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Research Papers

Processing of Small Scale Nitinol Billets by Induction Heated Nonconventional Isothermal Extrusion (IHNCIE)

[+] Author and Article Information
J. Butler, P. Tiernan, A. A. Gandhi, S. Beloshapkin

Materials and Surface Science Institute, University of Limerick, Limerick, Ireland

S. A. M. Tofail1

Materials and Surface Science Institute, University of Limerick, Limerick, Irelandtofail.syed@ul.ie

1

Corresponding author.

J. Eng. Mater. Technol 133(2), 021009 (Mar 04, 2011) (11 pages) doi:10.1115/1.4003108 History: Received March 16, 2010; Revised September 11, 2010; Published March 04, 2011; Online March 04, 2011

This paper describes a novel process designed specifically for extruding small scale billets, between 850°C and 950°C, in very short cycle times of 10 min. Induction heated nonconventional isothermal extrusion (IHNCIE) is used to produce wires of Nitinol and compare its efficacy with wires produced conventionally by hot rolling. With two four to one area reductions, a wire of 3 mm diameter was formed by IHNCIE. The extruded wires showed good superelastic tensile properties. This 3 mm diameter extruded wire exhibited a microstructure with grains of approximately 2μm without a recrystallization anneal. Our method offers an alternative route for the production of small scale billets into a wire.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the SE mechanism

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Figure 2

Schematic of the SME mechanism

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Figure 3

(a) The induction heater, vertical hydraulic press with extrusion tool, and control and monitoring computer are shown. (b) A typical induction heater coil, ice can be seen projecting from the coil.

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Figure 4

Calibration graph using three thermocouples in the billet and a fourth thermocouple in the barrel

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Figure 5

Schematic of the isothermal extrusion setup

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Figure 6

(a) Die drawing, (b) image of die after extrusion, and (c) copper push out block

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Figure 7

Typical improvement attainable through canning and glass lubrication, bottom curve. Top curve is for uncanned NiTi and middle is for NiTi just canned in Cu10Ni.

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Figure 8

(a) Cu10Ni canned NiTi billet, (b) Cu10Ni recanned extrudate, and (c) example of the extrudate with the Cu10Ni can still covering the NiTi

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Figure 9

(a) Close up view of the extrusion barrel being heated and (b) the extrusion barrel and copper shielding ring

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Figure 10

Profile of extrusion pressure versus displacement for the initial billet and for the re-extrusion

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Figure 11

Schematic representation of the classic extrusion pressure versus displacement curve

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Figure 12

Tensile test data for extruded and rolled NiTi 3 mm diameter wire

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Figure 13

Tensile test data for extruded NiTi 3 mm diameter wire loaded 3 times in succession

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Figure 14

DSC of (a) 9 mm billet, (b) 5 mm extruded rod, (c) 5 mm rolled rod, (d) 3 mm extruded wire, (e) 3 mm rolled wire, (f) 3 mm extruded and annealed wire, and (g) 3 mm extruded and annealed wire

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Figure 15

XRD of hot rolled and hot extruded 3 mm wires

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Figure 16

Extrusion and rolling direction from left to right. Microstructural images of (a) a 9 mm billet showing grain structure and TiC inclusions (optical), (b) same as (a), SEM, (c) same as (a) (optical and unetched), (d) a 5 mm extruded rod showing grain structure and TiC inclusions (optical), (e) same as (d), SEM, (f) same as (e) at a higher magnification, (g) a 5 mm rolled rod showing grain structure and TiC inclusions (optical), (h) same as (g), SEM, (i) same as (h) at a higher magnification, (j) a 3 mm extruded wire showing grain structure and TiC inclusions (optical), (k) same as (j), SEM, (l) same as (k) at a higher magnification, (m) a 3 mm rolled wire showing grain structure and TiC inclusions (optical), (n) same as (m), SEM, and (o) same as (n) at a higher magnification.

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Figure 17

Schematic representation of grain recrystallization during (a) rolling and (b) extrusion

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