颗粒增强改善搪瓷涂层的抗热震性能机制研究

IMR OpenIR

	颗粒增强改善搪瓷涂层的抗热震性能机制研究
	陈明辉
学位类型	博士
导师	牛焱 ; 朱圣龙
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	搪瓷涂层抗热震晶化颗粒增强裂纹扩展
摘要	"搪瓷制作成本低，内部氧迁移率低，可与金属发生化学结合并形成致密涂层，作为金属基体的高温防护涂层材料有其独特的优点。但是搪瓷软化点低及本征脆性限制了玻璃搪瓷涂层使用范围。当涂层的软化点低于服役环境温度时，搪瓷涂层将软化丧失刚度而失效；搪瓷涂层本征脆性使得涂层内热应力难以通过蠕变方式得到释放，裂纹扩展速率高，易于在冷热循环环境下剥落。因此，发展搪瓷涂层组织结构控制方法，提高其抗高温性能和抗热震性能，具有重要的科学意义和应用价值。 NiCrAlY合金颗粒对搪瓷的热学和力学性能均有影响。添加30%的NiCrAlY合金颗粒可使复合搪瓷的热膨胀系数提高约15%，而使断裂韧性提高约1倍。NiCrAlY合金颗粒增韧的主要机制为：通过裂纹的偏转和桥连，提高裂纹扩展功。添加刚玉颗粒也对搪瓷的的热学和力学性能也有显著影响，但其机制与NiCrAlY合金颗粒的增强机制有所不同。所研究的搪瓷与刚玉颗粒之间存在明显的界面反应，其反应产物为锌类晶石以及长石，这一反应减少了搪瓷基体中的助熔剂组元含量，相应地增加了网络形成剂组元（Al）的含量，从而大大提高了材料软化点。界面反应、第二相颗粒/裂纹的相互作用都对复合材料的力学性能有重要影响，本论文设计了分别以大颗粒刚玉增强搪瓷和小颗粒刚玉增强的两种搪瓷复合材料验证了这一观点。小颗粒刚玉具有较高的比表面积，其作用机制主要为界面反应或界面扩散机理（Interdiffusion mechanism），满足关系式： , 而大颗粒刚玉具有较低的比表面积，其主要增强方式为裂纹偏转机理（Deflection mechanism）以及桥连机理（Bridging mechanism），满足关系式：。其中σc、σm分别为搪瓷釉-氧化铝复合材料以及纯搪瓷釉的抗弯强度值，β为搪瓷釉/氧化铝界面处原子扩散所控制的参数，V为氧化铝颗粒添加的体积分数，ξ为常数（对于偏转机理ξ = 0.61；而对于桥连机理ξ = 4.35）。高温晶化处理可使搪瓷-氧化铝复合涂层显微组织稳定化，从而改善搪瓷-氧化铝复合涂层的抗高温氧化及抗热震性能。搪瓷-氧化铝-NiCrAlY三元复合涂层具有优异的1000℃抗氧化及抗热震能力。搪瓷基复合涂层/高温合金基体的主要界面反应为：基体合金中的Cr和Al与搪瓷中Zn发生置换反应，反应产物向涂层表面扩散，最后形成了锌类晶石（ZnCr2O4或ZnAl2O4）。"
其他摘要	"As high-temperature-corrosion-resistant coating materials on metals, glasses showed many specific merits such as low cost, low diffusion coefficient of oxygen in them, chemical bonds to the metal substrates and forming compact structures. However, the lower soft point and inherent brittleness limit their use in broader applications. At service temperatures higher than the soft point, glass coatings would be invalid in corrosion protection in terms of their softening and rigidity-losing then. Glass coatings could hardly release their thermal stresses by creep deformation due to their high inherent brittleness, which lead to cracks propagating at a high velocity, and thus to the spallation of coatings under thermal cycles. So, developing methods to control structures and enhancing resistances to high-temperature-oxidation and thermal shock are of great significance for the glass coatings both in scientific research and actual application. NiCrAlY alloy platelets inclusion could exert impacts both on the thermal and mechanical properties of the glass coatings. At a fraction of 30 wt.% of the NiCrAlY alloy inclusion, the TEC values of glass-NiCrAlY composites enhanced nearly by 15% while the fracture toughness enhanced by 100%. The main toughening mechanisms of NiCrAlY inclusion were associated with crack deflection and bridging, which increased largely the crack-propagating work siginificantly. Addition of corundum particles also affected the properties of glasses, but in a way different from those of NiCrAlY inclusions. Apparent interfacial reaction happened between the glass matrix and included corundum particles, which formed interfacial phases of gahnite and feldspar. It decreased the amount of network modifiers (such as Zn, K and Na) while increased the amount of network former (Al) in the glass network, accounting for the enhancement of soft point. Both the interfacial reaction and inclusion/crack interaction had important influences on the mechanical properties of the glass/corundum composites. In this thesis, by designing two glass/corundum composite systems (at different particle sizes of corundum), the strengthening mechanisms were demonstrated. For small corundum particles with a high surface ration, the strengthening function vs. inclusion fraction follows the interdiffusion mechanism as: ; while for large corundum particles with a lower surface ratio, the strengthening function vs. inclusion fraction follows deflection mechanism and bridging mechanism: . where σc and σm denote are the bending strength of glass/corundum composites and glass matrix respectively, β is a diffusion-controlled parameter, V the volume fraction of corundum particles and ξ equals 0.61 for deflection mechanism and 4.35 for bridging mechanism. The resistance against oxidation and thermal shocking could be enhanced by microstructure stabilization of the glass-alumia composite coatings via heat treatment at 850 oC for 100 h. Glass-alumina-NiCrAlY tri-composite coatings could possessed high resistances to oxidation and thermal shock at 1000 oC. At the interfaces of coatings/substrate, interfacial reaction happened between Cr (or Al) from the superalloy substrates and oxide of ZnO from the glass coatings. The reaction results dissolved and diffused in the glassy coatings to the out surface where gahnite (ZnCr2O4 or ZnAl2O4) formed finally."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64330
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	陈明辉. 颗粒增强改善搪瓷涂层的抗热震性能机制研究[D]. 北京. 中国科学院金属研究所,2011.