固溶冷却速度和后处理对新型FGH98Ⅰ镍基粉末高温合金γ′相析出和显微硬度的影响

Effect of Solution Cooling Rate and Post Treatment on γ′ Precipitation and Microhardness of a Novel Nickel-Based P/M Superalloy FGH98Ⅰ

摘要:

对新型镍基粉末高温合金FGH98Ⅰ分别进行过固溶和过固溶+亚固溶后处理，利用场发射扫描电镜和显微硬度仪研究了冷却速度对合金γ′相析出和显微硬度的影响。结果表明：随着固溶冷却速度增加，合金中二次和三次γ′相的尺寸减小，二次γ′相形状从蝶形向球形转变，γ′相的形状因子和颗粒密度增大，面积分数和晶界表观宽度减小。在冷却速度≤1.4 ℃/s时，冷却γ′相分两阶段形核；冷速越快，合金的硬度越高，时效后硬度增高越多；过固溶处理后的亚固溶处理使冷却γ′相粗化和方形化，形状因子减小，晶界γ′相析出密集区消失，硬度降低。另外，还建立了冷速与γ′相平均尺寸和合金硬度之间的函数关系式。该结果为FGH98Ⅰ合金实际双性能盘固溶热处理工艺的选择提供了理论参考。

Abstract:

The effects of solution cooling rate on γ′ precipitation and microhardness of a novel nickel-based powder metallurgy (P/M) superalloy FGH98Ⅰin superslovus and superslovus plus subslovus post treatment condition were studied by means of field emission scanning electron microscope (FESEM) and microhardness tester. The results show that the average sizes of secondary and tertiary γ' precipitates decrease with increasing of the cooling rate. Meanwhile, the shape of secondary γ' precipitates changes from the butterfly-like to the spherical, the shape factor and particle density increase, while the area fraction and the apparent width of the grain boundary decrease. It is also found that γ′ phases nucleate and precipitate in two stages if the cooling rate is not faster than 1.4 °C/s. The faster the cooling rate is, the higher the hardness is, and the more the hardness increases are after aging. Subslovus post-heat treatment makes the cooling γ' phases coarser and more cubic, decreases the shape factor, eliminates the γ′ precipitates-riched grain boundary and lowers the microhardness. In addition, the average sizes of γ′ phases and the hardness as a function of cooling rate are established. The above results can be used as a theoretical reference for the selection of actual superslovus processing of FGH98Ⅰdual-property disk.