Modification of M23C6 carbides by Ti addition in Ni-based polycrystalline superalloy

Abstract

The M₂₃C₆ phase is usually precipitated in high-Cr content Ni-based polycrystalline superalloys, which has significant effects on properties of the alloys. In this work, the role of Ti on the modification of M₂₃C₆ carbides was investigated. In the alloys without Ti (6.6Al-0Ti alloy), MC carbides decomposed and M₂₃C₆ carbides precipitated during primary aging treatment. In contrast, alloy containing Ti (3.8Al-3Ti alloy), MC carbides remained stable throughout aging process and M₂₃C₆ carbides precipitated during secondary aging treatment. Furthermore, M₂₃C₆ carbides distributed along grain boundaries in 6.6Al-0Ti alloy were larger and more regular. According to first-principle calculations, the formation energy of MC carbide in 3.8Al-3Ti alloy was lower, which indicated MC carbide was more stable, resulting in limited carbon available for M₂₃C₆ carbides precipitation. Therefore, the introduction of Ti would inhibit precipitation of M₂₃C₆ carbides due to more stable MC carbides in superalloy containing Ti.