Effects of Ti + Al content on the microstructure and mechanical properties of a new nickel-based superalloy fabricated by laser directed energy deposition

Abstract

Laser additive manufactured high γ′-phase nickel-based superalloys have a high cracking susceptibility due to the unique characteristics of superalloys, which can hinder their widespread application. This work overcomes the above challenges via a compositional optimization strategy, and a novel nickel-based superalloy with high γ′ phase has been developed via laser directed energy deposition (LDED). The effects of the various Al + Ti (1:1) contents (6.4, 6.6 and 6.8 wt.%) on microstructure and mechanical properties (room temperature, 850 °C and 900 °C) of the as-deposited and heat-treated specimens were investigated. Ultimately, the crack-free Ni-based superalloy has been successfully designed and fabricated by LDED, featuring a high γ′ phase content. The results indicated that the γ′ phase content and the number of the MC carbide particles increase with the increasing Ti + Al content. When the Ti + Al content is 6.6 wt.%, the newly designed Ni-based superalloy exhibits exceptional tensile properties (UTS: 1450 ± 42 MPa, YS: 1100 ± 36 MPa and EL: 16.5 ± 1.1%). After heat treatment, the γ′ phase, bulk-like (MC), long strips-like (M₂₃C₆) carbide and moderate amount of needle-like σ phase are present in the alloy with Ti + Al content of 6.6 wt.%. Therefore, the newly designed Ni-based superalloy exhibits superior tensile properties at 850 °C (UTS: 818 ± 34 MPa, YS: 774 ± 29 MPa and EL: 10 ± 0.7%) and 900 °C (UTS: 581 ± 28 MPa, YS: 558 ± 20 MPa and EL: 11.7 ± 0.9%). This approach provide a new alloy design route for achieving optimization of high-temperature mechanical properties and formability of nickel-based superalloys with high γ′ phase for laser additive manufacturing.