and microhardness tester, respectively. The effect of the modified surface layer of TC4 titanium alloy on fatigue behavior and its mechanism were investigated. The results demonstrate that the modified layer is composed of ZrN-TiN compound phase layer (mainly ZrN) and underlying nitrogen-rich Zr-Ti solid solution layer, and the surface hardness is 3.2 times higher than that of the substrate. Proper shot peening does not cause obvious damage of the ZrN layer, but increases the surface hardness which decreases with gradient distribution along depth. The modified surface layer dramatically reduces the fatigue resistance of base material, due to the low toughness of ZrN-TiN layer and large surface roughness. After combination with shot peening, the fatigue resistance of TC4 alloy is improved significantly, which is much higher than that of the base material and than that of the shot peening alone. It is attributed to combined shot peening introducing a deep and high-value residual compressive stress into the surface, which reduces the roughness and improves the surface microstructure of TC4 titanium, and thus restrains the initiation and early growth of fatigue cracks.