高温下钛合金微动疲劳行为及表面处理技术影响的研究

【作者】 张晓化；

【导师】 刘道新；

【作者基本信息】 西北工业大学 ， 材料学， 2004， 硕士

【摘要】 耐磨性能差是直接影响钛合金在航空发动机中安全使用的主要因素之一，由此可能引发压气机钛合金叶片榫头在工作过程中发生微动疲劳(FF)损伤而早期断裂。提高钛合金FF抗力是航空工业等部门关注的问题，但因FF过程的复杂性，FF机理尚不够清楚，FF研究中存在一定的盲目性，研究方法各异。本文针对上述问题，从影响高温下钛合金FF行为的关键环节入手，设计科学合理的高温FF试验方法。深入系统地研究FF影响因素对钛合金FF行为作用规律，探讨FF机理。结合对表面处理工艺技术及表层性能评价，研究喷丸强化三因素和表面膜层对钛合金FF抗力的影响。主要工作和取得的研究结论如下： (1)研究了位移幅度、接触压力、温度等几个主要因素对钛合金FF行为的影响。研究发现FF寿命位移幅度或接触压力增大呈现非单调变化规律，原因是位移幅度或接触压力变化影响疲劳和磨损在FF过程中所占比重，进而影响FF裂纹萌生几率和扩展驱动力，由此导致位移幅度或接触压力增大呈现非单调变化。温度升高加剧了环境的氧化和腐蚀作用，出现高温塑性变形机制(如蠕变)，并引起钛合金的变形抗力的下降，造成材料本身的疲劳性能恶化。 (2)喷丸强化是提高钛合金常温条件下FF抗力最为有效的方法，SP引入表面残余压应力，并使表面加工硬化和表面粗糙化。但对这三个因素在高温FF过程中所起的作用目前尚不明确。本文用分离三因素的方法研究了SP对高温下钛合金FF行为的影响。结果表明SP引入的表层残余压应力增加裂纹闭合力，是SP提高高温下钛合金FF抗力最为重要的因素；SP表面加工硬化作用在改善高温下钛合金的FF性能中为次要因素；SP造成的粗糙度增大在高温下对钛合金的FF性能的作用因表面存在机械损伤而呈现出不利的影响，这种影响同时与残余压应力的存在状态有关。 (3)研究了一种可望与SP联合作用能够提高钛合金FF抗力的新型表面处理技术离子束增强沉积CrMo、OCr18Ni9合金膜，探讨了该类膜层对高温下钛合金FF抗力的影响。利用X射线衍射技术、扫描电镜及光谱分析等手段，评价了IBED膜层的基本性能。结果表明，通过离子束增强沉积(IBED)技术，所获膜层致密度高，晶粒细化，空隙率低，膜基结合强度好。但CrMo合金膜层硬度高，韧性差，膜层脆性大，在以疲劳为主的FF过程中易发生破裂，形成裂纹快速进入基体，致使高温下钛合金FF抗力降低，与喷丸强化复合并未达到协同提高钛合金FF抗力的目标。更多还原

【Abstract】 Weak anti-abrasion property of titanium alloys can bring about early fracture of compressor blade tenon made from titanium alloys during working process because of Fretting Fatigue (FF), so it has become one of the main factors which affect the safe application of titanium alloys at room temperature and elevated temperature in aviation engine. It is important to improve FF resistance of titanium alloy in aeronautic industry and other fields. Due to the complexity of FF loading, FF mechanism is still not quite clear. The trial-and-error approach is usually used to find a way against FF in a given situation. In addition, investigations in FF tests have used different methods. In accordance with above-mentioned problems, an appropriate method of FF is designed by thinking the key annuluses which influence FF behavior of titanium alloy at elevated temperature. The mechanism of FF is discussed by studying the effects of major testing factors. The effects of the three factors of shot peening (SP) and surface coating on fretting fatigue resistance (FFR) are studied through evaluating surface treatment technique and the properties of surface coating. The main contributions are as fellows:(1) The effects of major testing factors, including slip amplitude, contact pressure and temperature, are investigated in the present study. The results indicate that the life of FF is changed non-monotonicly with increasing slip amplitude or contact pressure. Because slip amplitude and contact pressure affect the action of fatigue and wear in FF process, result in the change of crack initiation probability and crack propagating rate. Because the role of oxide etch is aggravated by elevating temperature, the deforming resistance of titanium alloy falls down and creep occurs and the fatigue property of materials is worsening.(2) Shot peening is the most efficient way in improving FF resistance of titanium alloys at room temperature. Working hardening, roughening and compressive residual stress are involved in the shot peened surface. There are different viewpoints on how the three factors of SP work at elevated temperature. The effect of SP on the fretting fatigue behavior of titanium alloys is studied in this paper by separating the three factors of SP. The major part of the three factors of SP for improving FFR at elevated temperature is compressive residual stress, which arrests the crack into closure. The role of working hardening is secondary. The effect of roughening for improving FFR at elevated temperature is bad, which is related with the state of compressive residual stress.(3) The effect of a new kind of surface treatment technique (IBED CrMo and OCr18Ni9 coating) which can be combined with SP on FFR of titanium alloys at elevated temperature has been studied. The properties of the modified surface have been evaluated by X-ray diffraction, SEM, optical spectrum analysis. The results indicate that ion beam enhanced deposition (IBED) can produce coating which has high density, small grain size, small void radio, good bonding strength. But the hardness of IBED CrMo coating is high with poor ductility and the coating is brittle. So the coating is easily broken when fatigue is major factor in the process of FF. Cracks can enter the bulk material quickly so that the FFR of titanium alloy is reducing. IBED CrMo coating combined with SP can not achieve the purpose of improving the FFR of titanium alloy.更多还原