title: The influence of carbon content on cyclic fatigue of NiTi SMA wires.
abstract: OBJECTIVE
  To evaluate two NiTi wires with different carbon and oxygen contents in terms of mechanical resistance to rotary bending fatigue (RBF) under varied parameters of strain amplitude and rotational speed.
  
  
  METHODS
  The wires produced from two vacuum induction melting (VIM) processed NiTi ingots were tested, Ti-49.81 at%Ni and Ti-50.33 at%Ni, named VIM 1 and VIM 2. A brief analysis related to wire fabrication is also presented, as well as chemical and microstructural analysis by energy dispersive spectroscopy (EDS) and optical microscope, respectively. A computer controlled RBF machine was specially constructed for the tests. Three radii of curvature were used: 50.0, 62.5 and 75.0 mm, respectively, R(1), R(2) and R(3), resulting in three strain amplitudes ε(a) : 1.00%, 0.80% and 0.67%. The selected rotational speeds were 250 and 455 rpm.
  
  
  RESULTS
  The VIM 1 wire had a high carbon content of 0.188 wt% and a low oxygen content of 0.036 wt%. The oxygen and carbon contents of wire VIM 2 did not exceed their maximum, of 0.070 and 0.050 wt%, according to ASTM standard (ASTM F-2063-00 2001). The wire with lower carbon content performed better when compared to the one with higher carbon content, withstanding 29,441 and 12,895 cycles, respectively, to fracture.
  
  
  CONCLUSIONS
  The surface quality of the wire was associated with resistance to cyclic fatigue. Surface defects acted as stress concentrators points. Overall, the number of cycles to failure was higher for VIM 2 wires with lower carbon content.
authors.affiliation: Instituto Tecnologico de Aeronautica-ITA, Sao Paulo, Brazil. tcmatheus@yahoo.com.br
authors.forename: T C U
authors.initials: TC
authors.lastname: Matheus
authors.forename: W M M
authors.initials: WM
authors.lastname: Menezes
authors.forename: O D
authors.initials: OD
authors.lastname: Rigo
authors.forename: L K
authors.initials: LK
authors.lastname: Kabayama
authors.forename: C S C
authors.initials: CS
authors.lastname: Viana
authors.forename: J
authors.initials: J
authors.lastname: Otubo
mesh_terms: D002244:Carbon / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry*; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004868:Equipment Failure; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D012390:Root Canal Therapy / Q000295:instrumentation*; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D002244:Carbon; D009532:Nickel; D014025:Titanium; D010100:Oxygen