Study On TiB₂-Al₂O₃ Coating By Laser Cladding

Wear is the main failure form for materials and half of the steel consumption is caused by this form in mechanical industrial per year. Therefore, using laser cladding to prepare high hardness and wear resistant coatings on mechanical products surface can improve the performance of equipments and extend their service, which will bring long-term economic benefits. In this paper, TiB2-Al2O3 composite coatings were produced on the surface of low carbon steel substrates with TiO2,B4C and Al powders as raw materials, using in-situ synthesis technologies and laser cladding. The microstructure, performance and formation mechanism were researched by optical microscope, digital microscope, X-ray diffraction (XRD), scanning electron microscope (SEM), Vickers hardness tester, sliding wear testing machine and so on.The influences of laser cladding parameters such as pre-powder thickness, laser power, scanning speed, shielding gas and overlapping rate on formation and properties of the cladding layers were studied in our work. The results showed that when the thickness was 1.0mm, the laser power was 1500W, scanning speed was 300mm/min, spot diameter was 3mm, shielding gas flow rate was 300L/h, and overlapping ratio was 30%, the cladding layers would have smooth surface, good shape and a good metallurgical bonding with the substrate.The microstructure, performance and formation mechanism of the enhance phase in cladding layer were affected by different ratios between the powder of the TiO2, B4C and Al. According to the ratio of chemical reaction, there were only TiB2 particles distributing in the cladding layers, which have blocky or strip shape. As the Al content was raised up to 25%, keeping the relative TiO2 and B4C unchanged, a few circular Al2O3 particles would exhibit in the cladding layers. TiB2 distributed in the a-Fe phase dispersedly and evenly, which significantly increased the hardness of the cladding layers. The cladding layers with Al2O3 produced had a slight increase in overall hardness. In particular, the hardness where Al2O3 generated had a more obvious increase and the highest point was up to 1065.1HV.Using Al, TiO2 and B4C as raw materials to prepare composite coatings, the wild phase produced in the coatings would distributed dispersedly and evenly. The cladding layers showed better wear resistance during the dry sliding wear test. In the same experimental conditions, the weight loss of composite cladding layers was 1/20 of the substrate materials, meaning that the wear resistance of composite coatings was nearly 20 times the low-carbon steel. It was adhesion-engagement mechanism between the coatings and the grinding wheel in the wear process. The coatings were micro-cut resulting in the local fatigue damage and being worn down slowly in the form of "cut-off". The results showed that the cladding layers had smooth grinding mark morphology and the overall wearing resistance was very good.