The reinforcement synthesized in situ is evenly distributed on the substrate, and the grains of the titanium alloy on the substrate are also relatively small. The morphology of the reinforcement is mainly equiaxed or near-equiaxed TiC titanium alloy particles and short fibrous TiB whiskers. The interface between the reinforcement and the matrix is good, and there are obvious dislocation rings in the titanium matrix. There are high-density dislocations on the titanium alloy of the matrix, which is conducive to improving the performance of the composite material. The addition of in-situ TiB and TiC reinforcements has significantly improved the mechanical properties of the alloy material, but the elongation has decreased relatively. The in situ generated reinforcement has a good interface with the metal matrix, and the thermodynamic stability of the production phase is good. There are no wetting and interface reactions between the reinforcement and the metal matrix. At the same time, the pollution of the reinforcement particles is avoided. This preparation method is the in-situ synthesis method.
In addition, the process requirements are strict and difficult to master, and the composition and volume fraction of the reinforced phase are not easy to control. The main methods are:
(1) Powder metallurgy. This method is the earliest process developed for the preparation of metal-based particle composite materials. This process first mixes the reinforcement and the matrix powder uniformly, and then produces the product through pressing, sintering, and subsequent processes. Because the interface reaction of sintering at a temperature lower than the melting point of titanium is greatly weakened, the particle size and volume ratio of the reinforcement can be adjusted in a wide range, and the choice of the reinforcement is large. After sintering, it can be further extruded, forged or hot isostatically pressed Improve densification and composite performance. In order to improve the compactability of the mixed powder and the sintering shrinkage rate. To improve the compactness of the sintered blank, more liquid phase sintering components can be added to the alloy. Commonly used reinforcements are SiC, TiC, TiB, TiB2 and so on. The room temperature and high temperature strength, hardness and wear resistance of the composite material prepared by this method are significantly improved.
(2) Solidification method. The solidification technology for preparing particle-reinforced titanium-based composite materials is simple in process, low in cost and easy to manufacture parts with complex shapes. Solidification technology introduces in-situ growth technology in the traditional casting process, which uses internally generated reinforcing particles. Replacing the traditional externally enhanced particles. This kind of particles generated during the solidification process has a “clean” interface with the substrate with good wettability.
(3) Exothermic diffusion (XD> method. It was invented by Martin Manietta, and is usually used in the early stage of traditional thermal processing technology (such as casting, forging, extrusion, rolling). It is two kinds of powder that will generate reinforcement (Such as Ti and C in TiC) and the matrix powder are mixed evenly. Then heated to a higher temperature than the melting point of the matrix, the two powders that produce the reinforcement react at high temperature, thereby forming a finely dispersed reinforcement in the matrix melt The body is then made by casting, extrusion, hot rolling and other forming processes. Because the reinforcement is also synthesized in situ, the interface between the matrix and the reinforcement is clean, good wettability, strong bonding, and the reinforcement is finely dispersed, thus Helps improve the performance of composite materials.
(4) Mechanical alloying. The method uses high-energy ball milling technology to manufacture special mixed powder, and then produces the product through ordinary pressing and sintering after high-energy ball milling. The mixed powder can be refined to nanometer size, and its surface activity is extremely large. Since the reinforcement is synthesized in situ during the ball milling process or in the subsequent sintering process, the interface bonding strength between it and the substrate is significantly increased. This process can obviously improve the composite effect, and has the advantages of uniformly distributed titanium rods with reinforcements, a large volume fraction range of reinforcements, and good product quality. The disadvantages are expensive equipment and low efficiency, and it is easy to bring impurities in the preparation process.
