【作者】 戴景杰；

【导师】 樊丁；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2006， 硕士

【摘要】 在优化工艺参数下,对TA2钛合金分别进行激光表面碳元素合金化,激光表面气体氮化,激光表面重熔和整体淬火处理。采用XRD,SEM和OM对试样组织结构进行表征,HVS-1000型显微硬度计和UMT-2MT型磨损试验机对显微硬度和摩擦系数进行测试。 激光表面碳元素合金化在工业纯钛TA2基体上成功制得TiC/Ti复合相涂层,涂层具有较高的硬度和良好的耐磨损性能。SEM结合XRD分析结果表明:合金化层中TiC组织具有发达树枝状、胞枝状、十字花瓣状和球状等形貌。不同形貌TiC显微硬度的测试表明:球状组织显微硬度最高,为475Hv;发达树枝状组织为450Hv;十字花瓣状为420Hv;胞枝状组织最低,为380Hv。TiC形成机理可分为扩散、反应和析出三个步骤。TiC枝晶形貌与冷却速率关系研究结果表明:随冷却速率的增加,TiC枝晶形貌由十字花瓣状转为发达树枝状。 激光气体氮化在基体上成功制得表面呈金黄色的氮化层。SEM结合XRD分析表明,氮化层主要由TiN和α′-Ti组成,不含Ti₂N相。显微硬度测试表明:氮化层具有较高的显微硬度,为500Hv。氮化层主要通过氮气向液钛中扩散,在随后的快速凝固过程中以δ-TiN_x形式析出形成。 激光表面重熔和淬火处理快速冷却组织均发生马氏体相变,获得α′-Ti组织。激光表面重熔层表层生成厚度约为3μm厚的TiN薄层。显微硬度测试表明:淬火处理使退火态TA2硬度仅提高约1/4,而激光表面重熔却使硬度提高1倍。激光表面重熔可有效的改善基体的耐磨性。更多还原

【Abstract】 Laser surface alloying, laser surface remelting and quenching were performed on commercial pure titanium TA2 with optimized process parameters. Microstructures were characterized using X-ray diffraction, optical microscopy and scanning electron microscopy. The wear properties and hardness were examined using UMT-2MT wear tester and HVS-1000 type microhardness tester.TiC/Ti composite layer was successfully fabricated by laser surface alloying with carbon. The microhardness and wear resistance of laser surface alloyed layer were greatly improved. The microstructure analyses showed that titanium carbide growth morphologies had a well-developed dendrite, cellular dendrite, globular microstructure and cross-petal microstructure and so on. The hardness measurement showed that the microstructure corresponding to the globular morphology for the titanium carbide phase had the highest microhardness. The mechanism of the formation of titanium carbides could be divided into three periods of diffusion, reaction and rapid solidification. The carbide morphology in the alloyed coating was directly dependent upon the solidification cooling rate. At a high cooling rate, the carbide morphology was well-developed dendrite. As the solidification cooling rate decreased, the growth morphology of titanium carbide changed to cross-petal-like with symmetrical arms.Nitrided layers with golden yellow color were fabricated by laser gas nitriding. The result of XRD showed that TiN was detected but no Ti₂N was detected. The microhardness of laser nitrided layer was about 500Hv and gradually decreased to 209Hv for the titanium substrate. Nitriding of titanium occurred via the inward diffusion of nitrogen in the molten pool. The diffusion coefficients of nitrogen in TiN and a-Ti（N） phases were determined.P-Ti to a’-Ti phase transformations occurred with rapid cooling rate by laser surface remelting and quenching. The morphologies of a’ martensite in the quenched and laser surface remelted samples were corresponding with the characterization of acicular martensite. The cross-section microstructure of laser melted layer showed that a 3 μm thick TiN continuous thin surface region formed on the top surface of laser remelted sample. The hardness measurement showed that the microhardness of laser remelted layer was improved to425 Hv while the microhardness of the quenched sample was improved to 275Hv from 225Hv for the annealed sample. Wearresistance were improved by laser surface remelting.更多还原