| Titanium alloy has many advantages such as high corrosion resistance and low density,but its application is constrained by the price.Stainless steel has excellent mechanical properties,is inexpensive and widely used,but has poor corrosion resistance and high density.Combining the excellent properties of titanium alloys with the low price of stainless steel can significantly reduce the weight of components and save costs while meeting performance requirements,but the metallurgical incompatibility between them makes the combination face many challenges.The metal additive manufacturing technology has brought a new direction for thinking about dissimilar material joining,among which laser melting deposition(LMD)has become the preferred method for dissimilar material joining due to its small heat-affected zone and high material and process flexibility.This work uses TC4 alloy and 316 L stainless steel as raw materials,mixes the two powders in five ratios of ball milling,and deposits a layer of 316 L stainless steel on 304 stainless steel substrate by laser melting deposition process,and then deposits a layer of mixed powder to study the effect of different powder composition ratios on the element distribution,microstructure morphology,crack defects and material corrosion resistance at the interface of 316 L stainless steel and mixed powder deposition layer.Multi-layer experiments with 316 L stainless steel and composition of 90% 316L+10%TC4 were conducted first,and the effects of laser power,scanning speed,powder feeding rate and lap rate on the surface quality and internal defects of the specimens were analyzed by metallographic observation and densitometry testing to select the best combination of process parameters.On this basis,laser melting deposition of heterogeneous materials was carried out,and the first layer was all 316 L stainless steel,and the composition of the second layer was 90%316L+10% TC4,80% 316L+20% TC4,70% 316L+30% TC4,60% 316L+40% TC4,and 50%316L+50% TC4,respectively.When the proportion of TC4 alloy is between 10% and 20%,there are no cracks and pores on the surface and inside of the specimen,the microstructure at the interface is honeycomb,and the transition to the intermixed morphology of dendrites and equiaxial crystals is gradual along the deposition direction,and the content of two main elements,Ti and Fe,at the interface is correspondingly stepped up and down;when the proportion of TC4 alloy is between 30% and 50%,there are obvious long cracks on the surface of the specimen,and the microstructure at the interface is intermixed with equiaxial crystals and dendrites.The microscopic morphology at the interface is mixed with isometric and dendritic crystals and remains constant along the deposition direction,and the content of Ti and Fe elements increases and decreases in a corresponding cliff-like manner.XRD and EDS analysis found that a large number of Fe Ti and other brittle intermetallic compounds existed at the interface,and the hardness of the mixed powder deposition layer increased by more than 191% compared with that of the 316 L stainless steel deposition layer,and the fracture morphology was all deconfined,which proved that the interface fracture was brittle fracture.Finally,the corrosion resistance of four specimens,90% 316L+10% TC4,80% 316L+20%TC4,TC4,316 L,under simulated marine environment was studied,and the pitting pits were observed by scanning electron microscopy.According to the results of polarization curve and electrochemical impedance spectrum,the corrosion resistance of the above four materials in descending order is: TC4>80% 316L+20% TC4>90% 316L+10% TC4>316L;by observing the morphology of the pitting pits,it is found that the increase of TC4 alloy content can effectively inhibit the occurrence of corrosion and reduce the size of corrosion pits,indicating that the deposition of 316 L stainless steel and TC4 alloy powder mixture deposition can improve the corrosion resistance of the material. |
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