A method for preparing high-performance molybdenum-rhenium alloy pipe based on superconducting magnetic field assisted forming

Abstract

This invention discloses a method for preparing high-performance molybdenum-rhenium alloy tubing based on superconducting magnetic field-assisted forming, aiming to solve the problems of coarse grains, significant anisotropy, poor wall thickness uniformity, and insufficient high-temperature performance in traditional processes. The core of this method lies in placing a mold containing molybdenum-rhenium alloy powder in a strong magnetic field environment of ≥10T generated by a superconducting magnet. Utilizing the paramagnetism of molybdenum and rhenium, the easy magnetization axes of the powder particles are oriented. By optimizing the direction and intensity of the magnetic field and the powder filling process, a preferred orientation structure is formed in the green blank at the microscopic level. After subsequent sintering and hot working, the tubing exhibits a strong texture and uniformly fine grains, significantly improving high-temperature strength and creep resistance in specific directions. This invention introduces structural control from the powder forming stage, providing a fundamental and innovative solution for high-performance molybdenum-rhenium alloy tubing.

Description

Technical Field

[0001] This invention belongs to the field of high-performance refractory metal pipe preparation technology, and specifically relates to a method for preparing molybdenum-rhenium alloy pipes by using external field (strong magnetic field) assisted technology to improve the microstructure of the material, thereby enhancing its performance. Background Technology

[0002] Molybdenum-rhenium alloy tubing plays a crucial role as a key structural component in the nuclear industry, aerospace, and other fields. These applications require tubing with excellent high-temperature strength, creep resistance, and structural reliability. Traditionally, this type of tubing is mainly produced through powder metallurgy billet preparation followed by hot extrusion or skew rolling piercing. However, these methods have inherent limitations: First, the grain orientation of the powder compact is usually random, resulting in anisotropy in the final product and significant performance differences in different directions; second, dynamic recrystallization is difficult to control precisely during subsequent hot working, easily leading to coarse grains or uneven microstructure, affecting the stability and consistency of high-temperature performance; finally, traditional processes have limited control over the uniformity of the tubing wall thickness, which may become stress concentration points. Summary of the Invention

[0003] The purpose of this invention:

[0004] To overcome the shortcomings of existing technologies, a preparation method is provided that can optimize the microstructure of molybdenum-rhenium alloy pipes from the source, thereby significantly improving their comprehensive performance, especially their high-temperature performance.

[0005] The technical solution adopted in this invention is as follows:

[0006] The core innovation of the preparation method of high-performance molybdenum-rhenium alloy tube lies in introducing a superconducting strong magnetic field in the powder forming stage, and using the anisotropy of magnetization energy to orient and arrange paramagnetic powder particles, thereby realizing the active design and control of the microstructure of the billet.

[0007] 1. Powder Loading and Magnetic Field Orientation: Molybdenum-rhenium alloy powder (both molybdenum and rhenium are paramagnetic materials) is placed in a very strong magnetic field. Each powder particle, due to its lattice anisotropy, possesses an easy magnetization axis. Under the influence of a sufficiently strong external magnetic field, the easy magnetization axes of the particles tend to align along the direction of the magnetic field. By optimizing the powder loading process (e.g., vibration), the particles are induced to rotate and rearrange, ultimately forming a macroscopic preferred orientation in the green body. By controlling the direction of the magnetic field (e.g., parallel to the tube axis), the texture type of the final tube (e.g., axial texture) can be preset.

[0008] 2. Stabilization treatment under magnetic field: Low-temperature heat treatment is carried out under magnetic field to strengthen the bonding force between oriented particles through mechanisms such as surface diffusion, "fixing" the oriented structure and preventing it from being damaged in subsequent handling or initial sintering stages.

[0009] 3. Sintering densification: During sintering, the grains of the green blank that has been pretreated with magnetic field orientation will preferentially grow along the preset orientation, thereby inheriting the orientation of the powder particles to the grains of the sintered body, and obtaining a sintered blank with strong texture.

[0010] 4. Hot forming: Subsequent hot forming (such as extrusion and rolling) will further strengthen and optimize the texture and densify the material, ultimately resulting in pipes with fine grains, obvious texture and excellent performance. Detailed Implementation

[0011] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0012] Example 1

[0013] (1) Magnetic field-assisted powder loading and orientation:

[0014] Mo-41Re alloy powder was loaded into a specially designed non-magnetic mold (inner diameter Φ60mm), which was placed at the center of a superconducting magnet. A strong axial magnetic field with a strength of 12T was applied. During the powder loading process, axial micro-vibrations were simultaneously applied to the mold at a frequency of 100Hz and an amplitude of 50μm for 30 minutes to promote the directional alignment of the powder in the magnetic field. After the powder loading was completed, the magnetic field was kept constant.

[0015] (2) Stabilization treatment under magnetic field:

[0016] Under the condition of continuous application of a 12T axial magnetic field, the green billet is heated to 1000℃ at a rate of 5℃ / min under argon protection, held at that temperature for 2 hours, and then cooled to 200℃ in the furnace before the magnetic field is turned off.

[0017] (3) Sintering densification:

[0018] The green blank, after magnetic field stabilization, was heated to 1800℃ in a hydrogen atmosphere at a rate of 8℃ / min and held for 3 hours to obtain a dense tube blank. The relative density after sintering is ≥97%.

[0019] (4) Hot forming:

[0020] The sintered tube blank is heated to 1300℃ under argon protection and hot extruded and pierced to obtain a rough tube. The rough tube is then hot rolled by multi-roll rolling (rolling temperature 1200℃, deformation per pass 15%) to finish the tube with an outer diameter of Φ50mm and a wall thickness of 5mm.

[0021] Product texture strength: X-ray pole figure shows strong <110> axial filament texture, Lotgering factor f≈0.85, grain structure: average grain size 25μm, grain size uniformity (Dmax / D50) <1.8, uniform equiaxed grains, room temperature mechanical properties (axial): tensile strength 920MPa, yield strength 850MPa, elongation after fracture 22%, anisotropy: ratio of radial to axial room temperature tensile strength ≥0.92, high temperature performance: creep life >500h at 1200℃ and initial stress 100MPa, wall thickness uniformity: full length wall thickness tolerance ±0.05mm.

[0022] Example 2

[0023] Process modification: In process (1), the direction of the magnetic field is changed to be perpendicular to the axis of the tube blank (radial magnetic field). The micro-vibration frequency is changed to 150Hz.

[0024] Product texture strength: exhibits <100> radial texture, Lotgering factor f≈0.78, grain structure: average grain size 28μm, uniformity <1.9, room temperature mechanical properties (radial): tensile strength 890MPa, yield strength 820MPa, elongation after fracture 24%, anisotropy: ratio of axial to radial room temperature tensile strength ≥0.90 (anisotropy is improved), high temperature performance: creep life at 1200℃ / 100MPa >480h, wall thickness uniformity: overall wall thickness tolerance ±0.05mm.

[0025] Example 3

[0026] Process modifications: In step (1), the magnetic field strength is adjusted to 8T. In step (2), the stabilization treatment temperature is adjusted to 900℃.

[0027] Product texture strength: <110> axial yarn texture, Lotgering factor f≈0.72 (texture weakens as magnetic field strength decreases), grain structure: average grain size 22μm, uniformity <1.7, room temperature mechanical properties (axial): tensile strength 940MPa, yield strength 870MPa, elongation after fracture 20%, anisotropy: radial to axial strength ratio ≥0.88, high temperature performance: creep life at 1200℃ / 100MPa >450h, wall thickness uniformity: full length wall thickness tolerance ±0.06mm.

[0028] Example 4

[0029] Process modifications: In step (1), the magnetic field strength is adjusted to 15T. In step (2), the stabilization treatment temperature is adjusted to 1100℃.

[0030] Product texture strength: <110> axial yarn texture, Lotgering factor f≈0.88 (stronger texture induced by strong magnetic field), grain structure: average grain size 30μm (grains are slightly larger at slightly higher temperatures), uniformity <2.0, room temperature mechanical properties (axial): tensile strength 900MPa, yield strength 830MPa, elongation after fracture 25%, anisotropy: radial to axial strength ratio ≥0.85, high temperature performance: creep life at 1200℃ / 100MPa >520, wall thickness uniformity: overall wall thickness tolerance ±0.04mm.

[0031] Example 5

[0032] Process modification: In step (2), the stabilization treatment heat preservation time is extended to 4 hours.

[0033] Product texture strength: <110> axial yarn texture, Lotgering factor f≈0.86, grain structure: average grain size 26μm, uniformity <1.8, room temperature mechanical properties (axial): tensile strength 915MPa, yield strength 845MPa, elongation after fracture 23%, anisotropy: radial to axial strength ratio ≥0.91, high temperature performance: creep life at 1200℃ / 100MPa >510h, wall thickness uniformity: overall wall thickness tolerance ±0.05mm.

[0034] Example 6

[0035] Process modification: In process (3), the sintering temperature is adjusted to 1700℃.

[0036] Product texture strength: <110> axial fiber texture, Lotgering factor f≈0.83, grain structure: average grain size 20μm (low sintering temperature, finer grains), uniformity <1.6, room temperature mechanical properties (axial): tensile strength 950MPa, yield strength 880MPa, elongation after fracture 19%, anisotropy: radial to axial strength ratio ≥0.89, high temperature performance: 1200℃ / 100MPa creep life >470h (fine grains slightly affect high temperature performance), wall thickness uniformity: full length wall thickness tolerance ±0.06mm, relative density: 96.0% (slightly lower density).

[0037] Example 7

[0038] Process modification: In process (4), the final hot rolling temperature is adjusted to 1100℃.

[0039] Product texture strength: <110> axial yarn texture, Lotgering factor f≈0.84, grain structure: average grain size 24μm, uniformity <1.7, some processing streamlines exist, room temperature mechanical properties (axial): tensile strength 935MPa, yield strength 865MPa, elongation after fracture 21%, anisotropy: radial to axial strength ratio ≥0.90, high temperature performance: creep life at 1200℃ / 100MPa >490h, wall thickness uniformity: full length wall thickness tolerance ±0.05mm.

[0040] Comparative Example 1

[0041] Process modification: The magnetic field-assisted orientation and stabilization treatments in steps (1) and (2) are omitted. The green body after powder loading is directly subjected to sintering in step (3) and hot processing in step (4).

[0042] Product texture strength: No obvious preferred orientation, random texture, Lotgering factor f < 0.2; Grain structure: Inhomogeneous grain size, mixed crystal phenomenon, uniformity > 2.5; Room temperature mechanical properties: Tensile strength 780 MPa, yield strength 710 MPa, elongation after fracture 18%; significant anisotropy, radial to axial strength ratio ≈ 0.75; High temperature performance: Creep life at 1200℃ / 100 MPa is about 250 h; Problem: It is impossible to obtain the preset strong texture and uniform structure, the performance anisotropy is large, and the high temperature performance is significantly worse than the example.

[0043] Comparative Example 2

[0044] Process modification: In step (1), no micro-vibration is applied during the powder loading process. The remaining parameters are the same as in Example 1.

[0045] Product texture strength: <110> axial filament texture, but the strength is relatively weak, Lotgering factor f≈0.65, grain structure: there are local orientation deviations, uniformity <2.2, room temperature mechanical properties (axial): tensile strength 880MPa, yield strength 810MPa, elongation after fracture 20%; performance fluctuations are increased, anisotropy: radial to axial strength ratio ≥0.87, high temperature performance: 1200℃ / 100MPa creep life >400h, problem: poor powder arrangement effect, resulting in decreased texture strength and uniformity, and poor performance consistency.

[0046] Comparative Example 3

[0047] Process modification: In step (2), the heating rate was too fast during the stabilization treatment under the magnetic field. It was set to 20℃ / min and the temperature was not kept at the stabilization temperature. Instead, it was directly cooled.

[0048] Product texture strength: <110> axial fiber texture, Lotgering factor f≈0.70, grain structure: microcracks appear in the green blank, and macro-cracks exist in the tube blank after sintering, making subsequent hot working impossible. Problem: Excessive heating and lack of heat preservation lead to uneven release of internal stress in the green blank, resulting in cracking, proving that stabilization treatment is crucial to maintaining the integrity of the orientation structure.

[0049] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-performance molybdenum-rhenium alloy tubing based on superconducting magnetic field-assisted forming, characterized in that, The preparation method shall be carried out according to the following steps: (1) Powder filling and magnetic field orientation: molybdenum rhenium alloy powder is loaded into a tubular elastic mold, and the mold is placed in a strong magnetic field environment generated by a superconducting magnet with a magnetic field strength of not less than 10 T; the powder is densified and filled under the action of the magnetic field by vibration or stirring, and the powder particles are oriented along the direction of the magnetic field to form a tubular green blank with micro-preferred orientation. (2) Stabilization treatment under magnetic field: Under the condition of maintaining magnetic field, the green blank is subjected to medium and low temperature heat treatment. The heat treatment temperature is lower than the significant sintering temperature of the powder to strengthen the orientation bonding between powder particles without causing obvious grain growth. (3) Sintering densification: The green blank treated with magnetic field is sintered at high temperature in a protective atmosphere or vacuum to obtain a densified tube blank with a preset texture. (4) Hot forming: The sintered tube blank is subjected to plastic processing such as hot extrusion or multi-roll hot rolling to finally obtain high-performance molybdenum rhenium alloy tube.

2. The preparation method according to claim 1, characterized in that, In process (1), the direction of the superconducting magnetic field is set to be parallel to, perpendicular to or at a specific angle to the tube blank axis, thereby inducing axial, radial or helical preferred orientation textures respectively.

3. The preparation method according to claim 1, characterized in that, In process (1), during the powder filling process, axial or radial micro-vibration is applied to the mold with a vibration frequency of 50-200Hz to promote the flowability and directional arrangement of the powder in the magnetic field.

4. The preparation method according to claim 1, characterized in that, In step (2), the stabilization treatment is carried out under the protection of argon or hydrogen, the treatment temperature is 800-1200℃, and the holding time is 1-4 hours.

5. A high-performance molybdenum-rhenium alloy tube prepared by the method according to any one of claims 1-4, characterized in that, It has a distinct preferred orientation texture, uniform grain size with an average size of no more than 30μm, room temperature tensile strength along the texture direction is more than 15% higher than that of similar pipes prepared without magnetic field orientation, and high temperature creep resistance is significantly improved.