Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems.The search for refrigeration materials displaying a unique combination of pronounced caloric effect...Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems.The search for refrigeration materials displaying a unique combination of pronounced caloric effect,low hysteresis,and high reversibility on phase transformation was very active in recent years.Here,we achieved increase in the elastocaloric reversibility and decrease in the friction dissipation of martensite transformations in the superelastic nano-grained NiTi alloys obtained by cold rolling and annealing treatment,with very low stress hysteresis(6.3 MPa)under a large applied strain(5%).Large adiabatic temperature changes(△T_(max)=16.3 K atε=5%)and moderate COP_(mater)values(maximum COP_(mater)=11.8 atε=2%)were achieved.The present nano-grained NiTi alloys exhibited great potential for applications as a highly efficient elastocaloric material.展开更多
With the deepening of human research on deep space exploration,our research on the soft landing methods of landers has gradually deepened.Adding a buffer and energy-absorbing structure to the leg structure of the land...With the deepening of human research on deep space exploration,our research on the soft landing methods of landers has gradually deepened.Adding a buffer and energy-absorbing structure to the leg structure of the lander has become an effective design solution.Based on the energy-absorbing structure of the leg of the interstellar lander,this paper studies the appearance characteristics of the predatory feet of the Odontodactylus scyllarus.The predatory feet of the Odontodactylus scyllarus can not only hit the prey highly when preying,but also can easily withstand the huge counter-impact force.The predatory feet structure of the Odontodactylus scyllarus,like a symmetrical cone,shows excellent rigidity and energy absorption capacity.Inspired by this discovery,we used SLM technology to design and manufacture two nickel-titanium samples,which respectively show high elasticity,shape memory,and get better energy absorption capacity.This research provides an effective way to design and manufacture high-mechanical energy-absorbing buffer structures using bionic 3D printing technology and nickel-titanium alloys.展开更多
A simple chemical method was developed for inducing bioactivity on NiTi alloys (50 at. pct by Ni/Ti). A layer of calcium phosphate was deposited on the surface to improve biocompatibility of the alloy. NiTi alloys wer...A simple chemical method was developed for inducing bioactivity on NiTi alloys (50 at. pct by Ni/Ti). A layer of calcium phosphate was deposited on the surface to improve biocompatibility of the alloy. NiTi alloys were first etched in HNO3 aqueous solution, and then treated with boiling diluted NaOH solution. A rough surface was created and a thin TiO2 layer was formed on the surface. Pre-calcification was then introduced by immersing the treated NiTi alloys in supersaturated Na2HPO4 solution and supersaturated Ca(OH)2 solution in turn before calcification in simulated body fluid (SBF). A dense and uniform bonelike calcium phosphate (Ca-P) bioactive layer was formed on the surfaces of the specimen, which would improve their biocompatibility. Morphology and element analysis on NiTi surfaces during the treatments were investigated in detail by means of environment scanning electron microscopy (ESEM), energy dispersion X-ray spectroscopy (EDXS), and X-ray diffraction (XRD).展开更多
Phase transformation from austenite to martensite in NiTi alloy strips under the uniaxial tension has been observed in experiments and numerically simulated as a localized deformation. This work presents an analysis u...Phase transformation from austenite to martensite in NiTi alloy strips under the uniaxial tension has been observed in experiments and numerically simulated as a localized deformation. This work presents an analysis using the theory of phase transformation. The jump of deformation gradient across the interface between two phases and the Maxwell relation are considered. Governing equations for the phase transformation are derived. The analysis is reduced to finding the minimum value of the loading at which the governing equations have a unique, real and physically acceptable solution. The equations are solved numerically and it is verified that the unique solution exists definitely. The Maxwell stress, the stresses and strains inside both austenite and martensite phases, and the transformation-front orientation angle are determined to be in reasonably good agreement with experimental observations.展开更多
A poly(ethylene glycol) (PEG-like) coating was developed to improve the biocom- patibility of Nickel-Titanium (NiTi) alloy implants. The PEG-like macromolecular coatings were deposited on NiTi substrates at a ro...A poly(ethylene glycol) (PEG-like) coating was developed to improve the biocom- patibility of Nickel-Titanium (NiTi) alloy implants. The PEG-like macromolecular coatings were deposited on NiTi substrates at a room temperature of 298 K through a ECR (electron-cyclotron resonance) cold-plasma enhanced chemical vapor deposition method using tetraglyme (CH3-O- (CH2-CH2-O)4-CH3) as a precursor. A power supply with a frequency of 2.45 GHz was applied to ignite the plasma with Ar(argon) used as the carrier gas. Based on the atomic force microscopy (AFM) studies, a thin smooth coating on NiTi substrates with highly amorphous functional groups on the modified NiTi surfaces were mainly the same accumulated stoichiometric ratio of C and O with PEG. The vitro studies showed that platelet-rich plasma (PRP) adsorption on the modified NiTi alloy surface was significantly reduced. This study indicated that plasma surface modification changes the surface components of NiTi alloy and subsequently improves its biocompatibility.展开更多
A dense and well-adhered diamond-like carbon (DLC) coating was prepared on the nickel-titanium (NiTi) alloys by plasma immersion ion implantation and deposition (PIIID). Potentiodynamic polarization tests indica...A dense and well-adhered diamond-like carbon (DLC) coating was prepared on the nickel-titanium (NiTi) alloys by plasma immersion ion implantation and deposition (PIIID). Potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by the DLC coating. The Ni ions release of the NiTi alloys was effectively blocked by the DLC coating.展开更多
In order to study the compositions and properties of NiTi alloy plasma arc welded joints, different temperatures of the heat-affected zone(HAZ) are simulated. Temperatures are set at 20 ℃, 400 ℃, 500 ℃, 600 ℃, 7...In order to study the compositions and properties of NiTi alloy plasma arc welded joints, different temperatures of the heat-affected zone(HAZ) are simulated. Temperatures are set at 20 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃ and 1 000 ℃. X-ray diffraction results of the thermal simulated specimens show that NiTi2 phase emerges in the alloy when the temperature is between 500 ℃ and 800 ℃, while NiTi2 and Ni3 Ti phases emerge when the temperature is between 800 ℃ and 1 000 ℃. Tensile strengths of specimens at 600 ℃ and 900 ℃ are only 68. 0% and 61.3% of the strength at the room temperature respectively due to the emergence of NiTi2 and Ni3 Ti phases.展开更多
NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME),superelasticity(SE),damping characteristics,high corrosion resistance,and good biocompatibi...NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME),superelasticity(SE),damping characteristics,high corrosion resistance,and good biocompatibility.Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components,additive manufacturing technology,especially laser powder bed fusion(LPBF),is appropriate for fabricating NiTi products.This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF,including printability,microstructural characteristics,phase transformation behaviors,lattice structures,and applications.Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys.The phase transformation behaviors between austenite and martensite phases,phase transformation temperatures,and an overview of the influencing factors are summarized in this paper.This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses,which comprise tensile mechanical properties,thermomechanical properties(e.g.critical stress to induce martensitic transformation,thermo-recoverable strain,and SE strain),damping properties and hardness.Moreover,several common structures(e.g.a negative Poisson’s ratio structure and a diamond-like structure)are considered,and the corresponding studies are summarized.It illustrates the various fields of application,including biological scaffolds,shock absorbers,and driving devices.In the end,the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.展开更多
The surface of NiTi alloy was roughened by NaOH-HC1 treatment, and the Ta-containing TiO2 films were coated on the pretreated NiTi alloy by the sol-gel method. Thermal analyses indicate that the evaporation temperatur...The surface of NiTi alloy was roughened by NaOH-HC1 treatment, and the Ta-containing TiO2 films were coated on the pretreated NiTi alloy by the sol-gel method. Thermal analyses indicate that the evaporation temperature of the organics decreases with the addition of tantalum ethoxide in the TiO2 sol, but the crystallization temperature of anatase increases. The NaOH-HC1 pre- treatment improves the film integrity, but cracks still form in the films at high Ta contents (_〉20 %, molar ratio) owing to the increasing film thickness. X-ray diffraction (XRD) confirms that the addition of Ta suppresses the crystalli- zation of anatase. X-ray photoelectron spectroscopy (XPS) reveals that Ta exists as Ta2Os in the film. With the increase of Ta content, the hydrophilic conversion of the films under UV illumination is impeded, but their corrosion resistance in 0.9 % NaC1 solution increases, tested by the potentiodynamic polarization. The coating samples have acceptable hemolysis ratios for biomaterials (〈5). The introduction of Ta improves the anti-aggregating function of the TiO2 film in the platelet adhesion test.展开更多
Plasma electrolytic oxidation (PEO) coatings, formed under various anodic voltages (320-440 V) on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during th...Plasma electrolytic oxidation (PEO) coatings, formed under various anodic voltages (320-440 V) on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during the PEO process under different anodic voltages was observed. The surface and cross-sectional morphologies, composition, bonding strength, wear resistance and corrosion resistance of the coatings were investigated by scanning electron microscopy (SEM), thin-film X-ray diffraction (TF-XRD), energy dispersive X-ray spectrometry (EDS), surface roughness, direct pull-off test, ball-on-disk friction and wear test and potentiodynamic polarization test, respectively. The results showed that the evolution of discharging sparks during the PEO process directly influenced the microstructure of the PEO coatings and further influences the properties. When the anodic voltage increased from 320 V to 400 V, the corrosion resistance and wear resistance of the coatings slowly increased, and all the bonding strength was higher than 60 MPa; further increasing the anodic voltages, especially up to 440 V, although the thickness and γ-AI203 crystallinity of the coatings further increased, the microstructure and properties of the coatings were obviously deteriorated.展开更多
In this study, the infl uence of laser remelting on the relative density, martensitic transformation temperatures(MTTs), and mechanical properties of a NiTi alloy fabricated by selective laser melting(SLM) at a laser ...In this study, the infl uence of laser remelting on the relative density, martensitic transformation temperatures(MTTs), and mechanical properties of a NiTi alloy fabricated by selective laser melting(SLM) at a laser power between 15 and 75 W were investigated. A relative alloy density of approximately 99% was achieved in the power range of 45–60 W corresponding to the forming energy density range of 65.45–87.27 J/mm3. The MTTs increased with the increase in the energy density;thus, the initial contents of the B2 and B19′ phases of the SLM-produced NiTi alloy can be tailored by the utilized technique. However, the number of defects such as metallurgical pores and microcracks considerably increased at higher energy densities(> 87.27 J/mm3). Interestingly, the concentration of these defects was reduced by remelting in the energy density range of 21.82–65.45 J/mm3, while the alloy relative density increased to 99.7% ± 0.1% at a remelting energy density of 65.45 J/mm3. The results of tensile testing revealed that when the remelting energy was 75% or 100% of the forming energy input, the ultimate tensile strength and elongation of the alloy significantly increased. Therefore, the remelting strategy represents a promising route for manufacturing NiTi alloys with desired MTT ranges and mechanical properties.展开更多
By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase trans...By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase transformation.The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner.Interestingly,the recovered structure exhibits signifi cant strength improvement,while the tensile plasticity is still comparable to that of the coarse-grained structure.This optimized mechanical performance is due to the strengthening eff ect of refi ned microstructure and the high work hardening capability rendered by moderate dislocation density.Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance,which is primarily ascribed to the high content of residue martensite formed during cryo-rolling.These results provide an eff ective route to optimize the mechanical and wear properties of NiTi alloys.展开更多
Nickel-titanium shape memory alloy (NiTi SMA) which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature (-150 ℃) by means of local canning compr...Nickel-titanium shape memory alloy (NiTi SMA) which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature (-150 ℃) by means of local canning compression. The microstructural evolution of NiTi SMA at the different deformation degree was investigated by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). At the deformation degree by 15%, a high density of dislocations occurs in the deformed NiTi sample. At the deformation degree by 25%, the deformed NiTi sample exhibits the martensite morphology due to the pinning of dislocations at the grain boundaries. At the deformation degree by 50%, a small amount of nanocrystalline phase arises in the deformed NiTi sample. At the deformation degree by 80%, severe plastic deformation (SPD) leads to the occurrence of a great deal of amorphous and nanocrystalline phase,展开更多
60NiTi alloy is highly promising for aerospace bearings and mechanisms.Shock load that is inevitably generated during launching process brings about an quick loading process and transient load duration,and may further...60NiTi alloy is highly promising for aerospace bearings and mechanisms.Shock load that is inevitably generated during launching process brings about an quick loading process and transient load duration,and may further results in an unnoticed but detrimental creep deformation.On this account,the nanoindentation creep behavior of solution-treated 60NiTi alloy at room temperature and the corresponding influencing mechanism were studied.The results show that creep displacement was dominated by strain rate at the very beginning of holding stage.Strain rate and flow stress at the very beginning of holding stage were increased with an increased loading rate but declined with increasing holding load or with simultaneously increasing loading rate and holding load.The underlying mechanisms were provided as nucleation and absorption of geometrically necessary dislocations(GNDs)associated with strain gradient plasticity theory rather than the model based on the consumption of creep deformation at loading stage.展开更多
The corrosion behavior of the nitinol alloy was studied in various corrosion media of different Cl^- ion concentrations. The results demonstrate that the Cl^- ion concentration has significant influences on the corros...The corrosion behavior of the nitinol alloy was studied in various corrosion media of different Cl^- ion concentrations. The results demonstrate that the Cl^- ion concentration has significant influences on the corrosion behavior of the nitinol alloy. In order to enhance the corrosion resistance, protective films were generated on the surface of the nitinol alloy by means of the electrochemical passivation method, for which five different electrolytic solutions were investigated. The surface analysis indicates full growth of all samples passivated in the different electrolytic solutions with layers, however, showing different morphological features. Without any defects like micro-cracks and pores, the surface of the samples passivated in the molybdate solution turns out smoother and denser than those passivated in other solutions. It is shown that the electro-chemical passivation will reduce Ni content but increase Ti content in the surface, reaching the Mole ratio of Ti:Ni = 9.01:1 on the outermost surface. Potentiodynamic polarization test demonstrates that the samples electrochemically passivated in the molybdate solution present a significant increase in breakdown potential due to titanium enrichment on the outermost surface.展开更多
This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain ...This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate(4×10~9 s^(-1)),while the temperature and initial pressure remained 300 K and 0 bar,respectively.It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials,which was vividly characterized by void nucleation,growth,and coalescence.The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes.Interestingly,it was discovered that the void evolution was characteristic of an almost double-linear behavior,and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size.More importantly,the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy.For small grain size,the existing voids propagated along the grain boundaries and in the grains,leading to intergranular and transgranular fracture.Contrarily,the intergranular-dominated fracture was responsible for the void propagation in the large grain.In addition,the starting time,ending time,and threshold of void nucleation were found to be weak sensitivity to GS,and a reverse effect was appropriate to the void growth.The results highlighted that as the GS increased,more complete stress relaxation and shorter duration time were produced,leading to larger void volume fraction and faster growth rate.展开更多
The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temper...The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0~4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pct; the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.展开更多
Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficientl...Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.展开更多
To protect the surface of NiTi from corrosion, an ion implantation method was proposed. In the present work, a surface oxidized sample was implanted with nitrogen at energy of 100 keV. The corrosion resistarwe propert...To protect the surface of NiTi from corrosion, an ion implantation method was proposed. In the present work, a surface oxidized sample was implanted with nitrogen at energy of 100 keV. The corrosion resistarwe property was examined by the anodic polarization method in a simulated body fluid (SBF) at a temperature of 37 ℃ and contrasted to non-implanted NiTi samples. The composition and structure of the implanted layers were investigated by XPS. The experimental results from the electrochemical measurements provide an evidence that the nitrogen ion-implantation increases the corrosion resistance of NiTi shape memory alloy.展开更多
基金Project supported by the Science Fund of the Key Laboratory of Cryogenic Science and Technology(Grant Nos.CRYO20230203 and CRYO202106)the National Natural Science Foundation of China(Grant Nos.51872299 and 52071223)the National Key Research and Development Program of China(Grant No.2019YFA0704904)。
文摘Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems.The search for refrigeration materials displaying a unique combination of pronounced caloric effect,low hysteresis,and high reversibility on phase transformation was very active in recent years.Here,we achieved increase in the elastocaloric reversibility and decrease in the friction dissipation of martensite transformations in the superelastic nano-grained NiTi alloys obtained by cold rolling and annealing treatment,with very low stress hysteresis(6.3 MPa)under a large applied strain(5%).Large adiabatic temperature changes(△T_(max)=16.3 K atε=5%)and moderate COP_(mater)values(maximum COP_(mater)=11.8 atε=2%)were achieved.The present nano-grained NiTi alloys exhibited great potential for applications as a highly efficient elastocaloric material.
基金Supported by National Key R&D Program of China(Grant No.2022YFE0138500)National Natural Science Foundation of China(Grant No.51975246)+2 种基金Science and Technology Development Program of Jilin Province of China(Grant No.20220101192JC)Capital Construction Fund Plan within the Budget of Jilin Province of China(Grant No.2023C041-4)Chongqing Municipal Natural Science Foundation of China(Grant No.CSTB2022NSCQ-MSX0225).
文摘With the deepening of human research on deep space exploration,our research on the soft landing methods of landers has gradually deepened.Adding a buffer and energy-absorbing structure to the leg structure of the lander has become an effective design solution.Based on the energy-absorbing structure of the leg of the interstellar lander,this paper studies the appearance characteristics of the predatory feet of the Odontodactylus scyllarus.The predatory feet of the Odontodactylus scyllarus can not only hit the prey highly when preying,but also can easily withstand the huge counter-impact force.The predatory feet structure of the Odontodactylus scyllarus,like a symmetrical cone,shows excellent rigidity and energy absorption capacity.Inspired by this discovery,we used SLM technology to design and manufacture two nickel-titanium samples,which respectively show high elasticity,shape memory,and get better energy absorption capacity.This research provides an effective way to design and manufacture high-mechanical energy-absorbing buffer structures using bionic 3D printing technology and nickel-titanium alloys.
基金This work was supported by the National Natural Science Foundation of China (59971032) by Foundation for University Key Teacher, the Ministry of Education (GG-805-10056-1603).
文摘A simple chemical method was developed for inducing bioactivity on NiTi alloys (50 at. pct by Ni/Ti). A layer of calcium phosphate was deposited on the surface to improve biocompatibility of the alloy. NiTi alloys were first etched in HNO3 aqueous solution, and then treated with boiling diluted NaOH solution. A rough surface was created and a thin TiO2 layer was formed on the surface. Pre-calcification was then introduced by immersing the treated NiTi alloys in supersaturated Na2HPO4 solution and supersaturated Ca(OH)2 solution in turn before calcification in simulated body fluid (SBF). A dense and uniform bonelike calcium phosphate (Ca-P) bioactive layer was formed on the surfaces of the specimen, which would improve their biocompatibility. Morphology and element analysis on NiTi surfaces during the treatments were investigated in detail by means of environment scanning electron microscopy (ESEM), energy dispersion X-ray spectroscopy (EDXS), and X-ray diffraction (XRD).
基金the National Natural Science Foundation of China(No.10272079)the joint grant from the National Natural Science Foundation of China and the Royal Society
文摘Phase transformation from austenite to martensite in NiTi alloy strips under the uniaxial tension has been observed in experiments and numerically simulated as a localized deformation. This work presents an analysis using the theory of phase transformation. The jump of deformation gradient across the interface between two phases and the Maxwell relation are considered. Governing equations for the phase transformation are derived. The analysis is reduced to finding the minimum value of the loading at which the governing equations have a unique, real and physically acceptable solution. The equations are solved numerically and it is verified that the unique solution exists definitely. The Maxwell stress, the stresses and strains inside both austenite and martensite phases, and the transformation-front orientation angle are determined to be in reasonably good agreement with experimental observations.
基金National Natural Science Foundation of China(No.30670562)Hubei Provincial Department of Education:Science Research Project(No.D200515009)
文摘A poly(ethylene glycol) (PEG-like) coating was developed to improve the biocom- patibility of Nickel-Titanium (NiTi) alloy implants. The PEG-like macromolecular coatings were deposited on NiTi substrates at a room temperature of 298 K through a ECR (electron-cyclotron resonance) cold-plasma enhanced chemical vapor deposition method using tetraglyme (CH3-O- (CH2-CH2-O)4-CH3) as a precursor. A power supply with a frequency of 2.45 GHz was applied to ignite the plasma with Ar(argon) used as the carrier gas. Based on the atomic force microscopy (AFM) studies, a thin smooth coating on NiTi substrates with highly amorphous functional groups on the modified NiTi surfaces were mainly the same accumulated stoichiometric ratio of C and O with PEG. The vitro studies showed that platelet-rich plasma (PRP) adsorption on the modified NiTi alloy surface was significantly reduced. This study indicated that plasma surface modification changes the surface components of NiTi alloy and subsequently improves its biocompatibility.
文摘A dense and well-adhered diamond-like carbon (DLC) coating was prepared on the nickel-titanium (NiTi) alloys by plasma immersion ion implantation and deposition (PIIID). Potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by the DLC coating. The Ni ions release of the NiTi alloys was effectively blocked by the DLC coating.
文摘In order to study the compositions and properties of NiTi alloy plasma arc welded joints, different temperatures of the heat-affected zone(HAZ) are simulated. Temperatures are set at 20 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃ and 1 000 ℃. X-ray diffraction results of the thermal simulated specimens show that NiTi2 phase emerges in the alloy when the temperature is between 500 ℃ and 800 ℃, while NiTi2 and Ni3 Ti phases emerge when the temperature is between 800 ℃ and 1 000 ℃. Tensile strengths of specimens at 600 ℃ and 900 ℃ are only 68. 0% and 61.3% of the strength at the room temperature respectively due to the emergence of NiTi2 and Ni3 Ti phases.
基金sponsored by the Natural and Science Foundation of China(Grant No.52275331)the Key-Area Research and Development Program of Guangdong Province(No.2020B090923001)+3 种基金the Key Research and Development Program of Hubei Province(No.2022BAA011)the Academic Frontier Youth Team(2018QYTD04)at Huazhong University of Science and Technology(HUST)the Hong Kong Scholars Program(No.XJ2022014)the Laboratory Project of Science and Technology on Power Beam Processes Laboratory。
文摘NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME),superelasticity(SE),damping characteristics,high corrosion resistance,and good biocompatibility.Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components,additive manufacturing technology,especially laser powder bed fusion(LPBF),is appropriate for fabricating NiTi products.This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF,including printability,microstructural characteristics,phase transformation behaviors,lattice structures,and applications.Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys.The phase transformation behaviors between austenite and martensite phases,phase transformation temperatures,and an overview of the influencing factors are summarized in this paper.This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses,which comprise tensile mechanical properties,thermomechanical properties(e.g.critical stress to induce martensitic transformation,thermo-recoverable strain,and SE strain),damping properties and hardness.Moreover,several common structures(e.g.a negative Poisson’s ratio structure and a diamond-like structure)are considered,and the corresponding studies are summarized.It illustrates the various fields of application,including biological scaffolds,shock absorbers,and driving devices.In the end,the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.
基金financially supported by the Fundamental Research Fund for the Central Universities(No.xjj2011096)the Opening Research Fund of State Key Laboratory of Porous Metal Materials(No.PMM-SKL-2-2012)the National Natural Science Foundation of China(No.50901058)
文摘The surface of NiTi alloy was roughened by NaOH-HC1 treatment, and the Ta-containing TiO2 films were coated on the pretreated NiTi alloy by the sol-gel method. Thermal analyses indicate that the evaporation temperature of the organics decreases with the addition of tantalum ethoxide in the TiO2 sol, but the crystallization temperature of anatase increases. The NaOH-HC1 pre- treatment improves the film integrity, but cracks still form in the films at high Ta contents (_〉20 %, molar ratio) owing to the increasing film thickness. X-ray diffraction (XRD) confirms that the addition of Ta suppresses the crystalli- zation of anatase. X-ray photoelectron spectroscopy (XPS) reveals that Ta exists as Ta2Os in the film. With the increase of Ta content, the hydrophilic conversion of the films under UV illumination is impeded, but their corrosion resistance in 0.9 % NaC1 solution increases, tested by the potentiodynamic polarization. The coating samples have acceptable hemolysis ratios for biomaterials (〈5). The introduction of Ta improves the anti-aggregating function of the TiO2 film in the platelet adhesion test.
基金the financial support from the National Natural Science Foundation of China (Grant No. 51101085)the National Natural Science Foundation of Jiangxi Province (Grant No. 20114BAB216014)+1 种基金the Science and Technology Plan Projects of Jiangxi Province (Grant No.20111BBG70007-2)the Science and Technology Plan Projects of Department of Education of Jiangxi Province (Grant No.GJJ12450)
文摘Plasma electrolytic oxidation (PEO) coatings, formed under various anodic voltages (320-440 V) on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during the PEO process under different anodic voltages was observed. The surface and cross-sectional morphologies, composition, bonding strength, wear resistance and corrosion resistance of the coatings were investigated by scanning electron microscopy (SEM), thin-film X-ray diffraction (TF-XRD), energy dispersive X-ray spectrometry (EDS), surface roughness, direct pull-off test, ball-on-disk friction and wear test and potentiodynamic polarization test, respectively. The results showed that the evolution of discharging sparks during the PEO process directly influenced the microstructure of the PEO coatings and further influences the properties. When the anodic voltage increased from 320 V to 400 V, the corrosion resistance and wear resistance of the coatings slowly increased, and all the bonding strength was higher than 60 MPa; further increasing the anodic voltages, especially up to 440 V, although the thickness and γ-AI203 crystallinity of the coatings further increased, the microstructure and properties of the coatings were obviously deteriorated.
基金financially supported by the National Natural Science Foundation of China(No.51801198)the Funds of Scientific and Technological Plan of Fujian Province(No.2020Y0083)+3 种基金the National Key Technologies Research and Development Program of China(2016YFC1100502)the Joint Funds of Scientific and Technological Innovation Program of Fujian Province(No.2017Y9059)the Natural and Science Foundation of Fujian Province(No.2019I0027)the Funds of Scientific and Technological Plan of Fujian Province(No.2020L3026)。
文摘In this study, the infl uence of laser remelting on the relative density, martensitic transformation temperatures(MTTs), and mechanical properties of a NiTi alloy fabricated by selective laser melting(SLM) at a laser power between 15 and 75 W were investigated. A relative alloy density of approximately 99% was achieved in the power range of 45–60 W corresponding to the forming energy density range of 65.45–87.27 J/mm3. The MTTs increased with the increase in the energy density;thus, the initial contents of the B2 and B19′ phases of the SLM-produced NiTi alloy can be tailored by the utilized technique. However, the number of defects such as metallurgical pores and microcracks considerably increased at higher energy densities(> 87.27 J/mm3). Interestingly, the concentration of these defects was reduced by remelting in the energy density range of 21.82–65.45 J/mm3, while the alloy relative density increased to 99.7% ± 0.1% at a remelting energy density of 65.45 J/mm3. The results of tensile testing revealed that when the remelting energy was 75% or 100% of the forming energy input, the ultimate tensile strength and elongation of the alloy significantly increased. Therefore, the remelting strategy represents a promising route for manufacturing NiTi alloys with desired MTT ranges and mechanical properties.
基金financially supported by the National Natural Science Foundation of China(No.51931003)the China Postdoctoral Science Foundation(No.2020M680223)。
文摘By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase transformation.The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner.Interestingly,the recovered structure exhibits signifi cant strength improvement,while the tensile plasticity is still comparable to that of the coarse-grained structure.This optimized mechanical performance is due to the strengthening eff ect of refi ned microstructure and the high work hardening capability rendered by moderate dislocation density.Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance,which is primarily ascribed to the high content of residue martensite formed during cryo-rolling.These results provide an eff ective route to optimize the mechanical and wear properties of NiTi alloys.
基金Funded by National Natural Science Foundation of China(No.51071056)the Fundamental Research Funds for the Central Universities of China(Nos.HEUCF121712 and HEUCF201317002)
文摘Nickel-titanium shape memory alloy (NiTi SMA) which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature (-150 ℃) by means of local canning compression. The microstructural evolution of NiTi SMA at the different deformation degree was investigated by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). At the deformation degree by 15%, a high density of dislocations occurs in the deformed NiTi sample. At the deformation degree by 25%, the deformed NiTi sample exhibits the martensite morphology due to the pinning of dislocations at the grain boundaries. At the deformation degree by 50%, a small amount of nanocrystalline phase arises in the deformed NiTi sample. At the deformation degree by 80%, severe plastic deformation (SPD) leads to the occurrence of a great deal of amorphous and nanocrystalline phase,
基金financially supported by the Fundamental Research Funds for the Central Universities(xzy022019015)the National Natural Science Foundation of China(51675409)。
文摘60NiTi alloy is highly promising for aerospace bearings and mechanisms.Shock load that is inevitably generated during launching process brings about an quick loading process and transient load duration,and may further results in an unnoticed but detrimental creep deformation.On this account,the nanoindentation creep behavior of solution-treated 60NiTi alloy at room temperature and the corresponding influencing mechanism were studied.The results show that creep displacement was dominated by strain rate at the very beginning of holding stage.Strain rate and flow stress at the very beginning of holding stage were increased with an increased loading rate but declined with increasing holding load or with simultaneously increasing loading rate and holding load.The underlying mechanisms were provided as nucleation and absorption of geometrically necessary dislocations(GNDs)associated with strain gradient plasticity theory rather than the model based on the consumption of creep deformation at loading stage.
基金Local Governmental Foundation of Guizhou province (2142005)
文摘The corrosion behavior of the nitinol alloy was studied in various corrosion media of different Cl^- ion concentrations. The results demonstrate that the Cl^- ion concentration has significant influences on the corrosion behavior of the nitinol alloy. In order to enhance the corrosion resistance, protective films were generated on the surface of the nitinol alloy by means of the electrochemical passivation method, for which five different electrolytic solutions were investigated. The surface analysis indicates full growth of all samples passivated in the different electrolytic solutions with layers, however, showing different morphological features. Without any defects like micro-cracks and pores, the surface of the samples passivated in the molybdate solution turns out smoother and denser than those passivated in other solutions. It is shown that the electro-chemical passivation will reduce Ni content but increase Ti content in the surface, reaching the Mole ratio of Ti:Ni = 9.01:1 on the outermost surface. Potentiodynamic polarization test demonstrates that the samples electrochemically passivated in the molybdate solution present a significant increase in breakdown potential due to titanium enrichment on the outermost surface.
基金the financial support of the Natural Science Foundation Project of CQ CSTC under grant number cstc2018jcyjAX0581the Fundamental Research Funds for the Central Universities under grant number XDJK2018B002+1 种基金the foundation of the National Key Defense Laboratory for Computational Physics under grant number HXo2020-74the Venture&Innovation Support Program for Chongqing Overseas Returnees under grant number cx2018078。
文摘This study focused on the effect of grain size(GS)on dynamic damage performance of nano-crystalline nickel titanium(NC NiTi)alloy.Molecular dynamics simulations were conducted to triaxially expand it at a high strain rate(4×10~9 s^(-1)),while the temperature and initial pressure remained 300 K and 0 bar,respectively.It was discovered that the superelastic NiTi alloy exhibited the similar damage response as ductile metallic materials,which was vividly characterized by void nucleation,growth,and coalescence.The stress-strain curves demonstrated that the void nucleations always occurred near the start of the strain softening region at various grain sizes.Interestingly,it was discovered that the void evolution was characteristic of an almost double-linear behavior,and the piecewise linearity became more prominent for the void volume fraction increase at larger grain size.More importantly,the fracture behavior was found to be strongly dependent upon the grain size in the NC NiTi alloy.For small grain size,the existing voids propagated along the grain boundaries and in the grains,leading to intergranular and transgranular fracture.Contrarily,the intergranular-dominated fracture was responsible for the void propagation in the large grain.In addition,the starting time,ending time,and threshold of void nucleation were found to be weak sensitivity to GS,and a reverse effect was appropriate to the void growth.The results highlighted that as the GS increased,more complete stress relaxation and shorter duration time were produced,leading to larger void volume fraction and faster growth rate.
基金Shanxi Province Natural Science FOundation State Key Laboratory of Solidilication Processing.
文摘The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0~4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pct; the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.
基金supported by the National Natural Science Foundation of China (11532010)
文摘Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.
基金Funded by the National Natural Science Foundation of China(20273012 ) and Education Government of Hainan Province(Hjkj200415)
文摘To protect the surface of NiTi from corrosion, an ion implantation method was proposed. In the present work, a surface oxidized sample was implanted with nitrogen at energy of 100 keV. The corrosion resistarwe property was examined by the anodic polarization method in a simulated body fluid (SBF) at a temperature of 37 ℃ and contrasted to non-implanted NiTi samples. The composition and structure of the implanted layers were investigated by XPS. The experimental results from the electrochemical measurements provide an evidence that the nitrogen ion-implantation increases the corrosion resistance of NiTi shape memory alloy.