高温轻量刚玉材料烧结的原位应力与超塑性关系及其微纳米封闭气孔形成机理研究

As furnace lining, lightweight refractories in high temperature industry can significantly reduce energy consumption, and largely benefit high temperature industry as a whole for energy-saving and emission-reduction, which is one of the important topics concerning this field now, the key point lies in the formation of mirco-closed pores. High temperature lightweight corundum materials with excellent performances is the goal of study. Firstly the superplasticities in high temperature of different nano-aluminas are compared, and the appropriate crystal form and critical temperature for superplasticity are determined. Then the constitutive relation of superplastic nano-alumina based on temperature is established, the effect of the nano-aluminas on performances and microstructures of lightweight corundum materials is studied, the sintering situation under the dual-scale effect is understood; The second phase, such as MgO and CaO, are introduced and their influence on performances and microstructure of lightweight corundum materials are investigated, the sintering behavior of lightweight corundum in condition of phase-stress-excess-vacancy diffusion is investigated, the matching relation between in situ stress and superplasticity of lightweight corundum during the sintering process is ascertained. Finally, the microscopy for high temperature process and finite element analysis method are applied, the superplastic deformation law of high temperature lightweight corundum materials under in-situ stresses is revealed, and the formation mechanism of micro-closed pores is ascertained,it provide a theoretical basis for preparation of new high-temperature lightweight corundum material.

高温工业炉衬耐火材料轻量化可大大降低工业窑炉能耗，对整个高温工业节能减排具有举足轻重的意义，也是目前国内外本领域所关注的重要课题，其关键在于形成大量微纳米封闭气孔。项目以轻量刚玉材料为研究对象，通过比较不同纳米氧化铝的高温超塑性，确定其合适晶型及临界超塑性温度，建立纳米氧化铝超塑性材料基于温度的本构关系，并明确纳米氧化铝引入方式及数量对高温轻量刚玉材料性能及显微结构的影响，了解微纳米双尺度效应下的材料烧结情况；同时研究不同MgO、CaO掺杂后高温轻量刚玉材料性能及显微结构的变化，探索掺杂相应力超额空位扩散条件下的应力-超塑性烧结行为，确立其烧结过程中的原位应力-超塑性匹配关系；利用高温过程显微技术研究处于原位应力作用下高温轻量刚玉材料的超塑性形变规律和材料微纳米封闭气孔形成机理，为制备新型高温轻量刚玉材料提供理论基础。

开发能够直接在工作层使用的轻量化耐火材料对整个高温工业节能减排具有举足轻重的意义，其关键在于制备显气孔率低、具有大量微纳米封闭气孔的轻量化材料。项目以高温轻量刚玉材料为研究对象，首先，比较了不同纳米氧化铝的高温超塑性，确定合适超塑性晶型并建立纳米氧化铝超塑性材料的本构关系；其次，研究了纳米氧化铝、MgO/CaO微粉引入方式及数量对高温轻量刚玉材料性能及显微结构的影响；最后，从晶界-气孔移动速率关系和曲面应力-相应力关系两方面探明高温轻量刚玉材料微纳米封闭气孔形成机理。.主要结论如下：（1）相比于纳米α-Al2O3，纳米γ-Al2O3具有更大的应变和更小的高温弹性模量，因此，具有更好的超塑性。（2）向α-Al2O3微粉中引入纳米氧化铝，其与氧化铝微粉组成的纳-微米双尺度烧结能够提供更大的曲面应力，促使纳米氧化铝超塑性发挥，晶界移动速率加快，气孔二次细微化时间缩短。试样的闭口气孔率增加，体积密度和显气孔率减小，孔径和导热系数降低，晶内气孔数量增多。然而，纳米氧化铝引入量过多时，由于其填充效应反而会对试样性能造成不利影响。（3）在α-Al2O3微粉和纳米氧化铝混合料基础上，添加MgO/CaO微粉，它们与Al2O3反应伴随体积膨胀所产生的应力，能够促使纳米氧化铝的超塑性进一步发挥，加快晶界移动速率，晶界快速封闭并分割气孔，试样闭口气孔率增加，体积密度和显气孔率降低，孔径和导热系数减小。然而，由于反应过程中的体积膨胀及第二相钉扎效应，纳米氧化铝超塑性无法完全发挥，试样晶粒减小，其主要为晶间气孔。当添加MgO/CaO微粉过多时，体积效应过于明显，产生的相应力过大将导致晶界迁移过快而发生断裂，试样结构松散。（4）对高温轻量刚玉材料烧结过程中的晶界扩散、晶粒生长、致密化等动力学过程开展研究，当试样内部原位张应力为15.89~17.18 MPa左右时，纳米颗粒超塑性可以较好发挥，加快晶界移动，从而形成封闭气孔。.项目的研究成果对于掌握性能优异的高温轻量耐火材料制备基础理论和关键核心技术具有重要意义。