3.1 Material performance parameters

The laser cladding simulation process belongs to transient thermal analysis. The thermal physical properties of the material, such as specific heat capacity and thermal conductivity, change with temperature. The base material selected this time is H13 steel, and the cladding layer material is Ni60A alloy powder. The thermophysical property parameters of H13 steel and Ni60A alloy powder are calculated based on the literature [18] and JMatPro software. And curve fitting of the mutation point data according to the liquid phase line of the material shown in Fig. 1 and Fig. 2, which shows that the melting point of H13 steel material is 1445°C and the melting point of Ni60A alloy powder is 1060°C. When the node temperature of the clad layer is higher than the liquid phase line temperature (1370°C), it is judged that the node belongs to the melt pool.

3.2 Model building

3.2.1 No-texture model establishment

In this article, three single-layer laser cladding for temperature field is simulated and stress field coupling is analyzed. The built-in modeling module of ANSYS is used to establish the laser cladding finite element model as shown in Figure 3. The laser cladding simulation model is a symmetrical model, and only half of the symmetrical model needs to be established. The size of the matrix model is 50mm×25mm×20mm, and the size of the cladding layer model is 50mm×6mm×0.5mm. The model grid is divided into local refinement. The grid size of the matrix material is 0.001mm, and the size of the cladding layer material is 0.001mm. The mesh size is 0.0005mm, and the selected element type is solid70, which has three-way heat conduction capability. The model meshing is shown in Figure 4.

3.2.2 Texture model establishment

The size of the texture model is kept the consistent with that of the model with non-textured model while the distribution of texture on the upper surface of the substrate model is shown in Figure 5. The shape of the texture is rectangular and the size is 0.8×0.8×0.5 mm. After the texture is preset, the texture is filled with Ni60A alloy powder material and the cladding layer is established on the base model. The solid70 unit is still selected and the model is meshed by the method of local refining. The layer and its nearby areas have texture, which is irregular, so the mesh is divided by unstructured mesh. The mesh size of the cladding layer is 0.0005mm, and the mesh size of the rest area is 0.001mm. The grid division result of the model is shown in Figure 6.

3.3 Heat source model and boundary conditions

The application of the heat source adopts the Gaussian heat source model, and the heat conduction control equation [19]is:

Among them, is the density; C is the specific heat capacity; v is the scanning speed; T is the temperature; t is the time; k is the thermal conductivity.

The convective heat transfer boundary condition is adopted in the finite element simulation process, without considering the effect of thermal radiation on the simulated process, and the convective heat transfer [20] is:

In which, h is the convective heat transfer coefficient, taken as 20W/(m²-℃); TS is the temperature of the solid surface; TB is the ambient temperature, taken as 25℃.

In addition, papers [21-23] investigated the effect of preheating temperature on the stress and strain during laser cladding by building a finite element model and found that the substrate preheating has a great influence on the residual stress. As the substrate preheating temperature increases, the residual stress of both substrate and the cladding reduces. And preheating will make the residual stress distribution more uniform. In this paper, the matrix material is preheated during the cladding simulation process, and the preheating temperature is 300℃.