阅读说明：本技术 一种NiTi-Al基合金的制备方法 (Preparation method of NiTi-Al-based alloy ) 是由 周磊 汪煜 邹金文 于 2021-09-30 设计创作，主要内容包括：本发明是一种NiTi-Al基合金的制备方法,该方法使用真空非自耗电弧炉制备NiTi-Al基铸态合金,从铸态合金中切取棒料,并将棒料表面的氧化皮打磨干净后,放入内壁有Y-(2)O-(3)烧结涂层的氧化铝陶瓷管中。将装有NiTi-Al基铸态合金棒料的陶瓷管装入液态金属冷却的Bridgman型定向凝固炉中,抽真空至3～5×10-3Pa后,充入高纯氩气使真空度达到0.05MPa,加热至1450℃～1650℃并保温20～40min,以0.05～0.2mm/min的速率抽拉后淬入液态金属中,最后进行固溶和时效处理,制备出NiTi-Al基合金。以上述工艺制备出的NiTi-Al基合金,其室温塑性和高温强度都得到了提升。(The invention relates to a preparation method of a NiTi-Al-based alloy, which uses a vacuum non-consumable arc furnace to prepare the NiTi-Al-based as-cast alloy, cuts a bar stock from the as-cast alloy, polishes an oxide skin on the surface of the bar stock, and puts the bar stock into a furnace with an inner wall provided with Y 2 O 3 Sintering the coated alumina ceramic tube. Putting a ceramic tube filled with a NiTi-Al-based as-cast alloy bar material into a Bridgman type directional solidification furnace cooled by liquid metal, vacuumizing to 3-5 multiplied by 10 < -3 > Pa, filling high-purity argon to ensure that the vacuum degree reaches 0.05MPa, heating to 1450-1650 ℃, preserving heat for 20-40 min, drawing at the speed of 0.05-0.2 mm/min, and quenchingAnd (3) adding the alloy into liquid metal, and finally performing solid solution and aging treatment to prepare the NiTi-Al-based alloy. The room temperature plasticity and the high temperature strength of the NiTi-Al-based alloy prepared by the process are improved.)

1. A preparation method of NiTi-Al-based alloy is characterized by comprising the following steps: the preparation method comprises the following steps:

step one, preparing a NiTi-Al-based as-cast alloy by using a vacuum non-consumable electric arc furnace;

step two, cutting a bar stock from the as-cast alloy prepared in the step one, and putting the bar stock into the die with Y on the inner wall₂O₃Sintering the coated alumina ceramic tube;

step three, putting the alumina ceramic tube filled with the NiTi-Al-based as-cast alloy bar material into a Bridgman type directional solidification furnace cooled by liquid metal, and vacuumizing to 3-5 multiplied by 10^-3And after Pa, filling high-purity argon to ensure that the vacuum degree reaches 0.05MPa, heating to 1450-1650 ℃, preserving the heat for 20-40 min, drawing at the speed of 0.05-0.2 mm/min, quenching into liquid metal, and finally performing solid solution and aging treatment to prepare the NiTi-Al-based alloy.

2. The method for producing an NiTi-Al-based alloy according to claim 1, characterized in that: and step two, cutting the bar stock from the as-cast alloy by adopting a wire cutting method.

3. The method for producing an NiTi-Al-based alloy according to claim 1, characterized in that: and step two, after the bar stock is cut, polishing the oxide skin on the surface of the bar stock.

4. The method for producing an NiTi-Al-based alloy according to claim 1, characterized in that: the liquid metal quenched In the third step is Ga-In-Sn alloy.

5. The method for producing an NiTi-Al-based alloy according to claim 1, characterized in that: the NiTi-Al-based as-cast alloy in the step one is Ni-43Ti-7Al as-cast alloy.

6. The method for producing an NiTi-Al-based alloy according to claim 5, characterized in that: the solid solution and aging treatment in the third step is solid solution and secondary aging treatment, and the solid solution treatment system is 1170 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 800 ℃ after 700 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

7. The method for producing an NiTi-Al-based alloy according to claim 1, characterized in that: the NiTi-Al-based as-cast alloy in the step one is Ni-41Ti-7Al-1Cr-1Nb as-cast alloy.

8. The method for producing an NiTi-Al-based alloy according to claim 7, characterized in that: the solid solution and aging treatment in the third step is solid solution and secondary aging treatment, and the solid solution treatment system is 1210 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 830 ℃ after 730 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

Technical Field

The invention relates to a preparation method of a NiTi-Al-based alloy, belonging to the technical field of preparation of light high-strength NiTi-Al intermetallic compounds.

Background

Since 1963 the American seaSince the experimental research of W.J. Buehler doctor research group in military weapons laboratory shows that NiTi alloy with near equal atomic ratio has good shape memory effect, through decades of research, NiTi-based alloy as a shape memory material has excellent mechanical property, corrosion resistance and biocompatibility, and is widely applied to the fields of aviation, aerospace, energy, medical treatment, building and the like. Meanwhile, as an intermetallic compound, it has attracted the attention of researchers because of its good plasticity at room temperature and high strength exhibited after a certain alloying. In 1997, NiTi-Al based ternary alloy based on NiTi was first reported by Y.Koizumi et Al in "NiTi-base intermetallic systems bonded by Al catalysis" Materials Science and Engineering A,1997,223(1-2):36-41, and the results show that adding Al element to NiTi alloy and forming a strengthening phase-Ni-on NiTi matrix phase after certain heat treatment₂TiAl phase. Ni₂The TiAl phase has a high melting point (1513 ℃), and the yield strength of the TiAl phase is 2-3 times higher than that of NiAl and TiAl at the temperature of more than 750 ℃, and in addition, Ni₂The creep resistance of TiAl is higher than that of NiAl with a B2 structure with high symmetry, the room temperature strength of the TiAl exceeds that of Ni-based superalloy Rene95, and the strength at 1000 ℃ is equivalent to that of the high-temperature alloy used in the middle temperature range at present; .

However, in the NiTi-Al based alloy, Ni is added to the strengthening phase₂Besides the TiAl phase, there is another precipitated phase-Ti₂Ni phase, and the volume fraction is generally more than 2% (atomic percent, the same applies below), such as in Ni-43Ti-7Al alloy, Ti₂The volume fraction of the Ni phase was about 2.5%. Kollerov found in the study of "Structural aspects of the manufacturing of semiconductor products from titanium nitride-based alloys" Russian metals (Metal),2007 (5): 408-414: ti₂The microhardness of the Ni phase reaches 10Gpa, which is 4-5 times of that of the B2 phase, so that the strength of the NiTi-Al-based alloy can be obviously improved. However, the results of the study by Mentz et al in "Improvement of Mechanical Properties of Powder metallic NiTi Shape Memory" Advanced Engineering Materials,2006,8(4): 247-: ti₂Ni phase is a typical brittle phaseOften large in size (on the order of microns), in the form of strips or droplets, which tend to initiate cracks when the alloy breaks, thus adversely affecting the room temperature plasticity of the alloy. At the same time, since Ti₂The Ni phase has a melting point of only about 984 deg.C, and Ti is present at high temperature (e.g. 800 deg.C)₂The Ni strengthening phase has begun to soften, essentially in the dynamic recovery and recrystallization stages, and even the addition of some high melting refractory elements does not significantly increase its high temperature strength.

Thus how to eliminate or reduce Ti₂Ni phase of elevated NiTi-Ni₂The key of the mechanical property of the TiAl two-phase NiTi-Al-based alloy is. Yen et al, however, found in "Shape memory characteristics and mechanical properties of high-sensitivity powder metal with a post-orientation heat arrangement" Materials Science and Engineering A,2011,528(15): 5296-: even if it exceeds Ti₂Annealing at a temperature (1004 ℃ C.) corresponding to the melting point (984 ℃ C.) of the Ni phase does not eliminate Ti₂A Ni phase. Panlivin et al reported in "directionally solidified ultrahigh strength NiTi-based authigenic composites", 2013, 1 (30): 141-146, the following research shows that: after the Ni-43Ti-4A-2Nb-2Hf alloy is subjected to vacuum homogenization heat treatment at 950 ℃, Ti is not eliminated₂Ni phase and also Ti₂The volume fraction of the Ni phase tends to increase with the time of the homogenization heat treatment. It can be seen that Ti₂The Ni phase, once formed in the NiTi-Al based alloy, is difficult to be eliminated by the subsequent heat treatment process. Furthermore, Xiaooyun Song et Al, in "microscopic and mechanical properties of Nb-and Mo-modified NiTi-Al-based intermetallic processing by y isothermal shaping" Materials Science and Engineering A,2014,594(15):229 234 found that even when Ti of large size is forged by isothermal forging₂Ni phase is broken, but Ti₂The Ni phase is still distributed at the grain boundary; although the elongation after room temperature fracture is improved compared with the cast alloy, the elongation is still lower but is less than 2 percent, thereby limiting the wide application of the NiTi-Al based alloy.

Disclosure of Invention

The invention provides a preparation method of a NiTi-Al-based alloy aiming at the prior art, and aims to solve the problems of low room-temperature plasticity and insufficient high-temperature strength of the NiTi-Al-based alloy in the conventional preparation process, and the obtained NiTi-Al-based alloy has excellent room-temperature plasticity and high-temperature strength performance.

To implement the above object, the technical solution of the present invention is as follows:

the preparation method of the NiTi-Al-based alloy comprises the following steps:

step one, preparing a NiTi-Al-based as-cast alloy by using a vacuum non-consumable electric arc furnace;

step two, cutting a bar stock from the as-cast alloy prepared in the step one, and putting the bar stock into the die with Y on the inner wall₂O₃Sintering the coated alumina ceramic tube;

step three, putting the alumina ceramic tube filled with the NiTi-Al-based as-cast alloy bar material into a Bridgman type directional solidification furnace cooled by liquid metal, and vacuumizing to 3-5 multiplied by 10^-3And after Pa, filling high-purity argon to ensure that the vacuum degree reaches 0.05MPa, heating to 1450-1650 ℃, preserving the heat for 20-40 min, drawing at the speed of 0.05-0.2 mm/min, quenching into liquid metal, and finally performing solid solution and aging treatment to prepare the NiTi-Al-based alloy.

In the implementation, in the second step, a bar stock is cut from the as-cast alloy by adopting a wire cutting method.

In the implementation, in the second step, after the bar stock is cut, the oxide skin on the surface of the bar stock is polished clean.

In the implementation, the liquid metal quenched In the third step is Ga-In-Sn alloy.

In practice, the NiTi-Al based as-cast alloy used in step one is a Ni-43Ti-7Al as-cast alloy. Further, the solid solution and aging treatment in the third step is solid solution and secondary aging treatment, wherein the solid solution treatment system is 1170 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 800 ℃ after 700 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

In practice, the NiTi-Al based as-cast alloy used in step one is an Ni-41Ti-7Al-1Cr-1Nb as-cast alloy. Further, the solid solution and aging treatment in the third step is solid solution and secondary aging treatment, wherein the solid solution treatment system is 1210 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 830 ℃ after 730 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

Compared with the traditional NiTi-Al-based as-cast or powder alloy, the NiTi-Al-based directionally solidified alloy prepared by the directional solidification preparation process has the advantages that not only is Ti contained in the NiTi-Al-based directionally solidified alloy₂The Ni phase has small size, is dispersed and distributed at the crystal boundary, and has greatly reduced volume fraction. In addition, since Ti₂The volume fraction of Ni phase is reduced, the Ni/Ti ratio and Al content on the alloy matrix are adjusted, and Ni is subjected to solid solution and aging treatment₂The precipitation of TiAl strengthening phase is more sufficient, thereby obviously improving the room temperature plasticity and the high temperature strength of the alloy.

The research shows that: ti₂One complete unit cell of the Ni phase is formed by stacking 8 distorted icosahedrons, and the presence of oxygen in the alloy melt can promote the occurrence of large amount of icosahedron clusters in Ti₂The Ni phase can be used as Ti when forming nucleus₂The embryo of Ni phase crystal nucleus can reduce its nucleation supercooling degree and promote Ti₂Nucleation of Ni phase, even in the NiTi single-phase region in the Ni-Ti binary phase diagram, Ti₂Ni phase also remains, and Ti₂The Ni phase, once formed, is difficult to remove by the subsequent heat treatment process.

The directional solidification process of the invention selects the heating temperature of 1450-1650 ℃, which can fully dissolve the NiTi-Al-based alloy and can not cause higher nucleation supercooling degree due to overhigh heating temperature, thereby promoting Ti₂Nucleation of the Ni phase.

During the directional solidification process, because the oxygen content is hardly dissolved in the matrix of the NiTi phase, the oxygen element is continuously discharged outwards during the nucleation growth of the NiTi phase. And the oxygen element is lighter, so that the density of a liquid phase between cells is lower, and the melt with lower density continuously floats to a solid-liquid interface. According to the directional solidification process, the drawing rate of 0.05-0.2 mm/min is selected, so that the oxygen element can be fully floated, and the oxygen element content (from an as-cast state) in a directional solidification steady-state stage is reducedMore than 400ppm of gold is reduced to less than 80 ppm), thereby greatly reducing Ti₂The volume fraction of the Ni phase (reduced from 2.5% or more to 0.5% or less of the as-cast alloy); but also inhibit NiTi + Ti₂The formation tendency of the Ni phase irregular eutectic structure leads the Ni phase irregular eutectic structure to be distributed at the grain boundary in fine points, further reducing Ti₂Harmfulness of the Ni phase.

The NiTi-Al-based alloy prepared by the directional solidification process is prepared by inhibiting Ti₂The growth of Ni phase greatly reduces Ti₂The volume fraction of the Ni phase adjusts the Ni/Ti ratio and Al content on the alloy matrix. After subsequent solution and aging treatment, Ni₂TiAl phase is fully precipitated, and the room temperature plasticity and the high temperature strength of the alloy are improved. The elongation after fracture at room temperature is more than 4 percent; the yield strength at 800 ℃ is more than 400 MPa.

The invention has the beneficial effects that:

(1) the NiTi-Al-based alloy prepared by the directional solidification process not only enables Ti to be used₂The volume fraction of Ni phase is greatly reduced (from more than 2.5 percent of as-cast alloy to less than 0.5 percent), the Ni/Ti ratio and Al content on the alloy matrix can be adjusted, and Ni is subjected to subsequent solid solution and aging treatment₂The precipitation of TiAl phase is more sufficient.

(2) The NiTi-Al-based directional solidification alloy prepared by the directional solidification process has the elongation rate of more than 4% after fracture at room temperature and the yield strength of more than 400MPa at 800 ℃.

Drawings

FIG. 1 is a photograph of the microstructure of an as-cast alloy in example 1 of the present invention.

FIG. 2 is a photograph of the microstructure of a cross section of a directionally solidified alloy of example 1 of the present invention.

FIG. 3 is a photograph of the microstructure of the as-cast alloy in example 2 of the present invention.

FIG. 4 is a photograph of the microstructure of a cross section of a directionally solidified alloy of example 2 of the present invention.

FIG. 5 shows fine Ti in example 2 of the present invention₂Transmission electron micrograph of Ni phase.

FIG. 6 is fine Ti in example 2 of the present invention₂Ni phaseAnd (4) performing electron diffraction spot on the axial selected region.

Detailed Description

The technical scheme of the invention is further detailed in the following by combining the drawings and the embodiment:

example 1

The method for preparing the NiTi-Al-based alloy comprises the following steps:

step one, preparing Ni-43Ti-7Al as-cast alloy by using a vacuum non-consumable electric arc furnace, wherein a microscopic structure photograph is shown in figure 1, the content of oxygen element is 415ppm, and Ti element is₂The volume fraction of the Ni phase was 2.5%;

step two, cutting a bar stock from the Ni-43Ti-7Al as-cast alloy, polishing an oxide skin on the surface of the bar stock, and putting the bar stock into a die with Y on the inner wall₂O₃Sintering the coated alumina ceramic tube;

step three, putting the ceramic tube filled with the Ni-43Ti-7Al as-cast alloy bar into a Bridgman type directional solidification furnace cooled by liquid metal, vacuumizing to 3-5 multiplied by 10 < -3 > Pa, filling high-purity argon to ensure that the vacuum degree reaches 0.05MPa, heating to 1550 ℃, preserving heat for 20min, drawing at the speed of 0.12mm/min, and quenching into the liquid metal (Ga-In-Sn alloy);

step four, carrying out solid solution and secondary aging treatment on the Ni-43Ti-7Al directional solidification alloy, wherein the solid solution treatment system is 1170 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 800 ℃ after 700 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

Compared with Ni-43Ti-7Al as-cast alloy, the Ni-43Ti-7Al directionally solidified alloy prepared by the process has the oxygen content of only 70ppm and Ti in the alloy₂The Ni phase is fine in size and has a volume fraction of only 0.3%. As shown in fig. 2.

The Ni-43Ti-7 Al-based alloy prepared by the process has the following room temperature properties: tensile strength 1956MPa, yield strength 1634MPa and elongation after fracture 4.4%; performance at 800 degrees: the tensile strength is 505MPa, the yield strength is 413MPa, and the elongation after fracture is 25.6%.

Example 2

The method for preparing the NiTi-Al-based alloy comprises the following steps:

step one, preparing Ni-41Ti-7Al-1Cr-1Nb as-cast alloy by using a vacuum non-consumable arc furnace, wherein a microscopic structure photograph is shown in figure 3, the oxygen content is 478ppm, and the volume fraction of a Ti2Ni phase is 3.0%;

secondly, cutting a bar stock from the Ni-41Ti-7Al-1Cr-1Nb as-cast alloy, polishing the oxide skin on the surface of the bar stock, and putting the bar stock into an alumina ceramic tube with an Y2O3 sintered coating on the inner wall;

step three, putting a ceramic tube filled with Ni-41Ti-7Al-1Cr-1Nb as-cast alloy bar stock into a Bridgman type directional solidification furnace cooled by liquid metal, vacuumizing to 3-5 x 10 < -3 > Pa, filling high-purity argon to ensure that the vacuum degree reaches 0.05MPa, heating to 1650 ℃, improving the directional solidification heating temperature In the embodiment compared with the embodiment 1 due to the addition of Cr and Nb refractory elements, preserving the heat for 20min, drawing at the speed of 0.06mm/min, quenching into the liquid metal (Ga-In-Sn alloy), increasing the viscosity of the alloy melt due to the addition of Cr and Nb refractory elements, and reducing the drawing speed In the embodiment compared with the embodiment 1;

step four, carrying out solid solution and secondary aging treatment on the Ni-41Ti-7Al-1Cr-1Nb powder alloy, wherein the solid solution treatment system is 1210 ℃/12 h/air cooling; the first-stage aging system is that the temperature is increased to 830 ℃ after 730 ℃/15h for second-stage aging, and the temperature is kept for 5h, and then the product is discharged from the furnace and cooled in air.

The Ni-41Ti-7Al-1Cr-1 Nb-based alloy prepared by the process has the oxygen content of only 78ppm, the Ti2Ni phase is fine in size, and the volume fraction is only 0.4%. As shown in fig. 4,5, 6.

The Ni-41Ti-7Al-1Cr-1 Nb-based alloy has the following room temperature properties: the tensile strength is 2031MPa, the yield strength is 1789MPa, and the elongation after fracture is 4.1 percent; performance at 800 degrees: tensile strength 524MPa, yield strength 427MPa, elongation after fracture 27.3%.