液氮强制冷却对Ti6Al4V激光熔覆WC/Ni60A涂层微观组织和性能的影响

Microstructure and property of composite on the Ti6Al4V by laser cladding WC/Ni60A under nitrogen cooling condition

摘要:

摘 要: 为改善Ti6Al4V钛合金的表面硬度和耐磨性能，采用液氮强制冷却辅助激光熔覆制备35％WC / Ni60A(质量分数)复合涂层，研究液氮强制冷却对熔覆层微观组织和力学性能的影响。基于X射线衍射（XRD）、光学显微镜（OM）、扫描电镜（SEM）和能谱仪（EDS）分析液氮强制冷却熔覆层的显微组织和物相组成；在室温条件下施加200N载荷以Si3Ni4陶瓷球为对偶件测试基体、空冷和液氮强制冷却熔覆层的滑动磨损性能，分析其磨损机理。结果表明：空冷和液氮强制冷却熔覆层都由α（Ti），WC，W2C，TiC，TiNi，Ti2Ni，TiNi3，NiB相构成。但与空冷熔覆层相比，液氮强制冷却熔覆层组织均匀致密，晶粒尺寸和析出强化相更加细小，并在结合界面处形成取向一致性更强，更加均匀细密的定向凝固组织，呈现出与基体良好的冶金结合。液氮强制冷却熔覆层的平均显微硬度达到1363 HV0.2，硬度较基体和空冷熔覆层分别提高4倍和1.61倍。此外，液氮强制冷却熔覆层耐磨性分别为基体和空冷熔覆层的5.39倍和1.77倍。液氮强制冷却能有效提高激光熔覆层的显微硬度和耐磨性能。

Abstract:

Abstract: To improve the hardness and anti-wear properties of Ti6Al4V alloy, composite coatings were produced on the Ti6Al4V substrate under liquid nitrogen cooling by laser cladding 35wt.% WC/Ni60A. The microstructural evolution and mechanical properties of coatings under liquid nitrogen cooling were investigated. The phase compositions and microstructures were investigated by X-ray diffractometer (XRD), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. Sliding wear tests of the composite coatings under different cooling medium and substrate were conducted at 200N with the Si3Ni4 ceramic ball as the counter-body, and the corresponding wear mechanisms are discussed. The results indicated that the coatings both under liquid nitrogen cooling and under air cooling were mainly composed of α(Ti), WC, W2C, TiC, TiNi, Ti2Ni, TiNi3, NiB. Compared with the coating under air cooling , microstructure of the coating under liquid nitrogen cooling is uniform and dense, grain and precipitation phase is more small. The coating under liquid nitrogen cooling shows the sound metallurgical ( the bonding line) free pores and cracks between the coating and the substrate，and the microstructure near the bonding line shows more dense and fine directional solidification microstructure with a highly preferred orientation. The average microhardness of the coating under liquid nitrogen cooling is about 1363 HV0.2, which is 4 times higher than the Ti6Al4V substrate and is 1.61 times than the coating under air cooling. The relative anti-wear resistance of the coating under liquid nitrogen cooling is 5.39 times higher than the Ti6Al4V substrate and is 1.77 times than the coating under air cooling. Liquid nitrogen cooling can effectively improve the microhardness and anti-wear properties of coating.