CN113373388A

CN113373388A - Method for improving plasticity and toughness of boron-containing eutectic alloy by utilizing double-structure

Info

Publication number: CN113373388A
Application number: CN202110471441.XA
Authority: CN
Inventors: 张柯; 张凤辉
Original assignee: Baoji University of Arts and Sciences
Current assignee: Baoji University of Arts and Sciences
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2021-09-10
Anticipated expiration: 2041-04-29
Also published as: CN113373388B

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

Method for improving plasticity and toughness of boron-containing eutectic alloy by utilizing double-structure

Technical Field

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

Background

Because of the rich texture pattern and excellent comprehensive performance, eutectic alloy is one of the most widely used alloys in industry, and the improvement of the alloy performance by regulating the texture of the eutectic alloy is also always of interest. The (Fe, Ni) -B eutectic alloy is researched and applied due to excellent soft magnetic property, good mechanical property and metallurgical property, the alloy structure determining the service performance of the alloy is often controlled by the solidification and the subsequent cold/hot processing process, and one of the key problems is the evolution of the alloy solidification structure and the subsequent transformation structure regulation. The non-equilibrium tissue which can not be realized under the equilibrium condition is obtained by the non-equilibrium coagulation technology, and is also always important content of the scientific and technical research of coagulation. The non-equilibrium solidification structure not only has mechanical and physical properties which are not possessed by the equilibrium structure, but also induces subsequent solid state transformation by combining a heat treatment means based on the metastable characteristic of the non-equilibrium solidification structure, thereby realizing further regulation and control of the alloy final state structure.

The ideal service performance of the alloy material is high strength and good plasticity, and the traditional strengthening method based on the dislocation theory leads the strength of the alloy to be improved at the expense of partial plasticity of the material. Numerous studies have found that by applying tissue non-equilibrium in combination with subsequent heat treatment solid state transformation, simultaneous improvement in material strength and plasticity can be achieved. In the conventional sense, the improvement of the metal structure performance is realized by means of subsequent static recrystallization transformation, and the improvement can be realized only in the metal material with cold deformation through subsequent recrystallization annealing. The non-equilibrium solidification is used as an effective means for generating alloy structure non-equilibrium, and if the non-equilibrium solidification is combined with subsequent heat treatment, the integral regulation and control of the alloy structure performance can be realized.

The research on the subsequent heat treatment transformation of the nonequilibrium solidification structure is carried out for many years along with the application of Fe-Ni-based alloy, but most of the research is focused on the monophase structure or monophase alloy, while the research on the subsequent transformation of the nonequilibrium solidification structure of eutectic alloy is few, which is mainly attributed to the fact that the subsequent transformation of the monophase structure is single, and the source, the process and the final structure of the transformation driving force are conveniently characterized from experiments and theories. In recent years, subsequent solid state transformation research on eutectic alloy solidification structures is carried out along with the fact that high-entropy alloys with excellent comprehensive properties become hot spots for material research and application, but research objects are mainly directed to conventional equilibrium or near equilibrium solidification structures, and the prerequisite for the subsequent recrystallization transformation of the structures is artificial introduction of non-equilibrium, namely that samples undergo large plastic deformation. This is due to the fact that the nonequilibrium solidification structure of the eutectic alloy is often generated by a non-single transformation process, the nonequilibrium solidification process of the eutectic alloy comprises the primary solidification of eutectic group structures and the subsequent solidification of residual liquid phases among the groups, even the formation of metastable phase structures, so that the nonequilibrium effect dissipation mode in the solidification process is diversified, the nonequilibrium of the structure can be released in various modes in the solidification and subsequent cooling processes, and the nonequilibrium in the alloy structure is less accumulated and stored under the conditions of equilibrium and near equilibrium solidification.

Disclosure of Invention

The method solves the defects in the prior art, provides the method for improving the ductility and toughness of the boron-containing eutectic alloy by utilizing the double-structure, obtains the alloy structure nonequilibrium by means of nonequilibrium solidification without artificial plastic deformation, and combines the alloy structure with the subsequent heat treatment integrated regulation and control technology to form the double-structure so as to improve the ductility and toughness of the boron-containing eutectic alloy.

The technical scheme adopted by the invention is as follows: 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 binary or ternary 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 a non-equilibrium solidification structure of the eutectic alloy;

s2: and (3) 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 the surface layer structure under the induction of the isothermal annealing heat treatment to form a single-phase structure layer which forms a double-structure with the irregular eutectic structure in the single-phase structure layer.

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

Preferably, in S1, the non-equilibrium solidified structure of the eutectic alloy is naturally cooled when the initial supercooling degree of the non-equilibrium solidified structure of the eutectic alloy is 170K or more, or the initial supercooling degree of the non-equilibrium solidified structure of the eutectic alloy is less than 100K, and the chilling treatment is performed.

Preferably, In S1, the chilling process monitors and collects temperature data of the supercooled alloy melt by means of an infrared thermometer, 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.

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

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

1. the method combines non-equilibrium solidification and subsequent heat treatment technologies, spontaneously realizes non-equilibrium accumulation in the alloy microstructure by using a rapid solidification method, and combines subsequent heat treatment transformation to obtain a double-structure, thereby realizing the improvement of the ductility and toughness of the alloy. Specifically, due to deep undercooling non-equilibrium solidification, a non-equilibrium metastable structure of an alloy structure can be realized, wherein the non-equilibrium metastable structure comprises a large number of micro defects, micro stress strain and other structure non-equilibrium; further combining with chilling, the structural unbalance is reserved to a greater extent, a subsequent recrystallization transformation driving force is formed, the surface layer structure is subjected to boron removal and recrystallization transformation simultaneously in the subsequent heat treatment process, a surface layer single-phase recrystallization plastic tissue layer is formed, and the interior of the surface layer single-phase recrystallization plastic tissue layer is of a double-structure with an irregular two-phase structure, so that the ductility and the comprehensive mechanical properties of the alloy are improved.

2. The method for realizing tissue integrated regulation and control without artificially introducing non-equilibrium (plastic deformation) simplifies the integration process and technique of the boron-containing eutectic alloy tissue performance on the one hand; on the other hand, the plasticity and the toughness of the obtained alloy structure can be obviously improved, which greatly enriches and promotes the existing method for regulating and controlling the structure and improving the performance of the eutectic alloy, and the method can also be popularized to the integrated regulation and control of the structure and the performance of other similar alloy materials, thereby having important production practice significance. Through non-equilibrium solidification technologies such as deep undercooling and chilling solidification, the alloy is solidified away from an equilibrium state, the structural non-equilibrium (such as a large number of microscopic defects, lattice distortion caused by stress and the like) is generated and is rapidly preserved, the accumulated structural non-equilibrium can be used as a driving force for subsequent transformation, and the structure is further transformed in the heat treatment process of the subsequent structure of the alloy. The existing aluminum alloy is chilled and sub-rapidly solidified, the structure of a multi-stage precipitated phase can be obtained by combining with a subsequent low-temperature annealing experiment, and meanwhile, the strength and the plasticity of the alloy are improved. In the laser rapid forming process of the alloy, the metal is subjected to non-equilibrium rapid solidification, the formation and evolution of a solidification structure are influenced by the solidification non-equilibrium effect, the subsequent heat treatment transformation is also influenced, and the final state performance of the material is determined by the solidification and the heat treatment together.

Drawings

Fig. 1 is a graph of alloy melt recalescence-cooling temperature curves of examples 1-2 of the present invention, wherein fig. 1(a) is a graph of an initial supercooling degree of 70K and 250K of Fe40Ni40B20 (at.%) eutectic alloy melt recalescence-cooling temperature curve of example 1, and fig. 1(B) is a graph of a machining size sample of a mechanical property test sample of Fe40Ni40B20 (at.%) alloy;

FIG. 2 is a schematic diagram of the deep undercooling nonequilibrium solidification structure and microstructure of the Fe40Ni40B20 (at.%) eutectic alloy prepared in example 1 of the present invention; wherein, fig. 2(a) is an alloy structure under an optical microscope, fig. 2(b) is a nonequilibrium structure of dislocation, stacking fault and the like in the structure under the transmission electron microscope, and fig. 2(c) is a XRD diffraction result of the alloy nonequilibrium structure phase composition;

FIG. 3 shows the surface layer and cross-sectional structure and phase composition of the deep undercooling nonequilibrium solidified Fe40Ni40B20 (at.%) eutectic alloy sample after isothermal annealing heat treatment in accordance with example 1 of the present invention; wherein FIG. 3(a) is the surface structure and phase composition XRD results, and FIG. 3(b) is the cross-sectional structure of the sample;

FIG. 4 shows the structure of Fe40Ni40B20 eutectic alloy with small overcondensated solidification and its isothermal annealed structure prepared in example 2 of the present invention; wherein, fig. 4(a) is a transmission electron microscope schematic diagram of eutectic alloy solidification structure and microstructure under small supercooling degree, and fig. 4(b) is a schematic diagram of surface layer structure morphology and XRD diffraction result after isothermal annealing treatment of small supercooling solidification sample;

FIG. 5 is a metallographic photograph of the surface layer and the structure near the surface layer of a large overcondensed solid sample obtained in example 3 of the present invention at different heat treatment durations; wherein the isothermal annealing durations of FIGS. 5(a) -5(e) are 0.5h, 4h, 12h, 40h, and 60h, respectively;

FIG. 6 shows the results of X-ray diffraction of the surface structure of a large overcondensed solid sample heat-treated at a lower isothermal annealing temperature in example 3 of the present invention; wherein FIG. 6(a) shows the results of 873K treatment for 1.5h, and FIG. 6(b) shows the results of 1073K treatment for 1 h;

FIG. 7 is a graph showing the relationship between the thickness of the recrystallized tissue layers of different supercooling degree samples 1173K after isothermal annealing and thermal treatment according to the embodiment of the present invention and the calculation results;

FIG. 8 shows a chilled non-equilibrium solidification structure of a eutectic alloy copper mold and a heat-treated structure thereof according to example 4 of the present invention; wherein, FIG. 8(a) is the alloy non-equilibrium structure, and FIG. 8(b) is the sample surface layer and nearby structure after 1173K isothermal annealing for 40h after the copper mold chilled non-equilibrium solidified sample is subjected to heat treatment;

FIG. 9 is a graph showing tensile properties of alloy specimens in different processing states in example 5 of the present invention, in which As-s represents a non-equilibrium solidification specimen and HT represents an isothermal annealing heat treatment specimen.

Detailed Description

In order to make the technical solutions of the present invention better understood and enable those skilled in the art to practice the present invention, the following embodiments are further described, but the present invention is not limited to the following embodiments.

Example 1

In this embodiment, a boron-containing ternary eutectic Fe40Ni40B20 (at.%) alloy is selected as an experimental alloy system, the eutectic transformation temperature is 1323K, a master alloy of the alloy is obtained by an arc melting method, and a supercooled alloy melt is obtained by further taking 20g of the master alloy and combining a molten glass purification and circulating superheating method by a high-frequency electromagnetic induction melting furnace. Naturally cooling the supercooled alloy melt to obtain an eutectic alloy non-equilibrium solidification structure; and (3) naturally cooling the supercooled alloy melt at the initial supercooling degree of more than or equal to 170K (the supercooling degree is 250K in the example), taking an alloy sample from the nonequilibrium solidification structure of the eutectic alloy, and chilling a cooling curve of the solidification process of the alloy melt by using a thermodetector, wherein the cooling curve is shown in fig. 1 (a). And then processing the alloy sample into a tensile and bending sample according to the non-standard sample size reference requirement in the mechanical property sample processing standard, wherein the size is schematically shown as figure 1(b), wrapping the sample with molten glass, sealing the sample in a quartz crucible, and placing the quartz crucible in a vacuum or common heat treatment furnace for isothermal annealing heat treatment, wherein the annealing temperature is 1173K, and the treatment time is 60 hours.

Sample preparation was carried out on the alloy sample obtained by the method of example 1, and the eutectic alloy non-equilibrium solidification microstructure phase composition and microstructure were analyzed by testing, as shown in fig. 2. The alloy structure after the isothermal annealing heat treatment is observed and analyzed, and the cross section, the microstructure and the phase composition of the surface structure of the alloy structure after the isothermal annealing heat treatment are shown in figure 3. As can be seen from FIG. 3, the alloy non-equilibrium deep super-cooling solidification structure is (FeNi)₃B and gamma-FeNi, wherein the alloy phase contains a large amount of dislocation networks, stacking faults and the like generated by accumulation of nonequilibrium effects; after isothermal annealing heat treatment, the surface structure of the alloy sample is subjected to deboronation and recrystallization transformation to form a surface single-phase gamma-FeNi solid solution, and the interior of the surface single-phase gamma-FeNi solid solution is still in a non-regular two-phase double-structure.

Example 2

The specific process of the embodiment is the same as that of the embodiment 1, except that the supercooling degree of the supercooled alloy melt is less than 100K. The method is mainly used for investigating whether the subsequent transformation of the natural solidification structure (near-equilibrium solidification structure) with small supercooling degree can occur or not so as to verify the driving effect of the tissue unbalance on the subsequent transformation. The super-cooled solidification structure optical mirror and transmission electron microscope photographs of the alloy sample are shown in figure 4(a), and the structure and phase composition XRD results after 1173K isothermal heat treatment for 60 hours are shown in figure 4 (b).

It can be seen that the structure of the alloy sample contains partial regular eutectic and is a near-equilibrium solidification structure, the accumulation of the non-equilibrium effect in the structure is weaker, and the defects such as dislocation and the like in the corresponding structure are fewer; the surface structure of the alloy sample after isothermal annealing heat treatment does not have obvious solid state transformation, and still is an irregular two-phase structure.

Example 3

The specific process of this embodiment is the same as that of embodiment 1, except that the temperature of the subsequent isothermal annealing heat treatment of the non-equilibrium solidified structure of the eutectic alloy is 1173K, the isothermal time periods are 0.5h, 4h, 12h, 40h and 60h, respectively, mainly for examining the influence of different heat treatment time periods on the subsequent transformation of the non-equilibrium solidified structure of the eutectic alloy, and the different isothermal annealing time periods correspond to the alloy surface layer and the nearby structure as shown in fig. 5; and simultaneously carrying out 1.5h and 1h isothermal annealing heat treatment on the nonequilibrium solidification structure of the eutectic alloy at 873K and 1073K respectively, mainly aiming at determining isothermal temperature at which subsequent transformation of the nonequilibrium solidification structure can occur, wherein the metallographic structure preparation needs to be ground, polished and corroded and cannot be obtained due to the fact that a single-phase layer of the surface structure of the alloy sample is very thin, so that the phase composition of the surface structure of the alloy sample at the corresponding isothermal temperature is analyzed by adopting an XRD diffraction method, and the alloy heat treatment process can be formulated according to the experimental results as shown in figure 6.

It can be seen that the surface layer starts to generate boron removal and recrystallization solid state transition after the alloy samples are subjected to heat treatment for 0.5h, the thickness of the surface layer recrystallization single-phase tissue layer of each alloy sample is measured in different isothermal annealing time periods, the annealing time is taken as a horizontal coordinate, the thickness of the single-phase layer is taken as a vertical coordinate for drawing, and meanwhile, a diffusion control solid state transition equation Zener equation is adopted for simple calculation, as shown in FIG. 7, the surface layer single-phase solid solution layer is thickened along with the increase of the isothermal treatment time, and the surface layer solid state transition process of the eutectic alloy non-equilibrium solidification structure conforms to the solid phase transition rule of diffusion and thermal activation control. The XRD diffraction results in FIG. 6 show that the transition of the surface layer of the samples of the deeply undercooled alloy is started after 873K heat treatment for 1.5h and 1073K heat treatment for 1h, which indicates that the transition can be started when the annealing temperature is higher than 873K.

Example 4

The specific process of the embodiment is the same as that of the embodiment 1, except that the supercooling degree of the supercooled alloy melt is less than 100K, and a non-equilibrium solidification means is chilled by the supercooled alloy melt. Monitoring the temperature curve of the supercooled alloy melt through an infrared thermometer, and rapidly quenching the supercooled alloy melt with the supercooling degree of less than 100K into a Ga-In alloy melt or a copper mold groove In the process of cooling the supercooled alloy melt to realize the rapid chilling solidification of the supercooled alloy melt. In this example, when the supercooling degree of the supercooled alloy melt was about 40K, the alloy melt was rapidly quenched into a copper mold, the structure of the quenched solidification structure was as shown in fig. 8(a), the non-equilibrium solidification structure of the eutectic alloy was heat-treated by the same method as the isothermal annealing heat-treatment in example 1 at the isothermal annealing temperature 1173K for 40 hours, and the surface layer and the structure in the vicinity of the alloy after heat-treatment were as shown in fig. 8 (b).

It can be seen that the eutectic alloy non-equilibrium solidified alloy structure obtained by the small supercooling combined chilling is an irregular two-phase structure, similar to a large supercooling solidified structure, the structure imbalance rapidly reserved in the alloy sample due to chilling can drive the subsequent solid state transformation of the alloy, and finally the alloy sample is composed of a double-structure with a single-phase recrystallized on the surface layer and an irregular two-phase structure still inside.

Example 5

For the samples in examples 1 and 2, and the small supercooling and large supercooling nonequilibrium solidification samples which are not subjected to the subsequent isothermal annealing heat treatment, a tiny mechanical property testing machine is adopted to test the tensile and bending properties of the alloy sample (the size of the mechanical property testing sample is shown in figure 1 (b)), and the tensile property testing result (stress-strain curve) is shown in figure 9; the results of the notch three-point bending fracture toughness calculations for the test specimens are shown in table 1.

Compared with a non-equilibrium solidification sample and an alloy sample obtained by combining small supercooling non-equilibrium solidification with subsequent isothermal annealing heat treatment, the tensile plasticity and the bending toughness of the alloy sample with the double-structure formed by combining large supercooling solidification with subsequent isothermal annealing heat treatment are obviously improved. Table 1 shows the results of calculating the three-point bending fracture toughness of the samples before and after the heat treatment of the solidification samples with different supercooling degrees (70K and 250K) in example 5.

TABLE 1

Sample state: AS-S, original coagulated tissue; HT, heat-treated test specimen

In conclusion, the invention utilizes deep undercooling and chilling non-equilibrium solidification technology to obtain a FeNiB eutectic alloy solidification structure accumulating a large amount of non-equilibrium, such as a dislocation network caused by plastic deformation of an alloy microstructure. Further, the alloy nonequilibrium solidification structure is subjected to subsequent isothermal annealing heat treatment, the surface structure of the alloy sample undergoes remarkable boron removal and recrystallization transformation, a gamma-FeNi single-phase solid solution is formed on the surface, and (FeNi) is formed inside the alloy sample₃B and gamma-FeNi are irregular two-phase double-structure; the mechanical property test result shows that the plasticity and the toughness of the alloy are greatly improved by forming a double-structure. And when the isothermal annealing heat treatment experiment is carried out on the small supercooling natural cooling structure under the same condition, the surface layer and the internal structure of the alloy are hardly changed, and the performance of the alloy is not changed. Obviously, the research results reveal the nonequilibrium accumulation of the boron-containing eutectic alloy large-overcreeding solidification structure and possible means, and simultaneously reveal the feasibility of further regulating and controlling the alloy structure performance by driving the subsequent transformation to occur due to the nonequilibrium of the solidification structure of the eutectic alloy. Therefore, the method greatly enriches and promotes the prior eutectic alloy structure and performance regulation and control technology, and can be used for regulating and controlling various physical properties of eutectic alloy materials.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of protection is not limited thereto. The equivalents and modifications of the present invention which may occur to those skilled in the art are within the scope of the present invention as defined by the appended claims.

Claims

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:

2. The method for improving the ductility and toughness of the boron-containing eutectic alloy with the double-structure as claimed in claim 1, wherein the eutectic alloy is Fe40Ni40B20 (at.%) alloy, and the eutectic transformation temperature is 1323K.

3. The method of claim 1, wherein in step S1, the nonequilibrium of the eutectic alloy is accumulated, and the eutectic alloy is naturally cooled when the initial supercooling degree of the nonequilibrium of the eutectic alloy is 170K or more, or the eutectic alloy is chilled when the initial supercooling degree of the nonequilibrium of the eutectic alloy is less than 100K.

4. The method of claim 3, wherein In step S1, the chilling process monitors and collects the temperature data of the cooling process of the supercooled alloy melt by means of an infrared thermometer, 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.

5. The method for improving the ductility and toughness of the boron-containing eutectic alloy with the double-structure as claimed in claim 1, wherein the isothermal annealing heat treatment is performed in S2 under vacuum or protective atmosphere, the annealing temperature is 873K to 1273K, and the annealing time is 1.5h to 60 h.