Powder metallurgy brazing method and use thereof

Abstract

The present application relates to the field of welding technology, in particular to a powder metallurgy brazing method and application thereof, comprising the following steps: processing the to-be-welded area into a concave shape; filling alloy powder filler into the to-be-welded area and compacting; taking brazing powder and binder, mixing to obtain paste-like brazing filler, and covering the paste-like brazing filler on the alloy powder filler; vacuum heating the to-be-welded part to 900-1100 DEG C, and keeping the temperature for 10-30 min; continuing to heat to 1150-1250 DEG C, keeping the temperature for 30-120 min, and cooling. The method is simple in operation, reliable in method, strong in applicability and universality, and convenient for process operation, can effectively reduce the formation of weld defects and brittle phases, can obtain a welded joint with excellent high-temperature tensile strength, and is beneficial to improve the welding qualification rate and production efficiency. The method can be applied to repairing the surface ablation area of a workpiece, can reduce the scrap rate of parts, and thus brings huge economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding technology, in particular to a powder metallurgy brazing method and application thereof. BACKGROUND

[0002] In power machinery, the ablation damage of the workpiece surface due to high-temperature working environment will seriously affect its high-temperature performance and service life. In order to prolong the service life of the workpiece and ensure the safe, economic and continuous operation of the equipment, it is of great significance to explore a better welding repair method.

[0003] At present, the repair methods for ablation damage of the workpiece mainly include fusion welding and brazing. In fusion welding, the overlaying method for repairing ablation damage has low efficiency in repairing large area damage and is easy to cause deformation, but it is not applicable to narrow space due to lack of accessibility. In contrast, brazing which can uniformly heat is a better choice. Conventional brazing uses capillary phenomenon to make liquid filler metal flow into and stay in the joint gap, but this method is generally only applicable to repairing cracks with a width of less than 0.1 mm. When repairing cracks with a width greater than 0.1 mm or repairing large area ablation area, the capillary effect fails, the flowability of the filler metal droplet decreases, and it is difficult to completely fill the damage area. It has been pointed out in some research that for damage with a width greater than 1 mm, the large gap brazing method shows obvious advantages. This method is to prefill brazing filler material in the gap and heat below the melting temperature of the base to form a dense brazed joint. However, in this method, the low-melting-point component and the high-melting-point component are generally mixed uniformly in proportion, and then filled into the large gap crack area. In the process, local low-melting-point component content is often insufficient due to uneven mixing of low-melting-point component and high-melting-point component, resulting in loose and hole defects in the weld, and too many brittle intermetallic compounds between local high-melting-point component particles. The larger the size of the damage area, the greater the probability of the above defects and brittle phases. The defects and brittle phases are difficult to eliminate even after a long time of heat preservation and diffusion process, which eventually leads to the deterioration of the mechanical properties of the welded part and even scrap. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects in the prior art that the use of brazing to repair large area damage of the workpiece is prone to loose and hole defects, the formation of brittle phases, and the influence on the mechanical properties of the workpiece and even the scrap, so as to provide a powder metallurgy brazing method and application thereof.

[0005] To this end, the present application provides the following technical solutions:

[0006] The present application provides a powder metallurgy brazing method, comprising the following steps:

[0007] S1: machining the to-be-welded area into a concave shape by a mechanical method to make the transition area smooth and transition;

[0008] S2: filling alloy powder filler into the area to be welded, compacting and filling, the alloy powder filler including, in terms of chemical percentage: Ni: 9%~12%, Cr: 20%~30%, W: 7%~8%, C: 0.2%~0.3%, the balance being Co and inevitable impurities, the components of which are the same or similar to those of the parts to be welded, being a high-temperature alloy powder;

[0009] S3: taking brazing filler powder and binder, mixing to obtain paste brazing filler, and covering the paste brazing filler on the alloy powder filler compacted and filled in S2, the brazing filler powder including, in terms of chemical percentage: Ni: 17%~19%, Cr: 18%~20%, W: 9%~11%, C: 0.6%~1.0%, Si: 2.5%~3.5%, B: 3.2%~3.7%, the balance being Co and inevitable impurities;

[0010] S4: vacuum heating the parts to be welded to 900~1100℃, holding time 10~30min;

[0011] S5: continuing heating to 1150~1250℃, holding time 30~120min, and cooling.

[0012] Preferably, in step S3, the brazing filler powder and the binder are taken in a mass ratio of 10:1~10:5.

[0013] Preferably, in step S2, the alloy powder filler filled accounts for 60%~100% of the volume of the area to be welded.

[0014] Preferably, in step S4, the vacuum degree of vacuum heating is <5.0×10 -3 Pa.

[0015] Preferably, the binder includes water-based binder, the water-based binder including, in terms of chemical percentage: ammonium chloride: 30%~50%, zinc phosphate: 20%~40%, polyethylene glycol: 10%~30%, butyl acrylate: 5%~15%, such as WCC-S.

[0016] Preferably, the particle size of the alloy powder filler is 50~150μm.

[0017] Preferably, the particle size of the brazing filler powder is 50~150μm.

[0018] Preferably, in step S5, the cooling mode includes: furnace cooling to room temperature, and air quenching to room temperature at a cooling rate of 50~150℃ / min after furnace discharge.

[0019] Preferably, after step S3 and before step S4, there is a step of applying a solder resist around the paste brazing filler.

[0020] The application provides an application of the powder metallurgy brazing method to repairing a surface ablation area of a workpiece.

[0021] Preferably, the workpiece comprises a gas turbine wheel turbine vane blade, and the material of the gas turbine wheel turbine vane blade comprises cast cobalt-based thin-wall alloy material such as X40, X45, FSX414, Steilite, K644, K44 and the like.

[0022] The technical scheme of the application has the following advantages:

[0023] The powder metallurgy brazing method provided by the application comprises the following steps: S1, processing a to-be-welded area into a concave shape by a mechanical method; S2, filling alloy powder filler into the to-be-welded area and compacting the alloy powder filler; S3, taking brazing filler powder and a binder, mixing the brazing filler powder and the binder to obtain a paste-like brazing filler, and covering the paste-like brazing filler on the compacted alloy powder filler in S2; S4, vacuum heating the to-be-welded workpiece to 900-1100 DEG C, and keeping the temperature for 10-30 min; S5, continuously heating to 1150-1250 DEG C, keeping the temperature for 30-120 min, and cooling. The method is simple in operation, reliable in method, strong in applicability and universality, and convenient for process operation. The method combines the layered arrangement of the alloy powder filler and the brazing filler, powder metallurgy and isothermal solidification brazing, can effectively reduce the formation of weld defects and brittle phases, can obtain a weld joint with excellent high-temperature tensile strength, is favorable for improving the welding qualification rate and production efficiency, and theoretically, as long as an ablation area is not burnt through, the ablation area can be repaired by the method. The composition of the high-temperature alloy powder filler comprises, in percentage by mass: 9-12% of Ni, 20-30% of Cr, 7-8% of W, 0.2-0.3% of C, and the balance of Co and inevitable impurities, so that the high-temperature alloy powder filler has a relatively high melting point; the composition of the brazing filler powder comprises, in percentage by mass: 17-19% of Ni, 18-20% of Cr, 9-11% of W, 0.6-1.0% of C, 2.5-3.5% of Si, 3.2-3.7% of B, and the balance of Co and inevitable impurities, so that the brazing filler powder has a relatively low melting point; under the action of high temperature in step S4, the high-temperature alloy powder filler is sintered to form a skeleton, so as to minimize the pores between the alloy powders, thereby reducing the filling amount of the brazing filler; under higher temperature in step S5, the brazing filler covered on the alloy powder filler is melted and enters the pores between the alloy powders under the capillary action of the pores of the skeleton, isothermally solidified and diffused to form a weld with uniform structure and perfect filling.

[0024] The powder metallurgy brazing method provided by the application comprises the step of applying a solder resist around the paste-like brazing filler, so as to avoid the overflow of the brazing filler during brazing.

[0025] The powder metallurgy brazing method can be applied to repairing the surface ablation area of a workpiece, and the repaired workpiece can be used until the next maintenance period, thereby reducing the scrapping rate of the part and bringing huge economic benefits, and has a wide application prospect.

[0026] The powder metallurgy brazing method can be applied to repairing the surface ablation area of a workpiece, and can be used for repairing the surface ablation area of a gas turbine wheel turbine stator blade, including active E-class, F-class and even H-class gas turbine turbine stator blades, that is, the method can be universally used for welding repair of the surface ablation damage of the in-service heavy gas turbine turbine stator blade, and has strong universality. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0028] Figure 1 It is a schematic diagram of the steps of the powder metallurgy brazing method in the present application;

[0029] Figure 2 It is a schematic diagram of the principle of the powder metallurgy brazing method in the present application;

[0030] Figure 3 It is a weld defect detection negative film of Example 1 in the present application;

[0031] Figure 4 It is a weld defect detection negative film of Example 2 in the present application;

[0032] Figure 5 It is a weld defect detection negative film of Example 3 in the present application;

[0033] Figure 6 It is a weld defect detection negative film of Comparative Example 1 in the present application;

[0034] Figure 7 It is a weld defect detection negative film of Comparative Example 2 in the present application;

[0035] Figure 8 It is a weld defect detection negative film of Comparative Example 3 in the present application;

[0036] Figure 9 It is a weld defect detection negative film of Comparative Example 4 in the present application;

[0037] Figure 10 It is a high-temperature tensile strength comparison diagram of the welding joints obtained in Example 1 and the comparative examples of the present application;

[0038] BRIEF DESCRIPTION OF DRAWINGS

[0039] 1-alloy powder filler; 2-paste solder. DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0041] Experimental raw materials:

[0042] High-temperature alloy plate Co-29Cr-10Ni-7.5W-0.25C-0.01B: 5mm thick, from the Institute of Metal, Chinese Academy of Sciences.

[0043] Alloy powder filler Co-25Cr-10Ni-7.5W-0.25C: particle size 50-150μm, from China Aviation Maite Company.

[0044] Cobalt-based solder powder Co-02(Co-19Cr-18Ni-10W-0.8C-3.0Si-3.5B): particle size 50-150μm, from Lanzhou Alloy Powder Company.

[0045] Example 1

[0046] This embodiment provides a powder metallurgy soldering method to repair the surface ablation area of high-temperature alloy plate Co-29Cr-10Ni-7.5W-0.25C-0.01B for service turbine vane, which is described by taking the high-temperature alloy plate Co-29Cr-10Ni-7.5W-0.25C-0.01B as an example, and the schematic diagram of the steps is shown in Figure 1 In this embodiment, the alloy powder filler 1 is alloy powder filler Co-25Cr-10Ni-7.5W-0.25C, and the paste solder 2 is obtained by uniformly mixing cobalt-based solder powder Co-02(Co-19Cr-18Ni-10W-0.8C-3.0Si-3.5B) and a binder (composition: ammonium chloride 45%, zinc phosphate 28%, polyethylene glycol 20%, butyl acrylate 7%) according to a mass ratio of 10:2. The specific steps include the following steps:

[0047] (1) To simulate the powder metallurgy soldering repair of the surface ablation area, first groove is opened on the above high-temperature alloy plate, the length and width of the groove are both 20mm, and the depth is 3mm, and the transition area is smoothly transitioned;

[0048] (2) Fill the alloy powder filler Co-25Cr-10Ni-7.5W-0.25C with similar composition to the high-temperature alloy plate into the welding area, until the whole ablation concave area is paved, and the alloy powder filler is compacted and filled;

[0049] (3) Take the cobalt-based filler powder Co-02 (Co-19Cr-18Ni-10W-0.8C-3.0Si-3.5B) and the binder (the composition is ammonium chloride 45%, zinc phosphate 28%, polyethylene glycol 20%, and butyl acrylate 7%) in a mass ratio of 10:2, mix uniformly to obtain the paste-like filler, and cover the paste-like filler on the compacted and filled alloy powder filler in (2);

[0050] (4) Apply the solder resist (Nicrobraz green solder resist, WCC Wall Colmonoy brand in the United States) around the paste-like filler to avoid the overflow of the filler during the soldering process;

[0051] (5) Place the high-temperature alloy plate in the vacuum soldering furnace, the vacuum degree is 3.0×10 -3 Pa, heat to 1050℃, and keep the temperature for 20 min;

[0052] (6) Continue to heat to 1180℃, keep the temperature for 40 min, and air quench after welding to room temperature.

[0053] The principle of the powder metallurgy soldering method in the application is that, under the high temperature in (5), the alloy powder filler is sintered to form a skeleton, so as to minimize the pores between the alloy powder, thereby reducing the filling amount of the filler; under the higher temperature in (6), the cobalt-based filler powder covered on the alloy powder filler is melted and enters the pores between the alloy powder under the capillary action of the pores in the skeleton, isocold solidified and diffused to form a weld with uniform structure and complete filling. The specific evolution process is shown in (a) to (d) in the figure: Figure 2 In (a), the cobalt-based filler powder is melted and fills the pores in the skeleton formed by sintering the alloy powder filler; in (b), the matrix at the solid-liquid interface is melted, and the liquid phase layer is thickened; in (c), the solid matrix grows into the liquid phase, and the isothermal solidification process occurs, and the liquid phase layer is thinned; in (d), the isothermal solidification is completed, and the joint is formed; finally, the composition of the joint area is homogenized, and the composition and structure are uniform and consistent with the matrix.

[0054] Example 2

[0055] The embodiment provides a powder metallurgy soldering method, which is different from the embodiment 1 only in that, in step (5), the temperature is heated to 900℃, and the temperature is kept for 10 min; and in step (6), the temperature is heated to 1150℃, and the temperature is kept for 30 min.

[0056] Example 3

[0057] The embodiment provides a powder metallurgy brazing method, which is only different from the embodiment 1 in that in step (5), the temperature is raised to 1100 DEG C, and the temperature is kept for 30 min; and in step (6), the temperature is raised to 1250 DEG C, and the temperature is kept for 120 min.

[0058] Comparative example 1

[0059] The comparative example provides a powder metallurgy brazing method, which is only different from the embodiment 1 in that the step (5) is not used.

[0060] Comparative example 2

[0061] The comparative example provides a powder metallurgy brazing method, which is only different from the embodiment 1 in that in step (5), the temperature is raised to 800 DEG C, and the temperature is kept for 5 min; and in step (6), the temperature is raised to 1100 DEG C, and the temperature is kept for 20 min.

[0062] Comparative example 3

[0063] The comparative example provides a powder metallurgy brazing method, which is only different from the embodiment 1 in that in step (5), the temperature is raised to 1200 DEG C, and the temperature is kept for 40 min; and in step (6), the temperature is raised to 1300 DEG C, and the temperature is kept for 140 min.

[0064] Comparative example 4

[0065] The comparative example provides a powder metallurgy brazing method, which is only different from the embodiment 1 in that the alloy powder filler Co-25Cr-10Ni-7.5W-0.25C, the brazing filler powder Co-02 (Co-19Cr-18Ni-10W-0.8C-3.0Si-3.5B) and the binder (the components are ammonium chloride 45%, zinc phosphate 28%, polyethylene glycol 20% and butyl acrylate 7%) are mixed uniformly and then filled into the to-be-welded area.

[0066] Test example 1

[0067] According to the method of GB / T 3323.1-2019 "Weld Nondestructive Testing Radiographic Testing", the welds obtained by brazing in the embodiment and the comparative examples are detected for defects, and the obtained weld defect detection negatives are as shown in Figures 3-9

[0068] From the figure, we can see that, Figures 3-5 the weld obtained by using the powder metallurgy brazing method in the embodiment is filled well, uniform in structure and free of obvious visible defects. In comparison, Figure 6 the weld obtained by not using high-temperature sintering in the comparative example 1, Figure 7 ​The high-temperature sintering temperature used in Comparative Example 2 is too low, and the weld structure is not uniform, with visible pores and defects, which is due to the fact that the pre-filled alloy powder filler cannot form a good combination and a strong skeleton, and after the solder is melted, the alloy powder filler migrates and segregates in the molten solder. Figure 8 and Figure 9 There are also visible pores and defects, because the sintering temperature and brazing temperature and holding time used in Comparative Example 3 are too high, although the alloy powder filler can achieve stable connection, but the high brazing temperature and holding time will inevitably lead to too many pore defects and brittle phases; in Comparative Example 4, the alloy powder filler, solder powder and binder are mixed uniformly and then filled into the welding area, which is prone to uneven mixing of low-melting-point components and high-melting-point components during heating, which may lead to insufficient local low-melting-point component content, thereby causing the weld to form loose and porous defects, and there may also be too large gaps between local high-melting-point component particles, resulting in too many brittle intermetallic compounds, which are difficult to eliminate even after a long time of holding and diffusion process. The powder metallurgy brazing method of the present application combines powder metallurgy with isothermal solidification brazing, and also adopts a method of layering the alloy powder filler and the solder, which can obtain a weld with complete filling, uniform structure and no obvious visible defects.

[0069] Test Example 2

[0070] According to GB / T 228.2-2015 "Metallic Materials-Tensile Testing-Part 2: Method of Test at Elevated Temperature", the high-temperature tensile strength of the weld joints obtained by brazing in Example 1 and Comparative Examples was tested at temperatures of 870℃ and 950℃, respectively.

[0071] The comparison chart of the high-temperature tensile strength of each welding joint is shown in Figure 10 The high-temperature tensile strength of the weld joint obtained by using the powder metallurgy brazing method of the present application in Example 1 is very close to that of the base material; the high-temperature tensile strength of the weld obtained in Comparative Examples 1 and 2 without high-temperature sintering and with too low high-temperature sintering temperature is less than half of that of the base material; the high-temperature tensile strength of the weld obtained in Comparative Example 3 with too high sintering temperature and brazing temperature and holding time is only about 60% of that of the base material; the high-temperature tensile strength of the weld obtained in Comparative Example 4 using mixed alloy powder filler, solder powder and binder to fill the defect area is only about 50% of that of the base material. The powder metallurgy brazing method provided by the present application can make the obtained weld filling more complete, the structure more uniform, and no obvious pore defects and brittle phases, thereby endowing the obtained weld joint with more excellent high-temperature tensile strength.

[0072] Obviously, the above embodiments are merely example for clearly illustrating but not limitation to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments need not and can not be enumerated. The obvious changes or variations derived from the above description are still within the protection scope of the present application.

Claims

1. A powder metallurgical brazing method, characterized in that, The method comprises the following steps: S1: machining the welding area into a concave shape by mechanical method; S2: filling alloy powder filler into the welding area, compacting and filling, the alloy powder filler comprising, in terms of chemical percentage, Ni: 9-12%, Cr: 20-30%, W: 7-8%, C: 0.2-0.3%, and the balance of Co and inevitable impurities; S3: taking brazing filler powder and binder, mixing to obtain paste-like brazing filler, and covering the paste-like brazing filler on the alloy powder filler compacted and filled in S2, the brazing filler powder comprising, in terms of chemical percentage, Ni: 17-19%, Cr: 18-20%, W: 9-11%, C: 0.6-1.0%, Si: 2.5-3.5%, B: 3.2-3.7%, and the balance of Co and inevitable impurities; S4: vacuum heating the welding part to 900-1100℃, and holding for 10-30 min; S5: continuing heating to 1150-1250℃, holding for 30-120 min, and cooling.

2. The powder metallurgy brazing method according to claim 1, characterized in that, In step S3, the brazing filler powder and the binder are used in a mass ratio of 10:1-10:

5.

3. The powder metallurgy brazing method according to claim 1, characterized in that, In step S2, the filled alloy powder filler accounts for 60-100% of the volume of the welding area.

4. The powder metallurgy brazing method according to claim 1, characterized by In step S4, the vacuum degree of the vacuum heating is < 5.0 x 10 -3 Pa.

5. The powder metallurgy brazing method according to claim 1 or 2, characterized in that, The binder comprises a water-based binder comprising, in terms of chemical percentage, ammonium chloride: 30-50%, zinc phosphate: 20-40%, polyethylene glycol: 10-30%, and butyl acrylate: 5-15%.

6. Powder metallurgical brazing method according to any one of claims 1 to 3, characterized in that The particle size of the alloy powder filler is 50-150μm. The particle size of the brazing filler powder is 50-150μm.

7. The powder metallurgy brazing method according to claim 1, characterized by In step S5, the cooling mode comprises furnace cooling to room temperature, and furnace-out cooling to room temperature at a rate of 50-150℃ / min.

8. Powder metallurgical brazing method according to any one of claims 1 to 7, characterized in that After step S3 and before step S4, a step of applying a solder resist around the paste-like brazing filler is further included.

9. Use of the powder metallurgy brazing method according to any one of claims 1-8 for repairing the surface ablation area of a workpiece.

10. Use according to claim 9, characterized in that, The workpiece comprises a gas turbine wheel turbine vane blade, and the material of the gas turbine wheel turbine vane blade comprises cast cobalt-based alloy material.

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