Product Code: ICA12_509

Structure of Ni-Alloys Deposited by Laser Powder Deposition on Single Crystal Superalloy Substrates
Authors:
Rui Vilar, Instituto Superior Técnico and ICEMS Instituto de Ciência e Engenharia de Materiais e Superfícies, Univ. Tecnica de Lisboa; Lisbon Portugal
Amelia Almeida, Instituto Superior Técnico and ICEMS Instituto de Ciência e Engenharia de Materiais e Superfícies, Univ. Tecnica de Lisboa; -
Edson Costa, Department of Mechanical Engineering, Kyushu Univ.; -
Presented at ICALEO 2012

Laser Powder Deposition is becoming one of the most promising methods for the repairing of the single crystal Ni-based superalloys components presently used in the hot section of gas turbine engines in order to extend their lifetime and reduce their overall cost. In the present paper recent results obtained by the authors in the study of the structure of multilayer depositions of NiCrAlY and René N4 on (100) single crystal substrates of SRR99 and CMSX-4 Ni-based superalloys will be summarized. The deposited material presents a columnar dendritic microstructure consisting of arrays of similarly oriented dendrites forming altogether a single crystal. Since solidification is epitaxial, the depositions inherit the orientation of the substrate. They also show a mosaicity and crystallographic perfection that is similar to or better than those of the substrate, but the scatter in orientation tends to increase as new layers of material are deposited. When aging is carried out in the laser deposited condition, the γ-Ni3Al precipitates do not present the cuboids required to ensure high temperature strength. It is shown that this behavior is due to chemical segregation within the primary dendrite arms resulting from solute partition during solidification. Heat treatments capable of homogenizing the material, leading to the precipitation of γ strengthening phase with the proper particle shape and size were devised. These heat treatments also dissolve detrimental, topologically close packed intermetallic compound particles formed in the interdendritic regions in some alloys.