Hot Rolling Process for Wide Phase Transformation Temperature Window of TiNi-Based Shape Memory Alloy

Abstract

The invention discloses a hot rolling process for a TiNi-based shape memory alloy with a wide phase transition temperature window, comprising the following steps: S1, using sponge titanium, electrolytic nickel and crystalline zirconium as raw materials, and preparing a TiNiZr alloy with a total mass of 100g according to a chemical composition of Ti36.5-Ni48.5-Zr15 atomic ratio; S2, placing the prepared raw materials in the crucible in a vacuum arc melting furnace according to the principle that the low-melting-point nickel material is placed at the bottom of the crucible and the high-melting-point crystalline zirconium is placed at the top of the crucible; S3, repeatedly melting the raw materials under the action of an arc for 5 times to prepare a TiNiZr alloy with uniform composition. The martensitic phase transition temperature window of the hot-rolled TiNiZr high-temperature shape memory alloy of the present invention is significantly broadened compared to the martensitic phase transition temperature window of the cast TiNiZr high-temperature shape memory alloy, which will help to improve the precise control of the intelligent driving material of the TiNiZr high-temperature shape memory alloy.

Description

Technical Field

[0001] The invention relates to the technical field of wide phase change of memory alloys, in particular to a hot rolling process of a TiNi-based shape memory alloy with a wide phase change temperature window. Background Art

[0002] Ti-Ni-Zr alloy has great potential application value in many high-temperature driving occasions such as drive devices in nuclear power plants, aircraft engines, current overload protection and fire alarm devices due to its advantages such as low price and adjustable martensitic phase transition temperature in a wide range. It is one of the most promising high-temperature shape memory alloys. However, similar to other Ti-Ni-based memory alloys, the martensitic phase transition temperature window (Ms(Af)-Mf(As)) of Ti-Ni-Zr high-temperature shape memory alloy is relatively narrow (maximum is about 60-70℃), which makes the actuator prepared from it less controllable. In recent years, researchers have designed and prepared "functional gradient memory alloys" by designing chemical composition gradients, geometric structure gradients and microstructure gradients in shape memory alloys to broaden the martensitic phase transition temperature window and thus achieve precise control of shape memory alloy actuators.

[0003] Despite this, the current technical means, such as diffusion annealing, magnetron sputtering, additive manufacturing, etc., are relatively cumbersome and difficult to control; therefore, it is urgent to develop new methods to broaden the martensitic phase transformation temperature window of Ti-Ni-Zr high-temperature shape memory alloy, thereby improving its precise control function of driving. Summary of the invention

[0004] The purpose of the present invention is to solve the above technical problems and to propose a hot rolling process for a TiNi-based shape memory alloy with a wide phase transition temperature window.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The hot rolling process of TiNi-based shape memory alloy with wide phase transition temperature window comprises the following steps:

[0007] S1, using sponge titanium, electrolytic nickel and crystalline zirconium as raw materials, a TiNiZr alloy with a total mass of 100 g is prepared according to a chemical composition of Ti36.5-Ni48.5-Zr15 atomic ratio;

[0008] S2, placing the prepared raw materials in the crucible in a vacuum arc melting furnace according to the principle of placing the low melting point nickel material at the bottom of the crucible and the high melting point crystalline zirconium at the top of the crucible;

[0009] S3, repeatedly melting the raw materials under the action of electric arc for 5 times to obtain a TiNiZr alloy with uniform composition;

[0010] S4, melting the uniformly smelted TiNiZr alloy again into a liquid state so that it flows into a copper mold of 10 mm×20 mm×100 mm under the action of gravity, and finally obtaining a long strip of alloy of 10 mm×20 mm×70 mm;

[0011] S5, placing the obtained long strip Ti-Ni-Zr alloy in a heating device for heat preservation and water quenching;

[0012] S6, putting the treated long strip Ti-Ni-Zr alloy into a rolling mill for hot rolling, with each rolling depth being 0.02 mm;

[0013] S7, after each hot rolling, the hot-rolled TiNiZr alloy is placed in a heating device for vacuum insulation at 900°C for 5 minutes, then taken out and hot-rolled again. This process is repeated until the plate-shaped alloy with a thickness of 10 mm is rolled to a thickness of 5 mm.

[0014] Preferably, before preparing the ingredients in S1, the sponge titanium, electrolytic nickel and crystalline zirconium raw materials are placed in anhydrous ethanol for washing to remove various impurities.

[0015] Preferably, before placing the prepared raw materials in the crucible of the vacuum arc melting furnace in S2, the furnace body is evacuated to 10 -3 Pa, and 0.5Pa of high-purity argon gas is injected into the vacuum arc melting furnace.

[0016] Preferably, in S5, a molecular pump is used to evacuate the heating device to a vacuum of 1.0×10 -3 Pa, then kept at 900°C for 6h and water quenched, and the homogenized TiNiZr alloy strips were placed in a heating device and heated to 900°C and kept for 5 minutes.

[0017] Preferably, the heating equipment includes a support frame, a vacuum tube furnace and a conveying mechanism are installed on the upper end of one end of the support frame, the conveying mechanism includes two support plates fixed on the support frame, and a plurality of conveying rollers rotate between the two support plates. The rolling mill is installed on the support frame, and the rolling mill includes a first U-shaped plate fixed on the upper ends of the two support plates, and three round rods that can rotate synchronously are penetrated on the first U-shaped plate. The bottoms of the three round rods are fixedly connected with screws, and the outer sleeve of the screw is provided with a threaded barrel threadedly connected to the screw. A second U-shaped plate is fixed to the bottom of the three threaded barrels, and a plurality of hot rolling rollers arranged in a V shape are installed on the bottom of the second U-shaped plate.

[0018] Preferably, three drive boxes are fixed on the first U-shaped plate, the three round rods respectively penetrate the relative drive boxes and are rotatably connected thereto, the three drive boxes are penetrated by drive rods that are rotatably arranged, three worms are fixed on the drive rods, worm wheels are installed on the upper ends of the three round rods, the worms are meshed with the worm wheels, a motor is installed on the drive box, and the output end of the motor is fixedly connected to the drive rod.

[0019] Preferably, it also includes a spraying mechanism for spraying anti-high-temperature oxidation coating on TiNiZr alloy, the spraying mechanism includes a material box installed at the bottom of the support frame, a high-pressure pump is installed on the material box, a delivery pipe is installed at the output end of the high-pressure pump, a U-shaped tube connected to the delivery pipe is fixed on the support plate, and a plurality of nozzles are provided on the U-shaped tube.

[0020] Preferably, the distance between the upper and lower inner walls of the U-shaped tube is greater than the diameter of the conveying roller.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The martensitic phase transformation temperature window of the hot-rolled TiNiZr high-temperature shape memory alloy of the present invention is significantly broadened compared with the martensitic phase transformation temperature window of the cast TiNiZr high-temperature shape memory alloy, which will help to improve the precise control of the TiNiZr high-temperature shape memory alloy intelligent driving material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 DSC curves of TiNiZr high temperature shape memory alloy after casting and hot rolling;

[0024] Figure 2 The metallographic diagrams of hot-rolled TiNiZr high-temperature alloy at different magnifications;

[0025] Figure 3 A schematic diagram of the structure of the heating equipment and the rolling mill in the hot rolling process of the TiNi-based shape memory alloy with a wide phase transition temperature window proposed by the present invention;

[0026] Figure 4 It is a schematic diagram of the structure of the driving box in the hot rolling process of the TiNi-based shape memory alloy with a wide phase transition temperature window proposed by the present invention;

[0027] Figure 5 A side view of a U-shaped tube in the hot rolling process of the TiNi-based shape memory alloy with a wide phase transition temperature window proposed by the present invention.

[0028] In the figure: 1 support frame, 2 vacuum tube furnace, 3 support plate, 4 conveying roller, 5 second U-shaped plate, 6 first U-shaped plate, 7 threaded barrel, 8 screw, 9 hot rolling roller, 10 worm gear, 11 round rod, 12 material box, 13 high pressure pump, 14 conveying pipe, 15 U-shaped pipe, 16 motor, 17 nozzle, 18 drive box, 19 drive rod, 20 worm. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] Reference Figure 1-Figure 5 The hot rolling process of TiNi-based shape memory alloy with a wide phase transition temperature window comprises the following steps:

[0031] S1, using sponge titanium, electrolytic nickel and crystalline zirconium as raw materials, a TiNiZr alloy with a total mass of 100 g is prepared according to a chemical composition of Ti36.5-Ni48.5-Zr15 atomic ratio;

[0032] S2, placing the prepared raw materials in the crucible in a vacuum arc melting furnace according to the principle of placing the low melting point nickel material at the bottom of the crucible and the high melting point crystalline zirconium at the top of the crucible;

[0033] S3, repeatedly melting the raw materials under the action of electric arc for 5 times to obtain a TiNiZr alloy with uniform composition;

[0034] S4, melting the uniformly smelted TiNiZr alloy again into a liquid state so that it flows into a copper mold of 10 mm×20 mm×100 mm under the action of gravity, and finally obtaining a long strip of alloy of 10 mm×20 mm×70 mm;

[0035] S5, placing the obtained long strip Ti-Ni-Zr alloy in a heating device for heat preservation and water quenching;

[0036] S6, putting the treated long strip Ti-Ni-Zr alloy into a rolling mill for hot rolling, with each rolling depth being 0.02 mm;

[0037] S7, after each hot rolling, the hot-rolled TiNiZr alloy is placed in a heating device for vacuum insulation at 900°C for 5 minutes, then taken out and hot-rolled again. This process is repeated until the plate-shaped alloy with a thickness of 10 mm is rolled to a thickness of 5 mm.

[0038] In the present invention, before preparing the ingredients in S1, the raw materials of sponge titanium, electrolytic nickel and crystalline zirconium are placed in anhydrous ethanol for washing to remove various impurities.

[0039] In the present invention, before placing the prepared raw materials in the crucible of the vacuum arc melting furnace in S2, the furnace body is evacuated to 10 -3 Pa, and 0.5Pa of high-purity argon gas is injected into the vacuum arc melting furnace.

[0040] In the present invention, the molecular pump is used in S5 to evacuate the heating device to a vacuum of 1.0×10 -3 Pa, then kept at 900°C for 6h and water quenched, and the homogenized TiNiZr alloy strips were placed in a heating device and heated to 900°C and kept for 5 minutes.

[0041] In the present invention, in order to avoid cracking of the alloy material due to the large temperature difference between the high-temperature lath-shaped TiNiZr alloy and the rolling mill roll, the temperature of the hot rolling roll is raised to 400°C. In addition, in order to prevent the lath TiNiZr alloy (because the TiNiZr alloy with a high Zr content is very easy to oxidize under high temperature conditions) from being taken out of the vacuum tube furnace and then being subjected to oxidation during the hot rolling process, the surface of the TiNiZr alloy is sprayed with a high-temperature oxidation-resistant coating. If edge cracks appear during the hot rolling process, a grinder is used to grind off the crack edges, and if the surface anti-oxidation coating is damaged during the rolling process, a high-temperature anti-oxidation coating is sprayed again.

[0042] In the present invention, Figure 1 As shown in the figure, the hot-rolled TiNiZr high-temperature shape memory alloy presents a typical dendrite morphology, and high-magnification metallographic photographs show that a high-density (Ti, Zr)2Ni second phase is distributed at the grain boundaries.

[0043] In the present invention, Figure 2 It can be seen that both the cast and hot-rolled TiNiZr high temperature shape memory alloys exhibit a one-step martensitic phase transformation during heating and cooling, which are B19 ˊ →B2 reverse martensitic transformation and B2→B19 ˊPositive martensitic transformation. By using the tangent method to obtain its martensitic phase transformation temperature, it can be found that the reverse martensitic phase transformation temperature window (Af-As) of the cast TiNiZr high temperature shape memory alloy during the heating process is about 82°C, and the positive martensitic phase transformation temperature window (Ms-Mf) during the cooling process is about 61°C; while the reverse martensitic phase transformation temperature window (Af-As) of the hot-rolled TiNiZr high temperature shape memory alloy during the heating process is about 129°C, and the positive martensitic phase transformation temperature window (Ms-Mf) during the cooling process is about 134°C. That is, the martensitic phase transformation temperature window of the hot-rolled TiNiZr high temperature shape memory alloy is significantly broadened compared to the martensitic phase transformation temperature window of the cast TiNiZr high temperature shape memory alloy, which will help to improve the precise control of TiNiZr high temperature shape memory alloy intelligent driving materials, among which, Figure 2 (a): as-cast; (b): hot-rolled.

[0044] The heating device in the present invention includes a support frame 1, a vacuum tube furnace 2 and a conveying mechanism are installed on the upper end of one end of the support frame 1, and the conveying mechanism includes two support plates 3 fixed on the support frame 1, and multiple conveying rollers 4 rotate between the two support plates 3. The multiple conveying rollers 4 are driven by chains, sprockets, etc. to achieve synchronous rotation, and TiNiZr high-temperature shape memory alloy can be conveyed between the vacuum tube furnace 2 and the rolling mill.

[0045] The rolling mill is installed on a support frame 1, and includes a first U-shaped plate 6 fixed on the upper ends of two support plates 3, three round rods 11 that can rotate synchronously are penetrated on the first U-shaped plate 6, three driving boxes 18 are fixed on the first U-shaped plate 6, the three round rods 11 respectively penetrate the relative driving boxes 18 and are rotatably connected thereto, the three driving boxes 18 are penetrated by driving rods 19 that are rotatably arranged, three worms 20 are fixed on the driving rods 19, worm wheels 10 are installed on the upper ends of the three round rods 11, the worm gears 20 are meshed with the worm wheels 10, a motor 16 is installed on the driving box 18, and the output end of the motor 16 is fixedly connected to the driving rod 19.

[0046] The bottom of the three round rods 11 is fixedly connected with a screw rod 8, the outer sleeve of the screw rod 8 is provided with a threaded tube 7 threadedly connected thereto, the bottom of the three threaded tubes 7 is fixed with a second U-shaped plate 5, and the bottom of the second U-shaped plate 5 is installed with a plurality of hot rolling rollers 9 arranged in a V shape, and the shape of the second U-shaped plate 5 matches the setting of the hot rolling rollers 9.

[0047] Specifically, the motor 16 drives the driving rod 19 to rotate, the driving rod 19 drives the worm 20 to rotate, the worm 20 drives the worm wheel 10 to rotate, so that the three worm wheels 10 rotate, and then the three round rods 11 rotate synchronously, and the round rod 11 rotates to drive the screw 8 to rotate. Since the first U-shaped plate 6 cannot rotate, the rotation of the screw 8 can realize the movement of the threaded barrel 7 and the second U-shaped plate 5, and the distance between the hot rolling roller 9 and the conveying roller 4 can be adjusted to hot-roll the alloy; since the bottom of the second U-shaped plate 5 is equipped with a plurality of hot rolling rollers 9 arranged in a V shape, the hot rolling distance of the alloy can be gradually increased through the hot rolling roller 9, which is more conducive to the hot rolling thinning treatment of the alloy.

[0048] The invention also includes a spraying mechanism for spraying high-temperature oxidation resistant coating on TiNiZr alloy, the spraying mechanism includes a material box 12 installed at the bottom of the support frame 1, a high-pressure pump 13 is installed on the material box 12, the liquid inlet end of the high-pressure pump 13 is connected to the material box 12 through a short pipe, a delivery pipe 14 is installed at the output end of the high-pressure pump 13, a U-shaped tube 15 connected to the delivery pipe 14 is fixed on the support plate 3, a plurality of nozzles 17 are provided on the U-shaped tube 15, the high-pressure pump 13 can work to deliver the oxidation resistant coating to the U-shaped tube 15 through the delivery pipe 14, and finally spray it out through the nozzle 17, the distance between the upper and lower inner walls of the U-shaped tube 15 is greater than the diameter of the conveying roller 4, so that when the alloy passes between the U-shaped tubes 15, an oxidation layer can be sprayed on the alloy.

[0049] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. Hot rolling process of TiNi-based shape memory alloy with wide phase transition temperature window, characterized in that: The following steps are involved: S1, using sponge titanium, electrolytic nickel and crystalline zirconium as raw materials, a TiNiZr alloy with a total mass of 100 g is prepared according to a chemical composition of Ti36.5-Ni48.5-Zr15 atomic ratio; S2, placing the prepared raw materials in the crucible in a vacuum arc melting furnace according to the principle of placing the low melting point nickel material at the bottom of the crucible and the high melting point crystalline zirconium at the top of the crucible; S3, repeatedly melting the raw materials under the action of electric arc for 5 times to obtain a TiNiZr alloy with uniform composition; S4, melting the uniformly smelted TiNiZr alloy again into a liquid state so that it flows into a copper mold of 10 mm×20 mm×100 mm under the action of gravity, and finally obtaining a long strip of alloy of 10 mm×20 mm×70 mm; S5, placing the obtained long strip Ti-Ni-Zr alloy in a heating device for heat preservation and water quenching; S6, putting the treated long strip Ti-Ni-Zr alloy into a rolling mill for hot rolling, with each rolling depth being 0.02 mm; S7, after each hot rolling, the hot-rolled TiNiZr alloy is placed in a heating device for vacuum insulation at 900°C for 5 minutes, and then taken out for hot rolling again, and this process is repeated until the plate-shaped alloy with a thickness of 10 mm is rolled to a thickness of 5 mm; In S5, a molecular pump is used to evacuate the heating device to 1.0×10-3Pa, and then the heating device is kept at 900°C for 6 hours and water quenched. The homogenized TiNiZr alloy strip is placed in the heating device again, heated to 900°C and kept at this temperature for 5 minutes. The heating equipment comprises a support frame, a vacuum tube furnace and a conveying mechanism are installed on the upper end of one end of the support frame, the conveying mechanism comprises two support plates fixed on the support frame, a plurality of conveying rollers are rotated between the two support plates, a rolling mill is installed on the support frame, the rolling mill comprises a first U-shaped plate fixed on the upper ends of the two support plates, three round rods that can rotate synchronously are penetrated on the first U-shaped plate, a screw is fixedly connected to the bottom of the three round rods, a threaded barrel threadedly connected to the screw is sleeved on the outside of the screw, a second U-shaped plate is fixed to the bottom of the three threaded barrels, and a plurality of hot rolling rollers arranged in a V shape are installed on the bottom of the second U-shaped plate; Three drive boxes are fixed on the first U-shaped plate, three round rods penetrate the opposite drive boxes respectively and are rotatably connected thereto, the three drive boxes are penetrated by drive rods that are rotatably arranged, three worms are fixed on the drive rods, worm wheels are installed on the upper ends of the three round rods, the worms mesh with the worm wheels, a motor is installed on the drive box, and the output end of the motor is fixedly connected to the drive rod; The invention also includes a spraying mechanism for spraying high-temperature oxidation resistant coating on TiNiZr alloy, the spraying mechanism includes a material box installed at the bottom of the support frame, a high-pressure pump is installed on the material box, a delivery pipe is installed at the output end of the high-pressure pump, a U-shaped pipe connected to the delivery pipe is fixed on the support plate, and a plurality of nozzles are arranged on the U-shaped pipe; The distance between the upper and lower inner walls of the U-shaped tube is greater than the diameter of the conveying roller.

2. The hot rolling process for a TiNi-based shape memory alloy with a wide phase transition temperature window according to claim 1, characterized in that: Before mixing in S1, the raw materials of sponge titanium, electrolytic nickel and crystalline zirconium are washed in anhydrous ethanol to remove various impurities.

3. The hot rolling process for a TiNi-based shape memory alloy with a wide phase transition temperature window according to claim 1, characterized in that: In S2, before placing the prepared raw materials into the crucible of the vacuum arc melting furnace, the furnace body is evacuated to 10-3Pa, and 0.5Pa of high-purity argon gas is injected into the vacuum arc melting furnace.

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