(北京航空材料研究院 先进高温结构材料国防科技重点实验室，北京 100095)
摘 要: 真空感应熔炼高Cr铸造Ni基高温合金K4648，重熔浇注成等轴晶成形试棒。对薄截面试棒和厚截面中柱管浇道进行(1 180 ℃, 4 h)固溶处理和(1 180 ℃, 4 h)+(900 ℃, 16 h)标准热处理。铸态和热处理态试样通过光学金相、定量金相、扫描电镜及能谱分析和X射线衍射分析确定合金中相的种类、形貌和成分。结果表明：K4648合金铸态组织中主要存在γ基体、初生α相和MC碳化物；初生α相是Ni、Mo和W在Cr中的过饱和固溶体，其中Ni含量(摩尔分数)可达30%以上，本研究中的α相可命名为α-(Cr, Ni)；在0.2 N载荷下，该α相的维氏显微硬度值为6.3 GPa，是一种硬而脆的相；经(1 180 ℃, 4 h)固溶处理，初生α相和MC碳化物都会回溶，并且转变为M23C6碳化物，M23C6碳化物比初生α相具有更高的Cr含量和更低的Ni含量。固溶处理后特别是在厚截面试样中还残存未转变的α相和MC碳化物。(1 180 ℃, 4 h)+(900 ℃, 16 h)标准热处理后，合金内部广泛析出片状次生α相和γ′-Ni3(Al, Ti ,Nb)相，且在晶界区补充析出粒状M23C6碳化物，起到强化合金的作用。
关键字: 镍基高温合金；K4648；α-(Cr, Ni)相；M23C6碳化物；显微组织
（National Key Laboratory of Advanced High Temperature Structural Materials,
Beijing Institute of Aeronautical Materials, Beijing 100095, China）
Abstract: High Cr content cast Ni-base superalloy K4648 was prepared by vacuum induction melting (VIM). The ingot was remelted and poured into the investment mold to make shape equiaxed test bars. The solid solution treatment of (1 180 ℃, 4 h, A.C.) and standard heat treatment of (1 180 ℃, 4 h, A.C.)+(900 ℃, 16 h, A.C.) were carried out on both the small size section shaped test bars and large size section runner riser. The as-cast and heat-treated specimens with different section sizes were analyzed by optical metallograhpy (OM), quantitative metallography (QM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD) to determine the type, morphology, and composition of phases in K4648 alloy. The results indicate that the primary phases in K4648 alloy are mainly γ matrix, α phase and MC carbide. The primary α phase is an oversaturated solid solution of (Ni+Mo+W) in Cr. The concentration (molar fraction) of element Ni can reach above 30%, thereby primary α phase in this study can be nominated as α-(Cr, Ni). At the load of 0.2 N, α-(Cr, Ni) possesses a Vickers microhardness of 6.3 GPa, which is a brittle and hard phase. The heavy section castings exhibit larger size and amount of primary α phase, which is a kind of harmful phase and needs to be controlled. The primary α phase and MC carbides will solid-solution and transform to M23C6 carbide after (1 180 ℃, 4 h) treatment. The M23C6 carbide possesses higher Cr content and lower Ni content than that of primary α phase. The residual primary α phase and MC carbides exist after (1 180 ℃, 4 h) solid-solution treatment especially in specimens with large section size. The plate-like secondary α phase and γ′-Ni3(Al, Ti, Nb) precipitate everywhere after (1 180 ℃, 4 h)+(900 ℃, 16 h) standard heat treatment. In addition, the granular M23C6 carbide further precipitates at grain boundary region, both of them can strengthen the alloy.
Key words: Ni-base superalloy; K4648; α-(Cr, Ni) phase; M23C6 carbide; microstructure
