碳化物增强新型因瓦合金的成分优化及热处理工艺研究

Composition Optimization and Heat Treatment Study of Carbide-Strengthened Novel Invar Alloys

摘要:

因瓦合金因其在居里温度下极低热膨胀系数的显著特性，可用于制备尺寸精度高或尺寸要求恒定的元器件，在航空航天和精密仪器等领域中受到广泛关注。然而，因瓦合金较低的强度限制了应用范围，细化晶粒、固溶强化和沉淀强化是提高因瓦合金强度的主要途径。为制备膨胀系数低且力学强度高的高性能因瓦合金，以典型因瓦合金Fe-36Ni为研究对象，在合金熔炼中添加钒（V）和碳（C）元素，借助金相显微镜、扫描电镜、透射电镜等表征技术，研究了V、C元素添加对热轧成型因瓦合金Fe-36Ni组织形貌的影响及作用机理。研究结果表明，适量添加V和C元素 ，可在基体中形成细小均匀的钒碳化物（VC）颗粒，该颗粒对基体形成沉淀强化，提高了基体奥氏体组织的均匀性，从而提高了基体强度。过量添加V和C元素，不仅容易造成VC颗粒偏聚，同时还会导致合金中的Si元素在晶界聚集，形成大块硅夹杂，使合金塑性变差，热膨胀系数提高。此外，采用合理的热处理工艺，即低温固溶、超长时效的热处理方法，不仅可使VC相在合金基体组织中均匀析出，形成沉淀强化，还可避免合金中的奥氏体组织的在热处理过程中的异常长大。本研究为制备力学强度高且膨胀系数低的高性能因瓦合金提供了理论支撑。

Abstract:

Invar alloys have attracted widespread attention in the aerospace and precision instrument fields in recent years due to their low thermal expansion coefficient. However， their relatively low strength limits their application range. Currently， researchers generally believe that grain refinement， solid solution strengthening， and precipitation strengthening are the main ways to improve the strength of Invar alloys. This paper mainly studies the effects and mechanisms of vanadium and carbide compounds （VC） on the microstructure of the typical hot-rolled Invar alloy Fe-36Ni， and solves the problem of grain secondary growth during the heat treatment process by changing the existing heat treatment methods. The microstructure of the Invar alloy is characterized by metallographic microscopy， scanning electron microscopy， transmission electron microscopy， and other means. The results show that adding appropriate amounts of V and C elements can form fine and uniform VC particles， which precipitate to strengthen the matrix and improve the uniformity of the matrix austenite structure. Excessive addition of V and C elements not only leads to the agglomeration of VC particles but also causes the accumulation of silicon elements at grain boundaries， forming large silicon inclusions， which reduces the plasticity and increases the thermal expansion coefficient of the alloy. In addition， through appropriate heat treatment processes， the growth of the matrix structure during VC precipitation can be effectively prevented. This study adopts a low-temperature solution treatment plus ultra-long aging heat treatment method， which effectively enables the carbide to uniformly precipitate in the alloy matrix to form precipitation strengthening， while also avoiding abnormal growth of the austenite structure in the alloy.