Microstructure evolution and mechanical characterization of Nd:YAG laser beam welded titanium tubes

R. Palanivel, I. Dinaharan, R. F. Laubscher

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

Grade 2 titanium tubes of outer diameter 60 mm and wall thickness 3.9 mm were effectively joined by Nd:YAG laser. The welding speed was varied in five levels (2.50, 2.75, 3.00, 3.25 and 3.50 m/min). The microstructure evolution was studied using optical microscopy and advanced characterization techniques. The bead geometry changed from parallel shape to wedge shape with increased welding speed due to changes in surface tension. The macrographs showed three zones namely fusion zone, heat affected zone (HAZ) and base metal. Coarse granular structure with irregular and serrated contours was observed in the fusion zone. Acicular α grains were observed at the extreme outer edge of the fusion zone due to rapid cooling. Spherical and irregular shaped pores were observed near the centerline of the fusion zone at lower welding speeds due to large amount of entrapped gases and downward sweeping solidification front. The grain size decreased with increased welding speed due to higher cooling rate. The misorientation angle distribution map showed three distinct regions. The increase in welding speed caused an increase in low angle boundaries and a reduction in very high angle boundaries. High density of dislocations was observed in the fusion zone due to thermal stresses caused by solidification. The microhardness of the fusion zone was recorded to be higher than base metal due to substructure boundaries, solute elements and dislocations. The increase in welding speed shifted the fracture location from fusion zone to base metal and fracture mode from brittle to ductile.

Original languageEnglish
Pages (from-to)225-235
Number of pages11
JournalMaterials Characterization
Volume134
DOIs
Publication statusPublished - Dec 2017

Keywords

  • Laser beam welding
  • Microstructure
  • Tensile strength
  • Titanium
  • Tube

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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