In-situ Synthesis Of TiC,TiB Reinforcement For Titanium Matrix Composites

Metal Matrix Composites (MMCs) have obtained widely industrial, due to their enhanced mechanical such as high hardness, superior strength, better wear risistance etc. One of the most typical representative of this kind is Titanium Matrix Composites (TMCs) which reinforcement is TiC,TiB. The preparing technique,microstructure and mechanical properties have been extensively studied. However, they paid more attention on additional technique. The objective of this paper is to fabricate TMCs of TiC,TiB reinforcement with in-situ synthesis. Compared with additional technique, the reinforcement of complex material fabricated by in-situ synthesis method is in situ synthesis, which avoids the pollution of reinforcement- matrix interface, and can fabricates material with better properties. Moreover, the low-cost method is simple, and can be combined with traditional smelting and powder metallurgy.In this paper, the TiC reinforcement and TiC,TiB mixed reinforcements were fabricated with the method of SPS,VS and VS-HIP, Using three kinds of reaction systems, such as Ti/Cr₃C₂,Ti/VC,Ti/B₄C. All kinds of react effectiveness of reaction systems have been analyzed, the growth mechanics of SPS technology in fabricating TMCs and pyknosis process of the material have been disclosured, and the thesis got the following conclusions:(1)ΔG (Gibbs free energy) in every reaction system has been calculated by thermodynamic theory. TheΔG of above reactions is negative, which indicates that all of the reactions can take place. It will generate TiC and TiB. To Ti/B₄C reaction system, due to the unstableness of TiB₂.(2) TMCs of TiC and TiC/TiB mixed reinforcements have been fabricated th rough SPSs VS and VS-HIP methods by using Ti/Cr₃C₂, Ti/VC and Ti/B₄C react ion systems. Compared with VS, VS-HIP, the reinforcements in complex material fabricated by SPS have smaller size, more uniform distribution, higher relative density and Vickers-hardness, and there is no obvious hole in the material body. Furthermore, the SPS is simple and high efficiency.(3) The growing mechanics of reinforcements and pyknosis process of the material have been disclosured in all three kinds of reaction systems. The pyknosis process of the material divides into three main characteristic stages: grain close packing period, neck mass formation period, structure growing till pyknosis. For the first stage, the main affecting factor is sintering pressure. The combined effect of the special impulsive current induced spark discharge between grains, joule heat, reaction heat release and pressure is the main factor in second stage. Joule heat and pressure work together to make hem be the main affecting factor of third stage of pyknosis process. TiC and TiB reinforcements chiefly generate in the second and third stages of the pyknosis process, each stage has different generating mechanics. In the second stage, the main reinforcements are grown from formative neck melt between grains, and the generation depended on the mechanics of solid phase diffusion reaction in the third stage.