An Effective Strengthening Strategy of Nano Carbide Precipitation and Cellular Microstructure Refinement in a Superalloy Fabricated by Selective Laser Melting Process

Abstract

An effective strategy to strengthen a superalloy processed by selective laser melting (SLM) is proposed. The aim is to increase the yield strength of Inconel 718 fabricated by SLM to beyond 1400 MPa, which has never been achieved before. In this study, various NbC additions (0.0%, 0.5%, 1.0%, and 5.0% by weight) were added in the powder bed of Inconel 718, and two types of post-SLM heat treatments were investigated, i.e., solution heat treated plus aging (STA) and direct aging (DA). With NbC addition, smaller depth of melt pool and finer dendritic cells were obtained. Both STA and DA promoted the precipitations of γ’ and γ”. STA eliminated the cellular dendrites and induced grain growth while DA retained the as-built cellular dendrites, grain size, and nano-carbide from NbC addition, rendering a significant 326.2 MPa increase in yield strength. In this work, 0.5% NbC addition exhibited a record-high yield strength of 1461 MPa and ultimate tensile strength of 1575 MPa for Inconel 718 processed by laser manufacturing process according to literature data to-date.

Effect of serrated grain boundary on tensile and creep properties of a precipitation strengthened high entropy alloy

“…For electron back scattering diffraction (EBSD) analysis, an AZtec EBSD system (Oxford Instruments, UK) was utilized, samples were electropolished in 20 vol% perchloric acid +80 vol% ethanol under 20 V at −20°C for 20 s with a platinum cathode. Raw EBSD data were post-processed by the Aztec Crystal software [ 57 ]; kernel average misorientation (KAM) analysis, which has been applied to analyze the internal strain through quantifying local lattice curvature and distortion of crystalline materials in previous work [ 58 ], was used to evaluate internal strain distribution. The grain size was determined as the mean of the equivalent diameters of the grains, and the particle size was estimated by ImageJ software [ 59 ].…”

Blown-Powder Direct-Energy-Deposition of Titanium-Diboride-Strengthened In718 Ni-Base Superalloy

“…However, IN718/CoAl 2 O 4 exhibits a very high ductility. The tensile strength of the L-PBF IN718/NbC in the as-built condition [79] is ~820 MPa, which increases to ~1400 MPa after the heat treatment; however, with a ductility reduction from ~20% to ~6%. The yield strength of ~950 MPa achieved in the IN718/TiB 2 -(V) from the current study without any post-processing heat treatment is significantly higher than IN718 processed using various AM techniques and other IN718-based MMCs in the as-built condition.…”

“…Hence, the summation method is used in the present investigation as it offers a more suitable approach to approximate the increase in yield strength in the case of IN718/TiB 2 . [36] and IN718/NbC [79]. All the data as summarised in Fig.…”