一种新型镍基高温合金组织及性能的研究

Study on the microstructure and properties of a new type of nickel-based superalloy

GH4742(俄ЭП742)合金属于典型的高合金化难变形镍基高温合金涡轮盘材料,本文通过调整Al、Ti、Nb的成分对GH4742合金进行改进,发明了一种新型镍基高温合金。利用JMatPro模拟得到平衡相图,再利用光学金相显微镜和场发射扫描电镜对合金的晶粒组织、碳化物以及γ′相分布情况进行观察,同时对力学性能进行了检测。结果表明:平衡状态下的合金从1 400℃到300℃的冷却过程中相转变可概括为L→L+γ→L+γ+MC→γ+MC+γ′→γ+γ′+MC+μ→γ+γ′+μ+MC+M_(23)C_(6)→γ+γ′+μ+MC+M_(23)C_(6)+σ,780℃下析出γ′相的质量分数为40.88%;锻造变形工艺为γ+γ′双相区变形,1 120℃固溶后经过标准双时效处理(850℃/6 h/AC+780℃/6 h/AC)后的显微组织明显可见两种不同尺寸晶粒,小晶粒(13μm)呈项链状分布于大晶粒(100μm)周围;该合金中的碳化物主要为大尺寸、不规则形状的MC(NbC、TiC、VC),断续穿晶和沿晶分布;强化相γ′相的分布状态也有大小两种不同尺寸,γ′_(I)相平均直径为600 nm,γ′_(II)相平均直径为150 nm,两种尺寸γ′相强化的良好匹配,使得该合金在具有较高强度的同时又具有较高的塑性,力学性能优异,室温抗拉强度1 478 MPa,尤其是650℃/863 MPa下的持久性能为194 h,远远超过GH4742合金650℃/823 MPa持久下50 h的标准。

GH4742(Russian ЭП742) alloy is a typical high-alloyed hard-to-deform nickel-based superalloy turbine disk material.In this paper,GH4742 alloy is improved by adjusting the composition of Al,Ti and Nb,and a new type of nickel-based superalloy was invented.Use JMatPro to simulate the equilibrium phase diagram,and then use optical metallographic microscope and field emission scanning electron microscope to observe the alloy′s grain structure,carbides and γ′ phase distribution,and at the same time to detect the mechanical properties.The results show that the phase transition of the alloy in the equilibrium state from 1 400 ℃ to 300 ℃ during the cooling process can be summarized as L → L+γ → L+γ+MC →γ+MC+γ′ → γ+γ′+MC+μ → γ+γ′+μ+MC+M_(23)C_(6) → γ+γ′+μ+MC+M_(23)C_(6)+σ.The volume fraction of γ′ phase precipitated at 780 ℃ is 40.88%.The forging deformation process is γ+γ′ dual phase zone deformation.After solution at 1 120 ℃,the microstructure after standard double aging treatment(850 ℃/6 h/AC+ 780 ℃/6 h/AC) clearly shows two different size grains.Small crystal grains(13 μm) are distributed around large crystal grains(100 μm) in a necklace shape.The carbides in this alloy are mainly MC(NbC,TiC,VC) of large size and irregular shape.The distribution state of the strengthening phase γ′ phase also has two different sizes.The average diameter of γ′_(I) phase is 600 nm,the average diameter of γ′_(II) phase is 150 nm.The good matching of the two sizes of γ′ phase strengthening makes the alloy have high strength and high plasticity at the same time,and excellent mechanical properties.The tensile strength at room temperature is 1 478 MPa,and the durability at 650 ℃/863 MPa is 194 h,which far exceeds the standard of 50 h at 650 ℃/823 MPa for GH4742 alloy.