| Tantalum-tungsten alloy is a high-melting-point alloy with well corrosion-resistant and is widely used in complex and harsh environments in aerospace,defense equipment,and other fields.When the tantalum-tungsten alloy is used as connectors with specific structure and function,it is unavoidable that the relative friction between the connector and the equipment.However,the connector's service effect is seriously affected by the low hardness and the poor wear resistance of the tantalum-tungsten alloy.To improve the service performance of tantalum-tungsten alloy in friction and wear environment,micro-arc oxidation(MAO)technology was used to fabricate a hard and wear-resistant coating on the tantalum-tungsten alloy,and its tribological properties were studied in the detail.The main innovative research and results of the study are as follows:(1)The MAO process of Ta-12W alloy was optimized in different electrolyte systems using Ta-12W alloy as the matrix.Compared with ethylene diamine tetraacetic acid(EDTA),the improvement of the MAO coating's morphology,structure,and hardness is more significant by NaF.The dissolution of Ta is promoted by the F-in the electrolyte,and loose nodules fall off from the MAO coating surface,causing the decrease of the nodule and the increase of the dense structure.EDTA promotes the detachment of nodules from the MAO coating surface by forming metal complexes with Ta.With NaF as an additive,the proportion of nodule area on the MAO coating surface decreases from18%to 4%,and the hardness increases to about 1300 HV.In addition,wear polishing occurs on the C-NaF coating surface applied the load of 2 N.(2)Referring to the surface texture technology,a surface texture-like MAO coating with high porosity(23.8%)and high hardness(1400 HV)was prepared on the Ta-12W alloy with NaF and NaOH as the adjustment agents.NaF contributes to the formation of big pores and oversized pores,while NaOH promotes the formation of middle pores.When the concentration of NaOH in the electrolyte is higher than that of NaF,the morphology of surface texture-like pores is primarily affected by NaOH,and the proportion of middle micropores amount is significantly increased.Conversely,the morphology of surface texture-like pores is primarily affected by NaF,and the ratio of big pores and oversized pores is dramatically promoted.(3)The MAO-PTFE composite coating,which showed a low friction coefficient(0.05-0.1),low wear rate(10-5),and high load capacity(50-70 N),was prepared by combining the MAO coating with PTFE material.PTFE material is directly stacked on the MAO coating surface with low porosity,resulting in poor bonding strength.However,PTFE material penetrates and is stored in the interior of the MAO coating with high porosity,forming an intermeshing structure and well-bonding strength.The exposed MAO coating has a high hardness value and is regarded as the“armor”of the MAO-PTFE composite coating.The“armor”provides space and physical support for the PTFE lubricating layer in the friction process,protecting the soft PTFE material and reducing its wear rate.As the“armor”is damaged under a high load,the PTFE material hidden in the pores is extruded and transferred to the point of contact,to offer continuous lubrication. |
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