JP2023143831A - Production method of metal - Google Patents

Abstract

To provide a production method of a metal capable of improving both yield stress and ductility of the metal.SOLUTION: A high-density pulse current is applied to an alloy based on Ti and containing Al and Nb. A product (A-ms/mm2) of a current density (A/mm2) and an application time (ms) of the pulse current is 11,000 or more and 13,000 or less. When applying the high-density pulse current so that the current density and the application time satisfy the restriction, yield stress and ductility of the alloy based on Ti and containing Al and Nb are improved simultaneously.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method of manufacturing metal.

Ti and alloys containing Ti have excellent mechanical properties and are used in many fields including the aerospace industry. Furthermore, in order to improve the energy-saving effect of the equipment used, it is essential to improve the strength of these materials. Furthermore, there is a problem that these metal materials are difficult to process. Therefore, there is a need for a technology that improves strength and ductility in advance.

Non-Patent Document 1 describes that tensile strength and ductility are improved by applying a high-density pulsed current to Ti alloy Ti-6Al-4V.

Sui Iwase, Yasuhiro Kimura, Yu Aoi Toku, and Yo Kyo, “Improvement of mechanical properties of titanium alloy using high-density pulsed current”, Japan Society of Mechanical Engineers M&M2019 Mechanics of Materials Conference Proceedings, OS0326

However, in Non-Patent Document 1, the material type is only Ti-6Al-4V, and it is unclear whether the tensile strength and ductility can be improved with other metal materials. Furthermore, the yield stress is not mentioned in Non-Patent Document 1.

Therefore, an object of the present disclosure is to provide a method for manufacturing a metal that can simultaneously improve the yield stress and ductility of the metal. Another object of the present invention is to provide a method for manufacturing a metal that can simultaneously improve the tensile strength and ductility of the metal.

One aspect of the present disclosure is
A method for producing a metal, in which a pulsed current is applied to an alloy mainly containing Ti and containing Al and Nb, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 11000 to 13000. be.

Further, other aspects of the present disclosure include:
The present invention provides a method for producing a metal, in which a pulse current is applied to Ti, and the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 1000 to 6500.

Further, other aspects of the present disclosure include:
The present invention provides a method for producing metal, in which a pulsed current is applied to stainless steel, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 900 to 4500.

Further, other aspects of the present disclosure include:
A method for producing a metal, in which a pulsed current is applied to an alloy mainly containing Ti and containing Al and V, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 15,000 to 17,000. be.

Further, other aspects of the present disclosure include:
The present invention provides a method for producing a metal, in which a pulse current having a current density of 140 A/mm ² or more is applied to Ti or an alloy mainly composed of Ti for a predetermined period of time to cause martensitic phase transformation.

According to the metal manufacturing method of the present disclosure, by applying a pulse current of a predetermined current density and application time to a predetermined metal material, the yield stress and ductility of the metal can be simultaneously improved. Alternatively, the tensile strength and ductility of metal can be improved at the same time.

A graph showing the waveform of pulse current. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 1. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 2. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 2. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 2. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 3. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 3. FIG. 3 is a diagram showing the measurement results of yield stress and ductility for Example 3. FIG. 4 is a diagram showing the measurement results of yield stress and ductility for Example 4. FIG. 4 is a diagram showing the measurement results of yield stress and ductility for Example 4. FIG. 4 is a diagram showing the measurement results of yield stress and ductility for Example 4. Crystal orientation map image for Example 2. 3 is a graph showing the length of twin boundaries for Example 2. Graph showing crystal grain size for Example 2. A map image of GND density for Example 2. A crystal orientation map image and a grain boundary map image for Example 3. 3 is a graph showing average grain size for Example 3. Map images of each element of C, Cr, and Ni and the compound Cr ₂₃ C ₆ for Example 3. A map image of the crystal phase for Example 3. 3 is a graph showing the proportion of delta ferrite phase in Example 3. Crystal orientation map image for Example 4. Graph showing the distribution of crystal grain size for Example 4. A map image of GND density for Example 4. 3 is a graph showing the distribution of GND density for Example 4. A map image combining a crystal phase map and a grain boundary map for Example 4. Graph showing the ratio of α phase and β phase for Example 4. 3 is a graph showing the length of grain boundaries for each type of grain boundary in Example 4. 2 is a graph showing the measurement results of tensile strength and ductility for Example 5. 2 is a graph showing the measurement results of tensile strength and ductility for Example 5. A crystal orientation map image for Example 5. A map image of grain boundaries for Example 5. 7 is a graph showing the relationship between the application time of high-density pulsed current and the ratio of twin boundaries in grain boundaries for Example 5. Graph showing the measurement results of tensile strength and ductility for Example 6. Graph showing the measurement results of tensile strength and ductility for Example 6. Crystal orientation map image for Example 6. A map image of grain boundaries for Example 6. 7 is a graph showing the relationship between the application time of high-density pulsed current and the ratio of twin boundaries in grain boundaries for Example 6. Graph showing the measurement results of tensile strength and ductility for Example 7. Graph showing the measurement results of tensile strength and ductility for Example 7. Crystal orientation map image for Example 7. A map image of grain boundaries for Example 7. 7 is a graph showing the relationship between the application time of high-density pulsed current and the ratio of twin boundaries in grain boundaries for Example 7.

The metal manufacturing method involves applying a pulsed current to an alloy mainly containing Ti and containing Al and Nb, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 11,000 or more and 13,000 or less. be.

In the above, the current density of the pulse current may be 25 A/mm ² or more and 300 A/mm ² or less, and the application time may be 20 ms or more and 550 ms or less. Further, the alloy may be Ti-6Al-7Nb. The number of pulses of the pulse current may be one.

In another metal manufacturing method, a pulse current is applied to Ti, and the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 1000 or more and 6500 or less.

In the above, the current density of the pulse current may be 5 A/mm ² or more and 30 A/mm ² or less, and the application time may be 10 ms or more and 500 ms or less. Further, the number of pulses of the pulse current may be one.

In another metal manufacturing method, a pulsed current is applied to stainless steel, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 900 or more and 4500 or less.

In the above, the current density of the pulse current may be 150 A/mm ² or more and 450 A/mm ^{2 or} less, and the application time may be 1 or more and 20 ms or less. Further, the stainless steel may be SUS316. Moreover, the number of pulses of the pulse current may be 1 or more and 10 or less.

A method for manufacturing other metals includes applying a pulsed current to an alloy mainly containing Ti and containing Al and V, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 15,000 or more and 17,000 or more. It is as follows.

In the above, the current density of the pulse current may be 50 A/mm ² or more and 100 A/mm ² or less, and the application time may be 150 ms or more and 250 ms or less. Further, the alloy may be Ti-6Al-4V. Further, the number of pulses of the pulse current may be one.

Another metal manufacturing method involves applying a pulse current with a current density of 140 A/mm ² or more to Ti or a Ti-based alloy for a predetermined period of time to cause martensitic phase transformation.

In the above, the proportion of twin boundaries in grain boundaries may be increased to 50% or more by applying a pulse current.

Further, in the above, a pulse current may be applied to Ti, and the current density of the pulse current may be 160 A/mm ² or more and 525 A/mm ² or less, and the application time may be 11 ms or more and 170 ms or less.

Further, in the above, a pulse current may be applied to an alloy mainly containing Ti and containing Al and Nb, and the current density of the pulse current may be 150 A/mm ² or more and 500 A/mm ² or less, and the application time may be 6 ms or more and 85 ms or less. .

Further, in the above, a pulse current may be applied to the alloy mainly containing Ti and containing Al and V, and the current density of the pulse current may be 140 A/mm ² or more and 310 A/mm ² or less, and the application time may be 12 ms or more and 105 ms or less. .

(First embodiment)
In the first embodiment, a high-density pulsed current is applied to an alloy mainly composed of Ti and containing Al and Nb. "Mainly containing Ti" means that the element having the highest wt% among the elements constituting the alloy is Ti.

Specifically, the alloy mainly containing Ti and containing Al and Nb is Ti-6Al-7Nb. In addition to Ti, Al, and Nb, Ta, Fe, etc. may be included.

The proportion of Ti in the alloy is, for example, 80 to 90 wt%. The proportion of Al is, for example, 4 to 8 wt%. The proportion of Nb is, for example, 5 to 9 wt%, and is preferably higher than the proportion of Al. Further, the proportion of Ta is preferably 2 wt% or less, and the proportion of Fe is preferably 2 wt% or less. The overall proportion of elements other than these is preferably 1 wt% or less.

The high-density pulse current applied to the alloy is a rectangular pulse wave as shown in FIG. The product of the current density (A/mm ² ) of the pulse current and the application time (ms) is 11,000 to 13,000 (A·ms/mm ² ). The current density of the pulse current is preferably 25 to 300 A/mm ² , more preferably 25 to 130 A/mm ² , even more preferably 50 to 125 A/mm ² . Further, the application time of the pulse current is preferably 20 to 550 ms, more preferably 30 to 550 ms, and still more preferably 90 to 250 ms. Particularly preferred is a current density of 55 to 65 A/mm ² and an application time of 150 to 250 ms. The current density and application time are appropriately set so that the current density and application time ranges described above are satisfied, and the product of the current density and application time of the pulse current satisfies the above range. Further, although a plurality of pulses may be applied, the number of pulses is preferably 4 or less, particularly 1, since the yield stress and ductility may decrease.

When such a high-density pulsed current is applied to an alloy mainly composed of Ti and containing Al and Nb, the yield stress and ductility of the alloy mainly composed of Ti and containing Al and Nb are simultaneously improved. The reason why the yield stress improves is thought to be that the crystal grains become finer and the dislocation density and the entanglement of dislocations increase. Moreover, the reason for the improvement in ductility is thought to be that the crystal phase changes from α phase to β phase and the number of slip planes increases.

By applying a high-density pulsed current with a current density and application time within the above range, the yield stress can be set to 900 to 960 MPa and the ductility to 3.5 to 4.5%, for example.

(Second embodiment)
In the second embodiment, a high-density pulsed current is applied to Ti. Here, Ti may contain impurities of 2 wt% or less.

The high-density pulse current applied to Ti is a rectangular pulse wave as shown in FIG. The product of the current density (A/mm ² ) of the pulse current and the application time (ms) is 1000 to 6500 (A·ms/mm ² ). The current density of the pulse wave is preferably 5 to 30 A/mm ² , more preferably 10 to 25 A/mm ² . Further, the application time of the pulse current is preferably 10 to 500 ms, more preferably 50 to 450 ms. The current density and application time are appropriately set so that the current density and application time ranges described above are satisfied, and the product of the current density and application time of the pulse current satisfies the above range. Further, although a plurality of pulses may be applied, the number of pulses is preferably 1 because the yield stress and ductility may decrease.

When such a high-density pulsed current is applied to Ti, the yield stress and ductility of Ti are simultaneously improved. The reason why the yield stress improves is thought to be that the crystal grains become finer and the dislocation density increases. This is thought to be due to the fact that dislocations moved toward grain boundaries due to the application of high-density pulsed current, and dislocations were deposited based on slip planes, resulting in an increase in dislocation density. In addition, the rotation of the crystals caused by the application of electric current caused the crystals to align, and a new twin boundary was formed. Since twins have weak resistance to dislocation movement, an increase in the number of twins is thought to be a factor in improving ductility.

By applying a high-density pulsed current with a current density and application time within the above range, the average crystal grain size of Ti changes from 9.4 to 9.6 μm to 8 to 9.2 μm, and the crystal grains become finer. Further, for example, the length of the twin boundary becomes 1.5 times or more. Further, for example, the average GND density becomes 1.5 times or more, 3×10 ¹⁴ m ⁻² or more, than before the application of the pulse current, and the dislocation density increases. Further, for example, the yield stress can be set to 220 to 250 MPa, and the ductility can be set to 50 to 60%.

(Third embodiment)
In the third embodiment, a high-density pulsed current is applied to stainless steel. Stainless steel is an alloy steel containing 10.5 wt% or more of Cr. For example, SUS304, SUS316, SUS316L, etc.

The high-density pulse current applied to stainless steel is a rectangular pulse wave as shown in FIG. The product of the current density (A/mm ² ) of the pulse current and the application time (ms) is 900 to 4500 (A·ms/mm ² ). The current density of the pulse wave is preferably 150 to 450 A/mm ² , more preferably 200 to 400 A/mm ² . Further, the application time of the pulse current is preferably 1 to 20 ms, more preferably 5 to 10 ms. The current density and application time are appropriately set so that the current density and application time ranges described above are satisfied, and the product of the current density and application time of the pulse current satisfies the above range. Further, although a plurality of pulses may be applied, the number of pulses is preferably 1 to 10 since the yield stress and ductility may decrease. More preferably 1 to 6, still more preferably 1 to 2.

Applying such a high-density pulsed current to stainless steel simultaneously increases the yield stress and ductility of the stainless steel. The reason for the improvement in yield stress is thought to be that the crystal grains become finer. When a high-density pulsed current is applied, the twins lose their structure and transform into high-angle grain boundaries. Furthermore, small grains are formed near low-angle grain boundaries due to dislocation motion induced by electron wind force. It is thought that this made the crystal grains finer and improved the strength based on the Hall-Petch law. Moreover, the reason for the improvement in ductility is considered to be that the degree of freedom of dislocation movement increases due to the generation of a new delta ferrite phase by dissolving Cr ₂₃ C ₆ .

By applying a high-density pulsed current with a current density and application time within the above range, the average crystal grain size of stainless steel changes from about 15 μm to 12 to 14.5 μm, and the crystal grains become finer. Further, the proportion of the delta ferrite phase increases from about 1% to 4 to 15%, for example. Further, for example, the yield stress can be set to 360 to 430 MPa, and the ductility can be set to 40 to 42%.

(Fourth embodiment)
In the fourth embodiment, a high-density pulsed current is applied to an alloy mainly composed of Ti and containing Al and V.

Specifically, the alloy mainly containing Ti and containing Al and V is Ti-6Al-4V. In addition to Ti, Al, and V, it may also contain Fe, C, and the like.

The proportion of Ti in the alloy is, for example, 85 to 95 wt%. The proportion of Al is, for example, 2 to 8 wt%. The proportion of V is, for example, 2 to 6 wt%, and is preferably lower than the proportion of Al. Further, the proportion of Fe is preferably 1 wt% or less. The overall proportion of elements other than these is preferably 1 wt% or less.

The high-density pulse current applied to the alloy is a rectangular pulse wave as shown in FIG. The product of the current density (A/mm ² ) of the pulse current and the application time (ms) is 15,000 to 17,000 (A·ms/mm ² ). The current density of the pulse current is preferably 50 to 100 A/mm ² , more preferably 60 to 95 A/mm ² , even more preferably 70 to 90 A/mm ² . Further, the application time of the pulse current is preferably 150 to 250 ms, more preferably 170 to 240 ms, and even more preferably 180 to 220 ms. Particularly preferred is a current density of 75 to 85 A/mm ² and an application time of 190 to 210 ms. The current density and application time are appropriately set so that the current density and application time ranges described above are satisfied, and the product of the current density and application time of the pulse current satisfies the above range. Further, although a plurality of pulses may be applied, the number of pulses is preferably 1 because the yield stress and ductility may decrease.

When such a high-density pulsed current is applied to an alloy mainly composed of Ti and containing Al and V, the yield stress and ductility of the alloy mainly composed of Ti and containing Al and V are simultaneously improved. In particular, by setting the current density and application time of the pulse current within the above ranges, the yield stress and ductility are greatly improved. The reason why the yield stress improves is thought to be that the crystal grains become finer and the dislocation density and the entanglement of dislocations increase. Further, the reason why the ductility is improved is considered to be that some crystal phases change from α phase to β phase and the number of slip planes increases. Furthermore, it is thought that the number of phase interfaces (αβ interfaces) increases due to grain refinement and phase transformation. Phase interfaces tend to have coherent properties, allowing dislocations to cross or slide across them. In other words, the yield stress can be increased without impairing ductility.

By applying a high-density pulsed current with a current density and application time within the above range, the average crystal grain size of an alloy mainly composed of Ti and containing Al and V changes from about 4 μm to 3 to 3.5 μm, and the crystal grain becomes finer. Furthermore, the average GND density increases, for example, by 1.2 times or more, or 2.3×10 ¹⁵ m ⁻² or more, compared to before the pulse current is applied. Further, the proportion of the β phase increases, for example, from about 8 to 9% to 10 to 12%. Furthermore, the coherent interface between the α phase and the β phase increases by more than twice. Further, for example, the yield stress can be set to 1060 to 1140 MPa, and the ductility can be set to 9 to 11%.

(Fifth embodiment)
In the fifth embodiment, a high-density pulsed current with a current density of 140 A/mm ² or more is applied to Ti or an alloy mainly composed of Ti for a predetermined period of time to cause martensitic phase transformation. As in the first embodiment, the Ti-based alloy may be an alloy that mainly contains Ti and contains Al and Nb, particularly Ti-6Al-7Nb. Further, as in the fourth embodiment, an alloy mainly composed of Ti and containing Al and V, particularly Ti-6Al-4V, can be used. Although a plurality of pulses may be applied, it is preferable that the number of pulses is 1 since the yield stress and ductility may decrease.

In addition, when using Ti, for example, the current density is set to 160 to 525 A/mm ² and the application time is set to 11 to 170 ms, and martensitic phase transformation is caused by appropriately selecting the current density and application time within this range. be able to.

When using an alloy mainly composed of Ti and containing Al and Nb, for example, by setting the current density to 150 to 500 A/mm ² and the application time to 6 to 85 ms, and selecting the current density and application time appropriately within this range, marten Site phase transformation can be caused to occur.

In addition, when using an alloy mainly containing Ti and containing Al and V, for example, the current density is set to 140 to 310 A/mm ² and the application time is set to 11 to 170 ms, and the current density and application time are appropriately selected within this range. martensitic phase transformation can occur.

When such a high-density pulsed current is applied to Ti or a Ti-based alloy, tensile strength and ductility are simultaneously improved. The reason why the tensile strength improves is thought to be that martensitic phase transformation occurs. The martensitic phase is a supersaturated solid solution with large lattice strain and high resistance to dislocation motion. Therefore, it is thought that the tensile strength is improved. A large number of twins are formed along with the martensitic phase transformation, which is thought to contribute to the improvement of ductility. The atomic arrangement of the twins is regular and the grain boundary energy is low, making it easy for dislocations to slip. Therefore, it is considered that the ductility is improved.

Due to martensitic phase transformation caused by application of pulsed current, the ratio of twin boundaries at grain boundaries becomes, for example, 50% or more and less than 100%. Further, in the case of Ti, for example, the tensile strength can be set to 410 to 450 MPa, and the ductility can be set to 42 to 55%. Further, in the case of an alloy mainly composed of Ti and containing Al and Nb, the tensile strength can be set to 920 to 1100 MPa, and the ductility can be set to 18 to 23%, for example. Further, in the case of an alloy containing Ti as a main component and Al and V, for example, the tensile strength can be set to 1000 to 1180 MPa, and the ductility can be set to 16 to 21%.

A high-density pulsed current was applied to a test piece made of Ti-6Al-7Nb, and then a tensile test was performed on the test piece to measure yield stress (MPa) and ductility (%). For comparison, the yield stress and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. Al is 6.05wt%, Nb is 7.12wt%, Ta is 0.15wt%, Fe is 0.10wt%, C is 0.04wt%, N is 0.02wt%, O is 0.12wt%, and the rest is Ti.

2 to 5 are diagrams showing the measurement results of yield stress and ductility. FIG. 2 shows the case where the high-density pulsed current is applied for 20 ms and the current density is varied from 180 to 300 A/mm ² . FIG. 3 shows the case where the high-density pulsed current is applied for 100 ms and the current density is varied from 100 to 140 A/mm ² . FIG. 4 shows the case where the high-density pulsed current is applied for 200 ms and the current density is varied from 50 to 70 A/mm ² . FIG. 5 shows the case where the high-density pulsed current is applied for 500 ms and the current density is varied from 25 to 35 A/mm ² .

The results shown in Figures 2 to 5 show that both yield stress and ductility are improved compared to the case where high-density pulsed current is not applied at a current density of 120 A/mm ² , an application time of 100 ms, and a current density of 60 A/mm ² . The current density was 25 A/mm ² and the application time was 500 ms. Therefore, if the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 11,000 to 13,000 (A・ms/mm ² ), it is considered that yield stress and ductility can be improved at the same time. It will be done.

Next, the yield stress and ductility were measured and compared using 1 and 5 pulses. FIG. 6 shows the case where the current density was 120 A/mm ² and the application time was 100 ms. FIG. 7 shows the case where the current density was 60 A/mm ² and the application time was 200 ms. As shown in FIGS. 6 and 7, when the number of pulses was increased to 5, the ductility deteriorated. As a result, it was found that the number of pulses is preferably 4 or less.

A high-density pulsed current was applied to a test piece made of Ti, and then a tensile test was performed on the test piece to measure yield stress (MPa) and ductility (%). For comparison, the yield stress and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. C is 0.08 wt%, H is 0.013 wt%, O is 0.15 wt%, N is 0.03 wt%, Fe is 0.20 wt%, and the remainder is Ti.

8 and 9 are diagrams showing the measurement results of yield stress and ductility. FIG. 8 shows the case where the high-density pulsed current is applied for 200 ms and the current density is varied from 12.5 to 90 A/mm ² . FIG. 9 shows the case where the current density of the high-density pulsed current is 12.5 A/mm ² and the application time is varied from 100 to 900 ms.

The results shown in Figures 8 and 9 show that both yield stress and ductility are improved compared to the case where high-density pulsed current is not applied at a current density of 12.5 to 30 A/ ^mm2 , an application time of 200 ms, and a current density of 12. This was the case at .5 A/mm ² and an application time of 100 to 500 ms. Therefore, it is considered that if the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 1000 to 6500 (A・ms/mm ² ), yield stress and ductility can be improved at the same time. It will be done.

Next, the yield stress and ductility were measured and compared using one pulse and two pulses. FIG. 10 shows the case where the current density was 12.5 A/mm ² and the application time was 200 ms. As shown in FIG. 10, when the number of pulses was set to 2, the yield stress worsened. As a result, it was found that the number of pulses is preferably 1.

FIG. 17 is a crystal orientation map image obtained by EBSD for the test piece. In FIG. 17, (a) is before the application of the high-density pulse current, and (b) is after the application of the high-density pulse current, and the current density of the high-density pulse current is 12.5 A/mm ² and the application time is 200 ms. , the number of pulses was set to 1. Comparing FIG. 17(a) and FIG. 17(b), it was found that small-angle grain boundaries decreased, large-angle grain boundaries and twin boundaries increased, and the crystal grains became finer.

Furthermore, the total length of the twin boundaries was determined from FIG. FIG. 18 is a graph showing the length of the twin boundary before and after the application of high-density pulsed current. As shown in FIG. 18, it was found that both the length of the {11-22} twin boundary and the length of the {10-12} twin boundary were increased by the application of high-density pulsed current.

In addition, the average crystal grain size of the test pieces was measured. Here, the crystal grain size is defined as the diameter of a circle having the same area as the crystal grain. FIG. 19 is a graph showing the crystal grain size before and after application of a high-density pulsed current. The current density of the high-density pulsed current was 12.5 A/mm ² , the application time was 100 ms, 200 ms, and 300 ms, and the number of pulses was 1. As shown in FIG. 19, it was found that the application of high-density pulsed current reduced the crystal grain size and made the crystal grains finer.

FIG. 20 is a map image of the GND density before and after the application of a high-density pulse current. The current density and application time of the high-density pulse current are the same as in FIG. 17. As shown in FIG. 20, it was found that the GND density increased after the application of the high-density pulsed current compared to before the application. Further, the average GND density was 2.3×10 ¹⁴ m ⁻² before application of the high-density pulse current and 3.8×10 ¹⁴ m ⁻² after application.

From FIGS. 17 to 20, it is thought that the reason why the yield stress is improved by applying a high-density pulsed current to Ti is because the crystal grains become finer and the dislocation density increases. Further, it is thought that the reason for the improvement in ductility is due to the increase in the number of twins.

A high-density pulsed current was applied to a test piece made of SUS316, and then a tensile test was performed on the test piece to measure yield stress (MPa) and ductility (%). For comparison, the yield stress and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. C is 0.05wt%, Si is 0.26wt%, Mn is 1.3wt%, P is 0.028wt%, S is 0.03wt%, Ni is 10.1wt%, Cr is 17.09wt%, Mo is 2.01 wt%, and the rest is Fe.

11 and 12 are diagrams showing the measurement results of yield stress and ductility. FIG. 11 shows the case where the high-density pulsed current is applied for 5 ms and the current density is varied from 200 to 400 A/mm ² . FIG. 12 shows the case where the current density of the high-density pulsed current is 400 A/mm ² and the application time is varied from 5 to 10 ms.

As shown in Figures 11 and 12, both yield stress and ductility are improved compared to when no high-density pulsed current is applied at a current density of 200 to 400 A/ ^mm2 , an application time of 5 ms, and a current density of 400 A/mm. ² , the application time was 5 to 10 ms. Therefore, it is considered that if the product of the current density (A/mm ² ) and application time (ms) of the pulse current is 900 to 4500 (A・ms/mm ² ), yield stress and ductility can be improved at the same time. It will be done.

Next, the yield stress and ductility were measured and compared by changing the number of pulses between 1 and 6. FIG. 13 shows the case where the current density was 400 A/mm ² and the application time was 5 ms. As shown in FIG. 10, when the number of pulses was 1 to 6, both yield stress and ductility were improved compared to when no high-density pulsed current was applied. As a result, it is considered that the number of pulses is preferably 1 to 10.

FIG. 21 shows a crystal orientation map image and a grain boundary map image obtained by EBSD for the test piece. FIG. 21(a) is a map image of crystal orientation before application of high-density pulsed current, and FIG. 21(b) is a map image of grain boundaries before application of high-density pulsed current. d) is a map image of grain boundaries after application of high-density pulsed current. Further, in FIGS. 21(c) and 21(d), the current density was 400 A/mm ² and the application time was 5 ms, and FIG. 21(c) had one pulse, and FIG. 21(d) had two pulses.

FIG. 22 is a graph showing the results of determining the average grain size by EBSD. In FIG. 22, S1 is before the application of the high-density pulsed current, S2 is after the application of the high-density pulsed current, and when the current density is 200A/mm ² , the application time is 5ms, and the number of pulses is 1, S3 is the time after the application of the high-density pulsed current. S4 is after the application of a high-density pulsed current, when the current density is 400 A/mm ² , the application time is 5 ms, and the number of pulses is 1 ^. It is. Hereinafter, in FIGS. 23 to 25, S1 to S4 have the same meaning.

As shown in FIGS. 21 and 22, it was found that the application of high-density pulsed current made the crystal grains finer. It was also found that the higher the current density, the more refined the crystal grains become.

FIG. 23 is a map image of the elements C, Cr, and Ni, and the compound Cr ₂₃ C ₆ . 23(a) shows the case of S1, (b) shows the case of S3, and (c) shows the case of S3, and S1 to S3 have the same meanings as in FIG. 22. As shown in FIG. 23, it was found that Cr ₂₃ C ₆ was dissolved by applying a high-density pulsed current.

FIG. 24 is a map image of the crystal phase of SUS316. 24(a) is the case of S1, (b) is the case of S2, (c) is the case of S3, and (d) is the case of S4. Further, FIG. 25 is a graph showing the proportion of the delta ferrite phase in each case of S1 to S4. As shown in FIGS. 24 and 25, it was found that the delta ferrite phase increases by applying a high-density pulsed current. It was also found that the higher the current density and the greater the number of pulses, the more the proportion of the delta ferrite phase increases.

From FIGS. 21 to 25, it is considered that the reason why the yield stress is improved by applying a high-density pulsed current to SUS316 is that the crystal grains become finer. Further, it is considered that the ductility is improved due to the dissolution of carbide Cr ₂₃ C ₆ and the formation of delta ferrite phase.

A high-density pulsed current was applied to a test piece made of Ti-6Al-4V, and then a tensile test was performed on the test piece to measure yield stress (MPa) and ductility (%). For comparison, the yield stress and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. Al is 6.15wt%, V is 4.00wt%, Fe is 0.15wt%, C is 0.016wt%, O is 0.18wt%, N is 0.007wt%, Y is less than 0.0004wt%, The rest is Ti.

14 to 16 are graphs and tables showing the measurement results of yield stress and ductility, and FIGS. 14 and 15 are shown as comparative examples. FIG. 14 shows the case where the current density of the high-density pulse current was 270 A/mm ² and the application time was 10 ms. FIG. 15 shows the case where the current density of the high-density pulse current was 240 A/mm ² and the application time was 20 ms. FIG. 16 shows a case where the current density of the high-density pulse current is 80 A/mm ² and the application time is 200 ms.

As shown in FIGS. 14 to 16, the yield stress and ductility were improved in all cases. However, in the case of Figure 14, the rate of increase in yield stress is 3.9% and the rate of increase in ductility is 10.2%, and in the case of Figure 15, the rate of increase in yield stress is 2.7%, and the rate of increase in ductility is 10%. .8%, whereas in the case of Fig. 16, the increase rate of yield stress was 8.0% and the increase rate of ductility was 26.5%, and the increase rate of yield stress and ductility was was significantly larger than in the case of Therefore, if the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 15,000 to 17,000 (A・ms/mm ² ), the yield stress and ductility can be greatly improved. Conceivable.

FIG. 26 is a crystal orientation map image obtained by EBSD for the test piece. FIG. 26(a) shows the state before application of the high-density pulsed current, and FIG. 26(b) shows the state after application. The current density was 80 A/mm ² and the application time was 200 ms. Moreover, FIG. 27 is a graph showing the distribution of crystal grain size. FIG. 27(a) shows the state before application of the high-density pulsed current, and FIG. 27(b) shows the state after application, and the current density and application time are the same as in FIG. 26(b). As shown in FIG. 27(a), before the high-density pulse current is applied, the average grain size of the α phase is 4.2 μm, the average grain size of the β phase is 2.7 μm, and the average grain size of each phase combined is 4.2 μm. It was 0 μm. On the other hand, as shown in FIG. 27(b), after the application of high-density pulsed current, the average grain size of the α phase is 3.7 μm, the average grain size of the β phase is 2.4 μm, and the overall average grain size is It was 3.1 μm. From FIGS. 26 and 27, it was found that the application of high-density pulsed current made the crystal grains finer.

FIG. 28 is a map image of the GND density, in which FIG. 28(a) is before application of a high-density pulse current, and FIG. 28(b) is after application. The current density and application time are the same as in FIG. 26(b). Moreover, FIG. 29 is a graph showing the distribution of GND density, in which FIG. 29(a) is before application of the high-density pulse current, and FIG. 29(b) is after application. As shown in FIG. 29(a), before the high-density pulse current is applied, the average GND density of the α phase is 1.92×10 ¹⁵ m ⁻² and the average GND density of the β phase is 0.20×10 ¹⁵ m ^{− 2} , the overall average GND density was 1.81×10 ¹⁵ m ⁻² . On the other hand, as shown in FIG. 29(b), after applying a high-density pulse current, the average GND density of the α phase is 2.55×10 ¹⁵ m ⁻² and the average GND density of the β phase is 0.23× 10 ¹⁵ m ⁻² , and the overall average GND density was 2.33×10 ¹⁵ m ⁻² . From FIGS. 28 and 29, it was found that the dislocation density increased by applying a high-density pulsed current.

Figure 30 is a map image that combines the crystal phase map image and the grain boundary map of Ti-6Al-4V, and Figure 30 (a) is before application of high-density pulsed current, and (b) is after application. be. The current density and application time are the same as in FIG. 26(b). Moreover, FIG. 31 is a graph showing the ratio of α phase and β phase before and after application of high-density pulse current. Further, FIG. 32 is a graph showing the length of grain boundaries for each type of grain boundary.

As shown in FIG. 31, it was found that the β phase increases by applying a high-density pulsed current. Furthermore, as shown in Fig. 32, the grain boundaries of all types increase due to the application of high-density pulsed current, but in particular, the coherent interface between the α and β phases (PBs (cohr.) in Fig. 32) It was found that the value increased from 0.4 to 0.9.

From FIG. 26-32, it is considered that the reason why the yield stress is improved by applying a high-density pulsed current to Ti-6Al-4V is due to the refinement of crystal grains and the increase in dislocation density. Further, the improvement in ductility is thought to be due to an increase in the β phase and an increase in the number of coherent interfaces between the α phase and the β phase.

A high-density pulsed current was applied to a test piece made of Ti, and then a tensile test was performed on the test piece to measure tensile strength (MPa) and ductility (%). For comparison, the tensile strength and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. C is 0.08 wt%, H is 0.015 wt%, O is 0.25 wt%, N is 0.03 wt%, Fe is 0.30 wt%, and the remainder is Ti.

33 and 34 are graphs showing the measurement results of tensile strength and ductility. FIG. 33 shows the case where the current density of the high-density pulse current was 160 A/mm ² and the application time was varied from 120 to 170 ms. FIG. 34 shows the case where the current density of the high-density pulse current was 525 A/mm ² and the application time was varied from 11.5 to 17 ms. Of the two bars at each application time, the left one shows tensile strength and the right one shows ductility.

As shown in Figures 33 and 34, ^both the tensile strength and ductility are improved compared to the case where high-density pulsed current is not applied. This was the case at mm ² and application time of 11.5 to 12 ms. Therefore, it was found that the tensile strength and ductility can be greatly improved by setting the current density to 160 A/mm ² or more and the application time to a predetermined range.

FIG. 35 is a crystal orientation map image obtained by EBSD for the test piece, and FIG. 36 is a map image of crystal grain boundaries. In Figures 35 and 36, (a) is before the application of the high-density pulsed current, and (b) is after the application of the high-density pulsed current, where the current density of the high-density pulsed current is 160A/mm ² and the application time is 135ms. , the number of pulses was set to 1. As shown in FIGS. 35 and 36, it was found that application of high-density pulsed current caused martensitic phase transformation.

FIG. 37 is a graph showing the relationship between the application time (ms) of high-density pulsed current and the ratio (%) of twin boundaries in grain boundaries. As shown in FIG. 37, it was found that the proportion of twin boundaries increased by applying a pulse current for 120 ms or more.

From FIGS. 33 to 37, it was found that tensile strength and ductility can be simultaneously improved by applying a high-density pulsed current with a current density of 160 A/mm ² or more to Ti for a predetermined period of time. Further, it is considered that the reason why the tensile strength is improved is that martensitic phase transformation occurs. Moreover, the reason for the improvement in ductility is thought to be due to the formation of a large number of twin boundaries.

A high-density pulsed current was applied to a test piece made of Ti-6Al-7Nb, and then a tensile test was performed on the test piece to measure tensile strength (MPa) and ductility (%). For comparison, the tensile strength and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. The content is 6.05 wt% Al, 6.95 wt% Nb, 0.34 wt% Ta, 0.2 wt% Fe, 0.03 wt% N, 0.12 wt% O, and the remainder is Ti.

38 and 39 are graphs showing the measurement results of tensile strength and ductility. FIG. 38 shows the case where the current density of the high-density pulsed current is 150 A/mm ² and the application time is varied from 55 to 85 ms. FIG. 39 shows the case where the current density of the high-density pulsed current is 500 A/mm ² and the application time is varied from 6 to 9 ms. The left side of the two bars at each application time is the tensile strength and the right side is the ductility.

As shown in Figures 38 and 39, ^both the tensile strength and ductility are improved compared to the case where high-density pulsed current is not applied. The current density was 500 A/mm ² and the application time was 6.5 to 8.5 ms. Therefore, it was found that the tensile strength and ductility can be greatly improved by setting the current density to 150 A/mm ² or more and setting the application time to a predetermined range.

FIG. 40 is a crystal orientation map image obtained by EBSD for the test piece, and FIG. 41 is a map image of grain boundaries. In Figures 40 and 41, (a) is before the application of the high-density pulsed current, and (b) is after the application of the high-density pulsed current, where the current density of the high-density pulsed current is 500A/mm ² and the application time is 7ms. , the number of pulses was set to 1. As shown in FIGS. 40 and 41, it was found that application of high-density pulsed current caused martensitic phase transformation.

FIG. 42 is a graph showing the relationship between the application time (ms) of high-density pulsed current and the ratio (%) of twin boundaries in grain boundaries. As shown in FIG. 42, it was found that the proportion of twin boundaries increased by applying the pulse current for longer than 6.5 ms.

From FIGS. 39 to 42, it was found that tensile strength and ductility can be simultaneously improved by applying a high-density pulsed current with a current density of 150 A/mm ² or more to Ti-6Al-7Nb for a predetermined period of time. Further, it is considered that the reason why the tensile strength is improved is that martensitic phase transformation occurs. Moreover, the reason for the improvement in ductility is thought to be due to the formation of a large number of twin boundaries.

A high-density pulsed current was applied to a test piece made of Ti-6Al-4V, and then a tensile test was performed on the test piece to measure tensile strength (MPa) and ductility (%). For comparison, the tensile strength and ductility were measured without applying high-density pulsed current. The detailed elemental composition of the test piece is as follows. Al is 6.0 wt%, V is 3.95 wt%, Fe is 0.2 wt%, O is 0.13 wt%, and the remainder is Ti.

43 and 44 are graphs showing the measurement results of tensile strength and ductility. FIG. 43 shows the case where the current density of the high-density pulse current was 140 A/mm ² and the application time was varied from 65 to 105 ms. FIG. 44 shows the case where the current density of the high-density pulse current is 310 A/mm ² and the application time is varied from 12 to 20 ms. The left side of the two bars at each application time is the tensile strength and the right side is the ductility.

As shown in Figures 43 and 44, ^both the tensile strength and ductility are improved compared to the case where high-density pulsed current is not applied. ^This was the case when the application time was 14 to 20 ms. Therefore, it was found that the tensile strength and ductility can be greatly improved by setting the current density to 140 A/mm ² or more and the application time to a predetermined range.

FIG. 45 is a crystal orientation map image obtained by EBSD for the test piece, and FIG. 46 is a map image of grain boundaries. In Figures 45 and 46, (a) is before the application of the high-density pulsed current, and (b) is after the application of the high-density pulsed current, where the current density of the high-density pulsed current is 140A/mm ² and the application time is 80ms. , the number of pulses was set to 1. As shown in FIGS. 45 and 46, it was found that application of high-density pulsed current caused martensitic phase transformation.

FIG. 47 is a graph showing the relationship between the application time (ms) of high-density pulse current and the ratio (%) of twin boundaries in grain boundaries. As shown in FIG. 47, it was found that the ratio of twin boundaries increased by applying a pulse current for 75 ms or more.

From FIGS. 43 to 47, it was found that tensile strength and ductility can be simultaneously improved by applying a high-density pulsed current with a current density of 140 A/mm ² or more to Ti-6Al-4V for a predetermined period of time. Further, it is considered that the reason why the tensile strength is improved is that martensitic phase transformation occurs. Moreover, the reason for the improvement in ductility is thought to be due to the formation of a large number of twin boundaries.

The present disclosure can be used to improve the mechanical strength and workability of metal materials.

Claims (20)

A method for producing a metal, comprising applying a pulsed current to an alloy mainly containing Ti and containing Al and Nb, and the product of the current density (A/mm ² ) and application time (ms) of the pulsed current is 11,000 or more and 13,000 or less. . 2. The metal manufacturing method according to claim 1, wherein the pulse current has a current density of 25 A/ ^mm2 or more and 300 A/mm2 ^or less, and an application time of 20 ms or more and 550 ms or less. The method for manufacturing a metal according to claim 1 or 2, wherein the alloy is Ti-6Al-7Nb. 3. The metal manufacturing method according to claim 1, wherein the number of pulses of the pulsed current is one. A method for producing a metal, wherein a pulse current is applied to Ti, and the product of the current density (A/mm ² ) and the application time (ms) of the pulse current is 1000 or more and 6500 or less. 6. The metal manufacturing method according to claim 5, wherein the current density of the pulse current is 5 A/ ^mm2 or more and 30 A/ ^mm2 or less, and the application time is 10 ms or more and 500 ms or less. 7. The metal manufacturing method according to claim 5, wherein the number of pulses of the pulse current is 1. A method for manufacturing metal, wherein a pulsed current is applied to stainless steel, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 900 or more and 4500 or less. 11. The metal manufacturing method according to claim 10, wherein the current density of the pulse current is 150 A/ ^mm2 or more and 450 A/mm2 ^or less, and the application time is 1 or more and 20 ms or less. The method for manufacturing metal according to claim 8 or 9, wherein the stainless steel is SUS316. The metal manufacturing method according to claim 8 or 9, wherein the number of pulses of the pulse current is 1 or more and 10 or less. A method for producing a metal, in which a pulsed current is applied to an alloy mainly containing Ti and containing Al and V, and the product of the current density (A/mm ² ) and the application time (ms) of the pulsed current is 15,000 or more and 17,000 or less. . 13. The metal manufacturing method according to claim 12, wherein the current density of the pulse current is 50 A/ ^mm2 or more and 100 A/ ^mm2 or less, and the application time is 150 ms or more and 250 ms or less. 14. The metal manufacturing method according to claim 12 or 13, wherein the alloy is Ti-6Al-4V. 14. The metal manufacturing method according to claim 12 or 13, wherein the number of pulses of the pulsed current is one. A method for manufacturing a metal, which involves applying a pulse current having a current density of 140 A/mm ² or more to Ti or an alloy mainly composed of Ti for a predetermined period of time to cause martensitic phase transformation. 17. The method for producing a metal according to claim 16, wherein the proportion of twin boundaries in grain boundaries is increased to 50% or more by applying a pulsed current. The metal manufacturing method according to claim 16 or 17, wherein a pulse current is applied to Ti, the current density of the pulse current is 160 A/mm ² or more and 525 A/mm ² or less, and the application time is 11 ms or more and 170 ms or less. A pulsed current is applied to an alloy mainly containing Ti and containing Al and Nb, and the current density of the pulsed current is 150 A/mm ² or more and 500 A/mm ² or less, and the application time is 6 ms or more and 85 ms or less. 18. The method for producing a metal according to 17. A pulsed current is applied to an alloy mainly containing Ti and containing Al and V, and the current density of the pulsed current is 140 A/mm ² or more and 310 A/mm ² or less, and the application time is 12 ms or more and 105 ms or less. 18. The method for producing a metal according to 17.