| 316L stainless steel is a classic18Cr-8Ni composite-modified alloy, and it is acorrosion resistant austenitic stainless steel. Because of its excellent corrosionresistance and high temperature mechanical properties, it has been widely used inmaking marine engineering equipment、 petroleum pipeline、 valve、 heatexchanger and medical instruments. Laser cladding technology is a rapidlydeveloped technology, which could improve the properties of metal surface. Thecladding powders which are pre-set on the metal substrate can be fused by the high-energy laser beam, then obtain cladding layers of low dilution rate and excellentmetallurgical combination due to cooling solidification. The layers not only canimprove the micro-hardness、 wear-resistance and corrosion-resistance,but alsorepair metal parts and extend their working life.This study is based on the Developing Project of Longwan District, Wenzhou,whose task is laser cladding316L stainless steel to improve its micro-hardness、wear-resistance and corrosion-resistance. Therefore, Co-based coatings were lasercladded on the surface of316L stainless steel by semiconductor laser.Themacroscopic cracks、 microstructure、 micro-hardness、 wear-resistance andcorrosion-resistance were investigated.Meanwhile, adding different contents of rareearth oxides，CeO2and Y2O3， to the Co-based powders. Properties of the layers oflaser cladding this composite powder were also investigated. The properties of theoptimal composite laser cladding layers of different rare earth oxides were comparedwith the layers without addition. Then the two optimal composite laser claddinglayers were compared with each other. The results show that the laser cladding coating consists of the cladding layer,the bonding layer with the substrate and the heat affected zone in the substrate.Themicrostructure is dendrites structure and grain in cladding layer and flat crystalstructure in bonding layer. The Co-based layer and composite layers mainlyconstituted by the same phases CoCx、Fe0.3Mn2.7C and Cr23C6.From the SEMphotographs we can see that in the cladding layers there are air holes, which is less inthe composite layer of adding1.5%CeO2. The EDS results shows that rare earthelements disperse uniformly when it is map scanning on the cross section ofcladding layer and when it is point scanning,rare earth elements appear on andbetween the dendrites and the contents are almost the same. When the laser scanningspeed is6mm/s, the coating appears the least macroscopic cracks, which are surfacecracks proved by microstructure observation. The micro-hardness of laser claddingcoating,468.3HV0.2, is about twice the micro-hardness of substrate,236.3HV0.2.The figures of weight of grinding loss and polarization curves showedthat the laser cladding coatings are more wear-resistant and corrosion-resistant.Theoptimal adding contents of CeO2and Y2O3are1.5%and1.0%, respectively. Due tothe purification and refinement of appropriate content of CeO2and Y2O3,the cracksalmost disappear and the microstructure became more compact. The micro-hardnessof laser cladding coatings of adding1.5%CeO2and1.0%Y2O3are554.6HV0.2and502.9HV0.2, increased by86.3HV0.2and34.6HV0.2respectively compared withCo-based laser cladding coating. The weight of grinding loss is about half of Co-based laser cladding coating and corrosion potential has a positive movementobviously, which shows the wear-resistance and corrosion-resistance improvedgreatly. And the effect of adding1.5%CeO2on the micro-hardness、wear-resistanceand corrosion-resistance of laser cladding coatings is better than that of adding1.0%Y2O3. |
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