Development of Oxide-Dispersion-Strengthened Nickel-Based Super Alloy Powders for Additive Manufacturing

Abstract

Oxide-Dispersion-Strengthened (ODS) Nickel-Based superalloy has been drawn a huge attention and developed with good oxidation resistance, corrosion resistance and high creep strength. It has been considered as critical materials for Additive Manufacturing (AM). The quality and the efficiency of fabrication methods of ODS limits the performance of itself on AM. The development of new type of ODS, new methodologies and evaluation techniques are required if the enhanced quality of ODS and enhanced efficiency of fabrication are to be achieved. Of the current fabrication techniques for AM, Gas Atomization (GA) is widely used since they can generate spherical powders with high qualities. However, GA is incapable of producing Ni-based ODS powders with uniform dispersion oxide contents since it requires the melting on constituent powders, and oxide contents have higher melting point than other major contents. Ball-milling (BM), is a prevailing and wellknown technique for ODS and has been proven with the capability of producing particles with nanocrystalline structures. Mechano-Chemical-Bonding (MCB) is another new type of technique by using mechanical alloying effect without adding any binders to produce ODS. In this research, MCB (MCB-only process) and its combined technique (MCB+BM process) were carried out to produce ODS powders with composition of Ni-20Cr-5Al-3W-1.5Y2O3 in wt%. The MCB is different with previous published techniques, raw element particles are subjected to breakdown, mixing, diffusion bonding, fracturing, shearing, and re-welding under different rotating speeds and different running durations. X-ray Diffraction (XRD) was adopted to prove that Y2O3 has been evenly distributed onto major particles. Also, the morphology, shape and size of particles are analyzed Scanning Electron Microscope (SEM). More spherical in shape and smoother particle surface produced by the MCB than the BM that benefits powder feeding during AM. Also, X-ray diffraction (XRD) was utilized to examine the lattice spacing of crystal structure. Three different batches of powders fabricated by the MCB process and its combined techniques were used in two different AM system. Results shows the powders were successfully deposited onto flat substrates and densified microstructures were obtained. In order to investigate the as-printed microstructure, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were employed. In conclusion, MCB-only technique can manufacture desirable Nickel-base alloy for AM by determining the particle shape, surface and size characteristics, as well as, reasonable alloy status and profound microstructure.

Development of Ni-based Oxide Dispersion Strengthened (ODS) powder particles for Metal Additive Manufacturing (AM) Applications

“…On the other hand, the columnar structure in Figure 5-15 (c) is still evident as the building direction moved forward. Thus, the input energy of 250W-7.55J/mm sample was not sufficient and decreased with advancement of the building direction comparing the 275W-8.33J/mm sample [44]. Unlike the ambiguous epitaxial characteristics shown in Figure 5-16 (b), the columnar dendrites generally displayed the epitaxial growth with a higher degree of clustering on increasing laser power.…”

“…Generally, the major input energy and heat induced by laser radiation were transmitted through the substrate of previous as-printed layers, which in turn facilitated the formation of typical columnar dendrite structures along the building direction [43,45,46]. Also, residual thermal stress as a result of the repeated rapid melting and solidification at a higher laser power was remained in the workpiece [47] which results in the generation of thermal cracks in both dendrite and inter-dendritic regions that were observed in the SEM micrographs [44].…”

“…Because the powders were processed by MCB+BM process, the PCA, stearic acid, with the composition of CH3 (CH2)16CO2H to boost the MA effect during the BM process. Some of the carbon remained after the BM process and reacted with major elements Ni, Cr, and Al to form carbides during the printing process [44].…”