Effect of TiB2 Content on Microstructure and Tribological Properties of TiBx/Ti Alloy Coatings

To improve the hardness and wear resistance of titanium alloy, the work aims to prepare the TiBx/Ti coatings with different TiB2 (10%, 20%, 30% and 40%) contents on the surface of T47Z alloy by plasma arc cladding technology. The microstructure, mechanical properties and wear resistance of the coating were studied by scanning electron microscope, X-Ray diffractometer, Vickers hardness fiber and UMT-2 friction and wear testing machine. After cladding, the thickness of the coating was about 2 mm, and there were no cracks and pores. The substrate phase of the coating was α phase, and the reinforcement phase was needle, rod TiB and granular TiB2. With the increase of TiB2 content in cladding powders, the matrix structure of the coating had no obvious change, and the number and size of the reinforcement phase increased gradually. It was also found that acicular TiB aggregation occurred when the content of TiB2 was 40%. When the content of TiB2 was less than 50%, the surface phase of the coating was α phase and the reinforcement phase TiB and TiB2. When the TiB2 content reached 50%, the Ti3B4 phase was detected on the coating surface. Combined with the Ti-B phase diagram, the formation of TiB phase was discussed in detail when the content of TiB2 was 40%. The coating hardness was up to 893.4HV0.2, which was 2.07 times that of the substrate. The average friction coefficient of the substrate was 0.335, and the friction coefficient of the coating with 10% TiB2 content was 0.359 at 0-700 s. The friction coefficient of the coating decreased with the increase of TiB2 content. When the TiB2 content was 40%, the average friction coefficient of the coating was 0.312. When TiB2 content reached 50%, the average friction coefficient of the coating was 0.334. The COF of the coating gradually increased on the grinding. This was mainly because the soft matrix phase of the coating was constantly worn during the grinding process with the friction pair, so that more and more hard particle reinforcement phased were exposed, and the particle reinforcement phases with greater hardness were not easily worn down, resulting in uneven coating surface, and these raised hard particles produced greater friction resistance during the wear process, resulting in an increase in the friction coefficient of the coating. The wear rate of the coating decreased firstly and then increased with the increase of TiB2 content. The lowest wear rate was 0.174 2×10–3 mm3/(N·m), decreasing by 53.7% compared with that of the substrate. The wear marks of T47Z alloy had obvious adhesion spalling and deep furrow, and the wear mechanism was serious adhesion wear and abrasive wear. The wear mechanism of the coating with 10% TiB2 content was mainly adhesive wear, and the abrasive wear was auxiliary. With the increase of TiB2 content, the furrow of the coating wear marks became shallow, the spalling caused by adhesive wear was relieved, and the wear mechanism gradually shifted to abrasive wear. When the TiB2 content is 40%, the furrows on the wear surface are thin and narrow, and the adhesive wear characteristics are almost not observed. The wear mechanism is mainly abrasive wear and the adhesive wear is supplemented. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.