An analysis method for streak defects of single crystal superalloy castings

Abstract

The application provides a single crystal high-temperature alloy casting strip streak defect analysis method and belongs to the technical field of structure analysis. Element analysis itself has a large error, only combining element analysis and strip streak crystal orientation research to study the formation mechanism of the strip streak, the evidence chain is not closed, it is plausible but not true, and there are loopholes. The application first uses a true color confocal microscope for strip streak defect analysis, and then combines element analysis and strip streak crystal orientation analysis, so that the mechanism causing the strip streak defect can be more accurately inferred, and it has important practical significance for controlling the formation of the strip streak defect in industrial production.

Description

Technical Field

[0001] This invention relates to the field of microstructure analysis technology, and in particular to a method for analyzing stripe crystal defects in single-crystal superalloy castings. Background Technology

[0002] Single-crystal high-temperature alloy castings are key components of aero-engines and ground-based heavy-duty gas turbines. With the continuous development of aerospace and gas turbine technologies, blade structures are becoming increasingly complex, blade sizes are increasing, and the number of alloying elements in blades is also increasing. This leads to a more complex growth environment for dendrites during the directional solidification process of blades, resulting in a continuous increase in the tendency of metallurgical defects to form in single-crystal blades. Consequently, the yield rate of single-crystal blades has been greatly reduced, and the difficulty and cost of production and manufacturing have increased dramatically.

[0003] Currently, there are few measures to control the formation of blade defects. The core reason is that the cause of stripe crystal formation is unclear. Without understanding the formation mechanism of stripe crystal, it is difficult to control stripe crystal at its source. Summary of the Invention

[0004] The purpose of this invention is to provide an analytical method for stripe crystal defects in single-crystal superalloy castings, which can quickly and effectively analyze the mechanism of stripe crystal formation and provide theoretical support for controlling stripe crystal formation in industrial practice.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides an analytical method for stripe crystal defects in single-crystal superalloy castings, comprising the following steps: using a true-color confocal microscope to observe a single-crystal superalloy casting sample containing stripe crystal defects, observing whether there are holes at the origin of the stripe crystals, and if so, measuring the depth and width of the holes at the origin of the stripe crystals.

[0007] The composition at the origin of the stripe crystals was characterized by using the energy dispersive spectroscopy attachment of a scanning electron microscope to obtain the elemental types at the origin of the stripe crystals and determine whether there is any intrusion of impurity elements.

[0008] The crystal orientation of the striped crystals was characterized by electron backscatter diffraction of a scanning electron microscope, and the angular difference in crystallographic orientation between the striped crystals and the matrix was obtained. Combined with the size and composition characterization results of the holes at the origin of the striped crystals, the mechanism causing the striped crystal defects was inferred.

[0009] Preferably, the true-color confocal microscope includes the OPTELICS C130 true-color confocal microscope.

[0010] Preferably, the scanning electron microscope includes a ZEISS Sigma 300 scanning electron microscope.

[0011] Preferably, when the angular difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and pores and shell element intrusion are found at the origin of the stripe crystal: if the depth and width of the pores are both ≥350μm, it is inferred that the stripe crystal is generated by dendritic fracture caused by the shell protrusion; otherwise, it is inferred that the stripe crystal is generated by dendritic deformation caused by the shell protrusion.

[0012] Preferably, when the angle difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and a hole is found at the origin of the stripe crystal, but no shell element intrusion is found: if the depth and width of the hole are both ≥350μm, it is inferred that the stripe crystal is generated by the dendrite fracture caused by excessive local stress; otherwise, it is inferred that the stripe crystal is generated by the dendrite deformation caused by excessive local stress.

[0013] Preferably, if the angle difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and no pores or shell elements are found at the origin of the stripe crystal, it is inferred that the stripe crystal is generated by the deformation of the dendrites due to excessive local stress.

[0014] This invention provides an analytical method for stripe crystal defects in single-crystal superalloy castings, comprising the following steps: observing a single-crystal superalloy casting sample containing stripe crystal defects using a true-color confocal microscope to observe whether there are pores at the origin of the stripe crystals; if so, measuring the depth and width of the pores at the origin of the stripe crystals; characterizing the composition at the origin of the stripe crystals using an energy dispersive spectroscopy (EDS) attachment of a scanning electron microscope to obtain the elemental types at the origin of the stripe crystals and determine whether there is any intrusion of impurity elements; characterizing the crystal orientation of the stripe crystals using an electron backscatter diffraction (ESD) attachment of a SES to obtain the angular difference in crystallographic orientation between the stripe crystals and the matrix; and combining the size and composition characterization results of the pores at the origin of the stripe crystals to infer the mechanism causing the stripe crystal defects.

[0015] Elemental analysis itself has a large margin of error. Studying the formation mechanism of striped crystals by only combining elemental analysis and striped crystal orientation results in an incomplete chain of evidence, which is ambiguous and contains loopholes. This invention is the first to use a true-color confocal microscope for the analysis of striped crystal defects. By combining elemental analysis and striped crystal orientation analysis, the mechanism causing striped crystal defects can be more accurately inferred, which has important practical significance for controlling the formation of striped crystal defects in industrial production. Attached Figure Description

[0016] Figure 1 This is a flowchart of the analytical method for stripe crystal defects in single-crystal high-temperature alloy castings according to the present invention;

[0017] Figure 2 These are single-crystal blades after corrosion;

[0018] Figure 3This is a surface morphology image observed using a true-color confocal microscope;

[0019] Figure 4 This is an elemental distribution map of the origin locations of the striped crystals observed by energy-dispersive spectroscopy.

[0020] Figure 5 These are the results of electron backscattering diffraction, in the x, y, and z directions, respectively. Detailed Implementation

[0021] like Figure 1 As shown, the present invention provides an analysis method for stripe crystal defects in single-crystal superalloy castings, including the following steps: using a true-color confocal microscope to observe a single-crystal superalloy casting sample containing stripe crystal defects, observing whether there are holes at the origin of the stripe crystals, and if so, measuring the depth and width of the holes at the origin of the stripe crystals.

[0022] The composition at the origin of the stripe crystals was characterized by using the energy dispersive spectroscopy attachment of a scanning electron microscope to obtain the elemental types at the origin of the stripe crystals and determine whether there is any intrusion of impurity elements.

[0023] The crystal orientation of the striped crystals was characterized by electron backscatter diffraction of a scanning electron microscope, and the angular difference in crystallographic orientation between the striped crystals and the matrix was obtained. Combined with the size and composition characterization results of the holes at the origin of the striped crystals, the mechanism causing the striped crystal defects was inferred.

[0024] This invention uses a true-color confocal microscope to observe single-crystal superalloy casting samples containing stripe crystal defects, observe whether there are holes at the origin of the stripe crystals, and if so, measure the depth and width of the holes at the origin of the stripe crystals.

[0025] The present invention does not have special requirements on the source of the single-crystal superalloy casting sample containing stripe crystal defects; it can be obtained by directly cutting the single-crystal superalloy casting in which single-crystal stripes are found.

[0026] In this invention, the true-color confocal microscope preferably includes an OPTELIC SC130 true-color confocal microscope. This invention allows for very direct observation of the sample surface condition using a true-color confocal microscope.

[0027] In this invention, observation reveals that if a hole exists at the origin of the stripe crystals, it is preliminarily inferred that the stripe crystal defect is caused by a protrusion in the mold shell. Furthermore, if both the depth and width of the hole are ≥350 μm, it is preliminarily inferred that the stripe crystals are generated by dendrite fracture caused by the protrusion in the mold shell. Otherwise, it is preliminarily inferred that the stripe crystals are generated by dendrite deformation caused by the protrusion in the mold shell. The specific formation mechanism needs to be further determined based on subsequent characterization results.

[0028] This invention characterizes the composition at the origin of stripe crystals using an energy dispersive spectroscopy (EDS) attachment of a scanning electron microscope, thereby obtaining the elemental types at the origin of the stripe crystals and determining whether there is any intrusion of impurity elements.

[0029] In this invention, the scanning electron microscope preferably includes a ZEISS Sigma 300 scanning electron microscope. In this invention, if a cavity exists at the origin of the stripe crystals, and elements from the mold shell are found at the origin of the stripe crystals, it further confirms that the stripe crystals are caused by protrusions in the mold shell. Because the entire investment casting process is strictly controlled, and workers operate in dust-free environments, the influence of external impurities can be eliminated.

[0030] This invention characterizes the crystal orientation of striped crystals using the electron backscatter diffraction attachment of a scanning electron microscope, obtaining the angular difference in crystallographic orientation between the striped crystals and the matrix. Combined with the size and composition characterization results of the holes at the origin of the striped crystals, the mechanism causing the striped crystal defects is inferred.

[0031] In this invention, when the angular difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and pores and shell element intrusion are found at the origin of the stripe crystal: if the depth and width of the pores are both ≥350μm, it is inferred that the stripe crystal is generated by dendritic fracture caused by the shell protrusion; otherwise, it is inferred that the stripe crystal is generated by dendritic deformation caused by the shell protrusion.

[0032] When the angle difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and a hole is found at the origin of the stripe crystal but no shell element intrusion is found: if the depth and width of the hole are both ≥350μm, it is inferred that the stripe crystal is generated by the dendrite fracture caused by excessive local stress; otherwise, it is inferred that the stripe crystal is generated by the dendrite deformation caused by excessive local stress.

[0033] If the angle difference between the crystallographic orientation of the striped crystal and the matrix is ​​less than 20°, and no pores or shell elements are found at the origin of the striped crystal, it is inferred that the striped crystal is generated by the deformation of the dendrites due to excessive local stress.

[0034] It should be noted that there are multiple possible causes for the formation of striped crystals. The analytical method of this invention can be applied under different mechanisms. After clarifying the geometric dimensions, composition, and crystal orientation of the origin of the striped crystals, the corresponding mechanism can be inferred based on different experimental results.

[0035] The following detailed description of the analytical method for stripe crystal defects in single-crystal high-temperature alloy castings provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] Figure 2The image shows a single-crystal blade after etching, revealing bright white striped crystals. The area circled in the image was cut and examined directly using a true-color confocal microscope (OPTELICS C130). The depth and width of the micropores at the origin of the striped crystals were measured. Figure 3 As shown, Figure 3 The black circle in the image indicates the location of the hole. Measurements show the hole depth to be approximately 130 μm and the width to be 126 μm (in this embodiment, the dendrite spacing is approximately 350 μm, and the hole depth and width are insufficient to penetrate the dendrites). It is preliminarily determined that the striped crystal defect is caused by a shell protrusion. Further analysis involves placing the sample in the sample chamber of a scanning electron microscope (ZEISS Sigma 300) and using the microscope's energy dispersive spectroscopy (EDS) accessory to automatically analyze the composition at the origin location. This accessory can automatically identify all element types and concentrations at the origin location. Figure 4 The distribution of aluminum and oxygen elements is listed, with red circles indicating oxygen-rich and aluminum-rich locations. Since oxygen and aluminum must originate from the mold shell (because only the mold shell is alumina, the entire investment casting process is strictly controlled, and workers operate in dust-free environments, eliminating the influence of external impurities), this confirms the initial judgment. The crystal orientation of the striped crystals was characterized using electron backscatter diffraction (ESD) with a scanning electron microscope (ZEISS Sigma 300), revealing the angular difference in crystallographic orientation between the striped crystals and the matrix, such as... Figure 5 In the inverse pole figure, the orientation points representing the matrix and the striped crystals are very close. The angle difference automatically given by the software is 4°. The small angle difference can further prove that the striped crystals are caused by dendritic deformation due to the protrusion of the mold shell.

[0038] This invention effectively controls the generation of stripe crystal defects by improving the shell-making process.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for analyzing striation crystal defects in single-crystal superalloy castings, characterized in that, Includes the following steps: A true-color confocal microscope was used to observe single-crystal superalloy casting samples containing stripe crystal defects. The presence of pores at the origin of the stripe crystals was observed. If pores were found, the depth and width of the pores at the origin of the stripe crystals were measured. If there are holes at the origin of the striped crystals, it is preliminarily inferred that the striped crystal defects are caused by the protrusion of the mold shell. The composition at the origin of the stripe crystals was characterized by using the energy dispersive spectroscopy attachment of a scanning electron microscope to obtain the elemental types at the origin of the stripe crystals and determine whether there is any intrusion of impurity elements. The crystal orientation of the striped crystals was characterized by electron backscatter diffraction of a scanning electron microscope, and the angular difference in crystallographic orientation between the striped crystals and the matrix was obtained. Combined with the size and composition characterization results of the holes at the origin of the striped crystals, the mechanism causing the striped crystal defects was inferred. When the angular difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and pores and shell element intrusion are found at the origin of the stripe crystal: if the depth and width of the pores are both ≥350μm, it is inferred that the stripe crystal is generated by dendritic fracture caused by the shell protrusion; otherwise, it is inferred that the stripe crystal is generated by dendritic deformation caused by the shell protrusion. When the angle difference between the crystallographic orientation of the stripe crystal and the matrix is ​​<20°, and a hole is found at the origin of the stripe crystal but no shell element intrusion is found: if the depth and width of the hole are both ≥350μm, it is inferred that the stripe crystal is generated by the dendrite fracture caused by excessive local stress; otherwise, it is inferred that the stripe crystal is generated by the dendrite deformation caused by excessive local stress. If the angle difference between the crystallographic orientation of the striped crystal and the matrix is ​​less than 20°, and no pores or shell elements are found at the origin of the striped crystal, it is inferred that the striped crystal is generated by the deformation of the dendrites due to excessive local stress.

2. The analytical method according to claim 1, characterized in that, The true-color confocal microscope includes the OPTELICS C130 true-color confocal microscope.

3. The analytical method according to claim 1, characterized in that, The scanning electron microscope includes the ZEISS Sigma 300 scanning electron microscope.

Images