Study On The Preparation And Formation Mechanism Of High Wear Resistance Composite Coating On The Steel

Steel is an important materials for the preparation of mechanical friction parts. The new technology that is the preparation of the high wear resistance and self-lubricating coating on steel surface has wide application value. Nano-particle reinforced electroless composite plating as a kind of excellent surface treatment technology is one of the advanced technologies in the research field of material surface, owing to the simple technic, homogeneous coating, the special composite structure, and the excellent coating properties. On the basis of the study on the electroless Ni-P coating, this dissertation studied the preparation of electroless multi-composite coatings with different functions Ni-P-SiC、 Ni-P-SiC-Al2O3and Ni-P-SiC-Al2O3-PTFE. The new technology of the preparation of the coating on45#steel surface with the high wear resistance has been got, through component design of coating, fabrication process of composite plating and the related mechanism research, so as to meet the needs of actual production.The morphology, microhardness, microstructure, wear resistance and formation mechanism of the samples were studied carefully by Metallographic microscope, Scanning Electron Microscope, Micro-hardness tester, X-ray diffraction and Friction-Wear tester. The results show as follows:The optimized dispensation of electroless composite plating through the experiments are showed as follows:NiSO425g/L, NaH2PO230g/L, CH3CH(OH)COOH25ml/L, CH3COONa15g/L, C2H5NO23g/L, CH4N2S3-5mg/L; pH=4.8, the temperature is88±2℃; The addition of nano-SiC was6g/L and nano-Al2O3was3g/L, the addition of PTFE emulsion was10ml/L. Using the optimized technology, the Ni-P-SiC-Al2O3-PTFE composite coating with nano-SiC and Al2O3enhanced, PTFE antifriction of high wear-resistant and low coefficient on the45steel surface was successfully prepared.The prepared coating of Ni-P、Ni-P-SiC、Ni-P-SiC-Al2O3and Ni-P-SiC-Al2O3-PTFE after plating was non-crystalline, the hardness were followed by572HV,649HV,726HV and 560HV. The coatings were converted from non-crystalline to crystalline by heat treatment and the hardness was increased obviously. Thus the optimized heat treatment parameter of Ni-P-SiC-Al2O3-PTFE composite coating was350℃for one hour when the hardness can be relatively achieved up to967HV and will not damage PTFE in the coating. So Ni-P-SiC-Al2O3-PTFE composite coating showed a perfect synthesis property.In the Ni-P-SiC-Al2O3-PTFE multiple composite coating, SiC and Al2O3particles and nickel-phosphorus coating form a complex phase through composite deposition. The hard particles greatly enhance the hardness and wear-resistance property of the coating. The PTFE particles have good property of self-lubricating. When the composite coating rubbing together with a counter-body, PTFE will spread on the coating surface through its layer delamination and form a lubricating membrane. So friction coefficient of composite coating was reduced. Co-action of both particles caused the Ni-P-SiC-Al2O3-PTFE coating to have an increase in wear resistance and self-lubricating performance.The prepared coating of Ni-P、Ni-P-SiC、Ni-P-SiC-Al2O3and Ni-P-SiC-Al2O3-PTFE grew in layer mode. Nano-particles were dispersed in composite coating equably, which greatly improved wear resistance performance of the coatings.