| γ-TiAl alloy has the advantages of low density and high strength,which is a promising aero-engine component manufacturing material.However,γ-TiAl alloy has"titanium fire"failure under certain conditions,which can cause serious accidents.In view of the above problems,this paper proposes a method for preparing NiCr/YSZ multiple coating on the surface ofγ-TiAl alloy and studies its preparation process,composition and structure.At present,there is no unified test standard and method for flame retardant performance at home and abroad.Based on the oxidation and friction factors of"titanium fire",this paper studies the high temperature oxidation resistance and friction and wear resistance of NiCr/YSZ multiple coating.On this basis,the laser ablation test method is used to explore the flame retardancy performance of NiCr/YSZ multiple coating.In this paper,the NiCr alloy layer was prepared by double glow plasma surface metallurgy technology,then the YSZ coating was prepared by multi-arc ion plating technology.The thickness of NiCr/YSZ multiple coating with metal droplets on the surface of it was about 21μm,of which the YSZ coating was about 13μm and the NiCr alloy layer was about 8μm.The XRD showed that the surface of NiCr/YSZ multiple coating was composed of t-Zr O2.The microhardness test showed that the average microhardness of the surface ofγ-TiAl was 299.71HV0.1 and that of NiCr/YSZ multiple coating was 872.56HV0.1.The thermal shock test showed that when the number of thermal shocks was48,the peeling area of NiCr/YSZ multiple coating was about 5%,indicated that the thermal shock resistance was well.The isothermal oxidation tests were used to study the high-temperature oxidation behavior ofγ-TiAl and NiCr/YSZ multiple coating at 850℃,950℃and 1050℃.The results showed that the oxidation kinetics ofγ-TiAl and NiCr/YSZ multiple coating at different temperatures were approximately parabolic.During the oxidation process,a mixed oxide film of Ti O2 and Al2O3 with loose structure was formed on the surface ofγ-TiAl.The oxidation product of NiCr/YSZ multiple coating at 850℃and 950℃was t-Zr O2,and that of NiCr/YSZ multiple coating at 1050℃was t-Zr O2and a small amount of Ti O.A TGO layer（Thermally Grown Oxide layer）was formed between YSZ coating and NiCr alloy layer.The NiCr/YSZ multiple coating can effectively block the diffusion of oxygen into interior ofγ-TiAl at high temperatures,which was beneficial to prevent the occurrence of"titanium fire".The friction and wear behavior ofγ-TiAl and NiCr/YSZ multiple coating under different loads and temperatures were studied by friction and wear tests.Under different loads at room temperature,the wear mechanism ofγ-TiAl was abrasive wear and the wear mechanism of NiCr/YSZ multiple coating was slight adhesive wear.At 500℃,the specific wear rate ofγ-TiAl was 0.2773mm3·N-1·m-1and the wear mechanism was abrasive wear and oxidation wear;the specific wear rate of NiCr/YSZ multiple coating was 0.1839mm3·N-1·m-1 and wear mechanism of it was adhesive wear and oxidative wear.The results showed that the NiCr/YSZ multiple coating can act as a lubricant during the friction process,which was beneficial to reduce frictional heat.The anti-ablation performance ofγ-TiAl and NiCr/YSZ multiple coating was studied by continuous laser ablation tests.The ablation morphology ofγ-TiAl included melting condensation region and thermal activation region;the ablation morphology of NiCr/YSZ multiple coating included ablation pit and heat affected zone.As power increased,“petal”-like cracks and conical protrusions appeared on the surface ofγ-TiAl in turn;the YSZ coating changed from a mesh to a ring shape,and depth and width of the ablation pits gradually increased.But the YSZ coating was still attached to the surface of ablation pits with had good protection forγ-TiAl. |
