Studies of Standard Heat Treatment Effects on Microstructure and Mechanical Properties of Laser Net Shape Manufactured I
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I.
INTRODUCTION
LASER net shape manufacturing (LNSM) is a laser cladding based freeform fabrication technology that uses a high energy laser beam to create three-dimensional geometries by precisely cladding thin layers of metal powder on a base material. As a rapid manufacturing method without the assistance of tooling, this technology enables quick access to new design concepts, shortens the new product introduction cycle, and enables near-net-shape repairs of costly components. One of the important applications of the LNSM technology developed at the General Electric Global Research Center is to provide an economic and flexible method to fabricate and repair high-performance components in aircraft engines, i.e., blisk blades, compressor blades, and turbine components. Geometric accuracy and material properties are the two basic, but challenging, requirements for final implementation of LNSM technology in the aircraft engine industry.
H. QI, Laser Processing Engineer, and M. AZER, Manager, Laser and Metrology Systems Laboratory, Material Systems Technologies, and A. RITTER, Principal Scientist, Ceramics and Metallurgy Technologies, are with General Electric Global Research Center, Niskayuna, NY 12309. Contact e-mail: [email protected] Manuscript submitted January 17, 2009. Article published online August 14, 2009 2410—VOLUME 40A, OCTOBER 2009
INCONEL* 718 (IN718) has been the most widely *INCONEL is a trademark of Inco Alloys International, Huntington, WV.
used nickel-based superalloy in the aircraft engine industry over the past 40 years. It has been used in many aircraft engine components, i.e., critical rotating parts, airfoils, supporting structures, and pressure vessels, accounting for over 30 pct of the total finished component weight of a modern aircraft engine.[1,2] IN718 was designed to retain high strength, creep resistance, and good fatigue life at high temperature up to 650 C. It can be strengthened by precipitating c¢¢ (Ni3Nb) and c¢ (Ni3(Al,Ti)) phases in the c matrix at normal volume fractions of approximately 16 and 4 pct, respectively, after a full heat treatment.[3] IN718 is known to have good weldability due to its relatively slow precipitation strengthening kinetics; however, the solidification process of cast or welded IN178 is often associated with segregation of high concentration refractory elements, such as Nb and Mo. As a result, a Nb-rich brittle intermetallic compound called Laves phase, represented as (Ni,Cr,Fe)2(Nb,Mo,Ti), often forms at the interdendritic regions.[4] Laves phase is known to be detrimental to the material tensile ductility, fatigue, and creep rupture properties,[3,5,6] as it depletes the principle elements needed for precipitation strengthening and aids in easy crack initiation and propagation. METALLURGICAL AND MATERIALS TRANSACTIONS A
Previous research showed that the morphology and composition of Laves phase depended strongly on the heat input and the cooling rate of a welding process;[7] i.e., welding processes with lower heat input and higher cooling rates
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