Study On Erosion Resistance Of CrAlN/CrAl Coating On TA15 Alloy Surface

TA15 alloy is a structural material with excellent performance and is widely used in aero engines.However,when the aircraft is flying in low altitude and sandy areas,the engine will inevitably inhale fine sand particles,which will cause relatively severe erosion wear on the engine compressor blades.The development and application of TA15 alloy is limited due to its low hardness and weak erosion resistance.Therefore,it is an urgent problem to improve its erosion resistance.In this experiment,a CrAlN/CrAl hard coating was prepared on the surface of TA15 alloy by magnetron sputtering to improve the erosion resistance of TA15 alloy,and the mechanism of erosion resistance was studied.By preparing coatings with different Ar/N₂ flow ratios and different sputtering times,the best process parameters are obtained by comprehensive research:Ar/N₂ flow ratio is 1;RF power during sputtering is 230 W;working pressure parameters is 0.5 Pa;the CrAl layer deposition time is 60 min;the CrAlN deposition time is 180 min;and the distance between target and substrate is 20 mm.The morphology,composition,and phase structure of the CrAlN/CrAl coating were analyzed by SEM,EDS,and XRD.The mechanical properties of the coating were studied using nanoindentation,scratch test,and friction and wear experiments.The erosive wear resistance and erosive mechanism of CrAlN/CrAl coatings under different number of erosion particles,different erosion speeds and different erosion angles were studied.The results showed that:(1)The thickness of the CrAlN/CrAl coating prepared under the optimal process parameters is 10.65?m,of which the CrAl layer is 5.07?m and the CrAlN layer is 5.58?m.The results of EDS composition analysis showed that the content of Cr,Al and N in the coating accorded with the stoichiometric ratio of nitrides.XRD diffraction results showed that the phases of the coating were mainly Al N,Cr₃Al₇N and Cr₂N.The average nano-hardness of the coating is 26.45 GPa and the average elastic modulus is 215.33 GPa,which is about 9 times higher than the substrate hardness of3.14 GPa.The nano-hardness of the coating first increases and then decreases with increasing Ar/N₂ratio.The adhesion strength of the CrAlN/CrAl coating and the substrate is 84.2 N,which is five times than that of the single-layer CrAlN coating(16.8 N).The friction and wear coefficient of the CrAlN/CrAl coating is 0.55.Its wear scar is narrow and shallow.(2)The erosion rate of CrAlN/CrAl coating and TA15 substrate both increased first and then decreased with the increase of erosion sand mass.The erosion threshold of the coating was 80 g,which was double the substrate threshold.The maximum erosion rate of the substrate is 0.006 mg/g,and the maximum erosion rate of the coating is only 0.00182 mg/g.Therefore,the coating significantly improves the erosion resistance of the substrate.The surface of the substrate after erosion was analyzed by EDS and XRD to find the existence of phases such as TiO,TiO₂ and Ti₆O.Under different erosion angles,the erosion rate of the substrate and the CrAlN/CrAl coating increased significantly with the increase of erosion speed,and erosion wear became more serious,and the erosion rate of the coating had a linear relationship with the erosion speed.With the increase of erosion angle,the erosion rate of TA15 alloy gradually decreased,and the maximum value was 0.005 mg/g when the erosion angle was15°.The erosion rate of CrAlN/CrAl coating slowly increased with the increase of erosion angle,and reached a maximum value of 0.001 mg/g when the erosion angle was 90°.At low erosion angles,the main effect of particles on the substrate is cutting,and the cutting marks and plow marks on the substrate are more obvious.At high erosion angles,the main effect of particles on the coating is hammering,which could cause pits or breakage of the coating at defects such as cracks in the coating.