多孔Ti3AlC2基过滤陶瓷骨架表面原位涂层形成/制备及其在过滤钛铝基合金过程中活性吸附夹杂的机理研究

TiAl based alloys have attracted broad attention as potential candidates for lightweight and high-temperature structural applications in the various fields. The induction furnace crucible method is expected to develop into an effective and low-cost casting process for TiAl alloys. Taking into account the high reactivity of TiAl alloys, some corrosion interactions between the alloy and the CaO/CaZrO3 crucible materials always occur, which leads to metal contamination. In this research work, the Ti3AlC2 based filter ceramic with in-situ coating is introduced to remove the CaO/ZrO2 inclusions, via the active adsorption method during TiAl alloys casting. Firstly, Ti3AlC2 has very similar chemical compositions with TiAl based alloys, which results in the chemical inertness between the filter ceramic and molten TiAl based alloys. Secondly, the in-situ coating can be formed on the surface of Ti3AlC2 based filters by controlling the kinetic parameters. The reactions between in-situ coating and CaO/ZrO2 inclusions can occur and transfer the inclusions into high-melting point phases, thereby remove inclusions from the TiAl based alloys effectively. In this program, the effects of heat-treatment atmosphere and temperature on the microstructures and chemical compositions of in-situ coating on Ti3AlC2 based filters will be investigated. Furthermore, the interface behaviors between various in-situ coatings and TiAl based alloy/inclusions will be discussed. These works will contribute to explore the adsorption mechanism for CaO/ZrO2 inclusions, also providing the theoretical guidance for high-efficiency and low-cost processing for melting TiAl based alloys.

钛铝基合金是航天航空等领域极其重要的轻质耐高温结构材料，具有广阔的应用前景。感应炉坩埚法是高效低成本熔炼钛铝合金最具潜力的途径之一，但在使用CaO/CaZrO3坩埚熔炼钛铝合金过程中，坩埚材料会溶解到合金中形成CaO/ZrO2夹杂从而污染合金。本项目拟制备具有原位涂层的Ti3AlC2基过滤陶瓷，利用化学反应活性吸附钛铝合金中的夹杂，为高质量钛铝合金制备提供技术支持。首先Ti3AlC2与钛铝合金组分相似，致使其对合金熔体呈化学惰性；再利用Ti3AlC2特殊高温行为在热处理过程中形成原位涂层，通过涂层与目标夹杂的化学反应形成高熔点相附着在涂层表面，最终达到过滤夹杂的目的。本项目将系统研究热处理气氛、温度等因素对Ti3AlC2基过滤陶瓷骨架表面原位涂层物相组成和显微结构的影响，探明不同原位涂层与钛铝合金熔体/夹杂界面反应行为，揭示原位涂层活性吸附夹杂的机理；为高效低成本熔炼钛铝合金提供理论基础。

Ni-TiAl基高温合金在航空、海洋工程等许多领域都有很大的应用潜力，真空感应炉坩埚法是高效低成本熔炼铸造含TiAl合金最具潜力的途径之一。但高温合金中TiAl反应活性高，坩埚与合金接触过程中必然会产生夹杂污染合金。本项目制备具有原位涂层的Ti3AlC2基过滤陶瓷，利用活性吸附法去除含TiAl合金中的目标夹杂。首先Ti3AlC2具有高抗热震性且对TiAl熔体呈化学惰性；利用Ti3AlC2特殊的高温行为，通过控制Ti3AlC2结构中Al的空位迁移以及调节气氛和温度参数，能在其表面原位形成Ti-Al-C-O-N体系涂层。通过涂层与目标夹杂的化学反应形成高熔点相附着在涂层表面，最终达到过滤夹杂的目的。本项目将系统研究热处理气氛、温度等因素对Ti3AlC2基过滤陶瓷骨架表面原位涂层物相组成和显微结构的影响，探明不同原位涂层与钛铝合金熔体/夹杂界面反应行为，揭示原位涂层活性吸附夹杂的机理；为高效低成本熔炼钛铝合金提供理论基。通过上述研究，得到以下结论：.(1) 采用Carbores® P作为添加剂制备了Ti3AlC2基过滤陶瓷，经过1100 °C埋碳处理后试样的主要物相仍然为Ti3AlC2，同时包含少量的TiC和α-Al2O3。随着Carbores®P含量增加，过滤陶瓷浆料的粘度会随之增大，进而增加过滤陶瓷孔筋的直径。此外Carbores® P的引入会改变Ti3AlC2基过滤陶瓷中Ti3AlC2颗粒的连结方式，使其连结更加紧密，最终使得其常温耐压强度由0.01 MPa左右提高至了0.20 MPa左右。.(2)采用四种不同方式(超声波法；动态脉冲激振法；动态法-谐振频率；三点测弯法)系统调查了开口过滤陶瓷的弹性模量；结果表明：对于四种测量方法而言，高度最小的样品因其加工过程中密度和均匀性更高，而导致E值最高。此外超声波法并不适合测试过滤陶瓷的弹性模量，这是因于捕捉音频信号的麦克风下方振动表面的减少，且泊松比假设值存在很大误差。.(3)Ti3AlC2试样与Ti6Al4V合金的界面实验表明在埋碳条件下经过1100°C预处理后具有最优的抗合金渗透能力，且合金中的V元素表现出最强的扩散能力，随着预热处理温度由1100°C升高到1500°C时，合金中V元素的渗透深度也由0.643 mm增长到1.324 mm。