氮气喷射成形FGH4095的组织特征

Microstructure of spray-formed superalloy FGH4095

以氮气为雾化气体采用喷射成形工艺制备了FGH4095高温合金沉积坯,记录了沉积过程坯体表面温度曲线,并采用定量金相法、排水法测试了坯体致密度,观察了坯体晶粒及γ'相的形貌.结果表明采用氮气作为雾化介质进行喷射成型喷射沉积坯基体致密度可达99%以上,但也存在着较大的(1—2μm)的气孔,经热等静压和近等温锻后宏观气孔闭合,氮以尺寸不超过1μm的碳氮化物形式存在.喷射沉积坯以等轴晶组织为主,坯体内部平均晶粒尺寸约为20-40μm,近表面区域晶粒较细,约为13μm;一次γ'相多数呈尺寸约0.3—0.5μm不规则块状形貌.喷射成形坯组织结构的形成与喷射成形过程的降温过程有密切关系.

Spray-forming technology can produce billets with similar microstructure and higher productivity compared with the P/M pro- cess. The nickel based superalloy FGH4095 billet was produced by spray-forming with nitrogen as atomization gas. The pressure of the atomization gas and the temperature of the deposit zone were recorded. The compactness of the deposit was characterized by quantitative metallography and Archimedes method. The grain structure of γ substrate and the size and morphology of γ′ phase were observed. Results show that the density of the deposit produced by nitrogen spray forming reaches about 99% and little amount of pores with diameters about 1--2 μm could be detected in the deposit matrix. While, pores could be enclosed by HIP and near iso-thermal forging process; Nitrogen was existed as carbonitride with diameters less than 1 μm. The average grain size of the equiaxed grains in the interior of the deposit is about 20-40 μm, while the grains near the surface of the deposit are finer with average grain size about 13μm; the primary γ′ phase which has diameters about 0.3-0.5 μm possesses irregular block feature. The microstructure of the spray deposit is related to the temperature history of the alloy during the spray forming process.