A method for improving the hardness of laser additive manufactured in 718 alloy

Abstract

The application discloses a method for improving the hardness of laser additive manufacturing In 718 alloy, wherein 1-5 wt.% of Al element is added into the In 718 alloy through a powder ball milling method, so that a large amount of Laves phase is precipitated during solidification; and after forming, solid solution and double-stage aging treatment are sequentially performed on the alloy, the solid solution treatment temperature is 1050-1200 DEG C, and the double-stage aging treatment temperature is 700-760 DEG C and 600-660 DEG C. The laser additive manufacturing In 718 alloy is firstly subjected to solid solution treatment, so that the chain-shaped and net-shaped Laves phase is changed into fine granular Laves phase which is dispersedly distributed in the matrix, then double-stage aging is performed to precipitate fine precipitated strengthening phases gamma' and gamma'' phase. Since the application adds appropriate Al element into the In 718 alloy, the gamma' phase can be fully precipitated, so as to make up for the problem of insufficient number of precipitated strengthening phases due to the lack of Nb element in the matrix caused by the precipitation of Laves phase. Through the double strengthening of the fine Laves phase particles and the sufficient number of precipitated strengthening phases which are dispersedly distributed to the gamma matrix, the microhardness of the nickel-based high-temperature alloy is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material alloying and heat treatment, and particularly relates to a method for improving the hardness of laser additive manufacturing In 718 alloy. BACKGROUND

[0002] In 718 alloy is widely used in the manufacturing of aero-engine parts due to its good high-temperature mechanical properties, corrosion resistance, oxidation resistance and fatigue properties. However, due to the complex structure of the aero-engine parts with many internal flow channels and thin-walled structures, the traditional manufacturing technology has problems such as long development cycle, great technical difficulty and material waste, which restricts the innovative development of aero-engine technology. Therefore, it is an urgent need to seek a more advanced processing and manufacturing method.

[0003] Laser additive manufacturing has gradually become an important way for the manufacturing of key aerospace parts because it can realize the near-net-shape free manufacturing of high-performance complex structure metal parts. However, due to the complex elements of In 718 alloy, microsegregation is prone to occur in the rapid solidification process of the laser additive manufacturing molten pool, and brittle and hard Laves phase is generated between the dendrites. The influence of Laves phase on the alloy performance depends on its morphology and size. Laves phase is usually precipitated in the form of large-size long strip between the dendrites, and it is generally believed that large-size long strip Laves phase will seriously affect the tensile plasticity, fracture toughness, fatigue and creep properties of the alloy. Small-size granular Laves phase dispersedly distributed in the gamma matrix of In 718 alloy can strengthen the alloy to a certain extent.

[0004] In laser additive manufacturing In 718 alloy, Laves phase will consume a large amount of Nb elements in the matrix, so that the precipitation of the gamma" (Ni3Nb) phase in In 718 alloy is limited. Usually, a long time of high-temperature solid solution treatment is needed to completely remelt Laves phase, so that there is enough Nb element in the gamma matrix to meet the uniform precipitation of the gamma" phase. However, long time of high-temperature solid solution will cause the grain coarsening of the alloy, which will irreversibly affect the microstructure and mechanical properties of the alloy. If the solid solution time and temperature are controlled, Laves phase cannot be completely remelted, Nb element cannot be fully remelted to the matrix, the precipitation of the gamma" phase is limited, and the mechanical properties of the alloy are lost. SUMMARY

[0005] Based on the deficiencies of the prior art, the technical problem to be solved by the present application is to provide a method for improving the hardness of laser additive manufacturing In 718 alloy, which can effectively make the gamma" phase precipitate and greatly improve the mechanical properties of the alloy.

[0006] To solve the above technical problems, the application provides a method for improving the hardness of laser additive manufacturing In 718 alloy, comprising the following steps:

[0007] The Al element is added into the In 718 alloy powder by the method of powder ball milling, and the laser additive manufacturing In 718 alloy is sequentially subjected to solid solution treatment and double-stage aging treatment, wherein the solid solution treatment temperature is 1050-1200℃, and the double-stage aging treatment temperature is 700-760℃ and 600-660℃.

[0008] As a preferred embodiment of the above technical solution, the method for improving the hardness of laser additive manufacturing In 718 alloy provided by the application further comprises part or all of the following technical features:

[0009] As an improvement of the above technical solution, the Al element is added in an amount of 1-5wt.%, and the ball milling time is greater than 10h.

[0010] The method for improving the hardness of additive manufacturing In 718 alloy is characterized in that:

[0011] As an improvement of the above technical solution, the selective laser melting system is used as the additive manufacturing system, the pulse energy is 180-220J, the pulse laser frequency is 8-12Hz, the single-layer powder thickness is 0.3-0.5mm, and the scanning speed is 5-10mm / s.

[0012] As an improvement of the above technical solution, the solid solution treatment time is 1-1.5h; after the solid solution treatment, the In 718 alloy obtained after the Laves phase solid solution treatment is cooled to room temperature.

[0013] As an improvement of the above technical solution, the cooling method is water cooling, air cooling or oil cooling.

[0014] As an improvement of the above technical solution, after the solid solution treatment, the In 718 alloy obtained after the Laves phase solid solution treatment is subjected to double-stage aging treatment.

[0015] As an improvement of the above technical solution, the double-stage aging treatment time is 8+8h; after the double-stage aging treatment, the In 718 alloy obtained after the double-stage aging treatment is cooled to room temperature.

[0016] As an improvement of the above technical solution, the cooling method is water cooling or air cooling.

[0017] As an improvement of the above technical solution, the atmosphere of the solid solution treatment and the double-stage aging treatment is independently air atmosphere, vacuum atmosphere or inert gas protection atmosphere.

[0018] As an improvement of the above technical solution, the inert gas is selected from argon.

[0019] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0020] The application provides a method for improving the hardness of laser additive manufacturing In 718 alloy. The method comprises the following steps: adding 1-5 wt.% of Al element into In 718 alloy by a powder ball milling method to make a large amount of Laves phase precipitate; and then sequentially performing solid solution treatment and double-stage aging treatment on the alloy. The solid solution treatment temperature is 1050-1200 DEG C, and the double-stage aging treatment temperature is 700-760 DEG C and 600-660 DEG C. In the application, 1-5 wt.% of Al element is added into In 718 alloy by a powder ball milling method, and the ball milling is performed for more than 10 hours. Due to the addition of the Al element, a large amount of Laves phase will precipitate in the laser additive manufacturing In 718 alloy after forming. Then, the formed In 718 alloy is first subjected to solid solution treatment at 1050-1200 DEG C, so that the chain-shaped Laves phase is dissolved into fine granular Laves phase uniformly distributed in the alloy matrix without causing the alloy grain to grow. Finally, the double-stage aging treatment is performed at 700-760 DEG C and 600-660 DEG C, so that a large amount of fine precipitated phase is precipitated in the matrix. Although the residual Laves phase particles lock a large amount of Nb element, the acceleration of the Al element enables the gamma prime phase to be uniformly and massively precipitated. At this time, a large amount of Laves phase particles and a large amount of precipitated gamma prime phase exist in the matrix, and the hardness of the alloy is obviously improved under the double strengthening effect.

[0021] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, the content of the specification can be implemented, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following will be described in detail in combination with the preferred embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical scheme of the embodiments of the application, the drawings of the embodiments will be briefly introduced below.

[0023] Figure 1 The microstructure diagram of the laser additive manufacturing In 718 alloy in the deposited state of example 1;

[0024] Figure 2 The microstructure diagram of the laser additive manufacturing In 718 alloy after solid solution treatment of example 1;

[0025] Figure 3 The microstructure diagram of the laser additive manufacturing In 718 alloy after double aging of example 1;

[0026] Figure 4High magnification morphology of laser additive manufacturing In 718 alloy after double aging of example 1;

[0027] Figure 5 Microhardness of laser additive manufacturing In 718 alloy of different states of example 1;

[0028] Figure 6 Microstructure of laser additive manufacturing In 718+3% Al alloy after solution treatment of example 2;

[0029] Figure 7 Microstructure of laser additive manufacturing In 718+5% Al alloy after solution treatment of example 3. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application are described in detail below, which illustrate the principles of the present application, other aspects, features, and advantages of which will become apparent to those skilled in the art upon reading the detailed description of the application.

[0031] The present application provides a method for improving the hardness of laser additive manufacturing In 718 alloy, comprising: adding 1-5 wt.% of Al element into In 718 alloy by powder ball milling method, and sequentially performing solution treatment and double aging treatment on the formed laser additive manufacturing In 718 alloy, the solution treatment temperature is 1050-1200℃, and the double aging treatment temperature is 700-760℃ and 600-660℃.

[0032] The present application first adds 1-5 wt.% of Al element into In 718 alloy by ball milling powder mixing method. Al element promotes the segregation of Nb element and the growth of secondary dendrite arm, so that a large amount of continuous chain and network distributed Laves phase is precipitated in the formed structure. In order to avoid the damage of a large amount of chain and network Laves phase to the mechanical properties of the alloy, the In 718 alloy is subjected to Laves phase solution treatment after forming, so that the chain and network Laves phase is dissolved into fine granular Laves phase which is beneficial to the performance of the alloy, and part of the solid solution strengthening elements is dissolved. In the present application, the solution treatment temperature is 1050-1200℃, and the solution treatment time is 1-1.5h.

[0033] The In 718 alloy after forming is preferably raised from room temperature to the temperature of Laves solid solution, and the time of the raising is preferably 1.5-2 h. The present application does not have special requirements for the heat treatment furnace used for the solid solution treatment, and preferably uses a muffle furnace and a vacuum heat treatment furnace with a maximum rated temperature greater than 1050℃ and a temperature control accuracy of ±1℃ and capable of long-term continuous operation. The present application does not have special requirements for the atmosphere of the solid solution treatment, and can basically be an air atmosphere, an inert gas protective atmosphere or a vacuum atmosphere.

[0034] After the solid solution treatment, the obtained In 718 alloy is subjected to a two-stage aging treatment. The In 718 alloy after the solid solution treatment is first cooled to room temperature, and the cooling method used is water cooling or oil cooling. Then it is subjected to a two-stage aging treatment, and the first-stage aging treatment of the two-stage aging treatment has a temperature rising rate of 10-30℃ / min, and further preferably 15-25℃ / min. In the present application, the first-stage aging treatment temperature of the two-stage aging is 700-760℃. The first-stage aging treatment time is 8 h.

[0035] After the first-stage aging treatment, the In 718 alloy is subjected to a second-stage aging treatment. The second-stage aging treatment needs to reduce the aging temperature from 700-760℃ of the first-stage aging treatment to 600-660℃ of the second-stage aging treatment. The cooling rate is preferably 10-30℃ / min, and further preferably 15-25℃ / min. In the present application, the second-stage aging treatment temperature is also 8 h. The two-stage aging treatment of the present application can make the precipitation strengthening phase in the alloy fully precipitate. Although the residual of a large number of Laves phase particles can lead to insufficient γ" phase precipitation during the first-stage aging treatment, the addition of Al element can make the γ' phase fully precipitate during the second-stage aging treatment. The combined action of a sufficient number of precipitation strengthening phases and a large number of unsolved Laves phases can significantly improve the hardness of the In 718 alloy. The present application does not have special requirements for the atmosphere of the solid solution treatment, and can basically be an air atmosphere, an inert gas protective atmosphere or a vacuum atmosphere.

[0036] After the two-stage aging treatment, the present application preferably further includes cooling the δ solid solution treated nickel-based high-temperature alloy to room temperature. In the present application, the cooling is preferably water cooling or air cooling.

[0037] The method for improving the hardness of laser additive manufacturing In 718 alloy provided by the present application is described below in combination with examples.

[0038] Example 1

[0039] (1) Laser additive manufacturing In 718 alloy

[0040] The In 718 alloy is added with 1% pure Al powder by ball milling, the pure Al powder and the In 718 alloy powder are fully mixed and uniform by ball milling for more than 10 hours, and then a bulk sample of In 718 alloy with a height of 10 mm is formed by selective laser melting. Among them, the pulse energy is 180 J, the pulse laser frequency is 12 Hz, the single layer powder thickness is 0.3 mm, and the scanning speed is 5 mm / s.

[0041] (2) Solution treatment of laser additive manufacturing In 718 alloy

[0042] The formed In 718 alloy sample is placed in a muffle furnace, and then heated at 1050°C for 1.5 hours, and then water-cooled to room temperature.

[0043] (3) Two-stage aging treatment of laser additive manufacturing In 718 alloy

[0044] The sample after solution treatment is again placed in a muffle furnace and heated to 700°C at a rate of 10°C / min, and then heated for 8 hours, then cooled to 600°C at a rate of 10°C / min, and then heated for 8 hours, and then air-cooled to room temperature.

[0045] Figure 1 The microstructure diagram of the laser additive manufacturing In 718 alloy sample after adding Al element in Example 1; from the figure we can see that the microstructure of the laser additive manufacturing In 718 alloy is fine cellular dendrite, the dendrite spacing is about 2-5 μm, and there are a large number of chain-shaped white granular precipitates between the dendrites. Figure 2 The microstructure diagram of the In 718 alloy sample obtained after solution treatment in Example 1; from the figure we can see that after solution treatment, the chain-shaped precipitates between the dendrites are converted into granules of different sizes, and most of the precipitates are dissolved in the matrix. Figure 3 The low-magnification microstructure diagram of the In 718 alloy sample obtained after solution treatment and two-stage aging treatment in Example 1; from the figure we can see that there are uniform precipitates at the grain boundaries and within the grains, including rod-shaped and granular morphologies, and the number is reduced compared with the as-deposited state. Figure 4 The high-magnification microstructure diagram of the In 718 alloy sample obtained after solution treatment and two-stage aging treatment in Example 1; from the figure we can see that in addition to the dispersed precipitates, there are a large number of γ' and γ" precipitates on the matrix, with a size of tens of nanometers. Figure 5 The microhardness results of the laser additive manufacturing In 718 alloy in different states can be seen, the hardness of the as-deposited sample is the lowest, which is 281 HV, the microhardness increases to 489 HV after solution treatment, and the hardness after solution + two-stage aging treatment is the highest, which is 498 HV.

[0046] Example 2

[0047] (1) Laser additive manufacturing of In 718 alloy

[0048] Pure Al powder was added to In 718 alloy by mixing powder for more than 10 h to make the pure Al powder and In 718 alloy powder fully mixed and uniform, and then a bulk In 718 alloy sample with a height of 12 mm was formed by selective laser melting. Among them, the pulse energy was 200 J, the pulse laser frequency was 10 Hz, the single layer powder thickness was 0.4 mm, and the scanning speed was 8 mm / s.

[0049] (2) Solution treatment of laser additive manufacturing of In 718 alloy

[0050] The formed In 718 alloy sample was placed in a muffle furnace, heat treated at 1100°C for 1.5 h, and then water cooled to room temperature.

[0051] (3) Double-stage aging treatment of laser additive manufacturing of In 718 alloy

[0052] The sample after solution treatment was again placed in a muffle furnace, heated to 720°C at a rate of 10°C / min, heat treated for 8 h, then cooled to 620°C at a rate of 10°C / min, heat treated again for 8 h, and then air cooled to room temperature. Figure 6 The microstructure of the obtained alloy is shown in Table 1.

[0053] Specimen Hardness / HV As-deposited 296 Solution treated 507 Solution + double ageing treated 517

[0054] Example 3

[0055] (1) Laser additive manufacturing of In 718 alloy

[0056] Pure Al powder was added to In 718 alloy by mixing powder for more than 10 h to make the pure Al powder and In 718 alloy powder fully mixed and uniform, and then a bulk In 718 alloy sample with a height of 12 mm was formed by selective laser melting. Among them, the pulse energy was 200 J, the pulse laser frequency was 10 Hz, the single layer powder thickness was 0.4 mm, and the scanning speed was 8 mm / s.

[0057] (2) Solution treatment of laser additive manufacturing of In 718 alloy

[0058] The formed In 718 alloy sample was placed in a muffle furnace, heat treated at 1100°C for 1.5 h, and then water cooled to room temperature.

[0059] (3) Double-stage aging treatment of laser additive manufacturing of In 718 alloy

[0060] The sample after the solution treatment is put into the muffle furnace again, heated to 740 DEG C at the rate of 10 DEG C / min, kept for 8h, then cooled to 640 DEG C at the rate of 10 DEG C / min, kept for 8h again, and then air-cooled to room temperature. Figure 7 In order to obtain the microstructure of the alloy, Table 2 is the microhardness results of the alloy after different heat treatments.

[0061] Specimen Hardness / HV As-deposited 338 Solution treated 519 Solution + double ageing treated 554

[0062] The raw materials listed in the present application, the upper and lower limits, interval values of each raw material of the present application, and the upper and lower limits, interval values of process parameters (such as temperature, time, etc.) can all achieve the present application, and examples are not listed one by one.

[0063] The above is only a preferred embodiment of the present application, of course, cannot limit the scope of the present application, should be noted that for ordinary skilled in the art, without departing from the principles of the present application, can also make a number of improvements and changes, these improvements and changes are also considered to be within the scope of the present application.

Claims

1. A method for improving the hardness of In 718 alloy manufactured by laser additive manufacturing, characterized in that, It includes the following steps: Al was added to In 718 alloy powder by powder ball milling. The In 718 alloy for laser additive manufacturing was subjected to solution treatment and two-stage aging treatment sequentially. The solution treatment temperature was 1050-1200℃, and the two-stage aging treatment temperatures were 700-760℃ and 600-660℃. The amount of Al added was 1~5 wt.%, and the ball milling time was greater than 10 hours.

2. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 1, characterized in that... Selective laser melting system is used as the additive manufacturing system, with pulse energy of 180-220J, pulse laser frequency of 8-12Hz, single-layer powder thickness of 0.3-0.5mm, and scanning speed of 5-10mm / s.

3. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 1, characterized in that: The solution treatment time is 1 to 1.5 hours; after the solution treatment, the In 718 alloy obtained after the Laves solution treatment is cooled to room temperature.

4. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 3, characterized in that: The cooling method is water cooling, air cooling, or oil cooling.

5. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 1, characterized in that: After the solution treatment, the In 718 alloy obtained by cooling the Laves phase solution treatment is subjected to a two-stage aging treatment.

6. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 1, characterized in that: The duration of the two-stage aging treatment is 8+8 hours; after the two-stage aging treatment, the In 718 alloy after the two-stage aging treatment is further cooled to room temperature.

7. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 6, characterized in that: The cooling method is either water cooling or air cooling.

8. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 1, characterized in that: The atmosphere for the solution treatment and the two-stage aging treatment can be independently an air atmosphere, a vacuum atmosphere, or an inert gas protective atmosphere.

9. The method for improving the hardness of In 718 alloy in laser additive manufacturing as described in claim 8, characterized in that: The inert gas is selected from argon.

Images