【摘要】 单晶涡轮叶片是航空发动机的关键热端部件,需要在高温和高腐蚀的环境下长时服役,这就需要单晶涡轮叶片具有优异的高温力学性能、较高的抗氧化和抗腐蚀性能,而镍基单晶高温合金作为航空发动机涡轮叶片的首选材料,近几十年来一直受到研究者的关注。为进一步提高先进镍基高温合金的承温能力,需不断提高先进镍基单晶高温合金中难熔元素(例如Re和W)的含量。同时,铸态镍基单晶高温合金中存在成分不均匀(严重的显微偏析)和组织不均匀(大量的枝晶间析出物)的缺陷,这种成分和组织的不均匀性如果不能被高温固溶处理消除,则将显著恶化单晶高温合金的力学性能与长时服役性能。因此,有必要探索适用于先进镍基单晶高温合金的固溶处理工艺。固溶处理工艺的发展可以分为两个阶段。第一阶段:第一代单晶高温合金,由于合金中不含Re元素,合金只需要在γ’回溶温度和初熔温度之间保温较短的时间即可实现合金组织和成分的均匀化。第二阶段:从第二代单晶高温合金开始,合金中难熔元素(尤其是Re元素)的含量不断增加,合金的成分均匀化难度显著增大,即固溶温度显著升高、固溶时间显著延长。因此,先进镍基单晶高温合金固溶处理工艺的研究重点从关注合金中各相的溶解温度和合金的初熔温度转变为合金中各元素的均匀化程度。大量的研究结果表明,低温段固溶的目的是通过固态相变的方式消除枝晶间析出物,而高温段固溶的目的是通过固相扩散的方式消除或降低合金元素的显微偏析。随着单晶高温合金的发展,先进单晶高温合金中难熔元素(例如Re和W)的含量显著提高,一方面,难熔合金元素在Ni中具有较低的互扩散系数;另一方面,难熔元素在铸态单晶高温合金中的显微偏析程度较高。因此对于先进镍基单晶高温合金,实现元素均匀化和制定合理的固溶处理工艺的难度显著提高。同时,单晶高温合金的相变温度也受到固溶处理工艺的影响。本文归纳总结了单晶高温合金固溶处理制度的研究进展,详细介绍了第二代和第三代镍基单晶高温合金的固溶处理制度,阐述了固溶处理对显微组织和成分分布的影响规律,对比了单晶高温合金传统的台阶式升温固溶处理工艺和新型的连续升温固溶处理工艺,并对重熔固溶处理工艺进行了介绍。更多还原

【Abstract】 Single crystal turbine blades are the key hot end components of aeroengine,which need serve at high temperature for relatively long time.Therefore,single crystal turbine blades should have excellent high temperature mechanical properties,good oxidation resistance and corrosion resistance at high temperature environment. As the preferred material of single crystal turbine blades,Ni based single crystal superalloy has been widely concerned by many researchers in the past few decades. In order to further improve the high temperature mechanical properties of advanced Ni based single crystal superalloys,the content of high refractory elements( such as Re and W) in advanced Ni based single crystal superalloys continuously increased. Meanwhile,typical as-cast single crystal superalloys contain inhomogeneities of composition( severe microsegregation) and microstructure( massive interdendritic precipitations). It should be noteworthy that if the inhomogeneities of composition and microstructure cannot be eliminated by high temperature solution treatment,the mechanical properties and long-term service properties of single crystal superalloys will be significantly deteriorated. Therefore,appropriate solution treatment regimes should be designed for advanced Ni based single crystal superalloys.The development of solid solution treatment process can be divided into two stages. The first stage: with regard to 1 st generation single crystal superalloys without Re element,the homogenization of microstructure and composition in this kind of alloy can be achieved by solution treated between the γ’-solvus temperature and the initial melting temperature of alloy for a relatively short time. The second stage started from the 2 nd generation single crystal superalloy,the content of refractory elements( especially Re element) in single crystal superalloy continuously increased the difficulty of homogenization of composition significantly increased,i.e. both the temperature and time of solution treatment obviously increased.Therefore,the research hotspot of solution treatment regimes of advanced Ni based single crystal superalloy changed from phase transformation temperature and incipient melting temperature of the alloy to the homogenization degree of alloying elements in single crystal superalloy.As cast Ni based single crystal superalloys contained numerous interdendritic precipitations and severe microsegregation of alloying elements.Therefore,in order to obtain uniform microstructure and composition,high temperature solution treatment is necessary. Previous studies indicated that the aim of solution treatment at low-temperature stage is to eliminate interdendritic precipitation,and the aim of solution treatment at high-temperature stage is to eliminate/reduce microsegregation degree of alloying elements. With the development of single crystal superalloy,the content of refractory elements in advanced single crystal superalloy( e.g. Re and W) obviously increased. On the one hand,refractory elements had relatively low interdiffusion coefficients in Ni,on the other hand,refractory elements had severe microsegregation in as-cast alloy. Therefore,it is difficult to eliminate microsegregation of refractory elements and design suitable solution treatment regimes. Meanwhile,phase transformation temperatures of single crystal superalloys were also affected by solution treatment regimes.In this paper,the research progress of solution treatment regimes of Ni based single crystal superalloy is summarized. Solution treatment regimes of 2 nd and 3 rd generation Ni based single crystal superalloys are detailed analyzed,and the effects of solution treatment on microstructure and microsegregation are also illustrated. Moreover,the conventional stepwise solution treatment method and newly developed continuous heating solution treatment method are compared. Meanwhile,the remelting solution treatment is also introduced in this paper.更多还原