CN101003868A - Method for preparing shape memory nickel titanium alloy with gradient porosity - Google Patents
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Abstract
This invention discloses a method for preparing shape-memory Ni-Ti alloy with gradient porosity. The method comprises: (1) mixing pure Ti powder and pure Ni powder uniformly; (2) mixing 0-40 wt. % of NH4HCO3 powder (pore-making agent) with the mixed powder; (3) pressing the mixture to obtain green body with radial or axial gradient initial porosity of 30-50%; (4) heating the green body to decompose NH4HCO3 pore-making agent; (5) performing multi-stage sintering to obtain shape-memory Ni-Ti alloy with gradient porosity. The method has simple process. The pore-making agent can be easily removed without the need for high temperatures. The product has high and controllable porosity, and good linear super-elastic deformation ability.
Description
Technical Field
The invention relates to the field of porous nickel-titanium shape memory alloys, in particular to a preparation method of a porous nickel-titanium shape memory alloy with gradient porosity and various pore characteristics.
Background
In modern life, injuries to hard tissues of the human body (femur, teeth, joints, vertebrae, etc.) are a common problem for manual workers, sports practitioners, various accidents, and the middle aged and elderly people. At present, the main treatment means is to implant artificial biomedical materials to replace or repair damaged human tissues, thereby achieving the purposes of treatment and function recovery. Therefore, the development of biomedical materials suitable for implantation into the human body is of great significance.
The compact nickel titanium shape memory alloy has good biocompatibility. The shape memory effect and the super elasticity of the material make the material have unique advantages as a biomedical material. At present, the compact nickel-titanium shape memory alloy has been used as a biomedical material in the medical fields of dentistry, orthopedics, cardiovascular system, urinary system and the like. However, the mechanical properties, including elastic modulus, of the compact nickel-titanium shape memory alloy (and other medical titanium alloys, stainless steel and the like) are greatly higher than the corresponding indexes of human hard tissues, and stress shielding effect is easily generated due to stress concentration acting on the implant material when a human body bears the load, so that the problems of osteoporosis, bone necrosis and the like in the adjacent area of theimplant material can be caused, and great pain is caused to a patient; in addition, the rigid and compact surface of the compact nickel-titanium shape memory alloy is not beneficial to the biological integration of human tissues with the compact nickel-titanium shape memory alloy, and can also be a problem hidden danger in the long term. In response to these problems, porous nitinol has been developed and has recently become a focus of research in this field.
The unique porous structure of the porous nickel-titanium shape memory alloy makes the mechanical property and the elastic modulus thereof closer to those of human tissues; in addition, the mechanical property and the phase change characteristic of the material can be changed by adjusting the porosity and the pore characteristics of the material, so that the use requirements of the material under different conditions are met. In addition, researches show that human tissues can grow into the porous nickel-titanium shape memory alloy with the surface pore size of 100-600 microns, so that the bonding strength between the human tissues and the implant material can be improved, and the biomechanical property of the human tissues is further improved. However, many problems still need to be solved in preparation of the porous nickel-titanium shape memory alloy suitable for biomedicine; in summary, these problems are mainly focused on controllability of the properties of the prepared samples and stability of the process.
The method for preparing the porous metal and the alloy mainly comprises the following steps: melt casting, metal deposition and powder metallurgy. Although the melt casting method has been successful in producing porous aluminum, lead, zinc, copper and alloys, the NiTi alloy has a high melting point (1310 ℃) and a relatively high density (6.45 g/cm)3) It is difficult to adopt such a production process. In addition, the melt casting process is difficult to prepare the porous nickel-titanium alloy with ideal structure and performance, and one important reason is that the higher reactivity of the NiTi alloy melt often causes segregation defects to be generated, so that the functionality and the mechanical property of the porous NiTi alloy are influenced. Thus, the currently more viable process is powder metallurgy. Namely, the unit Ni, Ti metal powder or NiTi prealloy powder is used for powder metallurgy sintering, wherein the common method is as follows: conventional Sintering (CS), Self-propagating High-temperature Synthesis (SHS), Hot Isostatic Pressing (HIP), and flash plasma Sintering (SPS).
The conventional sintering process is to mix, press and form Ti and Ni powder and then sinter the mixture for a long time at high temperature; the method has the advantages of simple process, easy control of reaction process, high homogenization degree of alloy components and high yield; the disadvantages are long sintering time, low porosity of the porous material (<45%), small pore size and irregular pore shape. The self-propagating high-temperature synthesis process is actually called combustion synthesis, and can be divided into a layer combustion mode and a thermal explosion mode according to a combustion mode. The former is to ignite the blank by external energy at a certain temperature to make the reaction self-spread and propagate from one end to the other end; the latter is to heat the sample to a high temperature by controlling the heating rate, so that the billet spontaneously reacts from outside to inside. The stratified combustion mode can generally obtain three-dimensionally connected porous NiTi alloy, and the porosity can be adjusted in a larger range (30-70%) by changing the preheating temperature. The method has the main advantages of simple process, short preparation time and energy conservation; but the obvious disadvantages are that the reaction process is difficultto control, the pores have a bias, the material is brittle (this disadvantage is fatal to the safety and reliability of biomedical material applications), and the material composition and properties are susceptible to the powder specification, green state and process parameters and are not easy to homogenize. The thermal explosion mode is mainly used for preparing compact NiTi shape memory alloy, and products equivalent to or even better than the products obtained by the conventional fusion casting method can be obtained. However, recent studies have shown that higher porosity porous NiTi alloys can be prepared if the heating rate is controlled within reasonable thresholds and assisted by adjustments to cold pressure and preheat time. The method has the advantages of thorough metallurgical reaction, less impurity phase of the product and capability of improving the performance of the alloy; but the requirements on the thermal explosion process and the sintering subsequent heat treatment process are strict, so that the method is not applied much. The porous TiNi shape memory alloy prepared by the hot isostatic pressing sintering method has the best comprehensive performance at present, but still has a certain difference with the requirements of biomedical application; for example, the superelasticity of porous TiNi shape memory alloys is of great importance in medical applications, but none of the reported results is satisfactory, and there is a gap with the superelastic capacity of dense TiNi shape memory alloys; when the mechanical property of the material meets the requirement, the shape of the micropore structure is not ideal, the pore size and the distribution characteristics are difficult to control accurately, and the spatial structure of the micropores is different from the real bone structure; in addition, the stability of the preparation process is not good.
Overall, the prior art suffers from three disadvantages: firstly, the porosity of the prepared sample is not high in controllability; secondly, the porous nickel-titanium alloy with large-size pore structure, uniform pore distribution and high porosity is difficult to obtain; thirdly, the mechanical property and the structural characteristic of the porous nickel-titanium alloy component with single pore characteristics are greatly different from those of the hard tissue of the human body. Specifically, the porosity of the sample obtained by the conventional powder sintering method and HIP method is small, and the pore characteristics are difficult to control; the self-propagating method has high porosity, but the reaction is severe, and the pores have serious anisotropy.
Disclosure of Invention
The invention aims to provide a preparation method of a porous nickel-titanium shape memory alloy with controllable pore characteristics and porosity, uniform pore distribution and high porosity aiming at three defects of the porous nickel-titanium alloy prepared by a powder metallurgy method.
The purpose of the invention is realized by the following technical scheme.
A method for preparing nickel-titanium shape memory alloy with gradient porosity is characterized by comprising the following steps and process conditions:
(1) according to the atomic ratio of 50-51%: 49-50%, and uniformly mixing pure titanium powder and pure nickel powder;
(2) 0-40% of pore-forming agent ammonium bicarbonate powder and the steps
(1) Fully mixing the obtained mixture;
(3) pressing the powder obtained in the step (2) into a sample blank with the original porosity of 30-50% and gradient porosity distribution at room temperature according to radial step lamination and axial step lamination;
(4) placing the pressed blank into a heating furnace under the protection of inert gas for preheating for 1-2 hours, and controlling the temperature to 200-300 ℃ to decompose and remove the pore-forming agent ammonium bicarbonate;
(5) heating up according to a step heating mode, wherein the step heating temperature ranges are respectively as follows: the temperature of 610-640 ℃ is a primary gradient temperature range; 770-810 ℃ is a secondary gradient temperature range; the temperature of 850-1050 ℃ is a three-level gradient temperature range; heating the blank to a first-stage gradient temperature range at a speed of 60-70 ℃ per minute, preserving heat for 3-5 minutes, then heating to a second-stage gradient temperature range at a speed of 20 ℃ per minute, and preserving heat for 3-5 minutes; and finally, heating to the third-stage gradient temperature range and preserving heat for 3-4 hours to obtain the nickel-titanium shape memory alloy with gradient porosity.
And (3) preparing the powder obtained in the step (2) into a blank at room temperature according to the following three methods: (a) raw material powder with different pore-forming agent contents (0-40 wt.%) is distributed in a gradient manner in the axial direction; (b) the raw material powder with different pore-forming agent contents (0-wt.40%) is distributed in a gradient way in the radial direction; (c) the powder with the same pore-forming agent content is respectively prepared into blanks. Wherein steps (a) and (b) are used to prepare gradient porosity samples, step (c) is used to prepare uniform porosity samples, and the porosity characteristics and porosity are determined by the morphology and content of the pore-forming agent. Finally pressing the materials into blanks with the original porosity of 30-50% by using a mould.
The method can obtain the porous nickel-titanium shape memory alloy with gradient porosity distribution and different porosity characteristics, the porosity range is 30-75%, the average size of pores can be changed between 50-500/mum according to different pretreatment processes, the opening degree can reach 90%, and the phase change characteristics and the temperature can be adjusted according to specific use requirements so as to meet the requirements of repairing and implanting hard tissues of a human body under different conditions.
The principle of the invention is as follows: first, the pores are prefabricated in the cold pressed blank by using solid pore-forming agent particles, and then the pores are prefabricated by using Completely removing the pore-forming material by decomposition reaction; and then the exothermic reaction of Ni + Ti → NiTi is combined to prepare the porous nickel-titanium alloy with good pore controllability. Products after the pore-forming agent is decomposed belong to gases which have little influence on the NiTi final product, and are removed before the nickel-titanium metallurgical reaction; the influence of the decomposition product of the pore-forming agent on the product performance is proved to be small, only the generation of trace TiN (the surface of the nickel-titanium alloy is modified to reduce the dissolution of Ni ions, and a TiN layer is also generated on the surface of the nickel-titanium alloy by methods such as injection and the like) is found on the product surface, which is derived from the action of trace ammonia gas and NiTi remained at high temperature, and experiments prove that the related performance of the material is not changed.
Compared with the prior art, the invention has the following advantages:
1) the product prepared by the invention has high porosity and good porosity controllability. According to the method, the porosity can be controlled by controlling the adding amount of the pore-forming agent (which can be decomposed at low temperature), and finally, the porous nickel-titanium shape memory alloy sample with the porosity of 75% can be obtained.
2) Products with different pore characteristics and gradient porosity characteristics can be obtained. The method can adjust the pore characteristics by changing the particle form of the pore-forming agent powder, and can also prepare the porous nickel-titanium shape memory alloy with gradient pore characteristics by controlling the distribution of the pore-forming agent in the blank.
3) The process adaptability is good. The method can prepare the ideal porous nickel-titanium shape memory alloy by adopting a hot isostatic pressing sintering mode or a common powder sintering mode and a step heating reaction mode, thereby overcoming the problems of insufficient sample porosity and insufficient pore size when a hot isostatic pressing sintering or powder sintering process is singly adopted.
4) The process is simple. The method is beneficial to compact forming, the process of removing the pore-forming agent is simple and convenient, and a particularly high reaction temperature is not needed.
Drawings
FIG. 1 is a scanning electron microscope image of the porous shape memory nickel titanium alloy prepared in example 1 and having gradient distribution of axial pores.
FIG. 2-1 is a scanning electron microscope image of the porosity of the rod-shaped porous Ni-Ti shape memory alloy sample of example 2 distributed in two layers along the radial direction.
2-2 are graphs showing good superelasticity when stressed for the round rod type porous Nitinol samples with radially graded porosity of example 2.
FIG. 3-1 is a gold phase diagram of a cross section of the macroporous character sample prepared in example 3.
FIG. 3-2 is an X-ray diffraction pattern of each sample prepared in examples 1, 3 and 4.
FIGS. 3-3 are Ti prepared in example 349Ni51Differential scanning calorimetry of large pore characterization samples.
FIG. 4-1 is a gold phase diagram of a cross section of a small pore feature sample prepared in example 4.
FIG. 4-2 is a photograph of example 4 preparationTi of (A)49.2Ni51.8Differential scanning calorimetry of small pore-characterized samples.
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings and examples, but the scope of the invention as claimed is not limited to the scope of the examples shown.
Example 1
Preparing a rod-shaped porous nickel-titanium shape memory alloy with axial pore gradient distribution:
pure titanium powder (average particle size of 70 microns) and pure nickel powder (average particle size of 61 microns) are fully mixed for 20 hours according to the titanium and nickel ingredients with equal atomic ratio to obtain raw material powder A. Then, the pore-forming agent ammonium hydrogen carbonate (NH) is added according to the proportion of 10 wt.%, 20 wt.% and 30 wt%4HCO3The average particle size is 250 mu m) is added into the A to prepare three powders of powder B, powder C and powder D. The powder B, the powder C and the powder D were mixed for 3 hours, and then left alone with the powder A. The powder A → the powder B → the powder C → the powder D were laminated in four layers in the order of 16 mm in diameter and 24 mm in length by using a dieRice and a blank with porosity of 40 percent are put into an electric heating tube furnace and heated to 200 ℃ under the protection of argon with purity higher than 99.99 percent and kept for 2 hours, so as to remove the pore-forming agent and activate the blank. Then heating the alloy to 610 ℃ at a heating rate of 70 ℃/min, preserving heat for 5 minutes, heating to 800 ℃ at a heating rate of 20 ℃/min, preserving heat for 5 minutes, finally heating to 900 ℃ at a heating rate of 70 ℃/min, preserving heat for 3 hours, and finally synthesizing the porous nickel-titanium shape memory alloy with the porosity gradient along the axial direction.
Fig. 1 is a scanning electron microscope image of the porous nitinol with gradient axial pores prepared in the present embodiment. As shown in FIG. 1, the porosity of the product prepared in this example is divided into four layers distributed along the axial direction. The porosity of the layers from left to right was 25.5%, 30.7%, 44.2% and 61.3%, respectively. The opening rate of the pores of the left two layers is respectively 30.4 percent and 40.2 percent; the right two layers had an open cell content of 64.3% and 75.6%, respectively (from left to right).
Example 2
Preparing a porous nickel-titanium shape memory alloy sample with rod-shaped radial gradient porosity and good linear superelasticity:
pure titanium powder (average particle size of 70 μm) and pure nickel powder (average particle size of 61 μm) were thoroughly mixed for 20 hours according to 49% by atomic ratio of titanium and 51% by atomic ratio of nickel to obtain raw material powder A. Adding 30 wt.% of NH to the powder of part A4HCO3(average particle size 250 μm) and mixed for 3 hours to obtain powder B. A, B were then added to the mold in two layers and pressed into a preform 12 mm in diameter, 18 mm in length and 40% porosity. Then put into an electric heating furnace to be heated to 250 ℃ under the protection of argon with the purity of more than 99.99 percent and kept for 1 hour and 30 minutes to remove the pore-forming agent and activate the blank. Then heating the alloy to about 630 ℃ at a heating rate of 60 ℃/min, then preserving heat for 5 minutes, heating to 760 ℃ at a heating rate of 20 ℃/min, then preserving heat for 5 minutes, finally heating to 850 ℃ at a heating rate of 70 ℃/min, preserving heat for 3 hours, and finally synthesizing the porous nickel-titanium shape memory alloy with the porosity in radial gradient distribution.
The sample prepared is shown in fig. 2-1, with an inner layer porosity of 19.5% and an outer layer porosity of 60.9%. The sample has good mechanical properties. As shown in fig. 2-2 (note: the experimental method was performed according to ASTM E9-89 a), the linear superelastic deformation capacity was greater than 4%. The outer layer of the sample has higher porosity, can ensure the requirement of tissue cell ingrowth after the material is implanted into an organism, can effectively improve the biomechanical compatibility of the implanted material, and improve the mechanical property matching; the lower porosity of the inner layer of the sample ensures that the implant material has sufficient mechanical property and super elasticity.
Example 3
Preparing a porous nickel-titanium shape memory alloy sample with high porosity and large pore characteristics:
pure titanium powder (average particle size of 70 μm) and pure nickel powder (flat)Average particle size of 61 μm) was mixed thoroughly for 20 hours with a nickel charge of 49 atomic percent titanium to 51 percent, and then 40 wt.% of a pore former NH was added4HCO3(average particle size 250 μm) and mixing was continued for 3 hours. The mixed powder was pressed at room temperature with a pressure of 100MPa to form a billet with a diameter of 16 mm, a length of 24 mm and a porosity of 30%. Then placing the mixture in an electric heating furnace under the protection of argon with the purity higher than 99.99 percent, heating the mixture to 300 ℃, preserving the heat for 1 hour, and removing the pore-forming agent. And then heating the sample to 640 ℃ at a heating rate of 65 ℃/min and preserving heat for 5 minutes, then heating to 780 ℃ at a heating rate of 20 ℃/min and preserving heat for 5 minutes, finally heating to 900 ℃ at a heating rate of 60 ℃/min and preserving heat for 4 hours, and finally obtaining the porous nickel-titanium shape memory alloy with high porosity and large pore characteristics.
As shown in figure 3-1, the prepared sample with high porosity and large pore characteristics has a metallographic morphology of a cross section, the porosity of 67.6%, the average pore size of 467 mu m and the aperture ratio of 90.5%. The X-ray diffraction pattern of the prepared porous alloy sample is shown as curve 4 in fig. 3-2 ( curves 1, 2, 3 and 4 in the figure correspond to samples with porosities of 32.3%, 44.2%, 61.3% and 67.6% respectively); diffraction analysis results show that the main component of the alloy is NiTi phase. Differential scanning calorimetry of the prepared samples is shown in FIG. 3-3, in which PmRepresenting the martensitic transformation and its inverse, PrRepresenting the R phase transition and its inverse, PmvRepresenting the transition between martensite and its variants. The results in the figure show that the sample has three corresponding phase changes (namely R phase change, martensite phase change and transformation between martensite and a variant thereof) and a reverse phase change process thereof in the processes of temperature reduction and temperature rise; it can be seen that the sample phase is between the R phase and the martensite phase at room temperature; at the moment, a large number of phase interfaces in the material enable the NiTi alloy to have good damping performance, and meanwhile, the high porosity of the sample can also contribute to damping; therefore, the sample is also suitable for being used as a high damping material for absorbing and absorbing shock.
Example 4
Preparing a porous nickel titanium shape memory alloy sample with low porosity and small pore characteristics:
pure titanium powder (average particle size of 70 μm) and pure nickel powder (average particle size of 61 μm) were thoroughly mixed for 20 hours in accordance with an atomic ratio of 49.2% titanium and 50.8% nickel. Then, a green body (here, no pore former) having a diameter of 16 mm, a length of 24 mm and a porosity of 50% was pressed in a mold. Then placing the furnace in a Hot Isostatic Pressing (HIP) furnace for vacuumizing, and filling argon with the purity higher than 99.99% into the furnace to ensure that the argon pressure reaches 20 MPa; heating to 620 ℃ at a heating rate of 60 ℃/min, preserving heat for 5 minutes, heating to 770 ℃ at a heating rate of 20 ℃/min, preserving heat for 5 minutes, adjusting the argon pressure to 50MPa, heating to 1050 ℃ at a heating rate of 70 ℃/min, adjusting the argon pressure to keep 50MPa, and finally preserving heat for 3 hours to obtain the porous nickel-titanium shape memory alloy with low porosity and small pore characteristics.
The metallographic morphology of the cross section of the prepared sample with the characteristics of low porosity and small pore is shown in figure 4-1. The porosity of the prepared sample was 32.3%, the average pore size was 54 μm, and the open porosity was 40.5%. The curve 1 in the X-ray diffraction pattern 3-2 of the prepared porous alloy sample shows that the main component of the alloy is NiTi phase. The differential scanning calorimetry pattern of the prepared samples is shown in FIG. 4-2. In the figure PmRepresenting the martensitic transformation and its inverse; prRepresenting the R phase transition and its inverse. The result of the graph shows that the R phase transformation is firstly carried out on the sample during the temperature reduction, then the martensite phase transformation is carried out, and the martensite reverse transformation is directly carried out during the temperature rise, so that the R phase transformation is not carried out; it can be seen that the sample is in an austenite phase at a temperature near the body temperature (36-37 ℃), which ensures the superelasticity of the sample and can exert the advantage that the sample can bear larger deformation when being used as a biomedical material.
Claims (10)
1. A method for preparing nickel-titanium shape memory alloy with gradient porosity is characterized by comprising the following steps and process conditions:
(1) uniformly mixing pure titanium powder and pure nickel powder according to the atomic ratio of 50-51% and 49-50%;
(2) according to the weight percentage, 0-40% of pore-forming agent ammonium bicarbonate powder is fully mixed with the mixture obtained in the step (1);
(3) pressing the powder obtained in the step (2) into an original porosity of 30-50% at room temperature according to radial step lamination or axial step lamination;
(4) placing the pressed blank into a heating furnace under the protection of inert gas for preheating for 1-2 hours, and controlling the temperature to 200-300 ℃ to decompose and remove the pore-forming agent ammonium bicarbonate;
(5) heating up according to a step heating mode, wherein the step heating temperature ranges are respectively as follows: the temperature of 610-640 ℃ is a primary gradient temperature range; 770-810 ℃ is a secondary gradient temperature range; the temperature of 850-1050 ℃ is a three-level gradient temperature range; heating the blank to a first-stage gradient temperature range at a speed of 60-70 ℃ per minute, preserving heat for 3-5 minutes, then heating to a second-stage gradient temperature range at a speed of 20 ℃ per minute, and preserving heat for 3-5 minutes; and finally, heating to the third-stage gradient temperature range and preserving heat for 3-4 hours to obtain the nickel-titanium shape memory alloy with gradient porosity.
2. The method according to claim 1, wherein the average particle size of the pure titanium powder in step (1) is 70 μm, and the average particle size of the pure nickel powder is 61 μm.
3. The method according to claim 1, wherein the average particle size of the pore-forming agent ammonium bicarbonate in step (2) is 250 μm.
4. The method of claim 1, wherein the inert gas in step (4) is argon with a purity of more than 99.99%.
5. The method of claim 1, wherein the furnace is a hot isostatic pressing sintering furnace or an electrically heated sintering furnace.
6. The method for preparing a shape memory alloy of nickel titanium with gradient porosity as claimed in claim 1, wherein the step (3) is to make the powder obtained in step (2) into a blank at room temperature according to the following three methods: (a) raw material powder with different pore-forming agent contents of 0-40 wt.% is distributed in a gradient manner in the axial direction; (b) the raw material powder with different pore-forming agent contents of 0 to wt.40 percent is distributed in a gradient way in the radial direction; (c) respectively preparing blanks from the powder with the same pore-forming agent content; wherein steps (a) and (b) are used to prepare gradient porosity samples, step (c) is used to prepare uniform porosity samples, and the porosity characteristics and porosity are determined by the morphology and content of the pore-forming agent.
7. The method according to claim 1, wherein the step heating of step (5) is performed by heating to about 610 ℃ at a heating rate of 70 ℃/min, keeping the temperature for 5 minutes, heating to 800 ℃ at a heating rate of 20 ℃/min, keeping the temperature for 5 minutes, heating to 900 ℃ at a heating rate of 70 ℃/min, and keeping the temperature for 3 hours.
8. The method according to claim 1, wherein the step heating of step (5) is heating at a heating rate of 60 ℃/min to 630 ℃ and maintaining the temperature for 5 minutes, heating at a heating rate of 20 ℃/min to 760 ℃ and maintaining the temperature for 5 minutes, and finally heating at a heating rate of 60 ℃/min to 850 ℃ and maintaining the temperature for 3 hours.
9. The method according to claim 1, wherein the step heating ofstep (5) is performed by heating to about 640 ℃ at a heating rate of 65 ℃/min, keeping the temperature for 5 minutes, heating to 780 ℃ at a heating rate of 20 ℃/min, keeping the temperature for 5 minutes, heating to 900 ℃ at a heating rate of 60 ℃/min, and keeping the temperature for 4 hours.
10. The method according to claim 1, wherein the step heating of step (5) is performed by heating to about 620 ℃ at a heating rate of 60 ℃/min under a thermal pressure of 50MPa, maintaining the temperature for 5 minutes, heating to 770 ℃ at a heating rate of 20 ℃/min, maintaining the temperature for 5 minutes, and finally heating to 1050 ℃ at a heating rate of 70 ℃/min and maintaining the temperature for 3 hours.
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| JPH09202901A (en) * | 1996-01-24 | 1997-08-05 | Tokin Corp | Production of sintered compact of titanium-nickel alloy |
| CN1172013C (en) * | 2001-12-25 | 2004-10-20 | 中国科学院金属研究所 | Preparation process for combustion synthesis of porous nickel-titanium marmem |
| DE10324271B4 (en) * | 2003-05-28 | 2006-09-21 | Daimlerchrysler Ag | Method for producing a clamping element |
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2006
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