Formation of nanocrystals with an identical orientation in sputter-deposited Ti Ni thin films

Kajiwara, Setsuo; Ogawa, Kazuyuki; Kikuchi, Toshiro; Matsunaga, Takashi; Miyazaki, S.

doi:10.1080/095008396179922

Cited by 58 publications

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“…This relates with nanometer scale substructures and nonequilibrium phase formed during recrystallization and following •annealing process [14]. These nanometer scale substructures are effective in increasing the shape memory characteristics by increasing the critical stress for slip.…”

Section: Introductionmentioning

confidence: 99%

Recent Developments in Sputter-Deposited Ti-Ni-Base Shape Memory Alloy Thin Films

et al. 1997

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Since 1992 the present authors have been successful in making Ti-Ni shape memory alloy thin films, which can show perfect shape memory effect and superelasticity equivalent to those of bulk materials, by utilizing a r.f. sputtering method. In the present paper, some of their recent results were reviewed. The alloys investigated are Ti-Ni, Ti-Ni-Cu and Ti-Ni-Pd, the alloy content ranging from 45.4 to 51.9 at%Ni for Ti-Ni, from 0 to 18.0 at%Cu for Ti-NiCu and from 0 to 21.8 at%Pd for Ti-Ni-Pd. The Ti-Ni films were used for investigating the effects of Ni-content and heat-treatment condition on the transformation and deformation behavior, the effect of cyclit deformation on the stability of shape memory behavior, the effect of nonequilibrium state created during crystallization process on the transformation behavior, etc. The Ti-Ni-Cu films were made in order to decrease the transformation hysteresis, while the Ti-Ni-Pd films were made in order to increase the transformation temperatures: both are effective to increase the response speed in actuation.

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Section: Introductionmentioning

confidence: 99%

Recent Developments in Sputter-Deposited Ti-Ni-Base Shape Memory Alloy Thin Films

et al. 1997

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“…Owing to those coherent subnanometric precipitates, the yield strength of the parent phase is greatly increased, about two times greater than that for the sample containing non-coherent TizNi spherical precipitates as shown in the previous paper [7] Figure 6 (a) and (b) shows recoverable strain, & , , , and plastic strain, & p, as a function of applied stress in the thermal cycling tests of shape memory effect, (a) for the sample heated at 745 K for 1 h and (b) for the sample heated at 873 K for 1 h It is seen fkom these figures that nearly 6 % recoverable strain is obtained without any appreciable plastic strain for an applied stress of about 300 MPa in the former case, whiie the corresponding value of A is only 2 % with an applied stress of about 100 MPa Furthermore, nearly 5 % recoverable strain is obtained with 1 % & p for an applied stress of about 600 MPa in the former case, whiie only 4 % recoverable strain is realized in the latter case, being accompanied by 2 5 % & p at the correspondiig applied stress Thus it is obvious that the specimens containing coherent subnanometric plate precipitates show better shape memory properties compared with those containing ordinary incoherent precipitates…”

Section: Resultsmentioning

confidence: 75%

“…The same specimens as those used in the previous studies [7,81 were employed also in the present work; that is, the sputter-deposited Ti48.2at.%Ni thin films of about 7 F( m thickness were heat treated at 745 K for 1 4 h. m e crystallization temperature of this alloy films was found to be 737 K by DSC measurement. Thin foil specimens fbr…”

Section: Experimextat Methodsmentioning

confidence: 99%

“…Very recently we found that, instead of employing these two step heat treatments, if as-sputtered Ti-Ni amorphous specimens with a Ti-rich composition are directly heated at relatively low temperatures, thin coherent plate precipitates and unique nanoctystals are formed [7,81. Uniformly distributed thin precipitates with only 0.5-1 nm thickness are produced by the heat treatment near the crystallization temperature, while nanocrystals of 2040 nm in diameter, which have the exact1y same orientation within one grain, are generated by the heat treatment at a temperature about SO0 below the crystaUization temperature.…”

Section: Introductionmentioning

confidence: 99%

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Coherent Subnanometric Plate Precipitates Formed during Crystallization of As-Sputtered Ti-Ni films

et al. 1997

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Abstract. It is shown by high resolution electron microscopy that coherent plate precipitates with 0.5-1 nrn thickness are formed in Ti-rich Ti-Ni thin films when heat treated directly eom the sputter-deposited amorphous state near the crystallization temperature. The precipitates are Ti-rich and formed on (100) planes of the B2 matrix phase with perfect coherency. The crystal structure of the precipitate is a body centered tetragonal with the oaxis normal to the habit plane. Owing to the existence of these coherent subnanometric precipitates, the parent phase is greatly strengthened, resulting in very excellent shape memory properties such as 6 % recoverable shape memory strain at the stress level of 300 MPa without any appreciable plastic deformation.

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“…After annealing thin films for a short time near the crystallisation temperature the martensitic and reverse martensitic transformation temperatures are highly depressed by the formation of coherent subnanometric Ti-rich plate precipitates which causes a strengthening of the austenitic matrix. These precipitates and their influence on the martensitic phase transformation (MPT) have been extensively studied by many authors [2,[5][6]. After annealing for longer time or at higher temperatures these plate shape precipitates do not appear any more but Ti 2 Ni spherical precipitates are formed within the NiTi grains.…”

Section: Introductionmentioning

confidence: 99%

TEM studies of in situ martensitic transformation in NiTi thin films

et al. 2001

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Abstract. Amorphous sputter-deposited Ti-rich NiTi thin films were annealed at different temperatures between 600°C and 900°C for 10 min to 3 hours inducing Ti 2 Ni precipitation. Differential scanning calorimetry (DSC) was performed on these specimens and their microstructure was investigated by transmission electron microscopy (TEM). In samples annealed at 600°C and 700"C for a short time, the DSC curves show, in addition to the R transformation, a multiple phase transformation with broad peaks. TEM observations reveal the presence of a great number of spherical Ti 2 Ni precipitates inside the grains and some larger precipitates at the grain boundaries. Annealing at higher temperature results in clear defined DSC peaks. The density of the precipitates inside the grains decreases while the number and the size of the precipitates at the grain boundaries increase. TEM studies of in-situ martensitic transformation showed that the distribution of the Ti 2 Ni precipitates strongly influences the martensitic transformation behaviour while the austenite/R-phase transformation is not affected. In samples with a large amount of precipitates inside the grains, a two-step transformation was observed : the martensite appears first along all the grain boundaries and then in the centre of the grains. This unusual feature of the martensitic transformation is considered to be responsible for the multiple transformation observed in the DSC curves.

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Formation of nanocrystals with an identical orientation in sputter-deposited Ti Ni thin films

Cited by 58 publications

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Recent Developments in Sputter-Deposited Ti-Ni-Base Shape Memory Alloy Thin Films

Recent Developments in Sputter-Deposited Ti-Ni-Base Shape Memory Alloy Thin Films

Coherent Subnanometric Plate Precipitates Formed during Crystallization of As-Sputtered Ti-Ni films

TEM studies of in situ martensitic transformation in NiTi thin films

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