TY - JOUR
T1 - Experimental study on dieless drawing of Nickel-Titanium alloy
AU - Twohig, E.
AU - Tiernan, P.
AU - Tofail, S. A.M.
N1 - Copyright © 2012 Elsevier Ltd. All rights reserved.
PY - 2012/4
Y1 - 2012/4
N2 - The effect of a dieless drawing process on commercial grade Nickel-Titanium rods, of 5mm diameter, was investigated by varying the established critical process parameters of temperature, cooling rate, drawing velocity, and heating/cooling velocity. The rods were successfully dieless drawn with a maximum steady state reduction in cross-sectional area of 54%. The thermal and mechanical loading profiles of the rod during processing, and the resulting changes in microstructure and hardness, have been investigated. Uniform levels of stress and strain resulted in uniform reduction of the rod cross-sectional area. The grain structure was highly deformed in the drawing direction and increased porosity was observed as a result of the process. The longitudinal section hardness of the rod was significantly reduced as a result of the dieless drawing process. Any failures that arose were due to discontinuities within the material microstructure caused by a high necking rate, shorter exposure time to the process temperature and low heating and cooling rates. A uniform oxidation layer was observed on the surface of the processed rods as a result of processing in atmospheric conditions. This oxidation layer has the potential to aid in the lubrication of subsequent cold working operations of the dieless drawn rods. Coupling the thermomechanical effects of the dieless drawing process with a cold drawing processing step has the potential to produce a NiTi wire in fewer passes, and therefore at a reduced cost.
AB - The effect of a dieless drawing process on commercial grade Nickel-Titanium rods, of 5mm diameter, was investigated by varying the established critical process parameters of temperature, cooling rate, drawing velocity, and heating/cooling velocity. The rods were successfully dieless drawn with a maximum steady state reduction in cross-sectional area of 54%. The thermal and mechanical loading profiles of the rod during processing, and the resulting changes in microstructure and hardness, have been investigated. Uniform levels of stress and strain resulted in uniform reduction of the rod cross-sectional area. The grain structure was highly deformed in the drawing direction and increased porosity was observed as a result of the process. The longitudinal section hardness of the rod was significantly reduced as a result of the dieless drawing process. Any failures that arose were due to discontinuities within the material microstructure caused by a high necking rate, shorter exposure time to the process temperature and low heating and cooling rates. A uniform oxidation layer was observed on the surface of the processed rods as a result of processing in atmospheric conditions. This oxidation layer has the potential to aid in the lubrication of subsequent cold working operations of the dieless drawn rods. Coupling the thermomechanical effects of the dieless drawing process with a cold drawing processing step has the potential to produce a NiTi wire in fewer passes, and therefore at a reduced cost.
KW - Dieless rod drawing
KW - Differential interference contrast
KW - High temperature processing
KW - Microstructure
KW - Nickel-Titanium
KW - Oxidation
UR - http://www.scopus.com/inward/record.url?scp=84856030549&partnerID=8YFLogxK
U2 - 10.1016/j.jmbbm.2011.12.013
DO - 10.1016/j.jmbbm.2011.12.013
M3 - Article
C2 - 22402150
AN - SCOPUS:84856030549
SN - 1751-6161
VL - 8
SP - 8
EP - 20
JO - Journal of the Mechanical Behavior of Biomedical Materials
JF - Journal of the Mechanical Behavior of Biomedical Materials
ER -