CN113943911A

CN113943911A - Two-phase high-strength high-plasticity titanium alloy with layered structure and preparation method thereof

Info

Publication number: CN113943911A
Application number: CN202111165042.7A
Authority: CN
Inventors: 张金钰; 张崇乐; 张东东; 刘刚; 孙军
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2022-01-18

Abstract

The invention discloses a two-phase high-strength high-plasticity titanium alloy with a layered structure and a preparation method thereof, wherein the alloy is subjected to heat preservation for 1-2 h in a beta single-phase region at the temperature of 1000-1100 ℃ in a muffle furnace, then quenched to room temperature to obtain uniform beta phase, the obtained alloy is heated to a temperature above a transformation point again, and is subjected to rolling after heat preservation for 10-20min, and finally a rolled plate is subjected to heat preservation for 1-2 min at the temperature of 5-10 ℃ above the transformation point and then quenched to room temperature to obtain a two-phase TRIP titanium alloy with the layered structure; the two-phase TRIP titanium alloy with the layered structure prepared by the method can obtain the following optimal properties: mechanical properties of 875MPa of yield strength and 36 percent of elongation at break. The yield strength is twice as high as that of the prior common TRIP metastable beta titanium alloy, and the plasticity is hardly lost. Based on the characteristics, the alloy has great competitive advantage in TRIP metastable beta titanium alloy.

Description

Two-phase high-strength high-plasticity titanium alloy with layered structure and preparation method thereof

Technical Field

The invention relates to the field of metal materials, in particular to a two-phase high-strength high-plasticity titanium alloy with a layered structure and a preparation method thereof.

Background

In the high-tech industry, high-strength materials with excellent ductility have been the target pursued by materials scientists, as structural materials face increasingly stringent service environments. The titanium alloy has the characteristics of high specific strength, high corrosion resistance, no magnetism, excellent strong plasticity matching and the like, and is widely applied to the fields of chemical engineering, medical instruments, navigation, aerospace and the like.

Due to excellent formability and corrosion resistance, the stainless steel or the Co-Cr alloy is widely applied to complex pipelines and structural parts in the fields of petrochemical pipelines, navigation and the like, but the yield strength is very low (about 200-300MPa), and failure accidents caused by overload often occur in the use process. The TRIP/TWIP metastable beta titanium alloy not only has higher corrosion resistance, but also has the yield strength reaching 500MPa which is about twice of that of stainless steel or Co-Cr alloy, thereby having extremely high application value. In addition, the TRIP/TWIP metastable beta titanium alloy has very good process plasticity and cold formability, can bear large deformation at room temperature without cracking, and thus realizes the preparation process of complex parts and shapes.

However, the yield strength of the single-phase TRIP titanium alloy is still insufficient (<500MPa), and it is difficult to meet the requirement of higher yield strength. In order to improve the mechanical properties of the TRIP titanium alloy, the current strategy of researchers is to introduce uniformly distributed alpha phase, obviously refine beta crystal grains and enhance the critical stress generated by TRIP. The stress-induced martensite is excited while the alloy yield strength is improved so as to maintain large plasticity and high work hardening rate. However, the precipitation of the alpha phase is often accompanied by redistribution of the elements, which changes the stability of the beta matrix. In addition, the uniformly precipitated alpha phase is difficult to obviously refine beta grains, and when a beta matrix is stable, a deformation mechanism is converted into dislocation slip, so that the elongation and the work hardening rate are obviously reduced. Therefore, the yield strength of TRIP titanium alloys has not been a practical breakthrough, which severely hampers the further development of metastable beta titanium alloys.

Based on the problems, the form and the size of the alpha phase and the beta phase are regulated and controlled, and the activation stress and the strain of the TRIP are stabilized to the maximum extent, so that the method has important scientific significance and application value for developing and designing the high-strength high-plasticity two-phase TRIP titanium alloy.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a two-phase high-strength high-plasticity titanium alloy with a layered structure and a preparation method thereof, the method can utilize a layered alpha precipitated phase to inhibit the growth of layered beta grains, and controls the layer thickness of a layered beta matrix through hot rolling reduction, thereby changing the critical stress of a TRIP deformation mechanism. The two-phase lamellar composite structure not only greatly improves the yield strength, but also hardly loses the original work hardening capacity and uniform elongation.

The invention is realized by the following technical scheme:

a preparation method of a two-phase high-strength high-plasticity titanium alloy with a layered structure comprises the following steps:

step 1, preserving the heat of a titanium alloy in a beta single-phase region at 1000-1100 ℃ for 1-2 h, and then quenching to room temperature;

step 2, raising the temperature of the titanium alloy obtained in the step 1 to a temperature above the phase change point again, and preserving the heat for 10-20 min;

step 3, rolling the titanium alloy subjected to heat preservation in the step 2 by adopting a beta-crossing rolling method, wherein the single-pass rolling reduction is 3-5% of rolling deformation, and the total rolling reduction is 85-96%;

and 4, preserving the temperature of the titanium alloy obtained in the step 3 above a phase transition point for 1-2 min, and then quenching to room temperature to obtain the two-phase high-strength TRIP titanium alloy with the layered structure.

Preferably, the phase transition point temperature in step 2 is 765. + -. 5 ℃.

Preferably, the heat preservation temperature in the step 2 and the step 4 is 5-10 ℃ above the temperature of the phase transformation point.

Preferably, after each pass of rolling in the step 3 is finished, returning and preserving heat for 1 min.

Preferably, the heat preservation time in the step 4 is 1 min.

A two-phase high-strength high-plasticity titanium alloy with a layered structure, wherein the layered structure comprises a layered alpha precipitation phase and a layered beta crystal grain which are alternately formed.

Preferably, the thickness of the lamellar alpha precipitation phase lamella is 50-400 nm.

Preferably, the thickness of the lamellar beta crystal grain is 0.23-4.1 mu m.

Preferably, when the total rolling reduction is 85%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.5-4.1 μm.

When the total rolling reduction is 90%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.7-1.5 mu m;

when the total rolling reduction is 92%, the thickness of a lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of a lamellar beta crystal grain lamella is 0.23-1.2 mu m;

when the total rolling reduction is 94%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.23-0.56 μm.

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

the invention provides a two-phase high-strength high-plasticity titanium alloy with a layered structure and a preparation method thereof. After hot rolling, a composite structure with alternating lamellar alpha precipitated phases and lamellar beta grains appears on the section (RD and TD surfaces) of the sample through simple solution treatment. The lamellar alpha has an inhibiting effect relative to the starting of a TRIP deformation mechanism and is represented as a hard lamellar layer; the lamellar beta grains have a promoting effect on the TRIP deformation mechanism and are represented as soft lamellae. When the alloy is subjected to macroscopic stress, the softening layer beta grains are firstly subjected to plastic deformation, the hardened layer alpha phase keeps elastically deformed, and meanwhile, the softening layer is surrounded by the hardened layer, so that a higher strain gradient and stronger mutual constraint are generated. This creates a back stress at the interface of the heterostructure that can simultaneously increase the work hardening capability and strain strengthening capability of the alloy, thereby allowing the alloy to exhibit a better combination of strength and plasticity. Meanwhile, the lamellar structures with different hardness and softness can coordinate the deformation of the two sides of the interface, so that stress concentration is avoided, and the alloy also keeps higher elongation at break. The performance of the two-phase TRIP titanium alloy is far superior to the mechanical property of TRIP materials of the same type, the structure of the optimal alloy performance of the two-phase TRIP titanium alloy with the laminated structure prepared by the method is HLS-0.8, the yield strength of the two-phase TRIP titanium alloy reaches unprecedented 890MPa, and the elongation at break of the two-phase TRIP titanium alloy is 36 percent;

drawings

FIG. 1 is a microstructure diagram and a statistical distribution diagram of beta sheet thickness of titanium alloy with different beta sheet thickness structures according to the present invention;

FIGS. 1(a) and 1(b) are a microstructure view and a beta sheet thickness statistical distribution view of the titanium alloy prepared in example 1;

FIGS. 1(c) and 1(d) are a microstructure view and a beta sheet thickness statistical distribution view of the titanium alloy prepared in example 2;

FIGS. 1(e) and 1(f) are a microstructure view and a beta sheet thickness statistical distribution view of the titanium alloy prepared in example 3;

FIGS. 1(g) and 1(h) are a microstructure view and a beta sheet thickness statistical distribution view of the titanium alloy prepared in comparative example 1;

FIG. 2 is a TEM image of a titanium alloy with a layered structure according to the present invention after deformation;

wherein, fig. 2(a) is a TEM picture of the titanium alloy of example 1 after deformation; FIG. 2(b) is a TEM picture of a titanium alloy of example 2 after deformation; fig. 2(c) is a TEM image of the titanium alloy having a layered structure of example 3 after deformation.

FIG. 3 is a graph of engineering strain-engineering stress-strain elongation for a layered titanium alloy equiaxed grain structure of the present invention;

FIG. 4 is a statistical graph comparing the performance of the layered titanium alloy of the present invention with that of a conventional TRIP/TWIP metastable beta titanium alloy.

Detailed Description

The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.

A preparation method of a two-phase high-strength high-plasticity TRIP titanium alloy with a laminated structure comprises the following steps:

step 1, preserving heat of a titanium alloy in a beta single-phase region in a muffle furnace at 1000-1100 ℃ for 1-2 h, and then quenching to room temperature to obtain a uniform beta phase;

and 2, raising the temperature of the alloy obtained in the step 1 to a temperature above the phase transformation point again, and rolling after heat preservation for 10-20 min.

The temperature of the transformation point is 765 +/-5 ℃, the temperature rise temperature is 10 ℃ above the temperature of the transformation point and 770-780 ℃.

And 3, carrying out beta-spanning rolling on the titanium alloy obtained in the step 2, carrying out rolling deformation with the single-pass reduction of 3-5%, and after each 1-2 passes of rolling, heating the titanium alloy to a temperature higher than the transformation point and preserving heat for 0.5-1 min again until the total rolling reduction of the alloy is 85-94%.

And 4, after the last rolling is finished, keeping the temperature of the titanium alloy rolled plate obtained in the step 3 above the phase transformation point for 1-2 min, and then quenching to room temperature to obtain the two-phase high-strength high-plasticity TRIP titanium alloy with the laminated structure.

The temperature above the phase transition point is 770-780 ℃.

The two-phase high-strength high-plasticity TRIP titanium alloy with the layered structure is prepared according to the method, and the layered structure is composed of layered alpha precipitated phases and layered beta crystal grains.

The thickness of the lamellar alpha precipitated phase lamella is 50-400 nm.

The thickness of the lamellar beta crystal grain is 0.23-4.1 mu m.

When the final rolling amount of the alloy is 85%, the thicknesses of the lamellar alpha precipitated phase lamellae are all 50-400 nm, and the thickness of the lamellar beta crystal grain lamellae is 0.5-4.1 mu m.

When the final rolling amount of the alloy is 90%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.7-1.5 mu m.

When the final rolling amount of the alloy is 92%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.23-1.2 mu m.

When the final rolling amount of the alloy is 94%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.23-0.56 mu m.

The section of the layered structure is an RD section or a TD section.

The two-phase high-strength high-plasticity TRIP titanium alloy with the layered structure obtained by the method has the layered structure formed by alternately forming a layered alpha precipitation phase and a layered beta crystal grain. By controlling the rolling reduction in the rolling process, the thickness of the layered beta grains is controlled, and different mechanical property matches can be obtained from the thickness of the superfine grain layer to the thickness of the coarse grain layer.

Example 1:

step 1, keeping the temperature of a Ti-Al-Mo-Cr-Zr metastable beta titanium alloy plate with the thickness of 10mm in a muffle furnace at 1000 ℃ for 60min, and then quenching to room temperature;

the metastable beta titanium alloy of Ti-Al-Mo-Cr-Zr comprises 0.5-1.5% of Al, 8-9% of Mo, 2.5-4% of Cr, 3-4% of Zr, and the balance of Ti and other inevitable impurities.

Step 2, preserving the heat of the Ti-Al-Mo-Cr-Zr metastable alloy plate with the thickness of 10mm for 10min at the temperature of 770 ℃ in a muffle furnace;

and 3, taking out the sample for rolling, wherein the single-pass reduction is 3%, the sample is returned to the furnace after each pass of rolling and is kept at 770 ℃ for 1min, and the total rolling reduction rate is 85%.

And 4, immediately putting the rolled sample into a muffle furnace, preserving the heat at 770 ℃ for 1min, and then quenching to room temperature to obtain a layered structure.

The two-phase TRIP/TWIP titanium alloy having a layered structure obtained by the above method has a layered structure composed of layered alpha precipitates and layered beta grains alternately. Wherein the lamellar alpha precipitated phase lamella thickness is 50-400 nm, and the lamellar beta crystal lamella thickness is 0.5-4.1 μm, as shown in fig. 1(a) and fig. 1 (b). Since the heat preservation is only carried out for 1min, the recrystallization process is not obvious, and a large amount of elongated grains and high-density dislocation are still contained. At this time, the deformation of the beta elongated grains is promoted by the activation stress of the stress-induced martensite restrained by the alpha sheet. The alloy has consistent strength and higher plasticity. Mechanical property tests show that the yield strength of the double-phase TRIP titanium alloy with the layered structure is 651MPa, the tensile strength is 984MPa, and the elongation at break is 36%.

Example 2:

a preparation method of a two-phase high-strength high-plasticity TRIP/TWIP titanium alloy with a layered structure comprises the following steps:

Step 2, preserving the heat of the Ti-Al-Mo-Cr-Zr metastable beta titanium alloy plate with the thickness of 10mm for 10min at the temperature of 770 ℃ in a muffle furnace;

and 3, taking out and rolling, wherein the single-pass reduction is 3%, the sample is re-melted after each pass of rolling and is kept at 770 ℃ for 1min, and the total rolling reduction is 90%.

And 4, immediately putting the rolled sample into a muffle furnace, preserving the heat at 770 ℃ for 1min, and then quenching to room temperature to obtain the high-strength high-plasticity TRIP metastable beta titanium alloy with the layered structure and the dual-phase structure.

The two-phase TRIP/TWIP titanium alloy having a layered structure obtained by the above method has a layered structure composed of layered alpha precipitates and layered beta grains alternately. Wherein the lamellar alpha precipitated phase lamella thickness is 50-400 nm, and the lamellar beta crystal lamella thickness is 0.7-1.5 μm, as shown in fig. 1(c) and fig. 1 (d). Obviously, the beta sheet thickness is further reduced, which leads to an increase in TRIP stress. Stress-induced martensite may preferentially initiate in the beta sheet and gradually expand into the adjacent beta sheet with increasing strain. The strength and the plasticity of the alloy are obviously improved through the back stress generated by heterogeneous deformation. Mechanical property tests show that the yield strength of the two-phase metastable beta titanium alloy reaches 759MPa, the tensile strength reaches 900MPa, the uniform elongation is more than 30 percent, the breaking elongation is as high as 34 percent, and the tensile curve of the two-phase metastable beta titanium alloy is shown as example 2 in figure 3 and has excellent strong plasticity matching.

Example 3:

a preparation method of a two-phase TRIP/TWIP titanium alloy with a layered structure comprises the following steps:

and 3, taking out the sample for rolling, wherein the single-pass reduction is 3%, the sample is re-melted after every two passes of rolling and is kept at 770 ℃ for 1min, and the total rolling reduction rate is 92%.

The two-phase TRIP titanium alloy having a layered structure obtained by the above method has a layered structure composed of a layered α -precipitate phase and a layered β -crystal grain alternately. Wherein the lamellar alpha precipitated phase lamella thickness is 50-400 nm, and the lamellar beta crystal lamella thickness is 0.23-1.2 μm, as shown in fig. 1(e) and fig. 1 (f).

The two-phase TRIP/TWIP titanium alloy with the layered structure has a layer thickness of 10-20 μm, wherein the layer thickness is more elongated crystal grains of alpha phase and recrystallized crystal grains containing a small amount of alpha. Since the holding time is 10min after the rolling is finished, the size of the lamination is further increased, and at this time, not only is the amount of the alpha precipitated phase reduced, but also the recrystallized grains have a larger size. The start of stress-induced martensite becomes easier, and the deformation unevenness between the alpha precipitate phase enriched sheet layer and the alpha precipitate phase deficient sheet layer is reduced, so that the yield strength of the alloy is reduced. Mechanical property tests show that the yield strength of the two-phase TRIP/TWIP titanium alloy with the layered structure is 875MPa, the tensile strength is 979MPa, the uniform elongation is more than 30 percent, and the fracture elongation is 36 percent.

Example 4:

step 1, keeping the temperature of a Ti-Al-Mo-Cr-Zr metastable beta titanium alloy plate with the thickness of 10mm at 1050 ℃ in a muffle furnace for 120min, and then quenching to room temperature;

Step 2, keeping the Ti-Al-Mo-Cr-Zr metastable alloy plate with the thickness of 10mm for 15min at the temperature of 775 ℃ in a muffle furnace;

and 3, taking out the sample for rolling, wherein the single-pass reduction is 4%, the sample is returned to the furnace after each two-pass rolling and is kept at 775 ℃ for 1min, and the total rolling reduction rate is 91%.

And 4, immediately putting the rolled sample into a muffle furnace, preserving the heat at 780 ℃ for 1min, and then quenching to room temperature to obtain a layered structure.

Mechanical property tests show that the yield strength of the double-phase TRIP/TWIP titanium alloy with the layered structure is 825MPa, the tensile strength is 950MPa, the uniform elongation is more than 30 percent, and the breaking elongation is 38 percent.

Comparative example 1:

a hot rolling method of a two-phase TRIP titanium alloy of a layered structure, comprising the steps of:

and 3, taking out the sample for rolling, wherein the single-pass reduction is 3%, the sample is re-melted after every two passes of rolling and is kept at 770 ℃ for 1min, and the total rolling reduction rate is 94%.

The two-phase TRIP titanium alloy having a layered structure obtained by the above method has a layered structure composed of a layered α -precipitate phase and a layered β -crystal grain alternately. Wherein the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.23-0.56 mu m. As shown in FIGS. 1(g) and 1 (h). We note that the thickness of the beta sheet approaches that of the nanocrystal due to further reduction in the amount of rolling. Stress-induced martensite has a size effect, and at such small sizes, activation of martensite is completely suppressed. At this time, dislocations dominate the entire plastic deformation process, increasing the strength, but drastically decreasing the plasticity. Mechanical property tests show that the yield strength of the two-phase TRIP titanium alloy with the layered structure is 976MPa, the tensile strength is 973MPa, and the elongation at break is only 8%.

Comparative example 2:

a hot rolling method of a single-phase TRIP/TWIP titanium alloy with a uniform isometric crystal structure comprises the following steps:

step 3, taking out and rolling, wherein the single-pass reduction is 3%, the temperature of a sample after each two-pass rolling is maintained at 770 ℃ for 1min, and the total rolling reduction rate is 90%;

and 4, immediately putting the rolled sample into a muffle furnace, preserving the heat at 800 ℃ for 30min, and then quenching to room temperature to obtain the single-phase metastable-state beta titanium alloy with the uniform isometric crystal structure.

The uniform equiaxed single-phase metastable beta titanium alloy structure contains single-phase beta grains with the grain size of 100-200 mu m. The sample composed of uniform equiaxed crystals has large and uniformly distributed crystal grain sizes. The stress-induced martensite has the smallest activation stress and thus its yield strength is further reduced. Mechanical property tests show that the yield strength of the uniform equiaxed single-phase metastable beta titanium alloy is 417MPa, the tensile strength reaches 605MPa, the uniform elongation is more than 30 percent, and the fracture elongation is 43 percent.

The invention discloses a two-phase high-strength high-plasticity TRIP/TWIP titanium alloy with a layered structure and a preparation method thereof, wherein the alloy is subjected to heat preservation for 1-2 h in a beta single-phase region at 1000-1100 ℃ in a muffle furnace, then quenched to room temperature to obtain uniform beta phase, the obtained alloy is heated to a phase transformation point again, and is subjected to rolling after heat preservation for 10-20min, and finally the rolled plate is subjected to heat preservation for 1-10 min at 765-775 ℃ and then quenched to room temperature to obtain the two-phase TRIP/TWIP titanium alloy with the layered structure; the biphase TRIP/TWIP titanium alloy with the laminated structure prepared by the method can obtain the mechanical property combination with the yield strength of 875MPa, the fracture elongation of 36 percent, the yield strength of 759MPa, the fracture elongation of 34 percent, the yield strength of 651MPa and the fracture elongation of 36 percent respectively.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a two-phase high-strength high-plasticity titanium alloy with a layered structure is characterized by comprising the following steps of:

2. The method for preparing a dual-phase high-strength high-plasticity titanium alloy having a layered structure according to claim 1, wherein the phase transition point temperature in step 2 is 765 ± 5 ℃.

3. The method for preparing a dual-phase high-strength high-plasticity titanium alloy with a laminated structure according to claim 1, wherein the holding temperature in the steps 2 and 4 is 5-10 ℃ above the transformation point temperature.

4. The method for preparing the dual-phase high-strength high-plasticity titanium alloy with the laminated structure according to claim 1, wherein the annealing and the heat preservation are carried out for 1min after each rolling in the step 3 is completed.

5. The method for preparing a dual-phase high-strength high-plasticity titanium alloy with a laminated structure according to claim 1, wherein the holding time in step 4 is 1 min.

6. A two-phase high-strength high-plasticity titanium alloy with a laminated structure, prepared by the preparation method according to any one of claims 1 to 5, wherein the laminated structure comprises a laminated alpha precipitation phase and a laminated beta crystal grain which are alternately composed.

7. The titanium alloy with a layered structure and a dual-phase high-strength high-plasticity according to claim 6, wherein the thickness of the layered alpha precipitation phase sheet layer is 50-400 nm.

8. The dual-phase high-strength high-plasticity titanium alloy with the laminated structure according to claim 6, wherein the laminated beta-crystal grain sheet layer has a thickness of 0.23-4.1 μm.

9. The dual-phase high-strength high-plasticity titanium alloy having a layered structure according to claim 6,

when the total rolling reduction is 85%, the thickness of the lamellar alpha precipitated phase lamella is 50-400 nm, and the thickness of the lamellar beta crystal grain lamella is 0.5-4.1 mu m;