Microstructure and Temperature Distribution in Laser Clad TiC Reinforced NiCrBSiC Coatings: Experiments and Finite Element Analysis
Y-W. Lei, R-L. Sun and Y. Tang
A good quality TiC reinforced NiCrBSiC coating with low dilution and a sound metallurgical bond was fabricated on a Ti6Al4V substrate by means of laser cladding with a CO2 laser . The microstructure of the coating was examined in detail. Three zones were distinguished in the coating: the clad zone (CZ), the bonding zone (BZ), and the heat affected zone (HAZ) of the substrate. The clad zone was seen to be divided into two sub-layers. The upper layer consisted of precipitated TiC particles in a rhombus or petal shape and γ-Ni dendrites uniformly distributed in the matrix. The bottom layer consisted of undissolved TiC particles with irregular shape and a small quantity of villiform in situ synthesized Cr7C3 phase uniformly distributed in the matrix. To understand the formation mechanism of the microstructure in the coatings a three-dimensional finite element model (FEM) was proposed to simulate the process. The FEA simulated results show that TiC particles in the upper 0.2 mm layer of the coatings were melted during the cladding process. The maximum depth of the meltpool was about 0.64 mm, which is slightly larger than the thickness of the preplaced layer, indicating that a thin layer of the substrate was melted during the process. The excellent agreement between the FEA simulated results and the experimental data verified that the model would be useful as a tool to optimize the laser processing parameters and reduce the experimental cost of laser cladding process.
Keywords: Ti6Al4V, TiC reinforced NiCrBSiC coating, CO2 laser, laser cladding, titanium alloy, microstructure, temperature distribution, finite element analysis (FEA) model