Heat Treatment Effect on Microstructure and Mechanical Properties of Re-Containing Inconel 718 Alloy

Abstract

The effect of Rhenium additions to the standard Inconel 718 (ST IN718) alloy as well as solution and aging treatments on microstructure and hardness property were studied. The microstructure of Re-containing alloys has higher volume fraction of δ phase than standard alloy. Conventional solution treatment (CST) at 1273 K for 1 h precipitates a thin film of δ phase at the grain boundaries as well as needle-like in  matrix; however, after modified solution at 1440 K for 3 h long, both types of δ phase precipitates entirely vanish from the microstructure. Small colonies of needle-like δ phase start to appear with aging at 1023 K for 4 h, after CST. Prolonging the aging time to 50 h, these colonies enlarge in size and spread in the matrix. XRD and TEM observations were used to identify the precipitation of hard " and ' phases.The changing in hardness measurements were evidence about the precipitation of these hard phases. CST have higher rate to increase in hardness with aging time comparing to modified solution specimens.

Degradation of Creep Resistant Ni - Alloy During Aging at Elevated Temperature Part II: Structure Investigations

“…Many attempts were made to increase stability of the structure of Ni-base superalloys. One and relatively simple method is appropriate design of chemical composition described in elaborations [2,3].…”

“…The strengthening of Ni-base superalloys arises from combined hardening mechanisms including: solid-solution atoms, precipitates and grain boundaries. Among them the most effective is precipitation hardening by coherent Ni 3 M -type intermetallic phases: γ" {Ni 3 (Nb, Ti, Al)} and γ' {Ni 3 (Al,Ti)} [1]. Precipitation of γ" phase characterizes with unique strengthening effect because of high coherency strain strengthening caused by large mismatch between them and γ matrix.…”