Influence of oxidation on the cracks of DZ125L nickel-based superalloy thin-walled parts in laser metal direct forming

Abstract

Purpose -The purpose of this paper is to investigate the influence of the oxidation on the cracks of DZ125L nickel-based superalloy thin-walled parts in laser metal direct forming (LMDF). Design/methodology/approach -Thin-walled cylinders were fabricated in protective atmosphere with different oxygen contents in order to reveal the influence of oxidation on the morphology of cracks. The influence of oxidation on the cracks was investigated in detail by measuring the wall thicknesses of cylinders, the residual stress in the top surface of the cylinders and the composition of the cracks. Finally, the validity of the results was verified by fabricating a thin-walled turbine blade in protective atmosphere. Findings -The experimental results showed that wall thickness fluctuation of cylinders, unequal residual stress distribution of cylinders and the oxides in the crack were all the critical factors which led to crack of DZ125L thin-walled parts. Thin-walled turbine blades with no cracks can be fabricated when the oxygen content was about less than 150 ppm in protective atmosphere.Research limitations/implications -The appropriate oxygen content in protective atmosphere is helpful for fabricating thin-walled parts of nickelbased superalloy like DZ125L, and the results can show what will happen at different oxygen levels. Moreover, the results show that the cracks can be eliminated as the oxygen content reduce to less than 150 ppm rather less than 10 ppm or even less, which can reduce the cost of protective gas as forming thin-walled parts of nickel-based superalloy such as DZ125L. Practical implications -The appropriate oxygen content in protective atmosphere is helpful for fabricating thin-walled parts of nickel-based superalloy like DZ125L. However, when heavy solid parts of some other material other than DZ125L were fabricated, the oxygen content of less than 150 ppm may be not suitable. Originality/value -The influence of oxidation on the cracks of DZ125L thin-walled parts in LMDF was investigated in detail, and a DZ125L thin-walled turbine blade with no cracks was fabricated by adjusting the oxygen content in protective atmosphere.

Tensile Fracture Behavior and Failure Mechanism of Additively-Manufactured AISI 4140 Low Alloy Steel by Laser Engineered Net Shaping

“…Irrespective of the type of oxides, compressive stress is established in this thermally-grown oxide because of the diffusion. This leads to plastic deformation inside the oxide and along the interface between the oxide and the matrix in an effort to release the stress, which incurs intergranular voids attributable to the grain boundary sliding [ 45 , 73 ], resulting in the crack initiation and propagation at areas of stress concentration [ 73 , 74 , 75 ].…”

Laser Engineered Net Shaping of Nickel-Based Superalloy Inconel 718 Powders onto AISI 4140 Alloy Steel Substrates: Interface Bond and Fracture Failure Mechanism

“…It was difficult to obtain the stoichiometry of the oxides from the quantitative composition in Table 3 because of the multiple elements detected. The results of the spot analyses on the oxides were unavoidably affected by the X-ray spectra from the matrix under the oxides due to the increased excitation volume caused by high accelerating voltage [ 62 , 63 ], which made it difficult to determine the ideal chemical formula such as Al 2 O 3 and TiO 2 . However, these oxide formations can be explained by thermodynamic data as follows.…”

“…As a result, plastic deformation occurs to release the stress within the oxide and along the interface between the oxide and the matrix, which generates intergranular voids due to the grain boundary sliding [ 67 ]. These voids and continuous plastic deformations result in the crack initiation and propagation at the stress concentration area [ 62 , 67 , 68 ].…”

Cracking behavior and control of Rene 104 superalloy produced by direct laser fabrication

“…Moreover, He et al (2013) and Zhong et al (2005) also reported the occurrence of cracking in manufacturing DZ125L (wt.% (Al+Ti) = 8.0%) and IN738 (wt.% (Al+Ti) = 7.0%) by DLF, respectively. Thus, as for Rene 104 containing about 7.1 wt.% (Al + Ti) as well as 8.3 wt.% refractory elements (Ta, W, Mo), it will even be more sensitive to cracking and defects during DLF than other series of superalloys.…”