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Challenges in thermal spraying techniques

The major drawback of thermal spraying techniques is that all the light alloys used in aeronautics (aluminum, magnesium, titanium alloys) are very sensitive to high temperature, exposure to fast cooling rates and oxygen contamination.

In particular the disadvantages of a high temperature approach are related to:

  • Melting of base materials; Thermal degradation could start at 200-300°C in the case of thermal treated alloys (i.e. aluminum-copper alloys)
  • Residual stresses development due to high cooling rate
  • Occurrence of mechanical distortions and limitations in the typology of repairable components
  • Oxidation and noticeable porosity development of both base materials and interface between base and added materials
  • Reduction of mechanical properties due to the oxide contents (in particular for titanium alloys) at the interface and in the repaired area
  • Bad adhesion between base material and repair due to the presence of pores, brittle and low adherent oxides (in particular for magnesium alloys)
  • Low achievable coating/repair thickness and unsatisfactory achievable level of porosity (in the case of plasma spray and thermal spray techniques) of the repaired part
  • Poor versatility of available materials (no magnesium alloys may be used and only a small fraction of aluminum and titanium alloys)