Study On Microarc Oxidation And Laser Surface Modification Of Zr-Ti Alloy

In this study, ceramic coating and laser surface treatment were conducted on the Zr702 and ZrTiAlV alloy, respectively, by using microarc oxidation processing equipment and laser processing equipment. Microstructure,mechanical properties and friction & wear performance of the Zr702 and ZrTiAlV alloy after above surface modification have been studied by means of metallographic microscope, X-ray diffraction(XRD), scanning electron microscope(SEM), microhardness tester, nano-indentation machine, cryogenic vacuum friction and wear facility.It is shown that after microarc oxidation treatment, a ceramic oxide layer with the thickness of about 2μm and 2.5μm were obtained on surface of the Zr702 and ZrTiAlV alloy, respectively. The oxide surface layer can be divided into the loose layer and dense layer. The ceramic coating layer on the surface of Zr702 is mainly composed of M-ZrO2 and T-ZrO2, and the M-ZrO2 is in the majority. The surface layer on Zr TiAlV alloy is composed of ZrTiO4 and a small amount of ZrO2. The hardness test results show that after microarc oxidation treatment, the nano-hardness of Zr702 and ZrTiAlV alloy were improved significantly, mainly due to formation of the ceramic layer on surface. Friction and wear test results indicate that the average friction coefficient and mass loss of Zr702 and ZrTiAlV alloy in air at room temperature and in vacuum at cryogenic temperature reduced significantly after microarc oxidation, displaying excellent wear resistance.After laser surface quenching or laser surface melting, a modified layer with a certain depth was obtained on surface of the ZrTiAlV alloy. Viewed from the cross section, the surface modified layer of ZrTiAlV alloy can be described as heat-affected zone and substrate after laser quenching, and the heat affected zone is composed of coarse lamellar β phase, because the high temperature β phase did not transferred to α phase but retained during the fast cooling process. After laser surface melting, the surface modified layer of ZrTiAlV alloy is made of melted zone, heat affected zone and untreated substrate region. The laser-melted region is consisted of coarse lamellar β phase, which is related with extension growth β grain during cooling of the molten pool. Hardness test results show that after laser surface treatment on ZrTiAlV alloy, the micro-hardness of the melted zone is lower than substrate, while the micro-hardness of the region between the heat-affected zone and substrate become higher. On the other hand, the nano-hardness was not improved obviously after laser surface treatment on ZrTiAlV alloy, and the coarse grain structure of the modified layer is the main cause. Friction and wear test results show that the average friction coefficient and wear loss of the ZrTiAlV alloy after laser surface treatment were not altered greatly, indicating that the laser surface treatment applied in this work could not obviously improve wear resistance of the Zr Ti Al V alloy.