A method of welding a molybdenum alloy

Abstract

The present application relates to the field of CT ball tube, and particularly relates to a welding method of molybdenum alloy, comprising the following steps: after pretreatment of the molybdenum alloy welding surface, molybdenum alloy welding material is placed between two welding surfaces, and welding is carried out under the conditions of 1800-2000 DEG C, 30-50t pressure, 30-60min holding time and 0.0001-0.01Pa vacuum. By using molybdenum alloy as welding material, the two elements are infinitely soluble, and good metallurgical bonding and solid solution strengthening can be formed after high-temperature diffusion reaction, so as to further improve the bonding strength between the molybdenum alloy matrix; at the same time, the molybdenum alloy itself is a high-melting-point material, and after forming the diffusion reaction, there is no problem of low remelting temperature of the welding interface, so as to ensure the stability of the finished product in the use process.

Description

Technical Field

[0001] This invention relates to the field of CT tubes, and particularly to a welding method for molybdenum alloys. Background Technology

[0002] The application scenarios for rotating anode target disks in CT X-ray tubes are characterized by high vacuum (10⁻⁶ Pa), high temperature (overall target disk temperature above 1300℃, with instantaneous temperature at the focal spot in the target disk track layer reaching 2600℃), and high rotation speed (target disk rotation speed of 8000-10000 r / min during operation). Therefore, high machining precision and bonding strength are required between the target disk substrates. Currently, most target disk substrate materials are molybdenum alloys, and the bonding between molybdenum alloy substrates is mainly achieved through vacuum brazing, for example:

[0003] The paper "Phase constitution and fracture analysis of vacuum brazed joint of 50Mo-50Re refractory alloys" describes the lap welding of 0.06mm thick 50Mo-50Re alloy using vacuum brazing. The base material was prepared by powder metallurgy. The filler material used in the brazing was Ni-19Cr-7.3Si-1.5B (mass fraction, the same below), with a melting point of 1081-1136℃. Under the conditions of 1200℃ and holding for 20 minutes, a well-formed welded joint was obtained without defects such as cracks and porosity. The article "Interfacial microstructure and joining properties of titanium-zirconium molybdenum alloy joints brazed using ti-28Ni eutectic brazing alloy" describes the use of vacuum brazing to weld 3mm thick Ti-Zr-Mo (TZM) alloy plates (Ti 0.5%, Zr 0.08%, C 0.04%) to obtain welded joints free of defects such as porosity and cracks. Ti-28Ni was selected as the eutectic brazing alloy, with a melting point between 940-980℃.

[0004] However, the low-melting-point components in the alloy solder used in the above methods are prone to producing volatile substances under high-temperature conditions, causing high-vacuum damage. Moreover, the strength and heat resistance of the interface bonding area are lower than those of the base metal, resulting in poor high-temperature service performance and making the target plate very easy to fail. Summary of the Invention

[0005] To address the problem that existing welding methods are not applicable to the manufacture of target plates for CT X-ray tubes, this invention provides a welding method for molybdenum alloys, comprising the following steps: after pretreating the molybdenum alloy surfaces to be welded, placing tungsten-molybdenum alloy solder between the two surfaces to be welded, and performing welding under vacuum conditions of 1800-2000℃, 30-50t pressure for 30-60min, and 0.0001-0.01Pa.

[0006] A further improvement involves machining multiple grooves on the surface to be welded; the tungsten-molybdenum alloy solder is tungsten-molybdenum alloy powder. When the tungsten-molybdenum alloy solder is in powder form, the grooves on the surface to be welded can trap the tungsten-molybdenum alloy powder, thereby ensuring the contact area between the solder and the surface to be welded.

[0007] Furthermore, the groove is serrated.

[0008] Further improvements include machining the surface to be welded into a plane with a surface roughness ≤0.4μm; and using a tungsten-molybdenum alloy solder, which is a tungsten-molybdenum alloy strip. Specific machining methods for the surface to be welded include precision turning, precision grinding, precision reaming, and lapping. When tungsten-molybdenum alloy powder is not suitable as the solder for the surface to be welded, its surface roughness needs to be controlled below 0.4μm to ensure sufficient contact between the tungsten-molybdenum alloy strip and the surface to be welded.

[0009] In a further improvement, the tungsten-molybdenum alloy solder comprises, by mass fraction, 0.1%-99.9% molybdenum and 0.1%-99.9% tungsten.

[0010] In a further improvement, after the surface to be welded is pretreated, it is cleaned and dried before welding to remove impurities and provide a good environment for subsequent welding.

[0011] Compared with the prior art, the welding method for molybdenum alloys provided by the present invention has the following beneficial effects:

[0012] This invention uses a tungsten-molybdenum alloy as a solder. The two elements are infinitely miscible, and after a high-temperature diffusion reaction, they can form a good metallurgical bond and solid solution strengthening, thereby further improving the bonding strength between the molybdenum alloy matrix. At the same time, the tungsten-molybdenum alloy itself is a high-melting-point material. After the diffusion reaction is formed, there is no problem of low remelting temperature at the welding interface, thus ensuring the stability of the finished product during use. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the welding strength and remelting temperature testing method provided by the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention provides a welding method for molybdenum alloys, comprising the following steps: after pretreating the molybdenum alloy surfaces to be welded, placing tungsten-molybdenum alloy solder between the two surfaces to be welded, and performing welding under vacuum conditions of 1800-2000℃, 30-50t pressure for 30-60min, and 0.0001-0.01Pa.

[0017] The tungsten-molybdenum alloy solder comprises, by mass fraction, 0.1%-99.9% molybdenum and 0.1%-99.9% tungsten.

[0018] The present invention also provides the following embodiments and comparative examples:

[0019] Example 1

[0020] Continuous serrated grooves were machined onto the welding surfaces of two molybdenum alloy substrates (Mo-Ti-Zr). The substrates were then cleaned and dried to ensure the welding surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and tungsten-molybdenum alloy powder (50% W and 50% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1950℃, a pressure of 35t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0021] Example 2

[0022] Continuous serrated grooves were machined on the welding surfaces of two molybdenum alloy substrates (Mo-Ti-Zr). The processed substrates were then cleaned and dried to ensure the welding surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and tungsten-molybdenum alloy powder (20% W and 80% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1850℃, a pressure of 40t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0023] Example 3

[0024] Two molybdenum alloy substrates (Mo-Ti-Zr) were machined to have flat surfaces with a surface roughness of 0.4 μm. The machined substrates were then cleaned and dried to ensure the surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and a tungsten-molybdenum alloy strip (30% W and 70% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1800℃, a pressure of 40t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0025] Example 4

[0026] Two molybdenum alloy substrates (Mo-Ti-Zr) were machined to have flat surfaces with a surface roughness of 0.4 μm. The machined substrates were then cleaned and dried to ensure the surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and tungsten-molybdenum alloy powder (30% W and 70% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1800℃, a pressure of 40t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0027] Comparative Example 1

[0028] Two molybdenum alloy substrates (Mo-Ti-Zr) were cleaned and dried to ensure that the surfaces to be welded were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing up, and tungsten-molybdenum alloy powder (50% W and 50% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing down. Both substrates were then placed in a hot press furnace for welding at a temperature of 1950℃, a pressure of 35t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0029] Comparative Example 2

[0030] Continuous serrated grooves were machined onto the welding surfaces of two molybdenum alloy substrates (Mo-Ti-Zr). The substrates were then cleaned and dried to ensure the welding surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and a tungsten-molybdenum alloy strip (50% W and 50% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1950℃, a pressure of 35t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0031] Comparative Example 3

[0032] Two molybdenum alloy substrates (Mo-Ti-Zr) were machined to have flat surfaces with a surface roughness of 0.6 μm. The machined substrates were then cleaned and dried to ensure the surfaces were free of impurities and oxides. One substrate was placed in a mold with the welding surface facing upwards, and a tungsten-molybdenum alloy strip (30% W and 70% Mo by mass) was added and spread evenly. The other substrate was then placed in the mold with the welding surface facing downwards. Both substrates were then placed in a hot press furnace for welding at 1800℃, a pressure of 40t, a holding time of 60min, and a vacuum degree of 0.0001Pa. After cooling, the connector was obtained.

[0033] The welding strength and remelting temperature of the connectors prepared in Examples 1-4 and Comparative Examples 1-3 were tested. The welding strength test method was as follows: Figure 1 As shown, a connector template with a total length of 50cm, a width of 10cm, and a thickness of 5cm (where 10 represents the molybdenum alloy matrix and 11 represents the weld joint) is placed in a shear test fixture. The stress point is kept on the weld interface of the template, ensuring the connector is cut parallel to the mating surface. The entire shear test fixture is then placed in a fixed position on the testing machine, and a load is applied smoothly until the connector breaks. The load value is recorded. The remelting temperature is tested using the same method. Figure 1As shown, a connector sample with a total length of 50cm, a width of 10cm, and a thickness of 5cm was placed on the firing platform, ensuring that one end of the connector was suspended. The suspended end was pressurized by a press at 0.1MPa. The test device was then placed in a high-temperature furnace, and the temperature was increased according to the process temperature until the welding interface of the connector showed bending deformation. The temperature value was recorded.

[0034] The test results are shown in Table 1.

[0035] Table 1

[0036]

[0037] As can be seen from the test results of Examples 1-4 in Table 1, the welding method of molybdenum alloy provided by the present invention can effectively weld the molybdenum alloy substrate, with a welding strength of over 162 MPa and a remelting temperature of over 2450°C after welding, making the molybdenum alloy substrate suitable for CT tube target plates. The comparison results of Example 1 and Comparative Examples 1 and 2 show that when no treatment is performed on the surface to be welded, or when grooves are machined on the surface to be welded before adding alloy strip-shaped solder, the contact area between the surface to be welded and the solder decreases, resulting in a reduction in welding strength. The comparison results of Example 3 and Comparative Example 3 show that increasing the surface roughness of the surface to be welded leads to a reduction in welding strength. This is because, under certain pressure, the greater the roughness in the vertical direction of the surface to be welded, the greater the initial void height and the larger the void volume, which adversely affects diffusion between interfaces, thus affecting welding strength.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method for molybdenum alloys, characterized in that, Includes the following steps: After pretreatment of the molybdenum alloy surfaces to be welded, tungsten-molybdenum alloy solder is placed between the two surfaces to be welded, and welding is carried out under vacuum conditions of 0.0001-0.01 Pa, with a holding time of 30-50 t at 1800-2000℃. The surface to be welded is processed into a plane with a surface roughness ≤0.4μm; the tungsten-molybdenum alloy solder is a tungsten-molybdenum alloy strip; the tungsten-molybdenum alloy solder, by mass fraction, consists of 50%-80% molybdenum and 20%-50% tungsten.

2. A welding method for molybdenum alloys, characterized in that, Includes the following steps: After pretreatment of the molybdenum alloy surfaces to be welded, tungsten-molybdenum alloy solder is placed between the two surfaces to be welded, and welding is carried out under the following conditions: 1800-2000℃, 30-50t pressure for 30-60min, and vacuum conditions of 0.0001-0.01Pa. Multiple grooves are machined on the surface to be welded, and the grooves are serrated; the tungsten-molybdenum alloy solder is tungsten-molybdenum alloy powder. The tungsten-molybdenum alloy solder, by mass fraction, consists of 50%-80% molybdenum and 20%-50% tungsten.

3. The welding method for molybdenum alloys according to claim 1 or 2, characterized in that: After the surface to be welded is pretreated, it is cleaned and dried before welding.

Images