钨钼烧结炉用氧化锆制品损毁形式及机制分析

Wear forms and mechanism analysis of zirconia products for tungsten molybdenum sintering furnaces

为提升高纯氧化锆制品在超高温环境下的应用性能,采用XRD和扫描电镜等手段对钨钼烧结中频炉用后氧化锆制品进行分析,探讨了其损毁机制。结果表明,2 000℃左右高温下,W或Mo蒸发、凝聚,沉积于氧化锆制品的气孔中,改变了其自身结构,温度变化时热应力开裂;W或Mo遇氧气氧化生成WO_3或MoO_3,进而与氧化锆晶格内的CaO稳定剂反应生成Ca WO_4和Ca MoO_4,稳定剂脱溶,导致氧化锆晶相失稳,由立方相或四方相转变为单斜相,升降温过程中,发生相变并伴随体积变化,使制品出现龟裂和断裂损毁;钨钼坯体在成型时采用了含碳结合剂,在还原性气氛烧结时结合剂高温分解成游离碳,并附着于氧化锆砖上形成局部强还原性气氛,将氧化锆碳化,进而与保护气氛中的N_2反应氮化,形成碳化锆或者碳氮化锆混合物,破坏氧化锆制品的显微结构,造成制品强度衰减。

In order to improve the application performance of high purity zirconia products in ultra high temperature environment,XRD and SEM were used to analyze the used zirconia products in an intermediate frequency furnaces to sinter tungsten and molybdenum. The damage mechanism was discussed. The results show that W or Mo evaporates and condenses at high temperatures of about 2 000 ℃,depositing on the pores of zirconia products and changing the structure of zirconia. Thermal stress cracking occurs when the temperature changes. W or Mo is oxidized to WO3 or MoO3 by oxygen,and then reacts with CaO stabilizer in the lattice of zirconia forming Ca WO4 and Ca MoO4,and the stabilizer dissolves,resulting in the destabilization of the crystal phase of zirconia and the transformation from cubic phase or tetragonal phase to monoclinic phase,and the volume changes correspondingly,which makes the products crack and rupture.The tungsten and molybdenum bodies adopt the carbon containing binder during shaping,and the binder is decomposed into free carbon at high temperatures when sintering in the reducing atmosphere. The free carbon attaches to the zirconia brick to form local strong reduction atmosphere,carbonizes zirconia,and thus reacts with N2 in the protective atmosphere to form a zirconium carbide or zirconium nitride mixture,which destroys the microstructure,and decreases the strength of zirconia products.