CN113862592B - Heat treatment method of iron-containing metastable beta titanium alloy - Google Patents
Heat treatment method of iron-containing metastable beta titanium alloy Download PDFInfo
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Abstract
The invention provides a heat treatment method of a metastable beta-titanium alloy containing iron, which comprises the steps of preparing a metastable beta-titanium alloy forming piece containing iron by an isostatic pressing technology or an additive manufacturing technology, carrying out high-temperature heat treatment on the metastable beta-titanium alloy forming piece containing iron, and then cooling the metastable beta-titanium alloy forming piece to room temperature along with a furnace to obtain a first metastable beta-titanium alloy containing iron. The heat treatment method can inhibit or avoid the formation of beta spots, ensure the mechanical property of the iron-containing metastable beta titanium alloy and obtain the titanium alloy material with medium strength and good plasticity.
Description
Technical Field
The invention relates to the technical field of heat treatment of titanium and titanium alloy, in particular to a heat treatment method of iron-containing metastable beta titanium alloy.
Background
Ti35421 (Ti-3 Al-5Mo-4Cr-2Zr-1 Fe) is a new type of low cost high strength titanium alloy, containing 1wt.% of iron element, molybdenum equivalent of about 13-14, aluminum equivalent of about 4, and is a metastable beta titanium alloy containing iron. As with other types of titanium alloys, the main research on metastable beta titanium alloy containing iron is focused on how to improve the strength of the titanium alloy and how to obtain a titanium alloy with high plasticity and high strength at the same time.
At present, a common treatment method is mainly solution-aging heat treatment, the iron-containing metastable beta titanium alloy has very good process plasticity and cold formability and good welding performance after solution treatment, and can reach very high strength after the solution-aging heat treatment, but a titanium alloy material with medium strength and good plasticity is difficult to obtain in the whole process, so that further strong plasticity matching cannot be carried out, and the requirements of different applications are met.
In addition, the traditional solution treatment is generally carried out near a phase transformation point, an iron-rich zone preferentially carries out beta phase transformation, the solubility of iron elements is continuously increased after the transformation, and then beta spots are formed, so that the plasticity and the fatigue performance are sharply reduced, the performance stability and the repeatability of the heat treatment are poor, the performance stability and the repeatability of the iron-containing metastable beta titanium alloy are influenced, but if the solution temperature is increased, crystal grains excessively grow, and the problem of irreversible deterioration of the alloy performance is caused.
Therefore, there is a need for a treatment method that can ensure the mechanical properties of the iron-containing metastable beta titanium alloy while inhibiting or avoiding the formation of beta spots, and obtain a titanium alloy material with moderate strength and good plasticity.
Disclosure of Invention
The invention aims to provide a heat treatment method of iron-containing metastable beta titanium alloy aiming at the defects of the prior art, which can ensure the mechanical property of the iron-containing metastable beta titanium alloy and obtain a titanium alloy material with medium strength and good plasticity while inhibiting or avoiding the formation of beta spots.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a heat treatment method of a metastable beta-titanium alloy containing iron comprises the following specific steps:
preparing a ferrous metastable beta titanium alloy forming piece by using ferrous titanium alloy powder as a raw material through an isostatic pressing technology or an additive manufacturing technology, and determining the beta phase transition temperature of the ferrous metastable beta titanium alloy;
placing the iron-containing metastable beta titanium alloy formed part in an air resistance furnace for heating treatment, and after heating to a first temperature interval, performing heat preservation treatment; the first temperature interval is controlled to be 90-110 ℃ above the beta phase transition temperature;
and after the heat preservation is finished, cooling to room temperature along with the furnace to obtain the first iron-containing metastable beta titanium alloy.
Preferably, the iron-containing titanium alloy powder comprises the following components: al: 2.80-3.20 wt.%, mo: 4.50-5.20 wt.%, cr: 3.50-4.20 wt.%, zr: 1.80-2.10 wt.%, fe: 0.80-1.20 wt.%, impurity element O less than or equal to 0.08wt.%, H less than or equal to 0.01wt.%, and C less than or equal to 0.01wt.%.
Preferably, in the heating treatment process of the iron-containing metastable beta titanium alloy forming piece in the air resistance furnace, the temperature is increased to 90-110 ℃ above the beta phase transition temperature at the speed of 20-50 ℃/min, and the heat preservation time is 1-2 h.
Preferably, the first iron-containing metastable beta titanium alloy has 70% to 80% of metastable beta phase and 20% to 30% of primary alpha phase.
Preferably, the heat treatment method further comprises the steps of:
and carrying out solution heat treatment on the obtained first iron-containing metastable beta titanium alloy in a second temperature interval, and then taking out and cooling to obtain a second iron-containing metastable beta titanium alloy, wherein the second temperature interval is controlled to be 20-50 ℃ below the beta phase transition temperature.
Preferably, the solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta-titanium alloy is less than or equal to 25mm, the heat preservation time of the solution heat treatment is more than or equal to 1h;
and when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is increased by 5mm, the heat preservation time is increased by a T1 period, wherein T1 is more than or equal to 10min.
Preferably, the solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is less than or equal to 25mm, a water cooling method, an oil cooling method or an air cooling method is adopted after the solution heat treatment;
and when the thickness or the diameter of the first iron-containing metastable beta-titanium alloy is larger than 25mm, adopting a water cooling or oil cooling method after solution heat treatment.
Preferably, the second iron-containing metastable beta titanium alloy has a metastable beta phase of 90-95% and a primary alpha phase of 5-10%.
Preferably, the heat treatment method further comprises the steps of:
carrying out aging heat treatment on the obtained second iron-containing metastable beta titanium alloy in a third temperature range to obtain a third iron-containing metastable beta titanium alloy;
wherein the heat preservation time of the aging heat treatment is 4-16 h, and the third temperature interval is controlled to be 480-560 ℃.
Preferably, the phase composition of the third iron-containing metastable beta titanium alloy includes a secondary alpha phase, a primary alpha phase, and a metastable beta phase.
The heat treatment method of the titanium alloy in combination with the technical scheme has the beneficial effects that:
1. according to the heat treatment method of the iron-containing metastable beta-titanium alloy, the iron-containing metastable beta-titanium alloy forming piece is prepared by an isostatic pressing technology or an additive manufacturing technology, and then the iron-containing metastable beta-titanium alloy forming piece is subjected to a heat preservation process at 90-110 ℃ above a beta phase transformation point, so that a primary alpha phase and a secondary alpha phase in an original tissue are completely transformed into the beta phase, and because the barrier of the alpha phase is reduced, an iron element can be fully diffused in the beta phase, and the segregation of the iron element is relieved; the furnace is cooled, because the air resistance furnace is adopted, the temperature can be reduced to be below the beta phase transformation point in a short time, the alpha phase is preferentially precipitated at the grain boundary, the reaquation of iron elements among crystal grains is effectively prevented, the beta spot caused by the iron elements is inhibited or avoided, the stability of heat treatment is improved, and the irreversible deterioration of the alloy performance caused by the excessive growth of the crystal grains is avoided; meanwhile, the primary alpha phase fully grows at the grain boundary and near the grain boundary due to furnace cooling, and as the strength of the alpha phase is higher than that of the beta phase and the plasticity of the beta phase is much higher than that of the alpha phase, crack propagation preferentially proceeds inside the beta crystal grain, and a large amount of energy is consumed when the beta crystal grain passes through the grain boundary, a metastable beta titanium alloy with 70% -80% of metastable beta and 20% -30% of primary alpha phase is obtained, and the metastable beta titanium alloy has medium strength and good plasticity.
2. According to the heat treatment method of the iron-containing metastable beta titanium alloy, the iron element is fully diffused in the beta phase, and the re-segregation of the iron element among crystal grains is effectively prevented, so that the stability and the reproducibility of the subsequent further solid solution aging treatment are ensured; the heat treatment method can be combined with solid solution treatment or solid solution aging treatment, so that the iron-containing metastable beta titanium alloy materials with different strong plasticity matching relations can be regulated and controlled according to actual requirements, and the requirements of different applications can be met.
Drawings
FIG. 1a is a microstructure view of an original Ti35421 titanium alloy obtained in example 1 of the present invention at a magnification of 100.
FIG. 1b is a microstructure view of the original Ti35421 titanium alloy at 500 times as obtained in example 1 of the present invention.
FIG. 2a is a microstructure view of a Ti35421 titanium alloy at a magnification of 100 times after heat treatment above the β phase transition point in example 1 of the present invention.
FIG. 2b is a microstructure view of the Ti35421 titanium alloy of example 1 of the present invention at 500 times or more after heat treatment at a β phase transformation point or higher.
FIG. 3a is a microstructure diagram of Ti35421 titanium alloy at 100 times after solution heat treatment in example 1 of the present invention.
FIG. 3b is a microstructure of the Ti35421 titanium alloy at 500 times after the solution heat treatment in example 1 of the present invention.
FIG. 4a is a microstructure of Ti35421 titanium alloy at 100 times after solution aging heat treatment in example 1 of the present invention.
FIG. 4b is a microstructure of the Ti35421 titanium alloy of example 1 of the present invention at 500 times after solution aging heat treatment.
FIG. 5 is a graph of tensile stress-strain at room temperature for Ti35421 titanium alloy at various stages of heat treatment in example 1 of the invention.
FIG. 6a is a microstructure view of a Ti35421 titanium alloy of comparative example 1 of the present invention at a magnification of 100.
FIG. 6b is a microstructure view of a Ti35421 titanium alloy of comparative example 1 of the present invention at a magnification of 500.
Detailed Description
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.
In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways.
The invention provides a heat treatment method of a metastable beta titanium alloy containing iron, which prepares a formed part of the metastable beta titanium alloy containing iron by using Ti35421 powder as a raw material through preparation processes such as an isostatic pressing technology or an additive manufacturing technology. And then carrying out high-temperature heat treatment on the iron-containing metastable beta titanium alloy formed piece to fully diffuse the iron element, inhibiting or avoiding beta spots caused by iron element segregation, increasing the performance stability and reproducibility of subsequent solution aging heat treatment, and simultaneously producing a coarser primary alpha phase at a crystal boundary or a crystal boundary accessory by furnace cooling to obtain medium strength and good plasticity.
In a specific embodiment, the specific steps include:
preparing a ferrous metastable beta titanium alloy forming piece by using ferrous titanium alloy powder as a raw material through an isostatic pressing technology or an additive manufacturing technology, and determining the beta phase transition temperature of the ferrous metastable beta titanium alloy;
carrying out high-temperature heat treatment on the iron-containing metastable beta titanium alloy molding piece, and completely converting an alpha phase into a beta phase to fully diffuse iron element;
and then cooling the mixture to room temperature along with the furnace to convert the beta phase into a coarse primary alpha phase as much as possible, thereby obtaining the first iron-containing metastable beta titanium alloy.
As an alternative, the foregoing high-temperature heat treatment process includes: and (3) placing the iron-containing metastable beta titanium alloy molding piece in an air resistance furnace for heating treatment, heating to a first temperature interval, preserving heat, and completely converting alpha phase into beta phase so as to fully diffuse iron element. Wherein the first temperature interval is controlled to be 90-110 ℃ above the beta phase transition temperature.
In a preferred embodiment, the iron-containing titanium alloy powder comprises the following components: al: 2.80-3.20 wt.%, mo: 4.50-5.20 wt.%, cr: 3.50-4.20 wt.%, zr: 1.80-2.10 wt.%, fe: 0.80-1.20 wt.%, impurity element O less than or equal to 0.08wt.%, H less than or equal to 0.01wt.%, and C less than or equal to 0.01wt.%.
In a preferred embodiment, the iron-containing metastable beta titanium alloy forming piece is placed in an air resistance furnace, and in the heating treatment process of the iron-containing metastable beta titanium alloy forming piece in the air resistance furnace, the temperature is raised to be 90-110 ℃ above the beta phase transition temperature at the speed of 20-50 ℃/min, and the heat preservation time is 1-2 h; particularly preferably, the furnace temperature control precision of the air resistance furnace is +/-5 ℃ so as to ensure linear and uniform temperature rise in the temperature rise process.
In a preferred embodiment, the first iron-containing metastable beta titanium alloy has 70% to 80% of metastable beta and 20% to 30% of primary alpha phase, and the first iron-containing metastable beta titanium alloy with medium strength and good plasticity is obtained.
In a preferred embodiment, after the iron-containing metastable beta titanium alloy formed part is obtained, the element distribution of the iron-containing metastable beta titanium alloy formed part should be determined, and a composition test can be performed at a plurality of positions, so that the element distribution of the iron-containing metastable beta titanium alloy formed part is required to be uniform, the difference between the main element contents of different positions is less than or equal to 0.3wt.%, that is, the absolute value of the deviation value of the main element contents of any two different test positions is controlled within the range of less than or equal to 0.3 wt.%.
In some embodiments, products with severe macrosegregation, with differences in the content of iron elements with a tendency to severe segregation of ≦ 0.2wt.%, should be excluded in particular. This is because the production process causes macrosegregation or makes it impossible to perform the heat treatment any more, and it is necessary to exclude the product of the batch.
In an alternative embodiment, the beta transus temperature is determined by metallography or differential thermal analysis when determining the beta transus temperature of the iron-containing metastable beta titanium alloy formed part.
In a preferred embodiment, the determination accuracy of the transformation temperature is controlled to be less than or equal to 5 ℃ when the beta transformation temperature is determined, because the beta transformation temperatures of different batches of iron-containing metastable beta titanium alloy may have large difference due to the deviation of the components.
In a preferred embodiment, before the iron-containing metastable beta titanium alloy forming piece is subjected to high-temperature heat preservation at a temperature of 90-110 ℃ above the beta transformation temperature, the iron-containing metastable beta titanium alloy forming piece is placed below the beta transformation temperature by 30-70 ℃ for heat preservation for 1-2 hours, and after the furnace is cooled to room temperature, the iron-containing metastable beta titanium alloy forming piece is subjected to high-temperature heat preservation at a temperature of 90-110 ℃ above the beta transformation temperature, so that the storage energy in the iron-containing metastable beta titanium alloy forming piece is reduced, and the grain growth in the subsequent process is synergistically inhibited.
In a preferred embodiment, the heat treatment method further comprises the steps of:
carrying out solution heat treatment on the obtained first iron-containing metastable beta titanium alloy in a second temperature interval, then taking out and cooling to convert most of primary alpha phase into beta phase again, then taking out and cooling, and rapidly cooling to keep the beta phase to room temperature to obtain a second iron-containing metastable beta titanium alloy; wherein the second temperature interval is controlled to be 20-50 ℃ below the beta phase transition temperature.
In a preferred embodiment, the solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is less than or equal to 25mm, the heat preservation time of the solution heat treatment is more than or equal to 1h, and the inside of the alloy is ensured to be completely burnt;
and when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is increased by 5mm, the heat preservation time is increased by a T1 period, wherein T1 is more than or equal to 10min.
In another preferred embodiment, the solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta-titanium alloy is less than or equal to 25mm, adopting a water cooling method, an oil cooling method or an air cooling method after solution heat treatment;
and when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is larger than 25mm, adopting a water cooling or oil cooling method after the solution heat treatment.
In another preferred embodiment, the solution heat treatment is rapid during water cooling or oil cooling, and the instantaneous temperature of the surface before entering water or oil is controlled within the interval [ t1, t2], wherein t1 takes the following values: the temperature of the solution heat treatment is-50 ℃, and t2 is the temperature of the solution heat treatment.
In a preferred embodiment, the second iron-containing metastable beta titanium alloy has a metastable beta phase of 90-95% and a primary alpha phase of 5-10%, and the second iron-containing metastable beta titanium alloy material with acceptable strength and excellent plasticity is obtained.
In a further preferred embodiment, the heat treatment method further comprises the steps of:
carrying out aging heat treatment on the obtained second iron-containing metastable beta titanium alloy at a third temperature interval to obtain a third iron-containing metastable beta titanium alloy;
wherein the heat preservation time of the aging heat treatment is 4-16 h, and the third temperature interval is controlled to be 480-560 ℃.
In a preferred embodiment, during the aging heat treatment, a large amount of secondary a phase is precipitated from the metastable β phase in the second iron-containing metastable β titanium alloy, and thus, the phase composition of the obtained third iron-containing metastable β titanium alloy includes the secondary a phase, the primary a phase, and the metastable β phase.
In the preferred embodiment, the solution heat treatment and the aging heat treatment are performed in an air resistance furnace, an atmosphere protection furnace or a vacuum furnace, and it is understood that the furnace temperature is controlled to within + -5 ℃ to maintain the accuracy.
It is to be understood that the first iron-containing metastable beta titanium alloy obtained has a moderate strength and good plasticity, the strength of the first iron-containing metastable beta titanium alloy being between the higher strength and the lower strength in the second iron-containing metastable beta titanium alloy and the third iron-containing metastable beta titanium alloy, relative to the strength and plasticity in the second iron-containing metastable beta titanium alloy and the third iron-containing metastable beta titanium alloy, and the plasticity of the first iron-containing metastable beta titanium alloy being also between the higher plasticity and the lower plasticity in the second iron-containing metastable beta titanium alloy and the third iron-containing metastable beta titanium alloy.
For better understanding, the present invention is further described below with reference to specific examples, but the processing is not limited thereto and the present disclosure is not limited thereto.
[ example 1 ]
Step 1, mixing T with specification of 53-235 mu mi35421 metal powder is tapped and put into a hot isostatic pressing sheath, vacuumized and sealed, a Ti35421 bar is prepared under 140MPa pressure according to the 840 ℃/4h/FC hot isostatic pressing process, and the bar is taken
Stick samples.
The metallographic phase of Ti35421 at this stage is shown in FIG. 1, and it can be seen from the figure that the grain boundary is a continuous alpha phase at this time, and the diffusion of iron element between the crystal grains is blocked; short primary alpha phase is distributed in the crystal grains, cracks are easy to bypass the alpha phase for diffusion, and the strength is low.
And 2, randomly taking three samples to perform chemical component test, wherein the results are shown in table 1.
TABLE 1
And 3, respectively testing the metallographic structures at 800 ℃, 810 ℃, 815 ℃ and 820 ℃ by using a quenching metallographic method, determining that the beta transformation temperature is about 815 ℃, and confirming the precision of the heat treatment furnace.
And 4, placing the Ti35421 titanium alloy rod-shaped sample in the step 1 in an air resistance furnace, heating to 920 ℃ at the speed of 30 ℃/min, preserving heat for 1h, and cooling to room temperature along with the furnace.
The metallographic phase of Ti35421 at the stage is shown in figure 2, and the figure shows that the grain boundary alpha phase is eliminated at high temperature, so that the homogenization of the iron element is facilitated, and the grain boundary alpha phase generated again after cooling can block the reaquation of the iron element; the coarse primary alpha phase near the grain boundary can effectively block crack propagation to increase strength, and a large amount of metastable beta phase in the grain is helpful for improving plasticity.
And 5, heating the air resistance furnace to 780 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 4 into the furnace, preserving the heat for 1h, taking out, and air-cooling to room temperature.
The metallographic phase of Ti35421 in a solid solution state is shown in FIG. 3, and it can be seen from the figure that, at this time, a large amount of primary alpha phase is converted into metastable beta phase by solid solution below the beta phase transition point, the strength is reduced, and the plasticity is remarkably improved.
And 6, heating the air resistance furnace to 540 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 5 in the furnace, preserving the heat for 8 hours, and taking out the sample to be air-cooled to the room temperature.
The metallographic phase of Ti35421 in a solid solution aging state is shown in figure 4, and as can be seen from the figure, a large amount of fine secondary alpha phases are precipitated from the metastable beta phase in the step 5 through aging treatment, so that the crack can be effectively and obviously expanded, the strength is rapidly increased, meanwhile, the metastable beta phase is greatly reduced, and the plasticity is rapidly reduced.
And 7, testing the room-temperature tensile mechanical properties of the rod-shaped Ti35421 titanium alloy material obtained in the steps 1, 4, 5 and 6 according to GBT228.1 'Metal Material Room temperature tensile test method', wherein the results are shown in Table 2, and the stress-strain curve is shown in FIG. 5.
TABLE 2
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 952MPa | 1070MPa | 9.9％ |
| Step 4 | 1014MPa | 1109MPa | 11.4％ |
| Step 5 | 859MPa | 893MPa | 15.2 |
| Step | |||
| 6 | 1194MPa | 1270MPa | 5.8％ |
Combining the results of fig. 5 and table 2, it can be seen that after the high temperature soak (step 4), the alloy material can obtain moderate strength and good plasticity relative to steps 5 and 6.
[ example 2]
Step 1, taking Ti35421 metal powder with the specification of 75-180 mu m, preparing a block sample by utilizing a laser directional energy deposition process, wherein the laser power is 1600W, the diameter of a laser spot is 3mm, the scanning distance is 1.6mm, the scanning speed is 600mm/min, the thickness of a preparation layer is 0.5mm, and taking
Stick samples.
And 2, taking the left, middle and right positions of the original Ti35421 block to perform chemical composition tests, wherein the results are shown in Table 3.
TABLE 3
And 3, respectively testing the metallographic structures at 790 ℃, 800 ℃, 810 ℃ and 820 ℃ by using a quenching metallographic method, determining that the beta phase transition temperature is between 800 and 810 ℃, and further determining that the phase transition temperature is about 805 ℃ by using a differential thermal analysis method.
And 4, placing the Ti35421 titanium alloy material in the step 1 into an air resistance furnace, heating to 910 ℃ at the speed of 30 ℃/min, preserving heat for 1h, and cooling to room temperature along with the furnace.
And 5, heating the air resistance furnace to 780 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 4 into the furnace, preserving the heat for 1h, taking out, and air-cooling to room temperature.
And 6, heating the air resistance furnace to 540 ℃, placing the rod-shaped Ti35421 titanium alloy material in the step 5 into the furnace, preserving the heat for 8 hours, and taking out the material to be air-cooled to the room temperature.
Step 7, testing the room temperature tensile mechanical properties of the Ti35421 titanium alloy rod-shaped sample in the steps 1, 4, 5 and 6 according to GBT228.1 "Metal Material Room temperature tensile test method", and the results are shown in Table 4.
TABLE 4
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 1429MPa | 1492MPa | 2.5％ |
| Step 4 | 1108MPa | 1184MPa | 6.2％ |
| Step 5 | 935MPa | 964MPa | 15.2 |
| Step | |||
| 6 | 1315MPa | 1368MPa | 4.1％ |
It can be seen from the table that after the high temperature holding (step 4), the alloy material can obtain medium strength and good plasticity compared with the alloy material obtained in step 5 and step 6.
[ example 3 ]
Step 1, preparing a sample by using a powder metallurgy process, compacting Ti35421 metal powder with the specification of 53-235 mu m in a hot isostatic pressing sheath, vacuumizing and sealing, preparing a Ti35421 bar by using a 840 ℃/4h/FC hot isostatic pressing process under the pressure of 140MPa, and taking the bar
Stick-shaped samples.
TABLE 5
And 3, respectively testing the metallographic structures at 800 ℃, 810 ℃, 815 ℃ and 820 ℃ by using a quenching metallographic method, determining that the beta transformation temperature is about 815 ℃, and confirming the precision of the heat treatment furnace.
And 4, heating the air resistance furnace to 765 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 1 into the furnace, preserving the heat for 1h, and taking out the furnace to cool to room temperature.
And 5, placing the Ti35421 titanium alloy rod-shaped sample in the step 4 in an air resistance furnace, heating to 920 ℃ at the speed of 30 ℃/min, preserving heat for 1h, and cooling to room temperature along with the furnace.
And 6, heating the air resistance furnace to 780 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 5 into the furnace, preserving the heat for 1h, and taking out the sample to cool to room temperature.
And 7, heating the air resistance furnace to 540 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 6 in the furnace, preserving the heat for 8 hours, and taking out the sample to be air-cooled to the room temperature.
TABLE 6
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 945MPa | 1054MPa | 9.5％ |
| Step 5 | 1054MPa | 1160MPa | 12.3 |
| Step | |||
| 6 | 890MPa | 933MPa | 16.4％ |
| Step 7 | 1217MPa | 1295MPa | 6.7％ |
It can be seen from the table that after the high temperature holding (step 4), the alloy material can obtain medium strength and good plasticity compared with the alloy material obtained in step 5 and step 6.
[ example 4 ]
Step 1, preparing a sample by using an additive manufacturing process, taking Ti35421 metal powder with the specification of 75-180 mu m, preparing a block-shaped sample by using a laser directional energy deposition process, wherein the laser power is 1600W, the diameter of a laser spot is 3mm, the scanning distance is 1.6mm, the scanning speed is 600mm/min, the thickness of a preparation layer is 0.5mm, and taking
Stick samples.
And 2, taking the left, middle and right positions of the original Ti35421 block for chemical composition test, wherein the results are shown in Table 7.
TABLE 7
And 3, respectively testing metallographic structures at 790 ℃, 800 ℃, 810 ℃ and 820 ℃ by using a quenching metallographic method, determining that the beta phase transition temperature is between 800 and 810 ℃, and further determining that the phase transition temperature is about 805 ℃ by using a differential thermal analysis method.
And 4, heating the air resistance furnace to 755 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 1 into the furnace, preserving the heat for 1h, and then taking out the furnace and cooling to room temperature.
And 5, placing the Ti35421 titanium alloy material in the step 4 into an air resistance furnace, heating to 910 ℃ at the speed of 30 ℃/min, preserving heat for 1h, and cooling to room temperature along with the furnace.
And 6, heating the air resistance furnace to 780 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 5 into the furnace, preserving the heat for 1h, and taking out the sample to cool to room temperature.
And 7, heating the air resistance furnace to 540 ℃, placing the rod-shaped Ti35421 titanium alloy material in the step 6 in the furnace, preserving the heat for 8 hours, and taking out the titanium alloy material to be air-cooled to the room temperature.
TABLE 8
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 1403MPa | 1481MPa | 3.1％ |
| Step 4 | 1141MPa | 1205MPa | 6.1％ |
| Step 5 | 952MPa | 989MPa | 15.9 |
| Step | |||
| 6 | 1334MPa | 1395MPa | 5.1％ |
It can be seen from the table that after the high temperature holding (step 4), the alloy material can obtain moderate strength and good plasticity relative to steps 5 and 6.
Comparative example 1
The same materials and procedure were used as in example 1, except that step 4 was omitted, and the results of the performance tests are shown in Table 9.
TABLE 9
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 952MPa | 1070MPa | 9.9％ |
| Step 5 | 862MPa | 892MPa | 13.5 |
| Step | |||
| 6 | 1184MPa | 1247MPa | 4.1％ |
Comparative example 2
The same materials and procedures as in example 2 were used except that step 4 was omitted, and the results of the performance tests are shown in Table 10.
[ COMPARATIVE EXAMPLE 3 ]
Step 1, preparing a sample by using a forging process, uniformly stirring sponge titanium, al-80Mo alloy, al-85V alloy, pure aluminum wire, pure chromium, pure iron and pure zirconium according to a certain weight ratio, preparing a Ti35421 plate by three times of smelting, two times of forging and one time of rolling, and taking the plate
A rod-like sample;
TABLE 11
Step 3, respectively testing metallographic structures at 790 ℃, 800 ℃, 810 ℃ and 820 ℃ by using a quenching metallographic method, determining that the beta phase transition temperature is between 800 and 810 ℃, and further determining that the phase transition temperature is about 803 ℃ by using a differential thermal analysis method;
step 4, placing the Ti35421 titanium alloy material in the step 4 into an air resistance furnace, heating to 910 ℃ at the speed of 30 ℃/min, preserving heat for 1h, and cooling to room temperature along with the furnace;
step 5, heating the air resistance furnace to 780 ℃, placing the Ti35421 titanium alloy rod-shaped sample in the step 5 into the furnace, preserving the heat for 1h, and taking out the sample to be air-cooled to the room temperature;
step 7, testing the room temperature tensile mechanical properties of the Ti35421 titanium alloy rod-shaped sample in step 1, step 5, step 6 and step 7 according to GBT228.1 "metal material room temperature tensile test method", and the results are shown in table 12:
TABLE 12
| Stage of heat treatment | Yield strength | Tensile strength | Elongation after fracture |
| Step 1 | 1288MPa | 1361MPa | 7.2％ |
| Step 4 | 1051MPa | 1168MPa | 8.5％ |
| Step 5 | 951MPa | 968MPa | 9.7 |
| Step | |||
| 6 | 1240MPa | 1313MPa | 4.6％ |
The tests of examples 1-4 show that by combining isostatic pressing and high temperature heat treatment, or additive manufacturing and high temperature heat treatment, alloy materials of moderate strength and good plasticity can be obtained, and irreversible deterioration of the alloy properties due to excessive grain growth is avoided, which may be due to insufficient recrystallization driving force, less internal storage energy, and no crushing of the grains during production.
The results of examples 3 and 4 show that after the alloy is shaped by isostatic pressing technology or additive manufacturing, the titanium alloy is subjected to heat preservation at 30-70 ℃ below the beta phase transformation temperature for 1-2 h and then subjected to high-temperature heat preservation treatment, so that the performance of the titanium alloy obtained in each step is better, probably because the storage energy of the titanium alloy can be further reduced after the titanium alloy is subjected to annealing treatment below the beta phase transformation temperature, and finally, the growth of crystal grains is further inhibited through the cooperation of each step.
As can be seen from the results of comparative examples 1 and 2, the alloys without high temperature holding had non-uniform diffusion of iron element, resulting in the formation of β -spots (circles in fig. 6), and did not achieve moderate strength and good plasticity; the results of comparative example 3 show that, when the forging method is combined with high-temperature heat preservation, the strength of the titanium alloy obtained in steps 4 and 5 is lower than that of the titanium alloy obtained in step 1, and the plasticity is not improved, while the strength and the plasticity of the titanium alloy obtained in step 6 are lower than those of the original state and are not improved, which indicates that the performance of the titanium alloy is degraded due to excessive grain growth.
In conclusion, the heat treatment method can inhibit or avoid the formation of beta spots, simultaneously ensure the mechanical property of the iron-containing metastable beta titanium alloy, avoid the irreversible deterioration of the alloy property caused by the excessive growth of crystal grains, and obtain the titanium alloy material with medium strength and good plasticity.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be defined by the appended claims.
Claims (9)
1. A heat treatment method of a metastable beta titanium alloy containing iron is characterized by comprising the following specific steps:
preparing a ferrous metastable beta titanium alloy forming piece by using ferrous titanium alloy powder as a raw material through an isostatic pressing technology or an additive manufacturing technology, and determining the beta phase transition temperature of the ferrous metastable beta titanium alloy;
placing the iron-containing metastable beta titanium alloy formed piece in an air resistance furnace for heating treatment, and after heating to a first temperature interval, performing heat preservation treatment; the first temperature interval is controlled to be 90-110 ℃ above the beta phase transition temperature;
after the heat preservation is finished, cooling the alloy to room temperature along with the furnace to obtain a first iron-containing metastable beta titanium alloy;
the ferrotitanium-containing alloy powder is Ti35421 and comprises the following components: al:2.80 to 3.20wt.%, mo:4.50 to 5.20wt.%, cr:3.50 to 4.20wt.%, zr:1.80 to 2.10wt.%, fe:0.80 to 1.20wt.%, impurity element O less than or equal to 0.08wt.%, H less than or equal to 0.01wt.%, and C less than or equal to 0.01wt.%.
2. The heat treatment method of the iron-containing metastable beta titanium alloy according to claim 1, characterized in that in the temperature rise treatment process of the iron-containing metastable beta titanium alloy molding in the air resistance furnace, the temperature rises to 90-110 ℃ above the beta transformation temperature at a speed of 20-50 ℃/min, and the heat preservation time is 1-2h.
3. The method for heat treating the iron-containing metastable beta titanium alloy according to claim 1, wherein the first iron-containing metastable beta titanium alloy has 70% to 80% of metastable beta phase and 20% to 30% of primary alpha phase.
4. The method of heat treating a ferrous metastable beta-titanium alloy according to claim 1, further comprising the steps of:
and carrying out solution heat treatment on the obtained first iron-containing metastable beta titanium alloy in a second temperature interval, and then taking out and cooling to obtain a second iron-containing metastable beta titanium alloy, wherein the second temperature interval is controlled to be 20-50 ℃ below the beta phase transition temperature.
5. The method of heat treating an iron-containing metastable beta titanium alloy according to claim 4, wherein said solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is less than or equal to 25mm, the heat preservation time of the solution heat treatment is more than or equal to 1h;
and when the thickness or the diameter of the first iron-containing metastable beta titanium alloy is increased by 5mm, the heat preservation time is increased by a T1 period, wherein T1 is more than or equal to 10min.
6. The method of heat treating an iron-containing metastable beta titanium alloy according to claim 4, wherein said solution heat treatment, wherein:
when the thickness or the diameter of the first iron-containing metastable beta-titanium alloy is less than or equal to 25mm, adopting a water cooling method, an oil cooling method or an air cooling method after solution heat treatment;
and when the thickness or the diameter of the first iron-containing metastable beta-titanium alloy is larger than 25mm, adopting a water cooling or oil cooling method after solution heat treatment.
7. The heat treatment method for the iron-containing metastable beta titanium alloy of claim 4, wherein the second iron-containing metastable beta titanium alloy has a metastable beta phase content of 90% -95% and a primary alpha phase content of 5% -10%.
8. The method for heat treating a ferrous metastable beta titanium alloy according to any of claims 4-7, characterized in that the method for heat treating further comprises the steps of:
carrying out aging heat treatment on the obtained second iron-containing metastable beta titanium alloy at a third temperature interval to obtain a third iron-containing metastable beta titanium alloy;
wherein the heat preservation time of the aging heat treatment is 4 to 169h, and the third temperature interval is controlled to be 480 to 560 ℃.
9. The method for heat treating the iron-containing metastable beta titanium alloy of claim 8, wherein the phase composition of the third iron-containing metastable beta titanium alloy comprises a secondary alpha phase, a primary alpha phase, and a metastable beta phase.
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| CN106521236A (en) * | 2016-10-25 | 2017-03-22 | 南京工业大学 | Low-cost high-strength Fe-containing near-Beta titanium alloy and preparation method thereof |
| CN113275599A (en) * | 2021-04-15 | 2021-08-20 | 西安理工大学 | Heat treatment method for improving toughness of 3D printing titanium alloy lattice structure |
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| CN106521236A (en) * | 2016-10-25 | 2017-03-22 | 南京工业大学 | Low-cost high-strength Fe-containing near-Beta titanium alloy and preparation method thereof |
| CN113275599A (en) * | 2021-04-15 | 2021-08-20 | 西安理工大学 | Heat treatment method for improving toughness of 3D printing titanium alloy lattice structure |
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