Study On The Micro-cracks In Fretting Wear Of Ti-6Al-4V Titanium Alloy

Ti-6Al-4V titanium alloy is the earliest,used largely and fully functional old titanium alloy,which is widely used in engine fan,compressor disc and blade.However,due to poor wear resistance of Ti-6Al-4V titanium alloy,various forms of fretting wear often occur in the actual engineering application,which restrict the use of the product performance,.in view of this,fretting wear of titanium alloy Ti-6Al-4V was investigated,the main research contents are as follows:(1)The fretting wear test of Ti6Al4 V titanium alloy and friction GCr15 steel was carried out by SRV fretting wear testing machine.In present study,three experiments were designed.The test group?and test group?were carried out under the same frequency,different loading levels and displacements in the air.While the test group III was tested under the same experimental parameter with the test group II but in the corrosive medium 3.5% Na Cl solution.By analyzing the friction coefficient curve,surface wear morphology and wear profile of the test,the initiation and propagation of microcracks in Ti-6Al-4V titanium alloy were studied emphatically and the main wear mechanism of fretting wear was discussed.(2)The change of friction coefficient indicates the change of the fretting wear process.By comparing with the friction coefficient curves of the three experiments,the results show that the friction coefficient curves of the three experiment change on different times and can be divided into three stages of run-in period,adhesive wear period and stable period.Different stages of fretting wear behavior is different.test?in the process of fretting wear was by the role of strong adhesion and test ?in the process of fretting wear produced a lot of debris,while test ? in the process of fretting wear was influenced by corrosion wear and Fretting wear together.(3)Compared with the friction coefficient curves between test group?and test group?,test group test ? and test group ?,respectively,results demonstrate that strong adhesion will aggravate the wear and tear between the contact surfaces and a large number debris after fragmentation and oxidation could reduce wear between contact surfaces.The corrosive medium Na Cl solution plays a good role of lubrication in the fretting wear.(4)The profile of specimens were observed by JSM6700 F field emission scanning electron microscopy and the SEM micrographs of three experiments were analyzed.Conclusions can be drawn from SEM photograghs of experiment ?andexperiment ?analyses: The fretting zone of test?and test? can be divided into abrasive layer,sub-surface layer and friction transition layer(TTS).The Z-type cracks were seen in the abrasive layer;micro-cracks in the sub-surface layer appear parallel to the surface or perpendicular to the surface.A certain angle of micro-cracks with the sub-surface was observed.in the TTS of the test II's sub-surface layer.The TTS is characterized by high hardness and high brittleness.The crack propagation rate is very fast.Once the crack occurs,the crack will expand rapidly.The formation of TTS is affected by the fretting wear load,displacement of two parameters and the thickness of the TTS becomes thicker as the load and displacement increase.Due to the combined effect of corrosion wear and fretting wear,the corrosion pits with depth of 10 ~ 20?m can be seen in the SEM view of the wear profile of test ?.(5)The surface wear morphology was observed with an optical microscope(OLYMPUS-GX51)and analyzed.Furthermore,combined with the friction coefficient curve and the wear profile of the three experiments,we can obtain that the main wearing mechanism of the experiment ?is fatigue splitting and the main wearing mechanism of the experiment ? is fatigue spitting,and abrasive wearing,while the main wearing mechanism of experiment? is abrasive wear and corrosion wear.