表面改性对钛合金高温微动疲劳行为影响的研究

【作者】 高广睿；

【导师】 刘道新；

【作者基本信息】 西北工业大学 ， 材料学， 2005， 硕士

【摘要】 钛合金耐磨性差,对微动疲劳损伤（FF）非常敏感,是限制钛合金在航空工业中应用的重要原因。通过表面处理技术提高钛合金高温FF抗力对发展高性能航空发动机有重要意义。本文在研究钛合金高温FF行为的基础上,探讨了离子束增强沉积（IBED）、非平衡磁控溅射（UBMS）、热喷涂技术及喷丸强化（SP）与这些表面改性技术复合对钛合金高温FF行为的影响,拟为提高钛合金FF抗力提供依据。主要研究结论如下: 1、Ti811钛合金高温FF以脱层为特征。位移幅度或接触压力对FF的影响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。由于温度升高促进钛合金的蠕变过程,使钛合金的常规疲劳性能下降,所以,蠕变是影响钛合金高温微动疲劳的重要因素。 2、通过IBED技术可以获得致密度高,晶粒细化,孔隙率低,膜基结合强度好的膜层。IBED 0Cr18Ni9膜层使Ti811合金的350℃高温FF寿命提高了66%,其原因是膜层具有较高的硬度,提高了钛合金的抗磨损能力:同时膜层具有良好的韧性,抗疲劳破坏的能力高。而IBED CuNi膜层不能提高基体的FF抗力。这是因为膜层的韧性低,同时膜基界面间有氧化现象,结合力较低,在微动疲劳的复杂应力作用下易产生裂纹,从而降低FF寿命。 3、UBMS MoS₂-Ti复合膜层使Ti811合金FF寿命提高了78%。膜层与基体间有很好的结合力;MoS₂膜层的润滑作用,降低了FF表面的摩擦力,改善了表面材料的受力状态;MoS₂-Ti膜层片状脱层的失效形式减小了裂纹萌生和裂纹向材料基体扩展的几率。 4、高温超音速喷涂（HVOF）和等离子喷涂获得的Co基WC涂层具有很高的硬度,耐磨性好。但该类涂层并不能提高钛合金350℃高温FF寿命,这主要是因为涂层的韧性低,在FF的复杂应力作用下很容易产生裂纹。 5、喷丸强化与IBED技术复合处理能否联合提高钛合金FF抗力与膜层性能有关。IBED技术可以制备结合力好,同时具有一定的韧性的0Cr18Ni9膜层,该膜层能够承受喷丸的冲击,与喷丸引入的表面残余压应力联合,起到了协同提高钛合金350℃高温下FF抗力的作用。IBED CuNi膜层本身性能差,与喷丸复合处理后达不到提高FF抗力的作用。先喷丸的试样在进行UBMS MoS2-Ti复合膜的过程中由于工艺温度高而降低了喷丸产生的表面残余压应力,因而其FF寿命不及单独喷丸试样。更多还原

【Abstract】 Poor tribological property and high susceptivity to fretting fatigue （FF） influence wide application of titanium alloy in aeronautical industry. It is important to improve FF resistance of titanium alloy by surface treatment techniques for developing advanced aero-engine. The behavior and mechanisms of FF of the titanium alloy at elevated temperature were investigated. Ion Beam Enhanced Deposition （IBED）, unbalance magnetron sputtering （UBMS） and thermal spraying techniques were solely employed or combined with shot peening （SP） to treat the titanium alloy surface in order to improve FF resistance of the alloy at high temperature. The main contributions are as follows:1. Delimitation is the character of FF damage of Ti811 titanium alloy at elevated temperature. The life of FF is changed non-monotonically 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. Creep is the important factor that influenced fretting fatigue failure process of Ti811 alloy at elevated temperature as creep deformation is easy and the plain fatigue property becomes poor under the high temperature conditions.2. IBED coating has high density, fine grain, low porosity and good bonding strength. The FF life of the IBED OCrl 8Ni9 coated specimens increases 66% of that of the base titanium alloy at 350"C, because the coating with higher hardness and high ductility improves the wear-resistant and plain fatigue resistance of the titanium alloy. However, IBED CuNi coating has not the good effect due to its low ductility and low adhesion strength to base materials.3. An increase in FF life of 78% was observed for specimens coated with UBMS MoS2-Ti at 350"C. This is due to the fact that the UBMS MoS2-Ti with good bonding strength lubricates Ti alloy surface and reduces surface stress at contact area and inhibits FF crack initiation and propagation.4. Co-WC coatings prepared by HVOF and plasma spraying techniques have high hardness and good wear-resistant. But those coatings can’t improve FF resistance of the titanium alloy at elevated temperature because of their low ductility.5. It relies on the properties of the surface coating whether SP and IBED coating can synergistically improve FF resistance of titanium alloy. IBED 0Cr18Ni9 has good bonding strength and ductility, therefore the coating can bear the shock of SP andsynergistic effect of improving FF resistance was realized by SP post treating IBED 0Crl8Ni9 coating. IBED CuNi coating combined SP hasn’t the synergistic effect as the coating is brittle. Because the process of UBMS MoS2-Ti coating reduces the residual compressive stress of the shot peened surface, the FF life of the duplex treated specimen by UBMS MoS₂-Ti and shot peening is shorter than that of shot peened one.更多还原