HIGH TEMPERATURE SHAPE MEMORY ALLOYS

Ch .Surya prakasaraoRoll no:155574Materials Technology Shape Memory Alloys and Applications

Contents :-

SHAPE MEMORY ALLOYS HISTORYINTRODUCTION TO SMAMECHANISM OF SMANiTiNOL (SMA)MANUFACTURINGNiTiX HTSMA NiTiPd HTSMA APPLICATIONSMERITSAND DEMERITSSUMMARY

History of shape memory alloys

The first reported steps towards the discovery of the shape-memory effect were taken in the 1930s by Otsuka and wayman.Greninger and Mooradian (1938) observed the formation and disappearance of a martensitic phase by decreasing and increasing the temperature of a Cu-Zn alloy.The basic phenomenon of the memory effect governed by the thermoelastic- behavior of the martensite phase was widely reported a decade later.The nickel-titanium alloys were first developed in 19621963 by theUnited StatesNaval Ordnance Laboratoryand commercialized under the trade nameNitinol(Nickel Titanium Naval Ordnance Laboratories).shape-memory polymershave also been developed, and became commercially available in the late 1990s

Introduction to SMA

Smart or intelligent materials are materials that have to respond to stimuli and environmental changes and to activate their functions according to these changes.The stimuli like temperature, pressure, electric flow, magnetic flow, light, mechanical, etc can originate internally or externally.Shape memory alloys are smart materials.Shape-memory alloys (SMAs) are a unique family of metals exhibiting an ability to recover macroscopic deformation introduced at low temperature simply by heating the material through a transformation temperature.Shape-memory effect (SME) is therefore the ability of a material to return to a pre-set shape upon finishing the transformation. The same alloys exhibiting SME also to some extent exhibit superelasticity.Thermoelastic martensite and Reversible transformation.

SMAExample: Copper-Aluminum-Nickel, Copper-Zinc-Aluminum, Iron- Manganese-Silicon and Nickel-Titanium alloys Ni-Ti-Pd Ni-Ti-Hf

MECHANISM SME occurs due to the change in the crystalline structure of materials.Thermoelastic martensitic transformation between high temparature austinite to low tempareture martensite.Two phases are:Martensite: Low temperature phase Relatively weakAustenite: High temperature phase Relatively strong

MARTENSITEDEFORMING MARTENSITEDEFORMED MARTENSITEAUSTENSITE

MARTENSITE

Martensite to Austenite transformation occurs by heating.Austenite to Martensite occurs by cooling.

characterstics:Phase transformation is reversibleDiffusionless transformationAtoms moves less than one lattice parameter(coordinated moment).The parent phase (austinate) is always ordered compound.

One-way vs. two-way shape memoryShape-memory alloys have different shape-memory effects. Two common effects are one-way and two-way shape memory.

SMA phases and crystal structures

Superelasticity:

SMAs also displaysuperelasticity, which is characterized by recovery of unusually large strains. Instead of transforming between the martensite and austenite phases in response to temperature, this phase transformation can be induced in response to mechanical stress This transformation can only occur in a temperature range where the critical stress for slip is greater than the critical stress for martensitic shear.

Methods for Determining Transformation Temperatures

The temperatures are commonly referred to as the martensite start (MS), martensite finish (MF), austenite start (AS), and austenite finish (AF).It is important to know these temperatures so that the alloy can be effectively used for a specific application. The thermal hysteresis (H), or difference in temperature between the AF and MS temperatures.METHODS differential scanning calorimeterBend force recovery testConstent load dilatometry

Differential scanning calorimetry (DSC) measures the heat transfer between a sample of the material and its surroundings as a function of temperature as it is heated and cooled through the transformation.Bend free recovery test (BFR), is often used to measure transformation temperatures, but is limited to measurement of only the reverse transformation.Load-bias testing, also known as Constant load dilatometry (CLD) can be used to measure transformation temperatures in a more realistic setting

Mechanical TestingMonotonic Isothermal Tension TestsLoad-Bias TestsTraining

MANUFACTURE:

Shape-memory alloys are typically made by casting, using vacuum arc melting or induction melting. These are specialist techniques used to keep impurities in the alloy to a minimum and ensure the metals are well mixed.

NiTinol: (Ni-Ti)

It Was discovered in Naval Ordnance Laboratory (NOL), Maryland, USA Ni- 50% , Ti- 50% NiTi, the high temperature B2 austenite phase transforms directly to monoclinic B19' upon cooling through the transformation, which reverts directly to B2 austenite upon heating.Binary NiTi has a useable transformation temperature (Ms) range from subzero to approximately (Af) 70 C.Nitinol has many properties desirable for actuators, including small hysteresis temperature, high work output, stable microstructure, and excellent corrosion resistance.Rapid manufacturing using lasers.Steps: design cad&cam,deposition on other materials.

Experimental setupPowder FeederHigh power Laser5 axes manipulator with CNC controlArgon atmosphere (965 mbar)No moisture!!Closed loop process control

NiTiX (HTSMA)To meet the need, several ternary alloy systems such as NiTiAu, NiTiHf, NiTiPd, NiTiPt, and NiTiZr, have been evaluated.Research conducted consisted mainly of a determination of transformation temperatures as a function of alloy content, and no-load recovery tests to determine shape-memory behaviour.Transformation temperatures decrease or remain relatively unchanged up to approximately 10 at.% ternary addition. At contents >10 at.%, transformation temperatures increase linearly in relation to ternary addition.Substitute for nickel, this increase in temperature continues until 50 at.% addition at which point the system becomes TiX.Substitute for titanium, transformation temperatures were only improved by additions up to approximately 20 at.%, above which the microstructure is no longer single phase.

NiTiPd (HTSMA)While not as effective as platinum additions in increasing the transformation temperatures.NiTiPd more desirable due to the large difference in material price between expensive platinum and the more economical palladium.NiTiPd alloys are more stable than Hf, Zr, and HfZr alloyed NiTi alloys with regard to microstructure and transformation temperature when thermally cycled.Five different ternary Ni49.5-XTi50.5PdX alloys (x = 15, 20, 25, 30, 46)

APPLICATIONSMedicineOptometryEnginesAerospaceRoboticsAutomotivePipingsCivil stucturesWater spinkersTextile

Merits and DemeritsmeritsdemeritsBio-compactibilitySimplicitySafty mechanismLight weightHigh corrosion resistensMore expensiveComplex controlPoor fatigue propertyHeat dissipation

Conclusion:Today, the most promising technologies for efficiency and improved reliability include the use of shape memory alloy materials and structures. Understanding and controlling the composition and microstructure of SAM materials are the ultimate objectives of research in this field, and is crucial to the production of good SAM materials. New and advanced SMA will definitively enhance properties.

RefrencesGlen S Bigelow, Effects of Palladium Content, Quaternary Alloying, and Thermomechanical Processing on the Behaviour of Ni-Ti-Pd Shape Memory Alloys for Actuator Applications, NASA/TM2008-214702.Jaronie Mohd Jani , Martin Leary a, Aleksandar Subic a, Mark A. Gibson, A review of shape memory alloy research, applications and opportunities, Materials and Design 56 (2014) 10781113.GLEN S. BIGELOW, SANTO A. PADULA II, ANITA GARG, DARRELL GAYDOSH, and RONALD D. NOEBE, The Minerals, Metals & Materials Society and ASM International 2010Masamine Imahashi a, M.ImranKhan a, HeeYoungKim a,n, ShuichiMiyazaki, The effect of Pd content on microstructure and shape-memory properties of TiNiPdCu alloys, Materials Science & Engineering A602(2014)1924

P.K. KUMAR AND D.C. LAGOUDAS, Introduction to Shape Memory Alloys, D.C. Lagoudas (ed.), Shape Memory Alloys, DOI: 10.1007/978-0-387-47685-81,Springer Science+Business Media, LLC 2008. Darel E. Hodgson, Shape Memory Applications, Inc., Ming H. Memry Corporation, and Robert J. Biermann, Harrison Alloys, Inc., Shape Memory Alloys, ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM Handbook Committee, p897-902 Copyright 1990 ASM International All rights reserved. www.asminternational.org Callisters Materials Science and Engineering Second Edition, Adapted by R. Balasubramaniam, Page no. 266.