液态置氢条件下TiAl基合金与铸型的界面反应机制研究

The reaction between TiAl based alloy and casting mould is the key factor for the controlling of casting quality, because it can affect the flowability and mold-filling capacity and is one source of the impurity phases. However, the reaction mechanism and controlling of reaction products have not been realized sufficiently. The applicant studied the melt hydrogenation of binary TiAl alloy, and found that the hydrogen could purify the molten alloy, decrease the viscosity, and increase the flowability, so it is supposed to be used for increasing the filling capacity and purity of TiAl based alloys. But there are not relative research reports, especially for the practical multicomponent TiAl based alloys. This project is proposed to expand the melt hydrogenation to multicomponent TiAl based alloys. First, the effects of hydrogen on the interface reaction, including thermodynamics, reaction process, wettability and reaction products, will be explored for the further controlling of interface reaction by hydrogen. Then, the combined action of interface reaction and hydrogen on the casting property and solidification microstructure will be studied. This project will reveal the mechanism of interface reaction between TiAl based alloy and casting mould under the action of hydrogen, and will also provide theory support for the control of the process and products of interface reaction. So this project is significative for both theory and practical application.

TiAl基合金与铸型的界面反应是控制铸件质量的关键因素，可影响合金的流动性和充型能力，也是杂质相的来源之一。但人们对该界面反应机制及产物控制等问题尚缺乏足够认识。申请人前期对二元TiAl合金液态置氢的研究发现，氢具有净化熔体、降低熔体粘度，提高流动性等作用，有望用于制备高纯复杂薄壁铸件。但目前仍没有该方面的研究报道，尤其是对于更具实用性的多元TiAl基合金。本项目拟将液态置氢拓展至多元TiAl基合金，主要研究液态置氢条件下合金与铸型的界面反应机制。首先研究氢对界面反应热力学、动力学、润湿性、反应产物的影响规律，获得合金与铸型界面反应机制的理论描述，进而利用氢对界面反应进行控制；同时探索界面反应与氢的耦合作用对铸造性能与微观组织演化的影响规律。本项目将揭示氢作用下TiAl基合金与铸型的界面反应机制，为控制界面反应过程和微观组织提供理论依据，具有较大的理论与实际意义。

本项目研究采用液态置氢的方法研究了氢对TiAl合金与铸型界面反应和铸造性能的影响，其中铸造性能的研究对象主要包括流动性和充型性，并对该过程中所涉及的热力学与动力学问题进行了分析。液态置氢是相对于传统的固态渗氢的一中新方法，实施过程是在一定氢分压的电弧炉中熔炼TiAl合金预制锭，氢气分解并扩散进入合金熔体中，从而达到快速置氢的目的，而氢溶解度决定于熔炼温度和氢分压。研究发现了如下结果：（1）通过测试不同置氢量的TiAl合金在标准的石墨螺旋形铸型中的流动长度，发现流动长度随氢分压提高而延长，说明氢可以提高TiAl合金熔体的流动性。（2）通过测试不同置氢量的TiAl合金在多孔薄壁石墨铸型中的充填率，发现充型率随着置氢量的提高而提高，说明氢提高了TiAl合金充填复杂薄壁型腔的能力。（3）通过对与石墨铸型界面处的TiAl合金中碳反应层的分析，发现随着置氢量的增加，碳反应层厚度减小，说明一定量的氢有利于改善TiAl合金与石墨铸型的界面反应。同时对氧化物铸型的测试表明，氢可以显著改善界面处的铸件表面质量。