Rapid and accurate characterization method for Cr23C6 type carbide and sigma phase in wrought superalloy
By using EPMA backscattering mode and elemental surface scanning technology, Cr23C6 type carbides and σ phase in deformed superalloys can be directly distinguished, solving the problem of difficult differentiation in existing technologies. This achieves an efficient and accurate characterization method, improves analytical efficiency, and provides reliable performance data.
Patent Information
- Application Number
- CN202511538157.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2026-02-13
AI Technical Summary
Existing technologies struggle to quickly and accurately distinguish between Cr23C6-type carbides and σ phases in deformed superalloys. Traditional methods are complex, time-consuming, and difficult to operate. Transmission microscopes make it difficult to differentiate between the two methods, hindering rapid and accurate characterization. Furthermore, EDS point analysis is susceptible to matrix interference.
Electron probe microanalysis (EPMA) with backscatter mode combined with elemental surface scanning was used to directly distinguish the two phases by observing the difference in atomic number and elemental distribution between Cr23C6 type carbide and σ phase. The determination was made by combining the surface scanning results of Cr, C and Mo elements.
It achieves rapid, simple, and low-cost large-area accurate characterization, improves analysis efficiency by more than 50%, avoids local sampling errors, and provides reliable performance optimization data.
Smart Images
Figure CN121521919A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of metal material microstructure characterization, and particularly relates to a method for rapidly and accurately characterizing Cr 23 C6 carbide and sigma phase. BACKGROUND
[0002] High-temperature alloys are the core materials of high-temperature components such as aero-engines and gas turbines, and the performance stability is closely related to the evolution of microstructure. In the environment of 550 DEG C to 800 DEG C, alloys (such as Inconel 617, Inconel 718, Incoloy 800H, Incoloy 925, etc.) will precipitate various strengthening phases and harmful phases. Among them, the synergistic precipitation of Cr 23 C6 carbide and sigma phase is particularly typical. The precipitation of Cr 23 C6 can pin the grain boundary to inhibit grain coarsening, but excessive precipitation will lead to a decrease in intergranular bonding force and an increase in intergranular corrosion tendency. Since the size of Cr 23 C6 is small and uniformly distributed, the harm to the overall performance of the alloy is controllable, and it is allowed to exist in an appropriate amount in engineering applications. The precipitation temperature of sigma phase overlaps with that of Cr 23 C6, but it lags behind Cr 23 C6 in dynamics. It usually nucleates at the phase boundary of Cr 23 C6 and the austenitic matrix, and expands along the grain boundary or the phase boundary. Since the sigma phase has extremely high hardness and extremely low toughness, its precipitation will reduce the intergranular bonding force and form a crack initiation source, resulting in a significant decrease in the impact toughness, creep resistance and corrosion resistance of the alloy. The allowable degree of sigma phase in engineering applications is low, and its content and distribution need to be strictly controlled.
[0003] Since the morphology and distribution characteristics of the two phases are extremely similar under a conventional metallographic microscope (such as the attached Figure 1 ) or a scanning electron microscope (such as the attached Figure 2 ), the gray scale and contrast difference are weak, and it is difficult to accurately distinguish them by morphology observation alone. Moreover, the selection of mixed etching solution for metallographic etching is extremely limited, and the etching process is easy to cause the carbonized phase to be etched off, so that effective characterization cannot be achieved.
[0004] In the prior art, in order to accurately characterize the two precipitated phases, it is often necessary to identify them by diffraction spot calibration of a transmission electron microscope (TEM), but the TEM sample preparation is complex, time-consuming and requires high technical requirements for the operator. In addition, the point analysis of energy dispersive spectroscopy (EDS) in the prior art is easily interfered by the matrix, and cannot achieve rapid and accurate determination in a large area. SUMMARY
[0005] The application provides a method for rapidly and accurately characterizing Cr 23The application discloses a rapid and accurate characterization method for C6 carbide and sigma phase.
[0006] The technical scheme of the application is as follows: Cr in wrought superalloy 23 The rapid and accurate characterization method for C6 carbide and sigma phase comprises the following steps: 1) sample preparation: a surface-finished wrought superalloy sample to be measured is obtained through step-by-step sandpaper grinding, mechanical polishing and electrolytic polishing; 2) EPMA backscattering mode observation: the wrought superalloy sample is observed in a backscattering mode, Cr 23 The C6 carbide is black due to a low atomic number and is continuously precipitated along grain boundaries; the sigma phase is bright white due to containing high-atomic-number elements and is attached to Cr 23 The C6 carbide nucleates at the phase boundary between the C6 carbide and the matrix; 3) EPMA element area scanning analysis: Cr, C and Mo element distribution scanning is performed on the target area which is black and bright white, Cr 23 The C6 carbide is enriched with Cr and C elements, and the sigma phase is enriched with Mo elements, and the phase type is accurately determined through element distribution differences.
[0007] The application has the following beneficial effects: 1) the application directly distinguishes Cr 23 C6 carbide and sigma phase through an EPMA backscattering mode, combines element area scanning verification, does not need complex sample preparation, and improves analysis efficiency by more than 50%; 2) compared with a TEM characterization method, the method is simple and low in cost, can be used for large-area analysis, and avoids local sampling errors; 3) the application accurately determines the phase type through C and Mo element content mapping, and provides reliable data support for alloy performance optimization. DETAILED DESCRIPTION
[0008] Figure 1 It is a metallographic microscope photo of a Ni-Cr-Fe-Mo-Nb high-temperature alloy after aging and precipitation, and Cr 23 C6 carbide and sigma phase are distributed along the grain, and the size, distribution characteristics and color are almost the same, and the two phases are difficult to distinguish under a metallographic microscope when being precipitated cooperatively; Figure 2 It is a scanning electron microscope photo of a Ni-Cr-Fe-Mo-Nb high-temperature alloy after aging and precipitation, and Cr 23 C6 carbide and sigma phase are both bright white, and the difference between the gray scale and contrast is small, and cannot be effectively distinguished; Figure 3EPMA backscattered morphology photo of Ni-Cr-Fe-Mo-Nb high-temperature alloy after aging precipitation; Figure 4 EPMA backscattered element distribution map of Ni-Cr-Fe-Mo-Nb high-temperature alloy after aging precipitation; wherein, (a) is the Cr element distribution map, (b) is the C element distribution map, and (c) is the Mo element distribution map. DETAILED DESCRIPTION
[0009] Select Ni-Cr-Fe-Mo-Nb high-temperature alloy as sample, and the sample is solid solution treated at 1150℃ for 0.5h, and then aged at 650℃ for 8h, so as to promote Cr 23 C6 type carbide and sigma phase precipitation; Cr 23 The rapid and accurate characterization method of C6 type carbide and sigma phase includes the following steps: 1) Sample preparation: through sandpaper step-by-step grinding, mechanical polishing and electrolytic polishing, 400 mesh, 800 mesh, 1200 mesh and 1500 mesh sandpaper are used in turn to polish the surface until there is no obvious scratch, 2.5μm diamond polishing agent is used for mechanical polishing for 5min, and then high-chloric acid-ethanol mixed solution (1:9) is used for electrolytic polishing, and the parameter setting is voltage 30V, time 30s; Obtain the surface-finished Ni-Cr-Fe-Mo-Nb high-temperature alloy sample; 2) EPMA backscattered mode observation: place the prepared sample in the electron probe microanalyzer (model JEOL JXA-8530F), and observe under backscattered mode, as shown in Figure 3 Cr 23 C6 type carbide is black due to low atomic number, and continuously precipitates along the grain boundary; Sigma phase is bright white due to containing high atomic number elements, and is attached to Cr 23 C6 type carbide and nucleates at the phase boundary between it and the matrix; 3) EPMA element area scanning analysis: element area scanning analysis is carried out in the morphology observation area of the sample, and Cr, C and Mo element distribution scanning is carried out on the target area with black and bright white color, as shown in Figure 4 Cr, C and Mo element distribution scanning is carried out on the target area with black and bright white color, as shown in 23 C6 type carbide, and Mo element enrichment is sigma phase, and the phase type is accurately determined by element distribution difference.
Claims
1. Cr in wrought high-temperature alloys 23 A rapid and accurate characterization method for C6 type carbides and σ phase, characterized in that, Includes the following steps: 1) Sample preparation: A smooth-surfaced high-temperature alloy sample to be tested was obtained by progressive sanding, mechanical polishing and electrolytic polishing. 2) EPMA backscattering mode observation: The deformed superalloy sample was observed in backscattering mode, Cr 23 C6-type carbides are black due to their low atomic number and precipitate continuously along the grain boundaries; the σ phase is bright white due to the presence of elements with high atomic numbers and adheres to Cr. 23 C6 type carbides nucleate at their phase boundary with the matrix; 3) EPMA elemental surface scan analysis: Cr, C, and Mo elemental distributions were scanned in black and bright white target areas. Cr and C were enriched as Cr. 23 C6 type carbides are enriched in the σ phase with Mo, and the phase type can be accurately determined by the difference in element distribution.