Potentials of manufacture and repair of nickel base turbine components used in aero engines and power plants by laser metal deposition and laser drilling

IntroductionExpensive turbine parts like HPT(HighPressure Turine)blades or vanes are replaced bynew parts in case of damage.For example theburn through of the inner side of a blade or vane(Figure 1)is a frequently appearing damage,which cannot be repaired…

Potentials of manufacture and repair of nickel base turbine components used in aero engines and power plants by laser metal deposition and laser drilling

High pressure turbine (HPT) parts like blades and vanes with integrated cooling channels are challenging concerning overhaul and repair.So far damaged parts have to be replaced by the operator.The aim is to design and implement a refurbishment process chain to avoid scrapping of used parts.This process chain implies three different laser applications 1.Direct Laser Forming (DLF),2.Laser Metal Deposition (LMD) and 3.Laser Drilling (LD).The laser processing was extended in the last years towards application near materials like Nickel and Titanium base alloys.Concerning LMD and DLF the achieved results are investigated regarding macro and micro structure,hardness,defects (e.g.cracks,bonding defects,porosity) and contamination with atmospheric elements (e.g.O, N,C and H) are presented for Titanium alloys like Ti-6Al-4V,Ti-6246 and Ti-17 as well as for Nickel base alloys like Inconel 718 and Rene 80.Suitable process parameters are presented with the achieved static (tensile) and dynamic mechanical properties (HCF) and compared to those of heat treated raw materials.One innovative solution (manufacturing case) is to fabricate the small and complex shaped geometrical elements by LMD and/or DLF.By LMD these elements are built-up directly.With DLF the elements are manufactured separately in the DLF machine and connected by a subsequent joining technique with the large parts.With DLF small complex shaped parts like combustor swirlers,HPT blades and vanes with internal cooling channels are manufactured completely.LMD and DLF can be used in combination with subsequent LD.Depending on the application two different drilling techniques by dominant melt ejection-percussion drilling and trepanning-are classified and characterised.The drilling techniques are exemplarily presented for stainless steel and nickel base alloys (diameter 0.2～0.6 mm,aspect ratio＜30,inclination up to 60°) using pulsed laser radiation (Nd:YAG,1064 nm,0.5～1 ms).The experimental results of coaxial process control,metallography and optical microscopy regarding hole depth and hole diameter as well as the thickness of recast are presented.