| As an indispensable material for aero-engines,sealing coating is located on the box of turbines and compressors of the engine,the position and function determine that it should work under the conditions of high temperature and high-speed airflow.It is very important to study performance variation of the wearable sealing coating under the thermal cycling condition because high proportion of the coating may loss after used more than once in aero-engine.In this paper,the nickel-graphite（Ni-C）coating and aluminum-silicon（Al-Si）coating were prepared respectively on TC11 alloy and stainless steel by plasma spraying（PS）.The micromorphology and phase changes of the two seal coatings after 100-500thermal cycles at 200-400℃were analyzed.The friction and wear mechanism of Ni-C and Al-Si coating at different test temperature(Ttest)were studied by using GHT-1000 high-temperature vacuum friction and wear tester.The effects of temperature and cycle number on the abrasion property of coatings were obtained.Moreover,the abrasiveness of Al-Si coating was tested by blade material scraping and wear test.The main research contents are as follows:（1）X-ray diffractometer（XRD）and scanning electron microscope（SEM）were used to characterize the microstructure and phase of the Ni-C and Al-Si coating before and after thermal cycling.The experimental results show that the PS-Ni-C/Al-Si coatings have compact microstructure.The Ni-C coating mainly contains C,Ni and Ni O phase,while the Al,Si and Al2O3 phase mainly exist in the Al-Si coating.The content of C and Al2O3 phase directly affects the sealing effect of the coatings.（2）Friction and wear properties of Ni-C coatings at room temperature（RT）to 400℃were investigated.The results show that the friction coefficient（FC）of Ni-C coating decreases firstly and then increases with the increase of thermal cycle temperature（TH）.With the increase of thermal cycle（N）,the FC decreases first,then increases and finally decreases gradually.The wear mass loss（ML）of Ni-C coating increases first and then decreases with the increase of TH.The Ni-C coating with N=300,TH=400℃have great ML which presumed that the coating has considerable flaws.The main wear mechanisms of the as-received Ni-C coating at RT is abrasive wear and lubricating of graphite.The Wear mechanism at Ttest=100℃involves adhesion and abrasive wear.Fatigue wear is the main wear mechanism at Ttest=200℃.It is speculated that the main wear mechanism is adhesive wear at Ttest=300℃,accompanied by the initial stage of fatigue wear.The wear mechanism at Ttest=400℃includes oxidation,adhesion and slight abrasive wear.Wear mechanism of Ni-C coating after different N at TH=300℃,Ttest=200℃was studied:abrasive wear accompanied by graphite phase’s adhesion is the main mechanism after N=100/200.The wear mechanism after N=300/400 are typical abrasive wear,after N=500are adhesion,initial stage of fatigue and oxidative wear.The wear mechanisms of Ni-C coating after different N at TH/Ttest=300℃:after N=100/200,the lubrication of graphite is the main wear mechanism.The wear mechanism after N=300 includes oxidation,fatigue and slight abrasive wear.After N=400/500,the main wear mechanism is the crack propagation stage of fatigue wear,with abrasive and oxidation wear.（3）Friction and wear properties of Al-Si coatings at room temperature（RT）to 400℃were investigated.The results show that the average CF and ML of Al-Si coating are least at TH=300℃.The wear mechanisms of the as-received Al-Si coating at different Ttest is as follows:fatigue wear of extrusion phase at Ttest=25,100,200℃while add abrasive wear at Ttest=300 and 400℃.The wear mechanism of the Al-Si coating after different N at TH=300℃,Ttest=200/300℃is as a joint result of abrasive,oxidation and fatigue wear.The blade-scraping and wear test of Al-Si coating was carried out at RT to 400℃,which shows that the Al-Si coating material has excellent wearability. |
