| High velocity oxy-fuel(HVOF)thermal spraying cermets coatings have been used widely in many fields which subjected to corrosion and abrasive wear,such as metallurgy,energy sources,construction industry as a result of their excellent abrasive wear resistance.It will be subjected to different forms of external force under the condition of service,which can cause various forms of damage and deformation.In this paper,the static pressure and multiple impact load were simulated by the indentation method and the falling ball impact respectively to study the deformation and damage of two kinds of thermal sprayed coatings.The following conclusions were drawn:The Knoop indentation method was used to test mechanical properties of the coatings.The results showed that the deformation resistance of WC-10Co4Cr coating was better than that of the NiCr-Cr3C2 coating under the condition of slow loading.And the deformation of the two kinds of coatings showed obvious directivity.Under the same load,the deformation and elastic recovery of coating surface and cross section of PP direction were significantly higher than those in section PV after unloading.It means that the PV direction has greater hardness and smaller elastic modulus.This was caused by the stress distribution on the Knoop indenter and the unique lamellar structure of the coating;The Vickers indentation method was used to test the hardness and depth of the surface of the carbide-based coatings under different loads.And based on the energy method,the relationship between the hardness and depth was discussed.The a value fitted by the experimental data which can be used to express the fracture toughness.The results showed that the a value of WC-10Co4Cr coating was significantly higher than that of the NiCr-Cr3C2 coating.It means the WC-10Co4Cr coating has a greater fracture toughness and smaller plastic deformation energy in compression.The stress distribution and deformation of the coatings were analyzed by means of Workbench.The results showed that the Knoop method had smaller pressure and deformation under the same load.Under high load used Vickers method,deformation and damage of the coatings has two aspects,one was the plastic deformation in the loading direction,mainly caused by Mises stress which was bigger than the yield strength,and the other was the brittle fracture around the indentation,mainly caused by shear stress which greater than the bonding strength.According to the concept of multi impact load,an experimental device was developed.The ball impact test was carried out by using this device to test the impact resistance of the two kinds of carbide-based coatings.The results showed that the coating thickness and its impact resistance was positively correlated,impact resistance of WC-10Co4Cr coating was lower than that of NiCr-Cr3C2 coating.Damage and crack propagation behavior of the coating under multiple impact loads were discussed based on the impact dynamics analysis of the deformation,it showed that the difference of impact resistance of the coatings with different thickness and different materials was due to the difference of the wave impedance.ANSYS Workbench explicit dynamic analysis module was used to simulate the falling ball impact behavior of coating to solve the impact load stress distribution under the surface of the coating,the results showed that under the single impact the stress was far less than the yield strength of the coating,but the residual stress was still existed in coating after impacting;The impact speed and energy-time curve were calculated by Autodyn,the results indicated that the speed change of reciprocating under a single impact and final attenuation to zero,but the internal energy was still stored in the coating after unloading.The simulation results were in good agreement with the theory of stress wave attenuation and energy absorption. |
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