表面粗糙度對鈦合金超高周疲勞性能的影響
發(fā)布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新時間：2016-03-03
采用自行研制的超聲疲勞實驗裝置, 研究不同表面粗糙度下 Ti-6Al-4V 合金的超高周疲勞性能.
表面粗糙度對鈦合金超高周疲勞性能的影響EFFECT OF SURFACE ROUGHNESS ON VERY HIGH CYCLE FATIGUE?BEHAVIOR OF Ti-6Al-4V ALLOY采用自行研制的超聲疲勞實驗裝置, 研究不同表面粗糙度下 Ti-6Al-4V 合金的超高周疲勞性能. 結(jié)果表明, 當表面凹痕寬深比 a/c (a 為凹痕寬度, c 為凹痕深度)在 2~10 之間時, Ti-6Al-4V 合金的臨界凹痕深度在 0.49～1.10 μm 之間. 當表面凹痕深度小于臨界深度時, 表面粗糙度對 Ti-6Al-4V合金的超高周疲勞性能沒有影響. 當表面凹痕深度大于臨界深度時, Ti-6Al-4V 合金疲勞壽命隨表面粗糙度的增加而下降, 并且隨著循環(huán)周次的增加,?Ti-6Al-4V 合金疲勞性能對表面粗糙度的敏感性下降. 隨著表面粗糙度的增加, Ti-6Al-4V 合金超高周疲勞裂紋的萌生方式發(fā)生變化. 超高周疲勞裂紋源有由 1 個向多個、由內(nèi)部向次表面轉(zhuǎn)移的趨勢; 當表面凹痕深度增加到一定程度后, 在超高周疲勞壽命區(qū)間, Ti-6Al-4V 合金疲勞壽命隨粗糙度的增加而大幅下降. 疲勞裂紋全部從合金表面凹痕根部處萌生, 沒有內(nèi)部萌生的情況.?
Ti-6Al-4V alloys are widely used in aero engine blades for their unique properties, such as high?specific strength, high specific stiffness and high fatigue strength. Aero engine blades usually suffer a variety of?cyclic loading during the period of services, which finally results in fatigue failure. Fatigue life of materials is?known to highly depend on the surface quality. Consequently, more and more researches about the influence of?machined surface roughness on the fatigue behavior of materials have been carried out in the last decades.?However, there are less relevant results about the relationship between surface roughness and very high cycle?fatigue (VHCF) properties of Ti-6Al-4V alloy. To investigate the effects of surface roughness on fatigue properties?of Ti-6Al-4V under very high cycle fatigue regimes, ultrasonic fatigue tests were conducted at the conditions of?20 kHz and stress ratio R=-1 at room temperature in air. During ultrasonic fatigue testing, each specimen was?water-cooled. The specimen surfaces were cut and grinded which gave different surface roughness. The surface?roughness was characterized using profilometry. In order to explain the high dependence of stress-fatigue life (S-N)?curves on the surface roughness, an approach based on the finite element analysis of measured surface topography?was proposed. The results show that the VHCF property of Ti-6Al-4V alloy was significantly affected by surface?roughness. The critical flaw size was 0.49~1.10 μm when the ratio between spacing and height of circumferential?grooves was between 2~10. When surface roughness was smaller than the critical flaw size, surface roughness?exerted no influence on fatigue life. While surface roughness was greater than critical flaw size, fatigue life?decreased with increasing surface roughness. Surface roughness played a more important role in long life regime?than that in VHCF regime in which with the growth of surface roughness, the crack initiation site changed from?single one to two or more ones, as well as changed from inside to subsurface. When the surface roughness was?large enough, all cracks initiated from surface even in super long life regime.?
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