超高温NiAl合金锥形薄壳件制备成形一体化新工艺

针对NiAl合金板坯制备及板坯成形锥形薄壳件存在的材料流动及组织性能控制困难的问题，提出了一种制备成形一体化新工艺。该工艺是将塑性成形和反应合成在同一工步中，即先将Ni/Al叠层箔置于模具中进行塑性成形，随后对成形的Ni/Al叠层箔原位加热加压反应合成NiAl合金薄壳件。采用三维扫描仪及Geomagic Studio/Qualify对锥形薄壳件的形状精度进行了分析，采用扫描电子显微镜( Scanning Electron Microscope, SEM )和电子背散射衍射( Electron Backscatter Diffraction, EBSD )技术对其微观组织进行了表征，并对构件的高温力学性能进行了测试。结果表明，采用该新工艺制备的锥形薄壳件成形效果良好，整体型面偏差尺寸在±0.1 mm以内；构件沿轴截面壁厚平均偏差为0.012 mm，沿横截面壁厚平均偏差为0.072 mm，构件轴截面壁厚分布均匀性及组织成分均匀性高于横截面。构件高温力学性能稳定，1000 °C时平均屈服强度为77.8 MPa，平均抗拉强度为82.6 MPa。NiAl合金构件的微观晶粒形貌与Ni箔的初始热处理状态及Ni/Al箔的初始厚度有关，未退火的Ni箔将延缓粗晶区晶粒的长大，减小初始箔材厚度可实现晶粒的进一步细化。

A New Integrated Process of Forming and Reaction Synthesis for Ultra-High Temperature NiAl Alloy Thin-Walled Conical Components

In order to solve the problems in material flow, microstructure and mechanical properties control during the process of preparing NiAl alloy sheets and forming thin-walled conical components, a new integrated process of forming and reaction synthesis is proposed. In the new process, plastic forming and reaction synthesis are accomplished in the same stage. The Ni/Al laminated foils are first alternately placed in the mold for plastic forming, and then, the formed Ni/Al laminated foils are heated and pressurized in-situ to synthesize into NiAl alloy thin-walled components. The shape accuracy of the thin-walled conical component was analyzed by 3D scanner and Geomagic Studio / Qualify. The microstructure was characterized by scanning electron microscope ( SEM ) and electron backscatter diffraction ( EBSD ) technology. The mechanical properties of the components under high temperature were tested. The results show that the thin-walled conical components manufactured by the new process have good forming precision, and the overall surface deviation size is within ±0.1 mm. The average deviation of the wall thickness along the axial section is 0.012 mm, and that along the transverse section is 0.072 mm. The uniformity of wall thickness and composition along the axial section are higher than those along the cross section. The mechanical properties of the components are stable under high temperature with the average yield strength of 77.8 MPa and the average ultimate tensile strength of 82.6 MPa at 1000 °C. The microscopic grain morphology of the NiAl alloy components is related to the initial heat treatment state of Ni foil and the initial thickness of Ni/Al foils. The unannealed Ni foil will postpone the growth of grains in coarse grain regions. The grain size of NiAl alloy can be refined by reducing the thickness of the initial Ni/Al foils.