| The good bonding state between the cladding layer and the substrate is not only a key factor for evaluating the performance of the coating,but also the primary condition for the coating to function.Due to the complex physical and chemical reactions at the interface during laser cladding,there are few researches on the bonding state of laser cladding layers at home and abroad.Traditional methods for measuring the interfacial bonding strength of coatings are difficult to apply to metallurgical bonding caused by laser cladding,with limited applicability and lack of repeatability.The purpose of this paper is to design a method for measuring the normal interface bonding strength of laser cladding layers,and to establish a solid theoretical basis for the measurement of laser cladding interface bonding strength in engineering.Therefore,this research is of great significance for the application of laser cladding technology in the field of surface modification.In this study,laser cladding technology was used to prepare 316 L stainless steel coating,17-4PH stainless steel coating on Q345 substrate,and 316 L stainless steel coating on 316 stainless steel substrate.A new type of T-shape notch specimen and related fixture were designed to fracture at the interface under tensile stress to study the interface fracture behavior and evaluate the bond strength.When the T-shaped specimen fracture at the interface,it can be expressed as the bonding strength between the laser cladding layer and the substrate.The fracture occurs between layers,indicating that the bonding strength between the laser cladding layer and the substrate is higher than the strength of the laser cladding layer itself.The fracture occurs in the matrix,indicating that the bonding strength of the laser cladding layer is higher than that of the matrix.Since laser cladding produces a certain dilution rate,a zero interface parallel to the substrate surface is defined.In this study,T-notch samples were prepared at the zero interface and at 0.15 mm and 0.3 mm below the zero interface in order to accurately measure the interface bond strength.When the notch width of T-shaped sample is 6 mm,the fracture of T-shaped sample at the interface is expressed as the interface bonding strength between laser cladding layer and matrix.In the system where the base material is Q345 and the coating is 316 L stainless steel,when the laser power is 2200 W,the prepared cladding layer forms a good metallurgical bond with the matrix and has a dense structure without defects such as pores and unfusion.The T-shaped specimen with the notch at the zero interface has a higher interfacial bonding strength of 637 MPa.Compared with the laser power at 2000 W and 2400 W,the interfacial bonding strength is increased by 5.6% and 1.9%,respectively.When the base material is Q345 and the coating is17-4PH stainless steel system,when the laser power is 2200 W,the dilution rate is moderately12.1%,and no defects such as pores and cracks are found on the surface and cross-section of the sample.The bonding strength of the T-shaped specimen with the notch at the zero interface is as high as 908 MPa,which is 4.0% and 8.9% higher than that when the laser power is 2000 W and 2400 W,respectively.In the system where the base material is 316 stainless steel and the coating is 316 L stainless steel,when the laser power is 2200 W,the interface bonding strength of the T-shaped specimen with the notch at the zero interface is 869 MPa,compared with the interface when the laser power is 2000 W and 2400 W.The bond strength was increased by 6.5%and 5.5%,respectively.The interfacial bonding strength of T-shaped specimens all showed a trend of decreasing as the distance from the notch to the interface increased.The fracture morphologies show obvious dimples and cleavage planes,indicating that the fracture mechanisms include ductile fracture and brittle fracture. |
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