先进超超临界机组用Inconel 740合金的组织稳定性研究

Study on Microstructure Stability of Inconel 740 for Advanced Ultra Supercritical Unit

采用SEM、FEG-SEM、TEM和EDS等测试方法研究一种先进超超临界机组用新型高温合金Inconel 740在固溶处理、沉淀硬化处理和750℃时效3 000 h过程中的组织稳定性。结果表明,固溶处理状态下的Inconel 740组织晶粒度3～4级,一些颗粒尺寸大的一次(Nb、Ti)C和TiN弥散分布于γ基体上,γ′相形核于晶内;沉淀硬化处理主要在晶内共格析出γ′相,在晶界析出大量的M23C6和少量的G相;750℃长期时效条件下,γ′相发生Ostwald熟化,颗粒粗化,γ晶界逐渐被G相占据,并且时效300 h时在晶界附近开始析出针状的η相,随时效的持续,η相长大并趋向于呈现魏氏组织形态。Inconel 740的组织稳定性有待于进一步改善。

Microstructures of Inconel 740, a new type nickel-based superalloy for advanced ultra supercritical steam boiler tubing, at different heat treatment conditions including solution treatment, precipitation treatment and ageing at 750 ℃ for 300, 1 000 and 3 000 h were investigated by using SEM （scanning electron microscope）, FEG-SEM（field emission gun scanning electron microscope）, TEM（transmission electron microscope） and EDS（X-ray energy dispersion spectroscopy）. The results indicate that the grain size is about ASTM No.3 to 4, many large primary （Nb,Ti）C and TiN precipitate in the matrix randomly and gamma prime phase nucleate after solution treatment. After precipitation treatment, a lot of M23C6 carbide and a little of G phase precipitate at grain boundaries, gamma prime phases precipitate coherently in the grains. Gamma prime phases grow with Ostwald ripening rule during ageing at 750 ℃, G phase become dominant on grain boundary after long term exposure, eta phase begin to precipitate along gamma grain boundary at 300 h, grow with ageing time and tend to show Widmanstatten pattern after 3 000 h. Microstructure stability of fuconel 740 requires further improvement.