Synergistic strengthening of nickel-cobalt alloy by trace element interaction and preparation thereof

Abstract

The application belongs to the field of casting component design and preparation, discloses a kind of synergistic toughening of nickel-cobalt alloy and preparation using trace element interaction, and the nickel-cobalt alloy is Ni 50‑x Co 50‑x Ti x C x Wherein, x is 0.3-0.7;In the nickel-cobalt alloy, the atomic percentage of Ni element and Co element is (50-x) %, and the atomic percentage of Ti element and C element is x %;By introducing Ti element and C element, the strength and toughness of nickel-cobalt alloy can be improved simultaneously.The application selects Ti and C element with suitable interaction strength, controls the content of solute elements Ti and C, so that it produces obvious element segregation characteristics during alloy solidification, forms element cluster without forming other phases, that is, in the case of still maintaining single-phase structure, the purpose of simultaneously improving the strength and toughness of alloy is achieved, which is especially suitable for toughening nickel-cobalt alloy castings.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of casting component design and preparation, and more particularly relates to a synergistic strengthening and toughening of nickel-cobalt alloy using trace element interaction and preparation. BACKGROUND

[0002] With the rapid development of aerospace, shipbuilding, automobile and energy industries, the use environment of large structural parts becomes more and more complex, which puts forward higher requirements for their mechanical properties. At present, nearly 99% of large structural parts on the market are still mainly prepared by casting, but the castings cannot directly meet the use mechanical property requirements and precision requirements, so it is necessary to assist with essential welding, heat treatment and forging means. This series of complex processing processes undoubtedly brings more difficulties and challenges to actual production and processing, to some extent, makes the processing process more complex, increases the preparation difficulty, prolongs the processing cycle and increases the preparation cost, so it is necessary to seek a more fast, economic and effective performance improvement method.

[0003] By directly controlling the microstructure and phase structure of the alloy composition design, the mechanical properties of the castings are further controlled, which is the most economical and effective way at present, and also the most fundamental way to affect the performance of the castings. For example, the widely used steel is produced by adding carbon, chromium, manganese, vanadium and other elements in iron, and by controlling the content of different elements to adapt to the performance in different environments. The solidification state nickel-cobalt binary alloy is mainly composed of coarse columnar crystals and a small amount of grains at the center, which is a single-phase face-centered cubic structure, has low strength and poor mechanical properties, and the mechanical properties of columnar crystals have directionality, so the whole metal also shows obvious anisotropy, so it is rarely used in actual industry. In order to improve the mechanical properties of nickel-cobalt, the previous strengthening method is to add Al, Cr, Cu, Mo, V and other elements in nickel-cobalt alloy to form nickel-cobalt alloy. These elements form L12 phase, carbide and other precipitates in the alloy, which can significantly improve the strength, but often greatly loses the plasticity, and the mutual swallowing effect between strength and toughness limits the application and development of nickel-cobalt alloy. In addition, although a variety of metal elements are added, the solidification state structure of nickel-cobalt alloy is still mainly coarse columnar crystal structure, so the anisotropy of the mechanical properties of the solidification state nickel-cobalt alloy cannot be eliminated, which also becomes another main reason for limiting the development of as-cast nickel-cobalt alloy.

[0004] Therefore, in view of the elimination of the anisotropy of nickel-cobalt alloy and the problem of mutual swallowing of strength and toughness, a new alloy composition design method is needed at present, which also becomes a problem to be solved at present. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide a kind of synergistic toughening nickel-cobalt alloy by trace element interaction and preparation, by selecting Ti and C elements with suitable interaction strength, and controlling the content of solute elements Ti and C, so that it produces obvious element segregation characteristics during alloy solidification, forms element cluster while not forming other phases, i.e. in the case of still maintaining single-phase structure, the purpose of simultaneously improving the strength and toughness of the alloy is achieved. The present application utilizes the solidification process interaction of equal atomic ratio Ti and C elements to optimize the microstructure, and produces element cluster synergistic toughening solidification state nickel-cobalt alloy, which is particularly suitable for toughening nickel-cobalt alloy castings, such as aerospace engines, aircraft landing gear, automobile wheel hub, steam turbine, industrial gas turbine, etc.

[0006] To achieve the above purpose, according to one aspect of the present application, a kind of synergistic toughening nickel-cobalt alloy by trace element interaction is provided, characterized in that the nickel-cobalt alloy is Ni 50-x Co 50-x Ti x C x Wherein, x is 0.3~0.7;In the nickel-cobalt alloy, the atomic percentage of Ni element and Co element is (50-x)%, and the atomic percentage of Ti element and C element is x%;By introducing Ti element and C element, the strength and toughness of the nickel-cobalt alloy can be simultaneously improved.

[0007] As a further preferred embodiment of the present application, the nickel-cobalt alloy is a single-phase face-centered cubic structure.

[0008] According to another aspect of the present application, the present application provides a preparation method of the above-mentioned nickel-cobalt alloy, characterized in that the preparation method is to melt and mix raw materials composed of Ni 50-x Co 50-x Ti x C x Source, Ti source and carbon powder in inert atmosphere;

[0009] Wherein, the Ni source is selected from pure Ni, nickel-cobalt binary alloy;

[0010] The Co source is selected from pure Co, nickel-cobalt binary alloy;

[0011] The Ti source is pure Ti.

[0012] As a further preferred embodiment of the present application, the melting is vacuum induction melting or vacuum arc melting;

[0013] Specifically, before melting starts, the hearth is repeatedly charged and discharged with inert gas for multiple times, and then the target Ni 50- xCo 50-x Ti x C x The nickel-cobalt alloy is poured into a mold after the solute in the sample is uniformly diffused, and a master alloy rod is prepared.

[0014] As a further preferred embodiment of the present application, the melting target Ni 50-x Co 50-x Ti x C x The nickel-cobalt alloy is at least turned over and remelted 5 times for each button ingot obtained by melting.

[0015] As a further preferred embodiment of the present application, the master alloy rod after pouring is also subjected to directional solidification crystallization using a directional solidification furnace.

[0016] As a further preferred embodiment of the present application, the inert atmosphere is argon.

[0017] Compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects:

[0018] 1、The present application is based on a nickel-cobalt binary alloy, by adding a small amount of Ti and C elements (the atomic percentage of Ti is controlled to be 0.3-0.7%, and the atomic percentage of C is also controlled to be 0.3-0.7%, and the atomic percentages of the two are equal), using the significant synergistic toughening effect of trace solute elements, the obtained strong and tough nickel-cobalt alloy has improved strength and toughness, and at the same time, the columnar crystals in the as-cast nickel-cobalt alloy structure are eliminated, and are replaced by uniform crystal structure, ensuring the isotropy of its mechanical properties. In the following examples, the tensile yield strength, tensile strength and elongation of the nickel-cobalt alloy with Ti and C elements at room temperature are not less than 120 MPa, 405 MPa and 36% respectively; compared with the binary nickel-cobalt alloy without Ti / C solid solution, the ductility of the solidified nickel-cobalt alloy at room temperature is significantly improved, the room temperature yield strength is increased by 15-34 MPa, the tensile strength is increased by 90-177 MPa, and the elongation at break is increased by 1-10%.

[0019] The present application is to introduce Ti and C elements into a nickel-cobalt binary alloy at an equal atomic ratio, and the obtained strong and toughened nickel-cobalt alloy is in a single-phase face-centered cubic structure without any precipitated phase, is composed of fine and uniform grains, and presents obvious Ti / C element synchronous segregation characteristics to form Ti / C clusters. Ti and C elements have a suitable strength of combination, can form co-segregation during solidification, produce small clusters, promote the alloy to obtain synergistic strength and toughness, and a small amount of Ti and C elements have obvious solid solution strengthening effect in the metal. C atoms are easy to segregate at the front of the solid-liquid interface due to small atomic radius and fast diffusion, and Ti and C have strong affinity, so Ti and C segregate simultaneously during solidification. At the same time, due to the low content of Ti and C, only mutual attraction but unable to combine to form carbides before solidification, so there is obvious Ti and C element co-segregation. Finally, Ti and C segregate in the cell wall instead of large-angle grain boundaries to form the spatial distribution of element clusters. Taking Ti element as an example, the atomic percentage of the Ti element enrichment area is between 0.99-1.15%, the atomic percentage of the Ti element deficiency area is between 0-0.3%, and there are element clusters. The element clusters produced by co-segregation hinder the dislocation movement, thereby greatly improving the work hardening rate, so as to improve the room temperature elongation of the alloy while strengthening, and achieve the purpose of synergistic strengthening and toughening. The alloy design idea of the present application ensures that the metal does not produce phase change and nanotwin during deformation, only uses clusters to affect the dislocation movement mode, and therefore also ensures the stability of mechanical properties.

[0020] 2、The present application is aimed at Ni 50 Co 50 alloy matrix, and realizes strengthening and toughening by introducing a small amount of Ti / C elements. The influence of the matrix cannot be ignored, and different matrices may not have similar effects. For example, the prior art known CrMnFeCoNiTi 0.3 C 0.3 alloy has higher yield strength than the CrMNFeCoNi matrix alloy, but the elongation has decreased obviously (Cheng, H., Chen, W., Liu, X., Tang, Q., Xie, Y., & Dai, P. (2018). Effect of Ti and C additions on the microstructure and mechanical properties of the FeCoCrNiMn high-entropy alloy. Materials Science and Engineering A, 719 (February), 192-198.). Similarly, Al 0.2 Co 1.5 CrFeNi 1.5Ti1C 0.5 Alloy compared to Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 The matrix alloy also only experienced strengthening, while the plasticity was severely lost (Xin, B., Zhang, A., Han, J., Su, B., & Meng, J. (2020). Tuning composition and microstructure by doping Ti and C for enhancing mechanical property and wear resistance of Al0.2Co1.5CrFeNi1.5Ti0.5high entropy alloy matrix composites. Journal of Alloys and Compounds, 836.).

[0021] 3. In addition, the application can make the components of the alloy diffuse uniformly through sufficient melting, and on this basis, preferred directional solidification crystallization can be performed to obtain a dense casting. Based on the application, the mother alloy rod can be prepared by using a mold (such as a copper mold) for drop casting during melting, and then re-solidification crystallization is performed using a directional solidification furnace, so that an alloy ingot with better uniformity and density can be obtained.

[0022] In summary, the NiCoTiC alloy obtained by the application is still a single-phase alloy, has excellent comprehensive mechanical properties, strong mechanical stability, a simple preparation process, and extremely low preparation cost, is suitable for the toughening field of nickel-cobalt alloy castings, such as aerospace engines, airplane landing gears, steam turbines, industrial gas turbines, and the like, and provides an innovative idea for designing solute components based on the toughening target and preparing high-toughness alloy castings. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The solidification structure of the alloy of Example 2.

[0024] Figure 2 The Ti element segregation feature map of the alloy of Example 2; wherein, Figure 2 The corresponding red lines in (a) and (b) are artificially marked grain boundaries (the scales in the figure represent 100 μm); Figure 2 The cold and warm color scales below (b) represent the content concentration of the Ti element, and the color from left to right represents that the concentration gradually increases, as shown in the figure, the atomic percentage of the Ti element enrichment area is 0.99-1.15% (shown as green in the figure), and the atomic percentage of the Ti element deficiency area is 0-0.3% (shown as black and blue in the figure).

[0025] Figure 3 The room temperature tensile curves of all the example and comparative example alloys are compared. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0027] In the present application, trace elements interact to synergistically strengthen and toughen the nickel-cobalt alloy. The atomic number of each element, in terms of atomic percentage of the total atomic number, satisfies the following requirements:

[0028] Ni: 49.3~49.7%, Co: 49.3~49.7%, Ti: 0.3~0.7%, C: 0.3~0.7%;

[0029] Among them, for the atomic percentage: Ni=Co, Ti=C.

[0030] The raw materials composed of Ni, Co, Ti and carbon powder can be fully melted under an inert atmosphere. Maintaining an inert atmosphere during melting can avoid material oxidation, and any common inert atmosphere melting furnace can be used for melting. For example, the melting equipment can use an electric arc furnace, each button ingot obtained by melting is turned over and remelted at least 5 times, and a copper mold is used for drop casting to prepare a master alloy rod, and then a directional solidification furnace is used for re-solidification and crystallization, so that an alloy ingot with better uniformity and density can be obtained.

[0031] The following are specific examples:

[0032] Example 1

[0033] The solidified nickel-cobalt alloy of the present embodiment, which is synergistically strengthened and toughened by trace solute elements, comprises, in terms of atomic percentage: Ni: 49.7%, Co: 49.7%, Ti: 0.3%, C: 0.3%.

[0034] The preparation method of the solidified nickel-cobalt alloy of the present embodiment, which is synergistically strengthened and toughened by trace solute elements, comprises the following steps:

[0035] 1) Raw material preparation: the components, in terms of atomic percentage, comprise: Ni: 49.7%, Co: 49.7%, Ti: 0.3%, C: 0.3%. The raw materials include: Ni, Co, Ti pure metals (purity > 99.9wt.%) and carbon powder (purity > 99%) totaling 120 grams.

[0036] 2) Melting step: Arc furnace melting. Put the above raw materials into the furnace crucible, vacuum the furnace to ~ 5 x 10 -2 Pa, then backfill argon, repeat three times, and then fill argon to ~ 5 x 10 4 Pa. Similar to the conventional operation, before formally melting the target, melt the industrial pure titanium for consuming the remaining oxygen. Start melting the button ingot and flip and remelt five times, then use copper mold casting.

[0037] 3) The drop cast master alloy ingot is prepared into a metal rod with a suitable diameter by wire cutting, and crystallization is performed using a directional solidification furnace.

[0038] Example 2

[0039] The solidification state nickel-cobalt alloy of the present embodiment includes, in atomic percentage, Ni: 49.5%, Co: 49.5%, Ti: 0.5%, and C: 0.5%.

[0040] The preparation method of the solidification state nickel-cobalt alloy of the present embodiment includes the following steps:

[0041] 1) Raw material preparation: The components include, in atomic percentage, Ni: 49.5%, Co: 49.5%, Ti: 0.5%, and C: 0.5%. The raw materials include 120 grams of Ni, Co, and Ti pure metals (purity > 99.9 wt.%) and carbon powder (purity > 99%).

[0042] 2) Melting step: Arc furnace melting. Put the above raw materials into the furnace crucible, vacuum the furnace to ~ 5 x 10 -2 Pa, then backfill argon, repeat three times, and then fill argon to ~ 5 x 10 4 Pa. Melt the industrial pure titanium for consuming the remaining oxygen. Melt the button ingot and flip and remelt five times, then use copper mold casting.

[0043] 3) The drop cast master alloy ingot is prepared into a metal rod with a suitable diameter by wire cutting, and crystallization is performed using a directional solidification furnace.

[0044] Example 3

[0045] The solidification state nickel-cobalt alloy of the present embodiment includes, in atomic percentage, Ni: 49.3%, Co: 49.3%, Ti: 0.7%, and C: 0.7%.

[0046] The preparation method of the solidification state nickel-cobalt alloy of the present embodiment includes the following steps:

[0047] 1) Raw material preparation: The ingredients include, in atomic percentage: Ni: 49.3%, Co: 49.3%, Ti: 0.7%, C: 0.7%. The raw materials include: Ni, Co, Ti pure metals (purity > 99.9 wt.%) and carbon powder (purity > 99%) for a total of 120 grams.

[0048] 2) Melting step: The arc furnace is used for melting. The above raw materials are placed in the furnace crucible, the furnace chamber is vacuumed to ~ 5 x 10 -2 Pa, then backfilled with argon, repeated three times, and then filled with argon to ~ 5 x 10 4 Pa. Industrial pure titanium is melted to consume the remaining oxygen. Button ingots are melted and remelted by turning five times, and then copper mold casting is used.

[0049] 3) The drop cast master alloy ingot is prepared into a metal rod with a suitable diameter by wire cutting, and crystallization is performed using a directional solidification furnace.

[0050] Comparative Example 1

[0051] This comparative example is a Ni 50 Co 50 alloy.

[0052] The preparation method of the Ni 50 Co 50 alloy of this example includes the following steps:

[0053] 1) Raw material preparation: The ingredients include, in atomic percentage: Ni: 50%, Co: 50%. The raw materials include: Ni, Co pure metals (purity > 99.9 wt.%) for a total of 120 grams.

[0054] 2) Melting step: The arc furnace is used for melting. The above raw materials are placed in the furnace crucible, the furnace chamber is vacuumed to ~ 5 x 10 -2 Pa, then backfilled with argon, repeated three times, and then filled with argon to ~ 5 x 10 4 Pa. Industrial pure titanium is melted to consume the remaining oxygen. Button ingots are melted and remelted by turning five times, and then copper mold casting is used.

[0055] 3) The drop cast master alloy ingot is prepared into a metal rod with a suitable diameter by wire cutting, and crystallization is performed using a directional solidification furnace.

[0056] Referring to Table 1, the tensile properties of the nickel-cobalt alloy materials of Examples 1-3 are tested at room temperature, and the nickel-cobalt alloy has excellent comprehensive mechanical properties, with a yield strength of not less than 120 MPa, a tensile strength of not less than 405 MPa, and an elongation of not less than 36%. In particular, Example 2 exhibits more excellent comprehensive mechanical properties. By comparison with Comparative Example 1, the room temperature yield strength of the examples is increased by 15-34 MPa, the tensile strength is increased by 90-177 MPa, and the elongation at break is increased by 1-10%.

[0057] Table 1 Room temperature yield strength, tensile strength and elongation at break of Examples 1-3 and Comparative Example 1.

[0058]

[0059] Referring to Figure 1 The microstructure of the alloy of Example 2 is observed. The alloy has a single-phase structure, no precipitates, and is composed of uniform grains, which indicates that the entire sample is a uniform crystal structure.

[0060] Referring to Figure 2 The distribution of Ti elements in the alloy of Example 2 is analyzed, and the Ti elements are segregated at the position of the non-crystal boundary to form obvious element clusters. Ti and C elements show obvious co-segregation characteristics, but do not segregate along the crystal boundary, but form Ti / C element clusters, and do not form precipitates.

[0061] Referring to Figure 3 The room temperature tensile mechanical properties of Examples 1-3 and Comparative Example 1 are analyzed, and it is found that the yield strength, tensile strength and elongation at break of Examples 1-3 are all improved compared with Comparative Example 1.

[0062] From the analysis of the above examples, it can be seen that trace amounts of Ti and C are added to the nickel-cobalt alloy, and by vacuum melting and directional solidification forming, a uniform crystal structure is obtained in the entire cast alloy, and a single-phase uniform grain is obtained, eliminating anisotropy. In addition, C is easy to diffuse due to its small atomic radius, and thus will segregate at the front of the solid-liquid interface. Ti and C have high affinity, and based on this point, the segregation of Ti and C elements is designed and realized, forming element segregation clusters, not only producing strong solid solution strengthening effect, but also hindering and pinning dislocation movement, improving the work hardening capacity, and obtaining a synergistic strengthening and toughening effect.

[0063] The above examples are only examples, and Ni 50-x Co 50-x Ti x C xThe value of x is only required to be greater than or equal to 0.3 and less than or equal to 0.7. In addition to the pure metals of Ni, Co, and Ti exemplified in the above examples, alloy materials can also be used as raw materials, provided that these alloys do not introduce other elements in addition to Ni, Co, Ti, and C, and the various raw materials satisfy the following conditions: Ni 50-x Co 50-x Ti x C x The nominal stoichiometric ratio is sufficient (for example, commercially available Ni 50 Co 50 The finished metal ingot and the raw materials composed of pure Ti and carbon powder are melted under an inert atmosphere. In addition, in the above, the room temperature mechanical properties of the alloy are tested by a universal testing machine, and the test sample is a dog bone-shaped tensile sample in accordance with international standards.

[0064] Those skilled in the art will readily understand that the above description is only preferred embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A synergistically strengthened nickel-cobalt alloy utilizing trace element interactions, characterized in that, The nickel-cobalt alloy is Ni 50- x Co 50-x Ti x C x wherein x is 0.3-0.7; in the nickel-cobalt alloy, the atomic percentage of Ni and Co is (50-x)%, and the atomic percentage of Ti and C is x%; by introducing Ti and C, the strength and toughness of the nickel-cobalt alloy can be simultaneously improved.

2. The nickel-cobalt alloy of claim 1, wherein The nickel-cobalt alloy is single-phase face-centered cubic structure.

3. The method of producing a nickel-cobalt alloy according to claim 1 or 2, wherein The preparation method is to melt and mix raw materials composed of a Ni source, a Co source, a Ti source, and carbon powder in an inert atmosphere according to a nominal stoichiometric ratio. 50- x Co 50-x Ti x C x The raw materials composed of a Ni source, a Co source, a Ti source, and carbon powder in an inert atmosphere according to a nominal stoichiometric ratio. The Ni source is selected from pure metal Ni and a nickel-cobalt binary alloy. The Co source is selected from pure metal Co and a nickel-cobalt binary alloy. The Ti source is pure metal Ti.

4. The preparation method according to claim 3, characterized in that, The smelting is vacuum induction smelting or vacuum arc smelting. Specifically, before the smelting starts, the hearth is repeatedly filled and discharged with inert gas for multiple times, and then the target Ni 50-x Co 50- x Ti x C x The nickel-cobalt alloy is poured into a mold after the solute in the sample is uniformly diffused to prepare a master alloy rod.

5. The preparation method according to claim 4, characterized in that, The smelted target Ni 50-x Co 50-x Ti x C x The nickel-cobalt alloy is at least turned over and remelted 5 times from each button ingot obtained by smelting.

6. The preparation method according to claim 4, characterized in that, The finished master alloy rod is also subjected to directional solidification crystallization in a directional solidification furnace.

7. The preparation method according to claim 3, characterized in that, The inert atmosphere is argon.

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