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A comparison of the precipitation behavior in PM gamma-gamma ' nickel-base superalloys

机译：PMγ-γ'镍基高温合金中析出行为的比较

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摘要

The precipitation of gamma' in three powder metallurgy nickel-base superalloys during continuous cooling following supersolvus solution treatment was quantified and compared using a fast-acting, mean-field analysis and selected independent experimental observations. The three alloys, LSHR, IN-100 and Rene 88, were chosen based on the range of gamma' solvus temperatures and diffusivities which they exhibit. With its intermediate solvus temperature, LSHR served as the baseline material. For all three alloys, the average size of secondary gamma' (), which is formed at higher temperatures, followed a dependence on cooling rate (theta) over dot of the form = B (theta) over dot(-0.5), in which B is a constant whose value increases with solvus temperature. This behaviour was rationalized on the basis of the narrow range of temperature over which nucleation occurs for secondary gamma', and hence the importance of precipitate growth in controlling precipitate size. The simulation results also revealed that the breadth of the distribution of secondary gamma' sizes was rather small with the ratio of the standard deviation to near 0.03 in all cases. In contrast to the behaviour for secondary gamma', tertiary gamma' was predicted to nucleate over a broad, but similar, range of temperatures for all of the alloys. Because nucleation and growth of tertiary gamma' occur at relatively low temperatures, and thus lower effective diffusivities, the sizes of these precipitates were predicted to be more than one order of magnitude smaller than that of the secondary gamma'.
机译：在超固溶处理后的连续冷却过程中，对三种粉末冶金镍基高温合金中γ'的沉淀进行了定量，并使用了快速作用，平均场分析和独立的实验观察进行了比较。根据伽马固溶线温度范围和扩散率选择了三种合金，即LSHR，IN-100和Rene 88。 LSHR的中间溶解温度为基准材料。对于所有三种合金，在较高温度下形成的次级γ'（）的平均尺寸，随冷却速率（θ）的变化而变化，其形式为 = B点（-0.5）上的θ，其中B是一个常数，其值随着固溶温度的增加而增加。基于次级γ′发生形核的狭窄温度范围，因此这种行为是合理的，因此，在控制沉淀尺寸方面，沉淀生长非常重要。模拟结果还表明，在所有情况下，次级伽玛值分布的广度都很小，标准偏差与的比率接近0.03。与次级γ'的行为相反，预计第三级γ'在所有合金的宽广但相似的温度范围内成核。由于叔γ′的成核和生长是在相对较低的温度下发生的，因此有效扩散率较低，因此这些沉淀物的尺寸预计比次级γ′的尺寸小一个数量级以上。

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