| The characteristics of TiAl based alloy are high strength, high temperature but greater brittleness and poor ductility. Nanocrystalline materials can significantly improve ductility, toughness. In this paper, high-energy ball milling, spark plasma sintering and high temperature vacuum sintering methods were used for the synthesis of nanocrystalline a2-Ti3Al phase and equiaxed γ-TiAl duplex alloy ultrafine grain and for organization and its sintering temperature oxidation resistance research, get the best sintering process and alloy composition.First,TiH2-47Al-0.2Si-5Nb(at.%),TiH2-47Al-0.2Si-7Nb(at.%),TiH2-47Al-0.2Si-5Nb-2. 38Co(at.%) and TiH2-47Al-0.2Si-7Nb-2.43Co(at.%) Alloy powders as four components were ball-milled in two cans for 12h and 24h, and the milled powders were sintered at high temperature spark plasma sintering (sintering temperature of 1000℃) and vacuum sintering (sintering temperature of 1200℃),separately. The alloy was analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy of tissue phase sintering characteristics and tissue morphology.The results show that:(1) alloy powders obtained after the high-energy ball milling were nanoscale powder particles, increasing the content of Nb powder, which helps to refine the powders. Besides, In the milling process combination of H and Nb is beneficial to the reduction of Ti in TiH2 and the formation of intermetallie compounds Al. Compared with the Co powders without added powders, powders containing Co powder agglomerates severe,the observed powders pellet is slightly larger than the size of the alloy powders of Co without added powders. By Milling process, the powders has not only been refined, but also achieved a low-temperature chemical reaction and the formationof Ti2Al and TiAl new crystalline phase, the reason was the powders produced a large number of defects or vacancies, to the effect of mechanical alloying.(2) The four components milled powders were used to spark plasma sintering and vacuum sintering process, equiaxed γ-TiAl-based, TiAl phase and two-phase nanoscale organization of superfine Ti3Al are formed. Description decided this was not a major factor in the organization state sintering process mode, but refined powder milling and mechanical alloying. Because of refined powder, forming a plurality of nuclei, the formation of ciystal grains after sintering and thus below the tissue grain size obtained by the conventional method. TiAl formation of equiaxed grains, with an average of less than <500nm,highly interconnected grains forni a large, stable trigeminal grain boundaries. This organizations larger angle grain boundaries, grain boundaries straight, in a high temperature environment not easy to grow, indicating that the powder complete the sintering process in a very short period of time.(3) The organization of TiAl based alloys for high temperature cyclic oxidation test results show that the sintering of organization at 1000℃ Hereinafter, there is no phase transition reaction. This suggests that y-TiAl and Ti3 Al alloy nanoscale is a relatively stable tissue state,such organizations once formed,when the temperature is repeatedly raised again to a high temperature state, remains the original stable state,even if nanoscale particles grow will not occur. Compared to the plasma discharge sintering process,it is more conducive to the preparation of a high-density TiAl alloy.(4) After several sintered structure in pure oxygen environment of high temperature cyclic oxidation results showed little oxidation weight gain, high temperature oxidation resistance. The first cycle of warming phase oxidation weight gain is more obvious,and the subsequent oxidation of multiple cycles of weight gain is very small. However,oxidation rate of TiH2-47Al-0.2Si-5Nb is slightly lower, and high temperature oxidation resistance is better. |
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