Recovery of microindents in a nickel–titanium shape-memory alloy: A “self-healing” effect

Ni, Wangyang; Cheng, Yang‐Tse; Grummon, David S.

doi:10.1063/1.1476064

Cited by 120 publications

(61 citation statements)

References 16 publications

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“…This method of detecting size effects would also avoid errors in the estimation of hardness at small scales due to problems in determining contact area. In addition to hardness, the analysis of the load-displacement curves can help determine whether size effects exist in other types of deformation phenomena, as demonstrated in recent studies of the microscopic shape memory and superelastic effects in shape memory materials [272,273]. Thus, a paradigm shift may be called for in the study of indentation size effects from hardness measurements to the direct examination of the shape of indentation load-displacement curves with dimensional analysis as a guide.…”

Section: Discussionmentioning

confidence: 99%

Scaling, dimensional analysis, and indentation measurements

Cheng

2004

Materials Science and Engineering: R: Reports

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We provide an overview of the basic concepts of scaling and dimensional analysis, followed by a review of some of the recent work on applying these concepts to modeling instrumented indentation measurements. Specifically, we examine conical and pyramidal indentation in elastic-plastic solids with power-law workhardening, in power-law creep solids, and in linear viscoelastic materials. We show that the scaling approach to indentation modeling provides new insights into several basic questions in instrumented indentation, including, what information is contained in the indentation load-displacement curves? How does hardness depend on the mechanical properties and indenter geometry? What are the factors determining piling-up and sinking-in of surface profiles around indents? Can stress-strain relationships be obtained from indentation load-displacement curves? How to measure time dependent mechanical properties from indentation? How to detect or confirm indentation size effects? The scaling approach also helps organize knowledge and provides a framework for bridging micro-and macroscales. We hope that this review will accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to materials scientists and engineers, and (2) providing a better understanding of instrumented indentation measurements. # 2004 Published by Elsevier B.V.

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Section: Discussionmentioning

confidence: 99%

Scaling, dimensional analysis, and indentation measurements

Cheng

2004

Materials Science and Engineering: R: Reports

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943

512

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“…3͒, even the material had experienced a large number of scratching cycles ͑e.g., 600͒. Ni et al 14 have observed such a self-healing effect due to M → A transformation by heating. Here, the selfhealing of the scratch track indicates that the groove was caused only by A → R → M phase transformation and that the wear rate under the spherical indenter was negligible at 22°C for the given load of 10 mN.…”

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Wearless scratch on NiTi shape memory alloy due to phase transformational shakedown

Feng

Qian

Yan

et al. 2008

Applied Physics Letters

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Cyclic microscratch tests were performed to examine the scratching behavior of NiTi shape memory alloy. It shows a superior wear resistance within the temperature range of 22-120°C, but the corresponding physical mechanisms are different at low and high temperatures. We introduced the concept of phase transformational shakedown to interpret the wear-resistant behavior. At room temperature, a scratch groove may be caused by repeated scratching, but its depth stops increasing after a certain number of scratching cycles once the phase transformational shakedown state has been achieved. The groove will be self-healed upon heating as a result of the shape memory effect. At 60 and 120°C, however, no evident scratch groove is observed under the same load due to the pseudoelastic effect and the increase in the phase transition stress with temperature. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2903106͔A challenge facing many and diverse technologies stems from the wear-associated failures.1 A zero or very low wear rate may greatly enhance the performance and extend the service life of thin films, coatings, and micromachines in surface engineering and microelectromechanical systems. Single layer or multilayer coatings, with a very high hardness are often used to reduce the wear rate.2,3 However, hard coatings are apt to brittle cracking due to high stress concentrations.Owing to its remarkable shape memory effect and superelastic behavior, nickel-titanium ͑NiTi͒ alloy has found important applications in areas such as medical surgery and microelectromechanical systems. [4][5][6][7][8] However, the wear properties of shape memory alloys ͑SMAs͒ are still far from being understood due to the inherent complexity of their deformation behavior, which involves temperature-dependent reversible phase transition and plasticity of both austenite and martensite phases. 9,10 In this letter, we report our experimental observation of wearless scratching of NiTi SMA under repeated sliding. Tension, microindentation, and microscratch tests were performed at different constant temperatures. It was found that the NiTi alloy exhibits a superior wear-resistance due to the diffusionless reversible transformation between the austenite ͑A͒ and the martensite ͑M͒ phases. Different physical mechanisms underlying the wear-resistant behavior of SMAs were revealed and discussed using the concept of phase transformational shakedown. 11NiTi polycrystalline sheets of 0.5 mm in thickness were purchased from Shape Memory Applications, Inc. ͑San Jose, CA, USA͒. The nominal alloy compositions are Ni 50.7 at. % and Ti 49.3 at. %. The grain sizes are about 100 nm, as observed by transmission electron microscope. With a differential scanning calorimeter ͑DSC 92, SET-ARAM, France͒, we measured the martensite start and finish temperatures of the alloy as 2.1 and −34.5°C during cooling, and the austenite start and finish temperatures as 21.3 and 59.1°C during heating, respectively. The material was first heated to 120°C and then cooled down to 22°C suc...

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“…Most experimental and modeling efforts on the NiTi shape memory alloys have focused primarily on the thermal-mechanical deformation characteristics and their micromechanisms [2][3][4][5][6][7][8][9]. Fatigue and fracture failure is one of important design considerations in many NiTi shape memory alloy products [1,10,11] but extensive experimental investigations are lacking [11].…”

Section: Introductionmentioning

confidence: 99%

Crack Initiation and Growth in a Notched NiTi Shape Memory Alloy Sheet

2003

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An experimental investigation was carried out to study the crack initiation and growth in a single-edge notched NiTi shape memory alloy sheet under tension. It is observed that a crack initiated at the tip of a V-shape notch before the peak axial load was reached and it grew steadily across the width of the NiTi sheet until final fracture. In-plane crack-tip deformation fields at various stages of the crack growth were measured based on an image correlation technique and the crack-tip opening displacement (CTOD) and crack-tip opening angle (CTOA) were subsequently determined. The fracture surface of the NiTi sheet was dimpled based on scanning electron microscopy examinations.

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Recovery of microindents in a nickel–titanium shape-memory alloy: A “self-healing” effect

Cited by 120 publications

References 16 publications

Scaling, dimensional analysis, and indentation measurements

Scaling, dimensional analysis, and indentation measurements

Wearless scratch on NiTi shape memory alloy due to phase transformational shakedown

Crack Initiation and Growth in a Notched NiTi Shape Memory Alloy Sheet

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