Microstructure and properties of laser cladding coating at the end of L415/316L bimetal composite pipe

This article attempts to use the laser cladding to realize the metallurgical combination of the ends of L415/316L bimetal mechanical lined pipe. For the convenience of the tests on mechanical properties, two kinds of nickel-based alloy powders, self-fluxing alloy powder (SFAP) and non-self-fluxing alloy powder (NSFAP), were cladded on substrate L415 sheet. The microstructure of two cladding coatings was analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and the mechanical properties and corrosion resistance of two cladding coatings were determined. The results show that two cladding coatings do meet the requirements of both low hardness and high corrosion resistance, and that two cladding coatings which mainly contain γ-Ni solid solution are composed of planar dendrites, cell dendrites, columnar dendrites and equiaxed dendrites. In addition, SFAP coating exhibits high tensile strength and low toughness, showing that SFAP coating is brittle. However, NSFAP coating exhibits good plastic toughness, high tensile strength and excellent impact Charpy energy, and excellent bending performance. SFAP coating is a quasi-cleavage fracture, which is a brittle fracture. The fracture of NSFAP coating is composed of a large number of dimples, which is a ductile fracture. Considering the three aspects of microstructure, chemical composition, and mechanical and corrosion properties, NSFAP is suitable for laser cladding at the end of mechanically lined bimetal pipe.