CN113373388B - A method for improving the ductility and toughness of boron-containing eutectic alloys by using dual structure - Google Patents

Abstract

The invention discloses a method for improving the plasticity and toughness of a boron-containing eutectic alloy by utilizing a double-structure, which is characterized in that the double-structure is obtained by means of an integrated regulation and control means of non-equilibrium solidification and subsequent isothermal annealing heat treatment, so that the plasticity and toughness of the boron-containing eutectic alloy are improved; and (3) carrying out subsequent isothermal annealing heat treatment on the non-equilibrium solidification structure of the eutectic alloy, so that a surface single-phase recrystallization tissue layer is obtained, the interior of the surface single-phase recrystallization tissue layer is a double-structure with two irregular phases, and the strength and the ductility and the toughness of the alloy are improved. The method combines the non-equilibrium solidification structure acquisition and the subsequent structure transformation of the boron-containing eutectic alloy by combining the non-equilibrium solidification method with the subsequent isothermal annealing heat treatment to obtain an alloy double-structure, thereby realizing the improvement of the comprehensive mechanical property of the alloy, greatly enriching and promoting the existing eutectic alloy structure property regulation and control method, and being used for regulating and controlling the mechanical property of boron-containing eutectic and similar alloy materials.

Description

A method for improving the ductility and toughness of boron-containing eutectic alloys by using dual structure

technical field

The invention belongs to the technical field of metal material processing, and in particular relates to a method for improving the plasticity and toughness of a boron-containing eutectic alloy by utilizing a dual structure.

Background technique

Due to its rich microstructure and excellent comprehensive properties, eutectic alloys have always been one of the most widely used alloys in industry, and people's attention has been paid to improving the properties of eutectic alloys by regulating the microstructure of eutectic alloys. (Fe, Ni)-B eutectic alloys have been studied and applied because of their excellent soft magnetic properties, good mechanical properties and metallurgical properties. The alloy structure that determines the service performance of the alloy is often controlled by its solidification and subsequent cooling/heating. One of the key issues is the evolution of the solidification structure of the alloy and its subsequent transformation and control of the structure. Obtaining non-equilibrium structures that cannot be achieved under equilibrium conditions by non-equilibrium solidification technology has always been an important part of solidification science and technology research. The non-equilibrium solidified structure not only has mechanical and physical properties that the equilibrium structure does not have, but also based on the metastable characteristics of the non-equilibrium solidified structure, combined with heat treatment to induce subsequent solid state transformation, the final state structure of the alloy can be further regulated.

The ideal service performance of alloy materials is high strength and good plasticity, and the traditional strengthening method based on dislocation theory leads to the increase of alloy strength at the expense of partial plasticity of the material. Numerous studies have found that the simultaneous improvement of material strength and plasticity can be achieved by applying structural nonequilibrium combined with subsequent heat treatment for solid-state transformation. In the traditional sense, the improvement of metal structure and properties by subsequent static recrystallization transformation can only be achieved by subsequent recrystallization annealing in metallic materials with cold deformation. Non-equilibrium solidification is an effective means to generate the non-equilibrium of the alloy structure. If combined with the subsequent heat treatment, the integrated control of the alloy structure and properties can be realized.

The research on the subsequent heat treatment transformation of non-equilibrium solidification structure has been carried out for many years along with the application of Fe- and Ni-based alloys, but most of them focus on single-phase structure or single-phase alloy, while the follow-up transformation of non-equilibrium solidification structure of eutectic alloys is rarely studied. It is mainly attributed to the single subsequent transformation of the single-phase organization, which is convenient to characterize the source, process and final organization of the transformation driving force experimentally and theoretically. In recent years, the follow-up solid-state transformation research on the solidification structure of eutectic alloys has been carried out with the high-entropy alloys with excellent comprehensive properties becoming a material research and application hotspot. The prerequisite is the artificial introduction of non-equilibrium, that is, the specimen undergoes large plastic deformation. This is attributed to the fact that the non-equilibrium solidification structure of eutectic alloys is often not produced by a single transformation process. The non-equilibrium solidification process of eutectic alloys includes the primary solidification of the eutectic cluster structure and the subsequent solidification of the residual liquid phase between the clusters, and even the formation of the metastable phase structure. , so that the non-equilibrium effect of the solidification process is dissipated in various ways, and the structure non-equilibrium can be released in various ways during the solidification and subsequent cooling process. Under the conditions of equilibrium and near-equilibrium solidification, the non-equilibrium in the alloy structure is less accumulated and stored.

SUMMARY OF THE INVENTION

The invention solves the deficiencies in the existing process methods, provides a method for improving the plastic toughness of a boron-containing eutectic alloy by using a double structure, and obtains the non-equilibrium of the alloy structure by means of non-equilibrium solidification, without artificial plastic deformation, and is compatible with subsequent The integrated control technology of heat treatment is combined to form a dual structure, which improves the plasticity and toughness of boron-containing eutectic alloys.

The technical scheme adopted in the present invention: a method for improving the plastic toughness of a boron-containing eutectic alloy by utilizing a dual structure, which is characterized in that it has the following steps:

S1: Select a boron-containing binary or ternary eutectic alloy, use a high-frequency electromagnetic induction melting furnace to smelt the eutectic alloy, use molten glass purification combined with a cyclic superheating method to obtain a supercooled alloy melt, and melt the supercooled alloy The body is naturally cooled or chilled to obtain a non-equilibrium solidification structure of the eutectic alloy;

S2: Perform isothermal annealing heat treatment on the non-equilibrium solidification structure of the eutectic alloy. The non-equilibrium accumulated in the non-equilibrium solidification structure of the eutectic alloy is used as the driving force. Crystallization transforms to form a single-phase structure layer, which forms a dual structure with its internal irregular eutectic structure.

Preferably, the eutectic alloy is Fe40Ni40B20 (at.%) alloy, and the eutectic transformation temperature is 1323K.

Preferably, in S1, the non-equilibrium solidification structure of the eutectic alloy accumulates a certain degree of non-equilibrium, and the non-equilibrium solidification structure of the eutectic alloy is naturally cooled when the initial undercooling degree is greater than or equal to 170K, or the non-equilibrium solidification structure of the eutectic alloy is The initial subcooling degree is less than 100K for chilling treatment.

Preferably, in S1, in the chilling treatment, the temperature data of the cooling process of the supercooled alloy melt is monitored and collected by means of an infrared thermometer, and when the degree of subcooling is less than 100K, the supercooled alloy melt is poured into the Ga-In liquid alloy or Chilled in a copper metal mold.

Preferably, in S2, isothermal annealing heat treatment is performed in a vacuum or a protective atmosphere, the annealing temperature is 873K to 1273K, and the annealing time is 1.5h to 60h.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention combines non-equilibrium solidification with subsequent heat treatment technology, utilizes the rapid solidification method to spontaneously realize non-equilibrium accumulation in the microstructure of the alloy, and combines the subsequent heat treatment transformation to obtain a dual-structure structure, thereby improving the plasticity and toughness of the alloy. Specifically, due to the non-equilibrium solidification of deep undercooling, the non-equilibrium metastable structure of the alloy structure can be realized, which contains a large number of microscopic defects, microscopic stress and strain and other microstructure non-equilibrium; further combined with chilling, the microstructure non-equilibrium can be preserved to a greater extent, forming The driving force of the subsequent recrystallization transformation, the deboronization of the surface layer and the recrystallization transformation occur at the same time during the subsequent heat treatment, forming a single-phase recrystallized plastic structure layer on the surface layer and a dual-structure structure with irregular two-phase structure inside, which improves the plastic toughness and comprehensive mechanics of the alloy. performance.

2. The method provided by the present invention does not require artificially introducing non-equilibrium (plastic deformation) to realize the integrated control of the structure. On the one hand, it simplifies the process and process of integrating the structure and properties of the boron-containing eutectic alloy; on the other hand, the plasticity and toughness of the alloy structure are obtained. It can be significantly improved, which greatly enriches and promotes the existing methods of eutectic alloy structure control and performance improvement, and this method can also be extended to other similar alloy materials. Through non-equilibrium solidification technologies such as deep undercooling and chilling solidification, the alloy is solidified away from the equilibrium state, resulting in structural non-equilibrium (such as a large number of microscopic defects, lattice distortion caused by stress, etc.), and quickly retained, and the accumulated structural non-equilibrium Equilibrium can be used as the driving force for subsequent transformation, and promote further transformation of the structure during the subsequent heat treatment of the alloy. Existing aluminum alloys have been sub-rapidly solidified by quenching. Combined with the subsequent low-temperature annealing experiments, the structure of multi-stage precipitation can be obtained, and the strength and plasticity of the alloy can be improved at the same time. In the process of alloy laser rapid prototyping, the metal also undergoes non-equilibrium rapid solidification. The non-equilibrium effect of solidification not only affects the formation and evolution of the solidified structure, but also affects the subsequent heat treatment transformation. Solidification and heat treatment jointly determine the final properties of the material.

Description of drawings

Fig. 1 is the re-brightening-cooling temperature curve of the alloy melt in Example 1-Example 2 of the present invention, wherein, Fig. 1(a) is the Fe40Ni40B20 (at.%) of the initial undercooling degree of 70K and 250K in Example 1. The re-glow-cooling temperature curve of the crystalline alloy melt, Figure 1(b) is the processing size of the Fe40Ni40B20 (at.%) alloy mechanical property test sample;

Figure 2 is a schematic diagram of the deep undercooling non-equilibrium solidification structure and microstructure of the Fe40Ni40B20 (at.%) eutectic alloy prepared in Example 1 of the present invention; wherein, Figure 2 (a) is the alloy structure under an optical microscope, Figure 2 (b) ) are the non-equilibrium structures such as dislocations and stacking faults in the microstructure under the transmission electron microscope, and Fig. 2(c) is the XRD diffraction result of the phase composition of the non-equilibrium microstructure of the alloy;

Fig. 3 is the surface layer and cross-sectional structure and phase composition of the deep undercooling non-equilibrium solidification Fe40Ni40B20 (at.%) eutectic alloy sample after isothermal annealing heat treatment in Example 1 of the present invention; wherein Fig. 3(a) is the surface layer structure and phase composition XRD results, Figure 3(b) is the cross-sectional structure of the sample;

Fig. 4 is the micro-undercooling solidification structure of Fe40Ni40B20 (at.%) eutectic alloy prepared in Example 2 of the present invention and the microstructure after isothermal annealing; Fig. 4(a) is the solidification structure and the apparent microstructure of the eutectic alloy under small undercooling degree. Schematic diagram of microstructure transmission electron microscope, Figure 4(b) is a schematic diagram of the surface microstructure and XRD diffraction results of the undercooled solidified sample after isothermal annealing;

Figure 5 is a metallographic photograph of the undercooled solidification sample in Example 3 of the present invention, with different heat treatment durations of the lower surface layer and the microstructure near the surface layer; wherein the corresponding isothermal annealing durations of Figures 5(a)-5(e) are 0.5h and 4h respectively , 12h, 40h, 60h;

Figure 6 is the X-ray diffraction result of the surface layer structure of the large undercooled solidification sample in Example 3 of the present invention, heat-treated at a lower isothermal annealing temperature; Figure 6(a) is the result of 873K treatment for 1.5h, and Figure 6(b) is 1073K Process 1h result;

Fig. 7 is the variation relation and the calculation result of the thickness of the recrystallized microstructure layer of the samples with different large undercooling degree 1173K isothermal annealing heat treatment with the treatment time in Example 3 of the present invention;

Fig. 8 is the non-equilibrium solidification structure of the eutectic alloy copper mold prepared in Example 4 of the present invention and the structure after heat treatment; wherein, Fig. 8(a) is the non-equilibrium structure of the alloy, and Fig. 8(b) is the cooling of the copper mold. Non-equilibrium solidification sample after heat treatment at 1173K isothermal annealing for 40h, the surface layer and nearby microstructure of the sample;

FIG. 9 is the tensile force performance curve of the alloy sample under different treatment states in Example 5 of the present invention. In the figure, As-s represents the non-equilibrium solidification sample, and HT represents the isothermal annealing heat treatment sample.

Detailed ways

In order for those skilled in the art to better understand the technical solutions of the present invention and implement them, the present invention will be further described below with reference to specific embodiments, but the embodiments are not intended to limit the present invention.

Example 1

In this example, boron-containing ternary eutectic Fe40Ni40B20 (at.%) alloy is selected as the experimental alloy system, and its eutectic transformation temperature is 1323K. The master alloy of this component alloy is obtained by the arc melting method. The high-frequency electromagnetic induction melting furnace combines molten glass purification and circulating superheating methods to obtain supercooled alloy melt. The non-equilibrium solidification structure of the eutectic alloy is obtained by natural cooling of the supercooled alloy melt; Fe40Ni40B20 (at.%) of Fe40Ni40B20 (at. ), take the alloy sample for the non-equilibrium solidification structure of the eutectic alloy, and use a thermometer to chill the cooling curve of the solidification process of the alloy melt, as shown in Figure 1(a). Then, according to the non-standard sample size reference requirements in the mechanical property sample processing standard, the alloy sample is processed into tensile and bending samples, the size of which is shown in Figure 1(b), and the sample is covered with molten glass and sealed in a quartz crucible. , placed in a vacuum or ordinary heat treatment furnace for isothermal annealing heat treatment, the annealing temperature is 1173K, and the treatment time is 60h.

We prepared samples of the alloy samples obtained by the method in Example 1, and tested and analyzed the phase composition and microstructure of the non-equilibrium solidification structure of the eutectic alloy, as shown in Figure 2. The microstructure of the alloy after isothermal annealing and heat treatment was observed and analyzed. It can be seen from Figure 3 that the non-equilibrium deep undercooling solidification structure of the alloy is a two-phase irregular eutectic composed of (FeNi) ₃ B and γ-FeNi, and the alloy phase contains a large number of dislocation networks generated by the accumulation of non-equilibrium effects. Stacking faults, etc.; after isothermal annealing and heat treatment, the surface structure of the alloy sample undergoes deboronization and recrystallization transformation, forming a single-phase γ-FeNi solid solution on the surface and a dual structure with irregular two-phase inside.

Example 2

The specific process of this example is the same as that of Example 1, the difference is only that the undercooling degree of the undercooled alloy melt is less than 100K. The main purpose is to investigate whether the subsequent transformation of the naturally solidified structure (near-equilibrium solidified structure) with small undercooling degree can occur, so as to verify the driving effect of the structure non-equilibrium on the subsequent transformation. The light microscope and transmission electron microscope photos of the supercooled solidification of the alloy sample are shown in Figure 4(a), and the XRD results of the microstructure and phase composition after isothermal heat treatment at 1173K for 60 h are shown in Figure 4(b).

It can be seen that the structure of the alloy sample contains part of regular eutectic, which is a near-equilibrium solidification structure, the accumulation of non-equilibrium effects in the structure is weak, and there are fewer defects such as dislocations in the corresponding structure; the surface structure of the alloy sample after isothermal annealing heat treatment also changes. No significant solid-state transformation has occurred, and it is still an irregular two-phase structure.

Example 3

The specific process of this example is the same as that of Example 1, the only difference is that the subsequent isothermal annealing heat treatment temperature of the non-equilibrium solidification structure of the eutectic alloy is 1173K, and the isothermal time durations are 0.5h, 4h, 12h, 40h, 60h respectively. In order to investigate the effect of different heat treatment time on the subsequent transformation of the non-equilibrium solidification structure of the eutectic alloy, the surface layer and nearby microstructure of the alloy corresponding to different isothermal annealing time are shown in Figure 5; at the same time, the non-equilibrium solidification structure of the eutectic alloy was subjected to 1.5h and 1h at 873K and 1073K, respectively. Isothermal annealing heat treatment is mainly to determine the isothermal temperature at which the subsequent transformation of the non-equilibrium solidified structure can occur. Since the single-phase layer of the surface structure of the alloy sample is very thin, the preparation of the metallographic structure requires grinding, polishing and corrosion, which cannot be obtained. Therefore, the corresponding isothermal temperature The surface structure of the lower alloy sample was analyzed by XRD diffraction method. The results are shown in Figure 6. The alloy heat treatment process can be formulated according to the above experimental results.

It can be seen that the surface layer of the alloy sample has begun to undergo deboronization and recrystallization solid state transformation after heat treatment for 0.5h. The thickness of the single-phase layer is plotted on the ordinate, and the Zener equation of the diffusion-controlled solid-state transformation equation is used for simple calculation. As shown in Figure 7, it can be seen that the surface single-phase solid solution layer increases with the increase of the isothermal treatment time, and the eutectic alloy solidifies non-equilibrium. The solid-state transformation process of the tissue surface conforms to the solid-state phase transformation law controlled by diffusion and thermal activation. The XRD diffraction results in Figure 6 show that the surface layer of the deep undercooled alloy samples after heat treatment at 873K for 1.5h and heat treatment at 1073K for 1h has begun to transform, indicating that the transformation can occur when the annealing temperature is higher than 873K.

Example 4

The specific process of this example is the same as that of Example 1, the only difference is that the degree of undercooling of the undercooled alloy melt is less than 100K, and the unbalanced solidification method of chilling the undercooled alloy melt is combined. The temperature curve of the supercooled alloy melt is monitored by an infrared thermometer. During the cooling process of the supercooled alloy melt, the supercooled alloy melt with a subcooling degree of less than 100K is quickly quenched into the Ga-In alloy melt or the copper model tank. , to achieve the rapid solidification of the supercooled alloy melt. In this example, when the undercooling degree of the supercooled alloy melt is about 40K, it is rapidly quenched into the copper mold groove, and the chilled solidification structure is shown in Figure 8(a). The structure was heat treated, the isothermal annealing temperature was 1173K, and the holding time was 40h. After heat treatment, the surface layer and nearby structures of the alloy were shown in Figure 8(b).

It can be seen that the non-equilibrium solidified alloy structure of the eutectic alloy obtained by the combination of small undercooling and chilling is an irregular two-phase structure, which is similar to the solidification structure of large undercooling. The non-equilibrium will drive the subsequent solid-state transformation of the alloy, and the final alloy sample is composed of a single-phase recrystallized surface layer, while the interior is still composed of a dual structure of irregular two-phase.

Example 5

For the samples in Examples 1 and 2, as well as the small undercooling and large undercooling non-equilibrium solidification samples without subsequent isothermal annealing heat treatment, the tensile and bending properties of the alloy samples were tested by a micro mechanical property testing machine (mechanics). The size of the performance test sample is shown in Figure 1(b)), and the tensile performance test results (stress-strain curve) are shown in Figure 9;

It can be seen that, compared with the non-equilibrium solidification sample, and the alloy sample obtained by small undercooling non-equilibrium solidification combined with subsequent isothermal annealing heat treatment, the tensile strength of the double-structured alloy sample formed by large undercooling solidification combined with subsequent isothermal annealing heat treatment The plasticity and flexural toughness are significantly improved. Table 1 shows the calculation results of the three-point bending fracture toughness of the solidified samples with different undercooling degrees (70K, 250K) in Example 5 before and after heat treatment.

Table 1

Specimen state: AS-S, original solidified structure; HT, heat-treated specimen

To sum up, the present invention utilizes deep undercooling and chilling non-equilibrium solidification technology to obtain a solidified structure of FeNiB eutectic alloy that accumulates a large amount of non-equilibrium, such as dislocation network caused by plastic deformation of alloy microstructure. Further, the non-equilibrium solidification structure of the alloy was subjected to subsequent isothermal annealing heat treatment, and the surface structure of the alloy sample underwent significant deboronization and recrystallization transformation, forming a single-phase solid solution of γ-FeNi on the surface and (FeNi) ₃ B and The dual structure of γ-FeNi irregular two-phase; the mechanical properties test results show that the formation of the dual structure greatly improves the plasticity and toughness of the alloy. However, in the isothermal annealing heat treatment experiment under the same conditions for the small undercooled natural cooling structure, the surface layer and internal structure of the alloy hardly changed, and the properties of the alloy did not change. Obviously, these research results reveal the possible means of non-equilibrium accumulation of boron-containing eutectic alloys under large undercooling solidification structure, and also reveal the feasibility of eutectic alloy solidification structure non-equilibrium to drive subsequent transformations to further control the alloy's microstructure and properties. . Therefore, this method greatly enriches and promotes the existing eutectic alloy structure and property control technology, which can be used to control various physical properties of eutectic alloy materials.

The above-mentioned embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope thereof is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention, and the protection scope of the present invention is subject to the claims.

Claims (1)

1. A method for improving the ductility and toughness of a boron-containing eutectic alloy by using a double-structure is characterized by comprising the following steps of:

s1: selecting a boron-containing eutectic alloy, smelting the eutectic alloy by adopting a high-frequency electromagnetic induction smelting furnace, obtaining a supercooled alloy melt by utilizing a molten glass purification combined cycle overheating method, and naturally cooling or chilling the supercooled alloy melt to obtain an unbalanced solidification structure of the eutectic alloy;

the eutectic alloy is Fe40Ni40B20 (at.%) alloy, and the eutectic transformation temperature is 1323K;

certain non-equilibrium is accumulated in the non-equilibrium solidification structure of the eutectic alloy, the initial supercooling degree of the non-equilibrium solidification structure of the eutectic alloy is naturally cooled when the initial supercooling degree is more than or equal to 170K, or the initial supercooling degree of the non-equilibrium solidification structure of the eutectic alloy is less than 100K for chilling;

in the chilling treatment process, an infrared thermometer is used for monitoring and acquiring temperature data of the supercooled alloy melt In the cooling process, and when the supercooling degree is less than 100K, the supercooled alloy melt is poured into a Ga-In liquid alloy or copper metal mold for chilling treatment;

s2: carrying out isothermal annealing heat treatment on the eutectic alloy non-equilibrium solidification structure, taking the non-equilibrium accumulated in the eutectic alloy non-equilibrium solidification structure as a driving force, and carrying out recrystallization transformation while carrying out boron removal on a surface layer structure under the induction of the isothermal annealing heat treatment to form a single-phase tissue layer which forms a double-structure with an irregular eutectic structure in the single-phase tissue layer;

and carrying out isothermal annealing heat treatment under vacuum or protective atmosphere, wherein the annealing temperature is 873K to 1273K, and the annealing time is 1.5h to 60 h.

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