**1. Introduction**

Ductile iron possesses the properties of high strength, toughness, wear resistance, shock absorption, easy cutting, notch insensitive, etc. However, due to the harsh working conditions, the surface wear of ductile iron can cause mechanical failure [1,2]. Surface modification technology is an effective way to enhance surface strengthen, overcome the limitations of shape and size, and reduce costs [3]. Due to its good properties and low cost, Ni-based powders are often used to improve the surface properties of substrates, such as strength, wear resistance, and corrosion resistance [4–6].

Mughal et al. [7,8] used the finite element method to study the process of metal additive manufacturing process. It has been proven that continuous deposition without interlayer cooling leads to high and uniform preheating of the substrate, which reduces the deformation of the cladding layer. However, at the same time, it was found that the continuous multilayer deposition causes a thermal storage effect, which results in the loss of control over dimensional tolerances.

Delinger et al. [9] studied the effect of interlayer cooling time on the distortion and residual stress of Ti–6Al–4V powder. The results show that a shorter interlayer cooling time produces lower distortion and residual stresses. Nevertheless, shortening the cooling time can excessively increase the energy input into the system. Overheating can consequently lead to undesirable remelting, poor surface finish, and poor dimensional tolerances in the final part.

Chen et al. [10] studied the effect of improving the base cooling effect on the metal additive manufacturing process. It is found that the crystal orientation of the specimens can be improved by imposing a continuous water flow on the back of the substrate. As described in the paper, due to the thermal storage during the deposition process, the microstructure of the deposition is uneven. This means that as the number of layers increases, the cooling e ffect becomes worse. Furthermore, it is only suitable for specimens with simple shapes, not for specimens with complex shapes.

At present, there are many studies on laser process parameters. Weng et al. [11] studied the e ffects of laser-specific energy on the microstructures and properties of the cladding layers. Liu et al. [12] compared the structural and mechanical properties of Inconel 718 prepared with or without argon protection during laser cladding. Cheng et al. [13] studied the e ffects of laser energy density and scanning speed on the properties of the cladding layer. However, few studies have been done on the effect of interlayer cooling. In this paper, the di fferences in the microstructure and properties of two Ni-based alloys deposited on ductile iron under interlayer cooling or non-interlayer cooling conditions were investigated. This work can improve the quality of the cladding layer, especially strength and hardness, and help control dimensional tolerances.
