A method for studying oxide dissolution and diffusion behavior in powder high-temperature alloy based on interrupted sintering

Abstract

This invention provides a method for studying the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, comprising: (1) short-time sintering of superalloy powder in a vacuum atmosphere to obtain a sintered body; (2) annealing the sintered body to obtain an annealed sample; (3) using an ultrathin sectioning method to cut the surface layer of the superalloy powder and combining it with TEM analysis to analyze the distribution law of impurity oxygen; (4) using FIB to cut the sintered neck of the sintered body and the annealed sample respectively, and analyzing the existence form and diffusion law of impurity oxygen on the surface of the superalloy powder after entering the interior of the annealed sample. The method of this invention can prepare near-net-shape blanks at different sintering stages in batches. By adjusting the annealing time and the applied pressure, the density of the bulk can be affected to simulate the influence of holding time and pressure on the dissolution and diffusion behavior of oxides. This provides raw materials for studying the dissolution and diffusion behavior of oxides on the surface of superalloy powder during hot isostatic pressing.

Description

Technical Field

[0001] This invention relates to a research method for the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, belonging to the field of superalloys. Background Technology

[0002] Compared with traditional cast and forged nickel-based superalloys, powdered nickel-based superalloys have the characteristics of fine grains, uniform structure, no macro segregation, and excellent hot working and mechanical properties, making them a new generation of superalloys with good application prospects.

[0003] During the powder preparation and storage of nickel-based superalloys, oxidation inevitably occurs on the powder surface. This leads to defects such as the segregation of oxide particles at original particle boundaries, grain boundaries, or phase boundaries during subsequent hot isostatic pressing (HIP). In subsequent cold working and hot deformation treatments, the significant difference in thermal expansion coefficients between the oxide particles on the powder surface and the matrix prevents them from deforming in harmony with the matrix. Consequently, microcracks easily form at the oxide-matrix interface, negatively impacting the alloy's mechanical properties.

[0004] In powder metallurgy nickel-based superalloys, the oxide particles at the original particle boundary (PPB) are small in size and low in content, and the oxide type is easily affected by the powder particle size and the oxygen content on the powder surface. Therefore, the diffusion mechanism of oxide particles at the PPB is an unsolved problem. Secondly, the excessively long holding time in hot isostatic pressing (HIP) allows elements to diffuse fully, making it impossible to observe the evolution process in the middle of the oxide film, which is not conducive to studying the diffusion behavior of oxides at the PPB of powder metallurgy superalloys. Summary of the Invention

[0005] This invention uses high-temperature alloy powder prepared by argon atomization as raw material. Based on spark plasma sintering, it utilizes short-time sintering and heat treatment methods to batch prepare sintered necks at different sintering stages. This provides raw materials for studying the dissolution and diffusion behavior of oxides on the surface of high-temperature alloy powder during hot isostatic pressing, thereby improving research efficiency.

[0006] The purpose of this invention is to provide a method for studying the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, comprising the following steps:

[0007] (1) High-temperature alloy powder is sintered in a vacuum atmosphere for a short time to obtain a pre-formed sintered body;

[0008] (2) Anneal the sintered body obtained in step (1) to obtain an annealed sample;

[0009] (3) Using the ultrathin sectioning method, the surface layer of the high-temperature alloy powder described in step (1) is cut off, and the distribution pattern of impurity oxygen is analyzed by transmission electron microscopy (TEM).

[0010] (4) Using a focused ion beam (FIB), the sintered necks of the sintered body in step (1) and the annealed sample in step (2) are cut off respectively, and the existence form and diffusion law of impurity oxygen on the surface of the alloy powder after entering the interior of the annealed sample are analyzed.

[0011] Preferably, in step (1), the high-temperature alloy powder is selected from at least one of nickel-based high-temperature alloys, iron-based high-temperature alloys, and cobalt-based high-temperature alloys, with nickel-based high-temperature alloys being preferred. High-temperature alloys refer to a class of metallic materials based on iron, nickel, or cobalt that can work for a long time at high temperatures above 600°C and under certain stress. They have excellent high-temperature strength, good resistance to oxidation and hot corrosion, good fatigue performance, fracture toughness, and other comprehensive properties, and are also known as "superalloys." They are mainly used in the aerospace and energy fields.

[0012] Preferably, in step (1), the sintering method is discharge plasma sintering, the heating rate is 100-200℃ / min, the sintering temperature is 800-1200℃, the pressure is 10-50MPa, and the sintering time is 3-10min. The term "short-time sintering" means that the sintering time does not exceed 10min. If the sintering time is too long, the sintered neck morphology in the initial stage of sintering cannot be obtained, as shown in Comparative Example 1.

[0013] Background art has documented that the excessively long holding time in hot isostatic pressing (HIP) allows for full element diffusion, making it impossible to observe the evolution process within the oxide film, which is detrimental to studying the diffusion behavior of oxides at the PPB (polypropylene oxide) sites in powder metallurgy superalloys. Furthermore, in actual production, HIP sintering is energy-intensive and complex, making it impossible to interrupt the process to observe the melting and diffusion of oxides. Therefore, this invention selects plasma sintering, which has a short sintering time and controllable sintering parameters, to simulate the changes in the oxide film during HIP.

[0014] Preferably, in step (2), the annealing temperature is 800-1200℃, the pressure is 10-200MPa, and the holding time is 5-300min.

[0015] Preferably, in step (3), an analysis method combining ultrathin sectioning and TEM is used to analyze the overall structural characteristics from the surface of the original alloy powder to the interior of the powder matrix, as well as the distribution pattern, existence form, and phases of impurity oxygen in the surface layer of the original alloy powder.

[0016] Preferably, in step (4), a focused ion beam (FIB) is used to cut the sintered body in step (1) and the annealed sample in step (2) along the sintering neck interface into the powder. Combined with the analysis methods of scanning electron microscopy (SEM), TEM and electron backscatter diffraction (EBSD), the existence form and diffusion law of impurity oxygen on the surface of the alloy powder after entering the interior of the annealed sample, as well as the change law of phase in the oxide layer of the original alloy powder, are analyzed.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) The method described in this invention can be used to study the distribution pattern, existence form and phases of impurity oxygen on the surface of the original alloy powder.

[0019] (2) The method described in this invention can prepare near-net-shape blanks at different sintering stages in batches. By adjusting the annealing time and the applied pressure, the density of the bulk can be affected to simulate the influence of holding time and pressure on the dissolution and diffusion behavior of oxides. This provides raw materials for studying the dissolution and diffusion behavior of oxides on the surface of high-temperature alloy powders during hot isostatic pressing, thereby improving research efficiency.

[0020] (3) The method described in this invention can analyze the existence form and diffusion law of impurity oxygen in the sintered body and annealed sample of the alloy powder surface, as well as the change law of the phase in the oxide layer of the original alloy powder, and provide ideas for the evolution law of the oxide film on the powder surface during the densification process of powder metallurgy high temperature alloy.

[0021] (4) The method described in this invention can provide ideas for the dissolution and diffusion of oxygen in other powder metallurgy alloy systems. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating the implementation of the method described in this invention;

[0024] Figure 2 This is a TEM image of the nickel-based superalloy powder produced by the method described in this invention;

[0025] Figure 3 These are SEM images of sintered bodies with different porosities obtained by the method described in this invention, wherein... Figure 3 (a) is the sintered body of Example 1. Figure 3 (a-1) is Figure 3 A magnified view of a. Figure 3 (b) is the sintered body of Example 2. Figure 3 (b-1) is Figure 3 (b) Enlarged view, Figure 3 (c) is the sintered body of Example 3. Figure 3 (c-1) is Figure 3 Enlarged view of c;

[0026] Figure 4 This is the SEM image of Comparative Example 1 prepared by the method described in this invention;

[0027] Figure 5 This is the SEM image of Comparative Example 2 prepared by the method described in this invention;

[0028] Figure 6 These are TEM images of the annealed samples obtained by the method described in this invention, wherein... Figure 6 (a) is the annealed sample from Example 1. Figure 6 (b) is the annealed sample from Example 2. Figure 6 (c) is the annealed sample of Example 3. Detailed Implementation

[0029] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0030] Example 1

[0031] A method for studying the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, the flowchart of which is shown below. Figure 1 As shown, the specific steps include:

[0032] (1) FGH96 nickel-based high-temperature alloy powder was sintered in a vacuum atmosphere for a short time using spark plasma sintering. The sintering temperature was 800℃ and the sintering time was 3min, resulting in a sintered body with a density of 65%.

[0033] (2) The sintered body obtained in step (1) was annealed under a certain pressure to simulate the effect of pressure on the dissolution and diffusion of oxide film during densification processes such as hot isostatic pressing. The annealing temperature was 700℃, the holding time was 5min, and the pressure was 10MPa to obtain the annealed sample.

[0034] (3) Using the ultrathin section (2100F) method, the surface layer of the nickel-based high-temperature alloy powder described in step (1) is cut off, and the distribution pattern, existence form and phases of impurity oxygen in the surface layer of the original alloy powder are analyzed by TEM. Figure 2This is a TEM image of the surface of the original FGH96 alloy powder. The image shows a uniform oxide layer covering the powder matrix (area within the double lines). Additionally, carbide precipitates are present on the powder surface (area within the dashed box).

[0035] (4) Using FIB, the sintered necks of the sintered body in step (1) and the annealed sample in step (2) are cut off respectively. During the sampling process, the sample is cut along the sintered neck interface into the powder interior. Combined with TEM and EBSD analysis methods, the existence form and diffusion law of impurity oxygen from the surface of the alloy powder entering the sintered body and the interior of the annealed sample are analyzed, as well as the change law of phases in the oxide layer of the original alloy powder.

[0036] Figure 3 (a) is a sintered body with a density of 65% that has not been annealed after sintering. Figure 3 (a-1) is Figure 3 (a) is an enlarged view. It can be seen from the figure that at this density, there are a large number of pores between the powder particles, as indicated by the arrow. Figure 6 (a) is a TEM image of the sintered body after annealing at 700°C and 10MPa for 5 min. It can be seen that after annealing, there are a large number of oxide particles (circled area) and a small amount of carbides (dashed box area) at the sintered neck interface.

[0037] Example 2

[0038] A method for studying the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, specifically including the following steps:

[0039] (1) FGH96 nickel-based high-temperature alloy powder was sintered in a vacuum atmosphere for a short time using spark plasma sintering. The sintering temperature was 900℃ and the sintering time was 4min, resulting in a sintered body with a density of 80%.

[0040] (2) The sintered body obtained in step (1) is annealed under a certain pressure to simulate the effect of pressure on the dissolution and diffusion of oxide film during densification such as hot isostatic pressing. The annealing temperature is 900℃, the holding time is 15min, and the pressure is 10MPa to obtain the annealed sample.

[0041] (3) Using FIB, the sintered necks of the sintered body in step (1) and the annealed sample in step (2) are cut off respectively. During the sampling process, the sample is cut along the sintered neck interface to the inside of the powder. Combined with TEM and EBSD analysis methods, the existence form and diffusion law of impurity oxygen on the surface of the alloy powder entering the sintered body and the inside of the annealed sample, as well as the change law of the phase in the oxide layer of the original alloy powder are analyzed.

[0042] Figure 3(b) is a sintered body with a density of 80% that has not been annealed after sintering. Figure 3 (b-1) is Figure 3 (b) is an enlarged view. It can be seen from the figure that at this density, the number of pores between powder particles is relatively reduced, as indicated by the arrow. Figure 6 (b) is a TEM image of the sintered body after annealing at 900°C and 10 MPa for 15 min. It can be seen that under this annealing condition, a large number of oxide particles present at the sintering neck interface disappear (circled area), and the oxide film on the powder surface dissolves. Simultaneously, a small number of large carbide particles are present at the sintering neck interface (boxed area), and small oxide particles are found within the carbides. This annealing condition may be the critical point for the dissolution of the powder oxide film.

[0043] Example 3

[0044] A method for studying the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, specifically including the following steps:

[0045] (1) FGH96 nickel-based high-temperature alloy powder was sintered in a vacuum atmosphere for a short time using spark plasma sintering. The sintering temperature was 1000℃ and the sintering time was 5min, resulting in a sintered body with a density of 90%.

[0046] (2) The sintered body obtained in step (1) is annealed under a certain pressure to simulate the effect of pressure on the dissolution and diffusion of oxide film during densification such as hot isostatic pressing. The annealing temperature is 1000℃, the holding time is 30min, and the pressure is 50MPa to obtain the annealed sample.

[0047] (3) Using FIB, the sintered necks of the sintered body in step (1) and the annealed sample in step (2) are cut off respectively. During the sampling process, the sample is cut along the sintered neck interface to the inside of the powder. Combined with TEM and EBSD analysis methods, the existence form and diffusion law of impurity oxygen on the surface of the alloy powder entering the sintered body and the inside of the annealed sample, as well as the change law of the phase in the oxide layer of the original alloy powder are analyzed.

[0048] Figure 3 (c) is a sintered body with a density of 90% that has not been annealed after sintering. Figure 3 (c-1) is Figure 3 (c) is an enlarged view. It can be seen from the figure that at this density, there are almost no pores between the powder particles. Figure 6(c) is a TEM image of the sintered body after annealing at 50 MPa for 15 min. It can be seen that after increasing the annealing pressure and extending the annealing time to 15 min, there are no oxide particles at the sintering neck interface. Only small oxide particles (circled area) are found inside the carbide. At the same time, the carbide particles (boxed area) have grown in size.

[0049] Comparative Example 1

[0050] FGH96 nickel-based superalloy powder was sintered in a vacuum atmosphere by spark plasma sintering at a temperature of 1000℃ for 30 minutes to obtain a sintered body with a density of 90%.

[0051] Figure 4 The image shows the morphology of the FGH96 alloy sintered body prepared using the above method. It can be seen from the image that the powder particles are completely dense. The intermediate state of sintering neck formation is not observable, indicating that the sintering is close to the hot isostatic pressing (HIP) sintering state.

[0052] Comparative Example 2

[0053] FGH96 nickel-based superalloy powder was sintered in a vacuum atmosphere using hot isostatic pressing at a temperature of 1000℃ for 5 hours and a pressure of 200 MPa to obtain a sintered body with a density of 99%.

[0054] Figure 5 The image shows the morphology of the FGH96 alloy sintered body sample prepared by hot isostatic pressing. It can be seen from the image that the powder particles are completely dense. The intermediate state of sintered neck formation cannot be observed.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. An analytical method for the dissolution and diffusion behavior of oxides in powder superalloys based on interrupted sintering, characterized in that, Includes the following steps: (1) High-temperature alloy powder is sintered in a vacuum atmosphere for a short time to obtain a pre-formed sintered body; (2) Anneal the sintered body obtained in step (1) to obtain an annealed sample; (3) Using the ultrathin sectioning method, the surface layer of the high-temperature alloy powder described in step (1) is cut off, and the distribution pattern of impurity oxygen is analyzed by TEM. (4) Using FIB, the sintered necks of the sintered body in step (1) and the annealed sample in step (2) are cut off respectively, and the existence form and diffusion law of impurity oxygen on the surface of the alloy powder after entering the interior of the annealed sample are analyzed. In step (1), the sintering method is discharge plasma sintering, the heating rate is 100-200℃ / min, the sintering temperature is 800-1200℃, the pressure is 10-50MPa, and the sintering time is 3-10min. In step (2), the annealing temperature is 800-1200℃, the pressure is 10-200MPa, and the holding time is 5-300min; In step (3), the analysis method of ultrathin section combined with TEM is used to analyze the overall structural characteristics from the surface of the original alloy powder to the interior of the powder matrix, as well as the distribution law, existence form and phases of impurity oxygen in the surface layer of the original alloy powder. In step (4), focusing FIB is used to cut the sintered body in step (1) and the annealed sample in step (2) along the sintering neck interface to the inside of the powder. Combined with the analysis methods of scanning electron microscopy (SEM), TEM and EBSD, the existence form and diffusion law of impurity oxygen on the surface of the alloy powder after entering the inside of the annealed sample, as well as the change law of the phase in the oxide layer of the original alloy powder, are analyzed.

2. The method according to claim 1, characterized in that, In step (1), the high-temperature alloy powder is selected from at least one of nickel-based high-temperature alloys, iron-based high-temperature alloys, and cobalt-based high-temperature alloys.

Images