【作者】 于存贞；

【导师】 魏德洲； 朱圣龙；

【作者基本信息】 东北大学 ， 矿物加工工程， 2007， 博士

【摘要】 钛合金具有比强度高、抗氧化和抗腐蚀性能好的特点被广泛应用于航空、航天领域。然而,高温下服役时,钛合金的氧化和氧脆问题严重影响了钛合金的热稳定性。目前提高钛合金抗氧化、抗腐蚀性能的措施很多,如合金化、表面处理和施加防护涂层等等,但仍存在诸多不足。如传统方法制备的氧化铝、二氧化硅涂层往往由于和基体之间存在膨胀系数的差异,很容易破裂而不能给基体提供良好的保护性能。因此利用新的技术制备或者开发新的涂层来提高钛合金的抗氧化、抗腐蚀性能就成了人们探究的热点。基于上述情况,本文利用新型溶胶凝胶技术在Ti6A14V合金表面制备了SiO2膜,研究了该法制备的SiO2膜作为抗氧化涂层的可行性,以及在氧化过程中SiO2膜与基体合金之间的反应。采用磁控溅射技术在Ti6A14V合金表面制备镍硅涂层,并对涂覆涂层的试样和基体样品进行了不同温度下氧化、腐蚀试验。利用X-射线、扫描电子显微镜、表面光电子能谱、红外光谱等试验手段进行了分析和表征。1.采用溶胶-凝胶法在钛合金表面通过直接加热的方式制备了均匀、不破裂的二氧化硅膜,厚度约为10μm。700-800℃恒温和循环氧化实验证明,二氧化硅膜不仅降低了氧化速率,而且消除了基体合金氧化过程中氧化膜的破裂、剥落和层化现象。二氧化硅膜导致了氧化物的重新分布,促进了氧化铝膜的生成,有利于混合氧化物中氧化铝含量的增加。2．涂覆SiO2膜的合金试样氧化后形成的氧化膜是多层的,在二氧化硅膜的下部形成了相对较厚的二氧化钛层和富铝层,表明氧通过二氧化硅膜向内扩散；在二氧化硅膜的上部形成了以氧化铝为主,少量氧化钛掺杂的混合氧化物层,说明Al和Ti通过二氧化硅膜向外扩散。由此推断出,这种多层的混合氧化物膜的生长是受向内扩散的氧和向外扩散的金属元素控制的。3.磁控溅射Ni3Si靶制备的Ni-Si涂层没有形成Ni3Si纳米晶涂层,而是形成了γ-Ni5S2和Ni(Si)固溶体。650℃氧化100h或600℃腐蚀10h后形成了有序Ni3Si相。4.Ni-Si涂层为Ti6Al4V合金提供了良好的抗氧化性能。650℃氧化以后涂层表面生成了氧化镍和硅氧化物。硅氧化物的形成影响了氧化镍的生长,使得氧化动力学曲线偏离了抛物线规律。5.Ni-Si涂层明显改善了基体合金在H2O/NaCl/O2条件下的抗腐蚀能力。600℃腐蚀10h后涂层表面生成了NiO/Ni/SixOy交替分布的层状结构氧化物。这种层状结构氧化物是由于Ni和NaCl/H2O/O2发生的多步反应、涂层中硅元素的低扩散率以及硅和氧化镍的替代反应造成的。更多还原

【Abstract】 Titanium alloys, with respect to their relative low density and high strength, have been the subject of recent investigations for the compressor part of aero-engines. However, poor oxidation resistance and oxygen-induced embrittlement of Ti alloys are well known to strongly limit their applications at high temperatures. Up to now, many approaches have been adopted to improve the oxidation and corrosion resistance of titanium alloys, such as alloying, surface treatment and protective coatings. However, the brittleness of the Al2O3 or SiO2 coatings and mismatch of coefficients of thermal expansion between them and their substrates could be problems leading to cracking and spalling by traditional fabricating techniques. Thus, new technologies for fabricating SiO2 coating need to be developed in order to improve the oxidation resistance of titanium alloys.The aim of the present work is to study the effect of sol-gel derived SiO2 thin film to explore the feasibility of using such a film as an oxidation resistant coating, and to investigate the solid reactions between SiO2 and titanium alloys during oxidation. Meanwhile, the effects of the sputtered Ni-Si coating on the oxidation behavior of Ti6A14V at 650℃and H2O/NaCl-induced corrosion behavior at 600℃were studied.1. Sol-gel SiO2 thin film has been successfully applied on the surface of Ti6Al4V alloy using directly sinter process, the thickness of SiO2 thin film was about 10μm. The isothermal and cyclic oxidation behaviors of the uncoated and coated alloys in air at 700 and 800℃were investigated. The SiO2 thin film had beneficial effects on the oxidation resistance of the alloy. The oxidation rates were significantly reduced. Cracking and spallation of the oxide scales were not detected on the coated specimens. The SiO2 film affected the distribution of oxide scales and favored the formation of the alumina.2. The scales formed on the SiO2 coated Ti6A14V specimens were multilayered. Beneath the silica film, formation of a thick rutile titania layer followed by a thin aluminum-rich layer occurred. Above the silica film, alumina plus minor titania layer formed. It is deduced that the growth of the multilayered and mixed oxide scales was dominated by both outward diffusion of metal and inward diffusion of oxygen.3. The as-received Ni-Si coatings on Ti6Al4V prepared by magnetron sputtering from a Ni3Si target were mixtures of y-Ni3Si2 and f.c.c. Ni, which transformed into ordered Ni3Si during oxidation at 650℃or corrosion at 600℃.4. The Ni-Si coatings possessed excellent oxidation resistances. External NiO scales along with silicic oxide precipitates formed on the coating surfaces during oxidation at 650℃. It is suggested that the formation of silicic oxide disturbs the growth of NiO scale, leading the kinetics deviate from the parabolic law.5. In the case of H2O/NaCl-induced corrosion, the Ni-Si coatings offered better corrosion resistance at 600℃for 10h. The external scales showed alternative lamellar structures, which consisted of lamellae of NiO, silicic oxide and metallic Ni, might result from the combination effects of multi-step reactions between Ni and NaCl/H2O/O2, the low diffusivity of Si and a displacement reaction between Si and NiO.更多还原