| Solid particle erosion wear is an importantreason for materials failurein some engineering applications,such as the fields ofaviation,aerospace,energy,machinery,and metallurgy.Especially,with the rapid development of high-tech fields,such as aeronautics and astronautics industry,the traditional materials is difficult to meet the requirements of anti-sand erosion.One of the effective ways to solve this problem is to prepare the protective coatings on the surface of engineering components by vapor deposition technology.The hard films applied in aero engine compressor has been reported by some groups in overseas.But in our country,the related research starts late and is not systematic.In particular,the anti-sand erosion behavior and the failure mechanism of the hard films is not clear,and the influence of the hard films on the substrates' fatigue properties is ambiguous.In the current work,Ti-Ti N-Zr-Zr N anti-sand erosion multilayers withalternate soft and hard layers were prepared by cathodic arc ion plating.The microstructure,residual stress and other mechanical properties of the multilayers were studied.The results are summarized as follows: 1)For the multilayers with the same thickness,as the cycle number increases,the thickness of every layer becomes thinner.Meanwhile,the surface quality,hardness,adhesion and anti-sand erosion of the multilayers improve,and the residual stress of the multilayers decreases.With RTi/Ti N:RZr/Zr N ratio in the films decrease,the residual stress tends to be increased,and the multilayers' hardness increases slightly;however,the adhesion of the film to substrate decreases,and the variation of anti-sand erosion performance is not obvious.If we augment RMe:RMe N ratio in the films,the films' hardness decreases,and the films' adhesion as well as the anti-sand erosion performance remain almost unchanged.The optimized parameters of Ti-Ti N-Zr-Zr N multilayers include: the thickness of every layer for each modulation cycle of about 200~300 nm,RMe:RMe N=1:6,RTi/Ti N:RZr/Zr N=2:1.As the thickness of the multilayers increases,the residual stress increases slightly,and the adhesion also increases.When the film thickness reaches a certain value(for example,7.54?m in this work),the films' hardness keeps stable above 30 GPa.2)The anti-erosion ability of the substrate can be effectively strengthened by Ti-Ti N-Zr-Zr N multilayers.With increasing the thickness of the multilayers,their ability of anti-sand erosion improves.The protective effect of multilayers at lower impact angle(30°)is much better than that at higher impact angle(90°).The erosion failure mechanism of TC11 titanium is typical plastic erosion.At low impact angles,plowing or cutting erosion plays a dominate role.But at high impact angles,fatigue fracture peeling caused by plastic deformation turns to be more important.The erosion failure mechanism of multilayers is the coating surface begins to crack in stress concentration areas.The cracks longitudinally extended to soft metal layer,where they can be partly cushioned and absorbed.Then,the cracks extend laterally along the interface between layers.When the cracks connect with each other,the coating will be separated from the multilayers in a sheet form along the interface of each layer.Based on the facts presented above,the sand erosion failure mechanism of the soft and hard alternative multilayers is established in this work.3)After 50 cycles of heat shock at 300? and 500?,the Ti-Ti N-Zr-Zr N multilayers are unimpaired.No crack,bubbling or spalling is observed.Only the films coloration little changes due to the surface oxidation,and few particles fall off from the surface of the multilayer.It implies that the multilayers can effectively protect the substrate under this condition.After 10 cycles of heat shock at 600?,the top layer of the films is powdered by oxidation and delaminated due to the crack propagation.Then,the films becomes ineffective.After 50 cycles of heat shock at 600 ?,Ti-Ti N-Zr-Zr N multilayers with a thickness of 10?m are completely ineffective,while Ti-Ti N-Zr-Zr N multilayers with a thickness of 20?m still work.Consequently,the using temperature of Ti-Ti N-Zr-Zr N multilayers are less than 500? in our experimental conditions.4)The fatigue limit of TC11 sample increases about 6.8%,from 440 MPa to 470 MPa,after coating with Ti-Ti N-Zr-Zr N multilayers.The stress-fatigue life relationship(S-N curve)shows that,when the stress is lower than 570 MPa,the fatigue life of TC11 sample is improved by coating multilayers;however,when the stress is higher than 570 MPa,the fatigue life of TC11 sample is reduced by coating the multilayers.For TC11 substrate,the cracks originate from the surface defects of the sample,and the number of the crack sources increase with increasing the stress level.The fracture mode of TC11 sample is ductile and cleavage mixed fracture.After plating multilayers,the films cover the surface defects of TC11 substrate.When the stress is less than 570 MPa,the coating sample has only one kind of crack source, and the multilayers with soft and hard alternating modulation structure can alleviate the crack propagation,thus increasing the fatigue life of the sample.As the stress level exceeds 570 MPa,the coating samples have multiple crack sources,and the multilayers were severely damaged,thereby reducing the sample's fatigue life.In addition,the fracture mode of Ti-Ti N-Zr-Zr N/TC11 sample is also ductile and cleavage mixed fracture.5)Under the same technological conditions,the surface roughness of the substrate has a significant influence on the properties of the Ti-Ti N-Zr-Zr N multilayers.Overall,low surface roughness of the substrate is benefit for improving the performance,such as adhesion,anti-sand erosion and salt spray resistance,of the multilayers.The optimal performance of Ti-Ti N-Zr-Zr N multilayer can be achieved in the condition of the surface roughness of the substrate lower than 0.4 ?m. |
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