| Q235 steel is a kind of carbon structural steel which belongs to medium and low-strength steel with good toughness.It has been widely used in various essential steel frame structures such as oil and gas resource gathering line and grinding.With the increasingly complex and harsh environment,the performance requirements of metal materials such as Q235 steel are gradually improved,especially in terms of wear and corrosion resistance.As a surface modification technology,electroless plating can improve the surface properties of materials,and has the advantages of simple operation,low price,no restrictions on the type and size of plated parts,gradually has become an important branch of surface treatment technology.Compared with the conventional Ni-P binary plating layer,the composite electroless plating layer prepared by adding the second-phase ultrafine particles to the plating solution,such as SiC,has more excellent comprehensive properties.However,the agglomeration of ultrafine particles,such as nano and sub-micron particles,is very serious due to the large specific surface area with high surface energy.It is difficult to achieve uniform dispersion in the plating solution.Low-temperature plasma technology is a new type of surface treatment method,which generates a large amount of active plasma,such as high-energy electrons,positive and negative ions and free radicals with strong oxidizing properties,to achieve grafting,modification and purification of the surface of the substrate.In order to further optimize the preparation process of electroless process and improve the uniform dispersion of the second phase particles in the plating solution,the micro-hardness is used as the evaluation index,the plating time is 2h,and the temperature,pH and SiC are optimized by orthogonal experiment.Three factors,such as the amount of addition,on the basis of comparative analysis of the wear resistance and corrosion resistance of the coatings obtained by different processes have been adjusted and optimized.The influence of heat treatment conditions on the structure and performance of the composite coating were analyzed.And then,the sub-micron SiC particles were modified to improve the dispersion in the electroless plating solution by low temperature plasma equipment with adjusting the working power and processing time.The structure of the chemical composite coating obtained by using the modified SiC particles was investigated,and the influence of heat treatment process to micro-hardness,wear resistance and corrosion resistance was investigated.The results obtained were as follows:1)Using the micro-hardness as the evaluation index,the three-factor and three-level orthogonal test method is used to determine the influence of the micro-hardness on the electroless plating layer as pH>temperature>SiC addition,and comparatively analyze the Ni-P layer and the composite coating obtained by other different conditions.The micro-hardness of the composite coating is up to 558HV0.1 at the temperature of 90?,pH 5,SiC addition of 6g/L.The surface of the coating is relatively flat,the thickness is about 18?m,and the interface with the substrate is clear and well combined.The wear resistance and corrosion resistance are the best,and the volume wear rate and self-corrosion current density are 1.73 × 10-4mm3·N-1·m-1 and 1.092?A/cm2,respectively.The micro-hardness of the electroless plating composite coating is further improved by holding at different heat treatment temperatures(200-800?)for 1 hour.After heat treatment at 400?,the hardness of the coating is up to 932.3 HV0.1 due to the coating crystallization and more Ni3P phase appears.It has been identified by XRD test.Also the cross-section of the plating layer and the interface of the substrate are blurred,and the uniformity of the thickness is deteriorated.Compared with that of before heat treatment,the average friction coefficient of the treated sample is reduced by 45%,and the wear resistance is improved.However,due to the poor flatness of the surface of the coating,partial cracks are generated,which affects the compactness of the coating and leads to a decrease in corrosion resistance.2)The sub-micron SiC particles were modified by low temperature plasma technology.The sedimentation test showed that the dispersion of the particles was best under the treatment conditions of 120W and 300s.The average particle size was 0.234?m and the Zeta potential value was-8.8mV.Infrared and XPS analysis showed that there were C=O and C-O groups on the surface of the modified SiC particles.SEM observation showed that the modified SiC particles were more evenly distributed.3)Two sets of optimized plating parameters was selected to prepare composite coatings by adding modified sub-micron SiC particles.The morphology,element distribution and micro-hardness of the coating were compared and analyzed.It was found that the surface morphology of the modified coating did not change significantly.EDS analysis showed that the surface Si content was improved,which may be due to the homogeneous dispersion of SiC in the coating obtained after modification.In addition,the increasing degree of the thickness and micro-hardness of the coating was not apparent.The friction test results show that the average friction coefficient of the modified coating is reduced by about 18%,and the surface of the wear scar has a grinding pit and a small amount of ploughing,which may be caused by the SiC particles falling off and the extraction during the wear process.EDS and XPS analysis showed that partial oxidation occurs on the surface of the coating and oxides of Ni are formed,and the Cr content on the surface of the coating is very low.There is no obvious element transfer phenomenon to the grinding pair(GCrl5 steel ball).The wear mechanism is mainly abrasive wear and friction oxidation.Corrosion test results showed that the corrosion resistance of the composite coating after SiC particle modification is better than that of the unmodified Ni-P/SiC composite coating.After holding at 400? for 1 hour,the micro-hardness and wear resistance of the SiC modified chemical composite coating are further improved.The micro-hardness is about 945HV0.1 and the volume wear rate is 0.60 ×10-4mm3·N-1·m-1. |
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