Evaluation of Mechanical Characteristics and Microstructure of Surface Hardness Coating by Laser Cladding

Abstract

Abstract. This study evaluated the mechanical properties and the microstructure of a surface hardness coating layer formed by laser cladding using a Bulk Metallic Glass (BMG) wire. The mechanical properties were measured by tensile strength test and micro-hardness test; microstructure and grain structure were analyzed by using a high-resolution scanning electron microscope and a transmission electron microscope. Surface coating was carried out by laser cladding and the GTAW process. The tensile strengths of the laser-cladded and GTAW coating layers were 2.0GPa and 1.7GPa, respectively. The tensile strength and micro hardness of the laser-cladded coating layer were about 15% and 14.3% higher than those of the GTAW coating layer, respectively. The laser-cladded coating layer showed finer grains and fewer dendrites due to their reduced distribution. The microstructure of the BMG coated layer showed a mix of α-Fe phase and amorphous phase.Keywords: Welding, GTAW, Laser cladding, BMG, Surface hardness coating, G.1-AW Mechanical PropertiesAs shown in Fig.1(a), the yield strengths of STS316L, GTAW, and Laser Cladding coated specimens were 292.1, 360.7, and 378.9 MPa, and the tensile strengths were 591.8, 534.8, and 568.9 MPa, respectively. The tensile strength of the substrate (STS316L) was higher than those of GTAW and Laser Cladding coated specimens by 9.63% and 3.86%, respectively, but the yield strengths of GTAW and laser cladding coated specimens were higher than that of the substrate (STS316L) by 19.02% and 22.91%, respectively.Generally, yield strength is a more important mechanical property than tensile strength for metals used in structural products. This is because elastic deformation does not affect a product's appearance, but plastic deformation changes a product's size or appearance, decreasing a product's value. The yield strength of the coating layer can be obtained by using Eq. (1) as follows.