【作者】 张高会；

【导师】 徐重； 潘俊德；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2004， 博士

【摘要】 钛及钛合金以其比强度高、中低温稳定性好、耐腐蚀性能优异、生物相容性好等一系列优异的特性而广泛的应用于航空航天、生物医学、化工、交通运输、文体及电子等行业,并有增长的趋势,但是,钛及钛合金硬度低、耐磨擦性能差,这一缺点极大的限制了它们的进一步广泛应用。 传统的渗碳技术用于提高钢铁材料的表面强度,早已被普遍使用并获得成功。对于钛及钛合金而言,氢与钛反应可形成钛的氢化物导致氢脆的发生,从而产生微裂纹、降低韧性等。所以,传统的渗碳方法不适用于钛及钛合金。针对这一现象,本文分析总结了钛及钛合金的性质特性及其表面处理的一般方法及这些方法的优缺点;讨论了钛合金的氢脆问题;针对其耐磨性差的缺点,提出采用双层辉光离子渗金属技术实行离子无氢渗碳及离子无氢碳氮共渗的新方法,对钛及钛合金进行表面处理,达到既能提高其耐摩擦性,又避免钛合金氢脆现象的发生,同时保留钛合金耐蚀性强和比强度高的两大优点。 利用双层辉光放电离子渗碳原理,以格栅状高纯度固体石墨做源极,钛及钛合金(Ti6Al4V)做阴极,氩气做工作气体,依靠辉光放电和空心阴极效应对钛及钛合金(Ti6Al4V)进行无氢渗碳处理,在纯钛及钛合金(Ti6Al4V)材料表面制备了具有特殊物理、化学性能的渗碳层;采用X射线衍射和辉光放电光谱分析了渗碳层的相组成及C元素分布;考察了渗层的摩擦磨损性能及电化学腐蚀性能。结果表明:复合更多还原

【Abstract】 The titanium and titanium alloys are widely used in aviation industry, medical science, chemical engineering, transportation, sports apparatus and electronics industry etc. for their high specific strength, high stability in low and medium temperature, excellent corrosion resistance and bio-compatibility etc. However, the titanium and titanium alloys have low hardness, poor wear resistance which limits their more applications .Conventional carburizing techniques, such as pack carburizing and gas carburizing, have been successfully used to improve the surface hardness and strength of iron and steels. However these methods are not applicable for titanium and its alloys due to the microcrack and embrittlement caused by the reactions between titanium and hydrogen in the carburizing media. This paper analyzes the properties of titanium and titanium alloys; evaluates various surface treatment methods; discuss hydrogen brittleness of titanium alloys. The double glow plasma hydrogen-free carburisation and double glow plasma hydrogen-free carbonitriding are adopted to enhance wear resistance of titanium and titanium alloys Ti6A14V , at the meantime avoid the hydrogen brittleness of titanium alloys and also keep their high corrosion resistance, high specific strength.The doubled glow plasma discharge hydrogen-free carburisation employs as grid shaped high purity solid graphite as the source electrode, the titanium or titanium alloy Ti6A14V as the cathode, argon as the working gas, the hollow cathode effect of the glow discharge is used to carburize the titanium alloys without hydrogen. Carburized layers with special physical and chemical properties are formed on the surface of the titanium or titanium alloys. The phase structure and the distribution of carbon are analyzed with the X-ray diffraction and the glow discharge optical spectrum; the friction and wear behavior and the electrochemical corrosion properties are examined. The results show that the high hardness phase (TiC) and the antifriction phase are formed in the compound carburized layer; the content of carbon is grade distributed; the surface hardness of carburized materials are increased significantly and the hardness profile from top to inside shows a gradient characteristic ; the antifriction and the abrasion resistance are greatly enhanced , the friction coefficient and the wear rate are reduced bymore than 50% and more than 3 orders of magnitude respectively. The corrosion resistance is increased by several times . Nick test shows that the materials’ surface brittleness is slight, and the hydrogen brittleness is avoided. Compared with the ion nitrided phase, the layer is thick and also has better abradability and corrosion resistance.Using the solid graphite as the source electrode, the titanium and titanium alloys as the cathode , inputting a certain ratio gas of nitrogen and argon, depending on the glow discharge hollow cathode effct, we get a carbonitriding layer without hydrogen which has special physical and chemical properties. The phase structure and the distribution of carbon, nitrogen are analyzed with the X-ray diffraction and the glow discharge optical spectrum. The friction wear property and the electrochemical corrosion properties are checked. The results show that the high hardness phase (TiC,TiN) are formed in the compound carbonitriding layer; the content of carbon and nitrogen is graded reduced from top to inside; the surface hardness are increased a lot, the hardness is graded reduced from top to inside ; the antifriction and the abrasion resistance are enhanced a lot, the friction factor goes down by more than 40%, the wear rate goes down by more than 3 orders of magnitude, also the corrosion resistance goes up by several times . Nick test shows that the materials’ surface fragility is gentle, and avoids the hydrogen brittleness as the existence of ion carburized phase. Compared with the ion nitrified phase, the layer is thick and also has nice abradability corrosion resistance.The results are analyzed in theoretically. The graded distribution of carbon (or carbon, nitrogen ) in the layer determines the graded distribution of TiC(or TiC, TiN) content, and further determines the graded distribution of hardness and the nonconstant variation rules of friction coefficient which varies from small to large gradually and finally tend to stabilization.Finally, the models of plasma transition in dynamic stable electric field are constructed; the differential pressure theory is put forward to with the statistic physics rules. Combined with the Fick’s first law, the diffusion coefficient is calculated. The results show that the diffusion coefficient is not large during the carburization without hydrogen in the titanium alloys, and TiC prevents carbon from diffusing ,which is formed from reaction between carbon and titanium.In summary, this paper demonstrates that the double glow plasma hydrogen-free carburization and hydrogen-free carbonitriding technology are feasible way to enhance the wear resistance of titanium and titanium alloys Ti6A14V without bringing about hydrogen brittleness.更多还原