Repair and manufacturing of single crystal Ni-based superalloys components by laser powder deposition—A review

Abstract

Laser powder deposition is one of the most promising methods for the repairing of the single crystal Ni-based superalloys components used in the hot-section of gas turbine engines in order to extend their lifetime and reduce their overall cost. The microstructure of Ni-based superalloys deposited on single crystal substrates of similar materials depends mainly on the materials involved, on the orientation of the deposited tracks in relation to the substrate and on the deposition parameters. In the present paper these relations are discussed and illustrated for the case of single and multiple layer depositions of NiCrAlY and Rene N4 on (100) single crystal substrates of SRR99 and CMSX-4 Ni-based superalloys. On the other hand, when the aging treatment is applied directly to the solidification microstructure resulting from laser deposition, abnormal γ/γ′ microstructures may result, due to the inhomogeneity created by alloying elements partition during solidification. Performing a homogenization annealing before aging circumvents this difficulty. The homogenizing annealing also eliminates undesirable brittle phases present in the solidification microstructure, such as carbides and topologically close-packed compounds.

A synchrotron study of microstructure gradient in laser additively formed epitaxial Ni-based superalloy

“…It is interesting that the crystal grain morphology in Zone II is different from that in Zone I and III but they are all epitaxial. This phenomenon was also observed by other researchers and it is believed to be related to the relative rate of solidification and laser scanning speed, although the detailed mechanism is still unclear 5 .…”

“…The absence of grain boundaries contributes to their outstanding performance when exposed to severe conditions, such as high temperature, vibration, corrosion, and creep rupture 4 . In order to extend the service life and reduce the overall cost of these expensive single crystal blades or vanes, new repair/reshaping techniques are desired, while preserving the single crystalline nature of the Ni-based superalloy 5 . One of the most promising techniques at present is laser additive forming, also known as 3-D printing, laser metal direct forming, or additive manufacturing 6 7 .…”

“…However, due to the influence of solidification kinetics, the preferred orientation sometimes may deviate from the axial direction of the actual growth, and thus stray grains, the crystal orientation of which is different from the substrate and epitaxial grains, are formed during the laser direct forming process 10 11 . Two of the major questions that remain to be answered for laser additive forming are how well one can preserve the single crystalline nature and how effectively one can avoid the thermal effects such as hot cracking 5 9 . It is therefore important to investigate thoroughly the disorientation between the laser deposited layers and the substrate and the defect density in the laser directly formed materials, which are the main index parameters of epitaxial growth quality and determine the materials resistance to external thermal and mechanical loading.…”

Mechanism of heat affected zone cracking in Ni-based superalloy DZ125L fabricated by laser 3D printing technique

“…The DZ125L alloy is a commonly used directionally solidified Nibased superalloy for fabricating turbine blades and vanes in China [18]. As a surrogate of repairing the tip of turbine blade fabricated by directional solidification along 〈001〉 crystallographic direction, the repair surface chosen in this study was parallel to the (001) crystal plane of the substrate [19][20][21]. Each cladding layer was deposited by feeding gas-carried DZ125L superalloy powders into the melt pool generated by laser heating at the surface and protected from oxidation by an argon atmosphere.…”

A Real-Time Method to Detect the Deformation Behavior during Laser Solid Forming of Thin-Wall Structure

“…The movement of the laser beam solidifies the molten pool and forms a deposited layer with full-density, crack-free deposit, and full-strength fusion bond to the substrate under appropriate operating conditions [6]. This process has been used for the direct fabrication of metal parts, surface coating, and repairing damaged components [7][8][9], and can also be used to produce functional-gradient materials [10,11] and composite materials [12,13], both of which cannot be fabricated via conventional means. Many pieces of research focused on the process, microstructure, and properties of LSF technology [14][15][16].…”