Effects of Ta Content on Thermodynamic Properties and Transformation Temperatures of Shape Memory NiTi Alloy

The present research aims to understand the transformation temperatures and recovery strain of NiTi wires during heating and cooling under various constrained stresses. Both constrained stress and annealing temperature have significant effects on the shape memory characteristics. In general, increasing constrained stress causes an increase of the austenitic and martensitic transformation temperatures and a decrease of the recovery strain. This effect can be attributed to that the constrained stress inhibits the austenitic transformation, and thus more volume fraction of the martensite is retained during heating. The high annealing temperature leads to the decrease in the recovery strain.

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The Effect of Hafnium and Thermal Cycling on the Transformation Temperatures of NiTi-Based Shape Memory Alloys

MRS Proceedings ◽

10.1557/proc-604-221 ◽

1999 ◽

Vol 604 ◽

Cited By ~ 2

Author(s):

Paul E. Thoma ◽

John J. Boehm

Keyword(s):

Shape Memory Alloys ◽

Thermal Cycling ◽

Shape Memory ◽

Phase Transformations ◽

Niti Alloy ◽

Thermal Cycles ◽

Transformation Temperatures

AbstractThe effect of thermal cycling on the austenite to martensite (A→M) and martensite to austenite (M→A) transformation temperatures (TTs) of Ni49.8Ti50.2 and Ni49.8Ti40.2Hf10 shape memory alloys is investigated. Test specimens are from arc melted buttons homogenized at 900°C for 100 hours. Results show that the A→M and M→A TTs for the alloys decrease with increasing number of thermal cycles through the phase transformations. The A→M TT of the NiTiHf alloy stabilizes more quickly than the A→M TT of the NiTi alloy when cycled. However, the M→A TT of the binary NiTi alloy stabilizes more quickly than the M→A TT of the NiTiHf alloy when cycled.

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Effect of Aging Treatment on Phase Transformation of a Pseudoelastic NiTi Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.936.1216 ◽

2014 ◽

Vol 936 ◽

pp. 1216-1223 ◽

Cited By ~ 2

Author(s):

Palloma Viera Muterlle ◽

Eduard Benavides Villamarin ◽

Paulo Herrera ◽

Edson Paulo da Silva

Keyword(s):

Phase Transformation ◽

Shape Memory ◽

Room Temperature ◽

Niti Alloy ◽

Aging Treatment ◽

Single Step ◽

Treatment Temperature ◽

Scanning Calorimetry ◽

Transformation Temperatures ◽

X Ray

The pseudoelasticity (PE) and shape memory effect (SME) are the two main behaviors presented by the shape memory alloys (SMA's) and are associated respectively to mechanical and thermally induced martensitic transformations. The aim of this work is to investigate the effects of heat treatment temperature on the microstructure properties and phase transformation temperatures of a NiTi alloy with 57 w.t. % Ni. The X-ray diffraction (XRD) was carried out to obtain the phases present. The phase transformation temperatures were measured by differential scanning calorimetry (DSC). The alloy chemical composition and hardness were obtained by X-ray fluorescence (XRF), hardness (HRC) and microhardness (HV) tests, respectively. The analysis were performed in the state as received and after aging treatment at different temperatures between 350 °C and 600°C. The samples as received contained a fully austenitic microstructure at room temperature and the DSC analysis showed the presence of a phase transformation in multiple steps (B19'-R-B2). After aging at 350 °C the R phase was observed at room temperature with the austenite. With the aging treatment at 600 °C the R phase was solubilized and the alloy phase transformation occurred in a single step, ie, direct transformation from austenite to martensite and vice versa. The transformation temperatures Af, As, Ms and Mf changed with the aging treatment temperatures.

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INFLUENCES OF HEAT TREATMENT ON TRANSFORMATION BEHAVIORS OF NEAR-EQUIATOMIC POROUS NITI SHAPE MEMORY ALLOY

International Journal of Modern Physics B ◽

10.1142/s0217979210065015 ◽

2010 ◽

Vol 24 (15n16) ◽

pp. 2410-2416

Author(s):

H. C. JIANG ◽

Y. CHEN ◽

S. W. LIU ◽

L. J. RONG

Keyword(s):

Heat Treatment ◽

Shape Memory Alloy ◽

Shape Memory ◽

Niti Alloy ◽

Niti Shape Memory Alloy ◽

Scanning Calorimetry ◽

Pore Characteristics ◽

Transformation Temperatures ◽

Porous Niti ◽

High Temperature Synthesis

The pore characteristics and pore size distribution of porous near-equiatomic NiTi shape memory alloy fabricated by self-propagating high-temperature synthesis (SHS) are described in detail. The effects of different heat treatments on the transformation of porous NiTi alloy were investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that heat treatment had strong influences on the transformation temperatures and latent heats of transformation. When the porous alloy was annealed at 648K and 748K for 3.6ks, two steps transformation including R transformation occurred during cooling and heating and the R transformation temperatures are lower than B 2↔ B 19' transformation temperatures. However, no transformation was detected within the experimental temperature range if the porous alloy was solution treated at 1133K for 2.4ks. This novel phenomenon was the results of extensive Ti2Ni intermetallic compound precipitation. The transformation temperatures of porous NiTi alloy after annealing at 1323K for 3.6ks were much lower than those of the untreated alloy.

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Effect of Cu on Structural and FF-Behavior of NiTi Shape Memory Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.442.301 ◽

2010 ◽

Vol 442 ◽

pp. 301-308

Author(s):

S. Rani ◽

M.S. Awan ◽

I.N. Qureshi ◽

F. Yasmin ◽

M. Farooque

Keyword(s):

Phase Transformation ◽

Electron Microscope ◽

Shape Memory Alloy ◽

Shape Memory ◽

Cold Working ◽

Niti Alloy ◽

Fatigue Behavior ◽

Optical Microscope ◽

Niti Shape Memory Alloy ◽

Transformation Temperatures

The functional fatigue behavior of Ti50Ni30Cu20 (at. %) shape memory alloy was investigated after subjecting to cold working and heat-treatment. Copper addition modified the phase transformation behavior with the introduction of B19-phase in the binary NiTi alloy. It was observed that aging after annealing and thermal cycling (-60 to 100)°C significantly effect the transformation temperatures. Observations in optical microscope and scanning electron microscope reveal inhomogeneity in the composition in the form of coarse Cu+Ti-rich precipitates. Investigations under transmission electron microscope showed growth of internally twined martensitic plates in solution treated sample. The phase transformation temperatures were determined with differential scanning calorimeter. The transformation temperatures were shifted towards lower side. Dislocations introduced during cold working and fine precipitation after aging, may be responsible for this change in the transformation characteristics of the material.

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Net-Shape NiTi Shape Memory Alloy by Spark Plasma Sintering Method

Applied Sciences ◽

10.3390/app11041802 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1802

Author(s):

Sneha Samal ◽

Orsolya Molnárová ◽

Filip Průša ◽

Jaromír Kopeček ◽

Luděk Heller ◽

...

Keyword(s):

Shape Memory ◽

Shape Memory Effect ◽

Spark Plasma Sintering ◽

Memory Effect ◽

Niti Alloy ◽

Niti Shape Memory Alloy ◽

Good Shape ◽

Plasma Sintering ◽

Shape Memory Effects ◽

Spark Plasma

An analysis of the shape memory effect of a NiTi alloy by using the spark plasma sintering approach has been carried out. Spark plasma sintering of Ti50Ni50 powder (20–63 µm) at a temperature of 900 °C produced specimens showing good shape memory effects. However, the sample showed 2.5% porosity due to a load of 48 MPa. Furthermore, an apparent shape memory effect was recorded and the specimens were characterized by uniformity in chemical composition and shape memory alloys of NiTi showed significant austenite phases with a bending strain recovery of >2.5%.

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Cyclic pseudoelastic training and two-way shape memory behavior of a NiTi alloy with small irrecoverable plastic strains:numerical modeling

International Journal of Solids and Structures ◽

10.1016/j.ijsolstr.2021.02.005 ◽

2021 ◽

Author(s):

J.S. Owusu-Danquah ◽

A.F. Saleeb ◽

M.A. Soudah

Keyword(s):

Shape Memory ◽

Niti Alloy ◽

Shape Memory Behavior

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Key Properties of a Bioactive Ag-SiO2/TiO2 Coating on NiTi Shape Memory Alloy as Necessary at the Development of a New Class of Biomedical Materials

International Journal of Molecular Sciences ◽

10.3390/ijms22020507 ◽

2021 ◽

Vol 22 (2) ◽

pp. 507

Author(s):

Mateusz Dulski ◽

Robert Gawecki ◽

Sławomir Sułowicz ◽

Michal Cichomski ◽

Alicja Kazek-Kęsik ◽

...

Keyword(s):

Surface Roughness ◽

Shape Memory Alloy ◽

Shape Memory ◽

Dermal Fibroblast ◽

Niti Alloy ◽

Bacterial Biofilm ◽

Niti Shape Memory Alloy ◽

Normal Human Dermal Fibroblast ◽

Water Contact ◽

Nano Coating

Recent years have seen the dynamic development of methods for functionalizing the surface of implants using biomaterials that can mimic the physical and mechanical nature of native tissue, prevent the formation of bacterial biofilm, promote osteoconduction, and have the ability to sustain cell proliferation. One of the concepts for achieving this goal, which is presented in this work, is to functionalize the surface of NiTi shape memory alloy by an atypical glass-like nanocomposite that consists of SiO2-TiO2 with silver nanoparticles. However, determining the potential medical uses of bio(nano)coating prepared in this way requires an analysis of its surface roughness, tribology, or wettability, especially in the context of the commonly used reference coat-forming hydroxyapatite (HAp). According to our results, the surface roughness ranged between (112 ± 3) nm (Ag-SiO2)—(141 ± 5) nm (HAp), the water contact angle was in the range (74.8 ± 1.6)° (Ag-SiO2)—(70.6 ± 1.2)° (HAp), while the surface free energy was in the range of 45.4 mJ/m2 (Ag-SiO2)—46.8 mJ/m2 (HAp). The adhesive force and friction coefficient were determined to be 1.04 (Ag-SiO2)—1.14 (HAp) and 0.247 ± 0.012 (Ag-SiO2) and 0.397 ± 0.034 (HAp), respectively. The chemical data showed that the release of the metal, mainly Ni from the covered NiTi substrate or Ag from Ag-SiO2 coating had a negligible effect. It was revealed that the NiTi alloy that was coated with Ag-SiO2 did not favor the formation of E. coli or S. aureus biofilm compared to the HAp-coated alloy. Moreover, both approaches to surface functionalization indicated good viability of the normal human dermal fibroblast and osteoblast cells and confirmed the high osteoconductive features of the biomaterial. The similarities of both types of coat-forming materials indicate an excellent potential of the silver-silica composite as a new material for the functionalization of the surface of a biomaterial and the development of a new type of functionalized implants.

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