Evolution of Lattice Spacing of Gamma Double Prime Precipitates During Aging of Polycrystalline Ni-Base Superalloys: An In Situ Investigation

Abstract

Inconel 718 derives the strengthening mainly from Ni 3 Nb c¢¢ phase. To investigate the evolution of lattice spacing of c¢¢ precipitates, in situ neutron diffraction experiments were performed during aging heat treatment of two Inconel 718 bar samples at 780°C for 8 hours. One sample was aged with a negligible applied stress (5 MPa) and the other with an applied tensile stress of 300 MPa. The diffraction data demonstrate three stages of lattice spacing evolution due to compositional and morphological changes during aging. (1) Stage I, the c lattice spacing decreases isotropically in the first hour of aging as the composition changes. (2) Stage II, the c lattice spacing decreases and the c¢¢ lattice spacing increases between 1 and 5 hours of aging, at this stage compositional change on the lattice evolution weakens with aging time and the morphological change becomes comparable. (3) Stage III, as aging proceeds, compositional change is negligible, while morphological change is dominant; the c lattice spacing decreases in the longitudinal direction but increases in the transverse direction; in contrast, the converse occurs in c¢¢ lattice spacing evolution.

In-Situ Determination of Precipitation Kinetics During Heat Treatment of Superalloy 718

“…[16][17][18][19][20] Challenges in characterizing the very fine microstructure typically formed in solution-treated-and-aged 718 via transmission or high-resolution-scanning electron microscopy and atom-probe tomography have spurred the development of other approaches to understand/quantify phase-transformation kinetics. These include non-destructive evaluation (in-situ) methods such as electrical resistivity, various ultrasonic methods, neutron diffraction (e.g., to determine the temporal evolution of lattice parameters under isothermal conditions [21] ), and differential thermal analysis (e.g., to establish the onset of precipitation or dissolution of c¢¢, c¢, and d during heating and cooling [22,23] ). Alternatively, several attempts have been made to develop modeling-and-simulation techniques which treat the detailed mechanisms of nucleation, growth, and coarsening of the precipitate phases in 718 (as well as related alloys such as 625 and 718Plus).…”

Investigation of the Superlattice Phases Formed in Ta72Ru28

“…the orientation of the α’’ phase coloured cyan in Figure 4 e corresponds with a positive strain in Figure 4 g, but not Figure 4 h. This demonstrates that whilst the b axis of the α’’ phase closely matches the A2 lattice parameter, the c axis is slightly longer than 3 times the lattice parameter of the A2 phase. This coherency strain relative to the A2 phase is less than some of the observed strains in the γ’’ phase in Ni superalloys [ 16 , 17 ]. It may be the case that, given a suitable (very) high-temperature solution treatment followed by quenching and ageing, that an improved distribution of α’’ phase can be obtained, akin to that found in nickel-base superalloys.…”

Tool Life and Surface Integrity Characteristics of SLM and C&W Inconel 718 in Dry and MQL Condition

“…During dry machining the temperature is more than 1000°C, a strong tendency to welding to the cutting tool alters the tool geometry by Build Up Edge (BUE) formation. The abrasive wear occurs due to the presence of hard carbides such as TiC and NbC trapped at the tool-chip interface generates groove marks on the chip and starches on the tool [26].…”