Microstructure And Properties Of (TiB+TiC) Hybrid Reinforcing Ti-6Al-4V Composites In-Situ Synthesized By SPS

Titanium matrix composites hybrid reinforced by various reinforcement can be synthesized by in-situ reaction,which can give full play to the advantages of different reinforcements and meet different performance requirements.Moreover,hybrid reinforced titanium matrix composites have better comprehensive properties and material design freedom than single reinforced titanium matrix composites.The development of hybrid reinforced titanium matrix composites has practical significance for the development and application of high-performance titanium matrix composites.At present,the size of the additives for in-situ synthesis is mostly micron-scale,but the size of the reinforcement is large,and it is not easy to react completely.However,there are few reports about the direct addition of nano-scale reactants.Therefore,the study of the morphology and distribution of reinforcement formed by nano-reactants in situ reaction and their effects on the structure and properties of composites is conducive to the development of high-performance titanium matrix composites.In this thsis,TiB and TiC reinforced titanium matrix composites were in situ synthesized by spark plasma sintering?SPS?using nano-B₄C and micron Ti-6Al-4V powders mixed by planetary ball milling.The effects of sintering process and B₄C content on the structure and properties of composites were studied.The composites were treated by solution and aging.The effects of B₄C content on the wear properties of heat treated composites were studied,and the wear mechanism was analyzed.The following results are obtained.The effects of sintering process and B₄C content on the structure and properties of the composites were studied.The results show that Ti-6Al-4V powders containing 2 wt.%B₄C in situ synthesized?TiB+TiC?hybrid reinforced Ti-6Al-4V composites in the temperature range of 1000-1150?.TiC particles distributed at the original Ti-6Al-4V powder boundary with the size of 2-5?m,while TiB was whisker-like,formed at the grain boundary and diffused into the matrix.With the increase of sintering temperature,the yield strength,compressive strength and engineering strain of the composites increased first and then decreased,and better comprehensive properties were obtained at 1100?.Ti-6Al-4V powder containing 0-3 wt.%B₄C was sintered at 1100?.With the increase of B₄C addition,the content of reinforcement increase,the microhardness increased and the engineering strain decreased.The yield strength and compressive strength reached the maximum at 2wt.%B₄C addition,which were 1410 MPa and 1771 MPa,64.20%and 23.18%higher than that of the matrix alloy,and the engineering strain decreased from 29.37%of matrix alloy to 17.78%.The effects of solution temperature and aging temperature on the structure and properties of Ti-6Al-4V matrix composites reinforced by TiB+TiC were investigated.With the increase of solution temperature,the content of primary alpha phase decreased,and the content of martensite obtained by quenching increased,resulting the increase of microhardness while the decrease of plasticity.During aging,martensite decomposed above450?and obtained dispersive distribution of a+?structure.However,when aging temperature exceeded 550?,the decomposition products were coarsened obviously.Composites solution at 960?for 1 hour and then aging at 500?for 6 hours can obtain the best performance,that the yield strength and compressive strength were 1632 MPa and 1970MPa respectively,which are increased by 14.93%and 11.23%compared with the as-sintered state,while engineering strain decreased from 17.78%in as-sintered state to15.23%.The wear properties of?TiB+TiC?composite reinforced Ti-6Al-4V composites were studied.The wear tests under different loads of composites with 2 wt.%B₄C were discussed,with the increase of loads,average friction coefficient decreased and wear loss increased.At low loads,the wear is mainly abrasive wear,and oxidation wear occurred with the increase of loads.Under the load of 50N,the average friction coefficient and wear loss decreased with the increase of B₄C content,wear mechanisms were abrasive wear and oxidation wear.The wear rate of the composites with 2 wt%B₄C addition were 36.69%lower than that of the matrix alloy.