Fabrication Of TiC+TiB₂ Locally Reinforced Carbon Steel Matrix Composites Using A (Ti,Fe)-B₄C System By SHS Reaction

The metal matrix composites (MMCs) have obtained the widespread concern of the materials researchers in the world owing to their unique properties, such as high specific strength, high specific modulus, excellent wear-resistant and high-temperature resistant, and become one of the most attractive materials in aerospace, automotive, mining, metallurgy and coal industry.The traditional method of fabricating MMCs is powder metallurgy, however, the application of this composite is rather limited due to its super-high cost Therefore, it is very necessary to develop a low-cost manufacturing technology and cheaper materials to ensure the composites wider application.In the present work, ferrotitanium powder, consisting of Fe and Ti elements, was used to fabricate the multiphase ceramics composites reinforced carbon steel matrix using a SHS-casting method. It will have good application value and market prospect if realized industrialization. On the one hand, ferrotitanium powder not only provides the titanium element which is necessary to the in-situ reaction, but also provides certain amount of iron as reaction diluents. At the same time, the price of ferrotitanium is only one-tenth of pure titanium powder, so it has a significant role to promote the practical use of the steel matrix composites. In addition, there are some impurity elements such as Si, Mn, P, S and Al in the ferrotitanium, and some of these elements play a certain role in improving the performance of the steel. On the other hand, the TiC + TiB₂ reinforced the carbon steel matrix composites fabricated by the SHS-casting technology have a good prospects, and the products can be used directly in the preparation of the mold and other wear-resistant parts. Therefore, it has a certain theoretical value to study on this technology deeply and systematically, has a certain meaning to promote the effective use of ferrotitanium and the industrial process of the TiC or TiB₂ or TiC + TiB₂ reinforced the composite materials.Firstly, effects of Ti content, ferrotitanium and B₄C particle size on the SHS reaction products in the (Ti,Fe)-B₄C system under the non-preheating and preheating conditions are studied. And then a optimized system is selected, TiC + TiB₂ particulates locally reinforced carbon steel matrix composites are successfully fabricated using the SHS-casting method, and also, the microstructure and wear resistance of the composites are studied. The main research contents and conclusions are as follows:(1) The glove-box experiments show that the Ti content plays a significant role in the phase composition and morphology of the SHS products before preheating. When the Ti content is 30% in the ferrotitanium powder, the phase composition consists of TiB₂, TiC and Fe. When the Ti content increases from 40% to 70%, the transient phase Fe2B appears, and the amount of Fe2B and TiB₂ increases, while the Fe and TiC decreases, as well as the ceramics grow up. In addition, the result indicates that the granularity of the (Ti,Fe) powder has little influence on the composition and morphology of the SHS products, and the SHS is incomplete. Moreover, B₄C has significant influence on the composition and morphology of the SHS products only when it increases to a certain level.(2) It is found the Ti content has little influence on the composition of the SHS products after the preheat experiment. The size of ceramic particulates is bigger after preheating at 600°C when the Ti content is the same. However, B₄C particle size has a certain influence on the composition of the SHS products after the preheat experiment. With the preheat temperature increasing, the reaction becomes complete and the transient phase Fe2B in the final SHS reaction products decreases and disappears. It also has a certain influence in the morphology of the products, after the preheating, the ceramic particulates become irregular.(3) In-situ TiC and TiB₂ particulates locally reinforced carbon steel matrix composite is successfully fabricated by SHS-casting method. The locally reinforced steel matrix composites consist of three distinct regions: a TiC and TiB₂ particulate-reinforced region, a transition region and a steel matrix region, respectively. The steel matrix and reinforcing region combine very well by a wide transition region forming between them.(4) The XRD patterns of the TiC and TiB₂ local reinforcing regions of the steel matrix composites show that the type of products synthesized with different Ti content is all the same mainly consisting of Fe, Fe2B, TiC and TiB₂ phase. The size of TiC and TiB₂ particulates in the reinforcing region decreases with the increase of Ti content. The products synthesized under different B₄C particle size are composed of Fe, TiC and TiB₂ phase. Furthermore, the size of TiC and TiB₂ particulates in the reinforcing region decreases with the increase of B₄C particle size, and their distribution becomes uniform.(5) It is interesting to note from the wear tests that the TiC and TiB₂ particulates reinforced composite with 70%Ti in the reactants showed the best wear resistance, the next is Ti content at 50%, and the steel matrix is the worst. There are a lot of deep and wide grooves on the worn surface of the unreinforced carbon steel matrix. However, the amount of groove was substantially less on the worn surface of the TiC and TiB₂ reinforced region, and the grooves were shallow and narrow. The results indicate the wear mechanisms mainly as the plough wear.In a word, TiC + TiB₂ locally reinforced the carbon steel composites have a brilliant future for application and a great development space owing to the excellent combination of properties. Therefore, it is expected that the present study could establish some experimental and theoretical foundation for the TiC + TiB₂ locally reinforced the carbon steel composites.