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Dilution rate is an important factor affecting the properties of laser cladding. However, the exact estimate of dilution rate in direct laser fabrication is still not fully developed. In this study, high-strength and wear-resistant YCF102 alloy powder is used to laser clad on the steel substrate. The area of the cladding layer is replaced by a part of the circle, and the relationship among the deposition angle, the clad width, and the area of the cladding layer is established. The geometry of the fusion zone is replaced by polynomial function of the fourth degree, and the relationship among the thermal tension angle, the clad width, the melting pool depth, and the area of the fusion zone is established. The value of the dilution rate is obtained by the area of the cladding layer and the fusion zone. The correlation coefficient of the area of cladding layer, the area of the fusion zone, and the dilution rate is also obtained. The estimate results coincident with the measurement results very well. The proposed theoretical model offers a basis for estimate of dilution rate in laser cladding. [ABSTRACT FROM AUTHOR]

This paper studies the different lap joint methods of YCF101 alloy powder by direct laser fabrication (DLF) technology and analyzes the structure, porosity, cracks, and surface topography of multichannel forming parts fabricated by DLF to optimize the ideal lap joint mode. The selection basis of lap joint modes is based on the surface adhesion powder of single-layer cladding surface, inner cracks and porosity, and microstructure of the forming parts under different scanning modes. Regardless of any scanning method, there would be obvious sticky powder at the lap joint, and the pore and cracks are mainly present at the lap joint. The uneven energy density of the weld during the fusion process makes a great difference in the microstructure of the molten pool and the lap joint, the structure of molten pool is small isometric crystal, and the structure of lap joint is bulky dendrite. The defects caused by the uneven energy distribution and sticky powder had been improved by different lap joint modes between layers. The uniform distribution of the linear trace poles at the outer contour surface improved the surface quality of the forming part. As the mesh size of the cladding region that is divided by the cladding trajectory becomes smaller, the quality of forming parts has changed. The double decussation and outline mode has the smallest mesh size, the porosity is 0.47%, the microstructure of the lap joint area is no longer just dendrites, there appears isometric crystal and structure refining, the crack reduces, and the compressive strength is improved. To some extent, the problem brought by sticking powder and uneven heat distribution had been worked out. [ABSTRACT FROM AUTHOR]

• Annular convection and longitudinal convection occur in the molten pool. • The Marangoni movement drives the formation of the deposit layer. • Gravity has almost no effect on convection in the molten pool. • Convection mainly drives heat transfer. • CET occurs in the solidification process of the molten pool. Metal Laser Direct Deposition (MLDD) is an additive manufacturing method involving multiple physical processes. Due to the existence of various complicated physical processes inside the molten pool, it is necessary to study the convection mode and solidification morphology in the molten pool. The convection of the molten pool generates heat and rapid solute transfer in the molten pool, which has an important influence on the solidification morphology of the deposited layer. In this study, the constructed MLDD numerical model was used to analyze the internal convection morphology of the molten pool. The convection form in the molten pool was revealed by setting different physical conditions. The results show that the Marangoni movement is the main factor in the formation of cladding layers. The impact force generated by the protective gas has an influence on the convective morphology, while the influence of gravity on the convection is limited. Through the numerical calculation, the relevant solidification parameters of the molten pool were obtained and verified by the MLDD experiment of the iron-based alloy powder. Numerical analysis and experimental results show that the Marangoni motion caused by the temperature gradient is the decisive factor leading to the solidification structure, and the phenomenon of columnar to equiaxed transition (CET) from the bottom to the top of the molten pool occurs. [ABSTRACT FROM AUTHOR]