title: Influence of stress corrosion on the mechanical properties of laser-welded titanium.
abstract: BACKGROUND
  Whether laser-welded (LW) titanium can resist the stress corrosion produced by the combination of fluoride ions and stress in the oral environment is unknown.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to investigate the influence of stress corrosion on the mechanical properties of LW titanium.
  
  
  METHODS
  Twenty-seven titanium bars (25×2 mm) with a circular cross-section were cut in half and laser-welded, while another 27 nonwelded (NW) bars were used as the control. Thirty bars were submitted to a flexural load of 480 N at 1 Hz and immersed in artificial saliva at pH 6 (S1) or in 1000 ppm fluoride-containing saliva at pH 6.0 (S2) or 2.0 (S3) at room temperature for up to 4000 cycles. After the stress corrosion simulation, the tensile strength and Vickers microhardness were determined (n=5). Twelve LW and NW bars were submitted to the corrosion immersion test media for 51 days (n=2) to determine polarization curves (n=2) in an artificial saliva media. The corroded surface was examined with scanning electron microscopy (SEM).
  
  
  RESULTS
  The combination of fluoride and low pH significantly decreased the tensile strength of LW (P<.05). Stress corrosion did not affect the hardness of LW or NW (P>.05). NW bars immersed in S3 exhibited progressive surface dissolution, while LW bars spontaneously fractured at the welded area after 25 days of immersion in the same medium. SEM images demonstrated pitting corrosion without the presence of cracks in both groups immersed in S3.
  
  
  CONCLUSIONS
  Stress corrosion caused by acidic fluoride-containing saliva and flexural load cycling decreased the tensile strength and hardness of LW titanium bars.
authors.affiliation: Professor, Department of Dentistry, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Nancy
authors.initials: N
authors.lastname: de Assis Ferreira
authors.affiliation: Professor, Health Sciences Center, Unigranrio University, Rio de Janeiro, Brazil. Electronic address: pliniosenna@live.com.
authors.forename: Plinio Mendes
authors.initials: PM
authors.lastname: Senna
authors.affiliation: Professor, Department of Chemistry, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Dalva Cristina Baptista
authors.initials: DC
authors.lastname: do Lago
authors.affiliation: Professor, Department of Chemistry, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Lilian Ferreira
authors.initials: LF
authors.lastname: de Senna
authors.affiliation: Professor, Department of Dentistry, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Helio Rodrigues
authors.initials: HR
authors.lastname: Sampaio-Filho
mesh_terms: D003343:Corrosion; D007834:Lasers; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D012464:Saliva, Artificial; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D012464:Saliva, Artificial; D014025:Titanium