Microstructure and Properties of TiB2/TiC Reinforced Fe-based Coating Grown in Situ by Laser Cladding

The preparation of ceramic phase reinforced metal matrix composites by laser cladding is currently an important research direction of wear resistant coatings. According to the way of adding the reinforcing phase, they are generally classified into two categories, i.e., the ex-situ method and the in-situ growth method. The significant advantage of in-situ growth is that this method not can only improve the interface problem, effectively control the morphology and size of the ceramic phase, but also contribute to good thermomechanical stability of the grown ceramic phase. Therefore, in this paper, the in-situ growth of TiB2 and TiC ceramic phases on 45 steel's surface with laser cladding technique was used to improve the wear resistance of Fe-based coatings. The 45 steel of 60 mm×40 mm×10 mm was selected as the experimental substrate, and the surface oxide was polished and cleaned with sandpaper to remove the oxide. Fe-based powder, Ti powder and B4C powder were used as precursor powder materials. Different proportions (0%, 10%, 20%, and 30% quality scores) of (Ti+B4C) were added as a cladding powder in the Fe-based powder according to 3Ti+B4C→2TiB2+TiC molar ratio. The experiments were carried out with a YAG solid-state laser, model JJM-IGXY-800B, with the following laser melting process parameters after preliminary process optimisation: current 200 A, scanning speed 180 mm/min, pulse width 6 ms, frequency 8 Hz, out-of-focus volume 0 mm, lap rate 50%. Argon was used as the protective gas with a gas flow rate of 12 L/min. At the end of the experiment, the samples were cut, ground and polished and finally etched with aqua regia. The microstructure, phase morphology, elemental distribution and energy spectrum of the composite coatings were analyzed with a field emission scanning electron microscopy (-IGMAHDTM). The phase composition of the composite ceramic phases was investigated with an X-ray diffractometer (PANalytical Empyrean Series 2). The microhardness of the coating along the cross-sectional depth was determined with an HVS-1000Z microhardness tester. Frictional wear experiments were carried out with an MS-T3001 rotary friction machine, the macroscopic morphological profile was characterized with a white light interferometer, the amount of wear was calculated and then the wear marks were photographed to study the wear mechanism. The results showed that after the addition of Ti and B4C to the Fe-based powder, a uniformly distributed TiB2 and TiC ceramic phase grew in situ, and the number of which increased with the addition of (Ti+B4C). Scanning electron microscopy combing with EDS determined that TiB2 was mostly rectangular in shape, and TiC was spherical or petal-shaped. During in-situ growth, TiB2 was formed preferentially, while TiC was mostly attached to TiB2 in a granular form. The microhardness of the composite coating increased with the addition of (Ti+B4C), and the hardness of 30% (Ti+B4C) composite coating was 1 086HV0.2, which was 0.78 times higher than that of iron base coatings (611HV0.2). The wear performance of the composite coating was significantly improved, with a minimum wear rate of 5.48×10-6 mm3/(N·m) for the 30% (Ti+B4C) addition, which was 2.67 times higher than that of the Fe-based coating 2.01×10-5 mm3/(N·m). As the amount of (Ti+B4C) added increased, the wear mechanism of the composite coating changed from adhesive wear to slight abrasive wear. In conclusion, the addition of Ti and B4C to the Fe-based powder enables the in-situ growth of TiB2 and TiC through laser cladding technology, and the hardness and friction and wear properties of Fe-based coating can be improved significantly. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.