【作者】 李振华；

【导师】 程先华；

【作者基本信息】 上海交通大学 ， 机械设计及理论， 2007， 博士

【摘要】 钛镍基合金具有优良的形状记忆效应和伪弹性,在航天航空、机械、电子、化工、生物医学等领域获得了广泛的应用。随着应用领域的不断扩大,钛镍基合金的摩擦和磨损等问题越来越突出,极大地限制了其优异性能的发挥。因此,钛镍基合金的摩擦学性能研究逐渐成为摩擦学研究领域的热点之一。晶粒细化是提高钛镍基合金力学性能和摩擦学性能的有效手段。基于微观组织是影响合金材料综合性能的关键因素,根据钛镍基合金的加工特性,本论文利用先进的等径弯角挤压技术对钛镍基合金进行热加工处理,以有效地细化钛镍基合金的微观组织,进而提高钛镍基合金的力学性能和摩擦学性能,取得了原创性的研究成果。第一,采用高温ECAE工艺对钛镍基合金进行热加工处理,通过显微组织观察,研究了预热温度、挤压道次和退火处理对钛镍基合金显微组织的影响,确定了钛镍基合金的高温ECAE加工工艺,并且探讨了高温ECAE工艺细化钛镍基合金组织的作用机理。结果表明:钛镍基合金经过850℃第一道次挤压和750℃第二道次挤压后,形成了细长的纤维状组织;经400～600℃退火处理后,其纤维状组织得到回复,形成细小组织。第二,从热力学角度探讨了高温ECAE工艺对钛镍基合金马氏体相转变温度和伪弹性应变回复的影响,通过示差热(DSC)分析和伪弹性分析,阐明了高温ECAE工艺对钛镍基合金马氏体相转变行为和伪弹性的作用机理。结果表明,高温ECAE工艺降低了马氏体相转变温度和提高了钛镍基合金的伪弹性;且在500℃退火时,有大量细小的Ti3Ni4相析出,强化了基体,提高了母相强度,从而提高了合金的摩擦学性能。第三,系统地研究了钛镍基合金在干摩擦和油润滑条件下的摩擦学性能。结果表明,高温ECAE工艺大大提高了钛镍基合金的摩擦学性能,并且在相同的试验条件下,经过高温ECAE工艺处理的钛镍基合金的摩擦学性能显著优于未经过ECAE挤压处理的钛镍基合金的摩擦学性能,且经过ECAE挤压、500℃退火时的钛镍合金具有最优的摩擦学性能。第四,研究了钛镍基合金在干摩擦和油润滑条件下的磨损机理。干摩擦时,未经过ECAE挤压处理钛镍基合金的磨损形式主要为磨粒磨损、氧化和表面疲劳磨损,经过高温ECAE工艺处理后,钛镍基合金的组织细化、伪弹性和硬度提高,其主要的磨损形式为较轻微磨粒磨损和氧化磨损。油润滑时,在摩擦副表面形成了油膜,将合金与对摩件表面隔开,润滑油带走摩擦热,减轻了对摩件对合金表面的犁削作用,阻止了合金表面氧化,其主要的磨损形式为磨粒磨损。第五,探讨了高温ECAE工艺对钛镍基合金摩擦学性能影响的作用机理。高温ECAE工艺处理显著细化了钛镍基合金的微观组织,提高了钛镍基合金的伪弹性和显微硬度,在磨损过程中减小了塑性区域面积,增强了合金弹性变形能力,从而降低了合金的磨损;当退火温度为500℃时,钛镍合金的伪弹性和显微硬度达到了适当的平衡,从而获得最优的摩擦学性能。本论文首次利用高温ECAE工艺对钛镍基合金进行加工处理,研究了高温ECAE工艺对于钛镍基合金微观组织和摩擦学性能的影响,并采用示差热分析和拉伸实验等手段对钛镍基合金的马氏体相转变行为和伪弹性进行了表征,系统地研究了干摩擦和油润滑条件下钛镍基合金的摩擦磨损性能,获得了其摩擦磨损性能与试验参数之间的变化规律及其磨损机理。研究结果促进了高温ECAE工艺的研究,为提高钛镍基合金性能以及促进其在工程领域的应用提供了依据。更多还原

【Abstract】 With shape memory effect and pseudo-elasticity, Ti-Ni based alloys are widely used in the fields of spaceflight, aviation, machine, electron, chemical industry, biomedicine, etc. With the spread of the application fields, friction and wear become more serious, and that may significantly influence the performance of Ti-Ni based alloys. Therefore, the tribological behavior of Ti-Ni based alloys becomes a hot spot for research. Grain refinement has been an effective way to improve the mechanical and tribological properties of Ti-Ni based alloys.In this study, in view of the microstructure is a key factor which influences the performance of the Ti-Ni based alloys, and machining characteristic of Ti-Ni based alloys is poor at a low temperature, an advanced equal channel angular extrusion technology has been used to process Ti-Ni based alloys in order to refine the microstructure, and then improve the mechanical and tribological properties of the alloys. Some significant original results have been obtained.Firstly, high temperature ECAE processing was used for the microstructural refinement of Ti-Ni based alloys, the effects of preheating temperature, extrusion numbers and annealing treatment on the microstructure of Ti-Ni based alloys were analyzed by optical microstructure photographs, and the microstructural refinement mechanism produced by high temperature ECAE processing was discussed. The results showed that the elongated fibriform microstructure of Ti-Ni based alloys was obtained when the first preheating temperature was 850℃and the second was 750℃. After annealing at 400~600℃, the fibriform microstructure of the alloys was restored and refined microstructure was obtained. Secondly, the effects of high temperature ECAE processing on the phase transformation temperature and the pseudo-elastic strain recovery of Ti-Ni based alloys were analyzed from the thermodynamic point of view. In addition, different scanning calorimeter (DSC) and pseudo-elasticity were used to analyze the mechanism of high temperature ECAE processing for the phase transformation and the pseudo-elasticity of Ti-Ni based alloy. The results showed that high temperature ECAE processing reduced the martensitic phase transformation temperature and extended the range of pseudo-elasticity of Ti-Ni based alloy. Moreover, the second phase was precipitated during annealing at 500℃after ECAE, which strengthened the matrix, increased the parent strength, and then improved the friction and wear behaviors of Ti-Ni based alloys.Thirdly, the friction and wear behaviors of the Ti-Ni based alloys under both dry sliding and oil-lubricated conditions were investigated in detail. The results showed that the tribological properties of the alloys were greatly improved by high temperature ECAE processing. The Ti-Ni based alloys treated by high temperature ECAE processing registered the better tribological properties than untreated alloys, and the alloys treated by high temperature ECAE and annealing at 500℃showed the best tribological behaviors.Fourthly, the wear mechanisms of the Ti-Ni based alloys under dry sliding and oil-lubricated conditions were investigated. Under dry sliding condition, the main wear modes of untreated Ti-Ni based alloys are abrasive wear, oxidization and surface fatigue wear. When high temperature ECAE processing was used, the microstructure of Ti-Ni based alloys was refined, and the pseudo-elasticity and the hardness were increased, therefore, the main wear modes of the alloys were slightly abrasive wear and oxidization. Under oil-lubricated condition, the direct contact of the friction pair was reduced by the oil film. The friction heat was carried away by oil, resulting in a great decrease in plowing. The surface oxidization of the alloy was prevented, and the main wear mode was only abrasive wear.Fifthly, the mechanism of the influence of high temperature ECAE processing on the tribological properties of the Ti-Ni based alloys was discussed. High temperature ECAE processing refined the microstructure and increased the pseudo-elasticity and the hardness of Ti-Ni based alloys. It also reduced the plastic areas and strengthened the elastic deformation ability of the alloy, and then decreased the wear of the alloys. The superior tribological properties of Ti-Ni based alloy were obtained due to proper balance between the pseudo-elasticity and the hardness when the annealing temperature was 500℃. It is the first efforts to use high temperature ECAE processing for Ti-Ni based alloys, and investigate the influence of high temperature ECAE processing on the microstructure and tribological properties of the alloys. DSC and tensile test were used to characterize the martensitic phase transformation behaviors and the pseudo-elasticity. The friction and wear behaviors of the Ti-Ni based alloys under both dry sliding and oil-lubricated conditions were investigated in detail. The interrelationship between the friction and wear behaviors of the alloys and experimental conditions was obtained. The wear mechanism the alloys was analyzed. This study is promising to be improved in the properties of Ti-Ni based alloys and the application of the alloys.更多还原