Contrasting Effects of TiN and W on Cracking in LPBF Inconel 939

Abstract

Inconel 939 (IN939) is a crack-sensitive nickel (Ni)-based superalloy when processed by laser powder bed fusion (LPBF), which limits its broader adoption for additively manufactured turbine components. This study comparatively evaluates two distinct alloying strategies—ceramic particle reinforcement (1 wt.% titanium nitride [TiN]) and solid-solution strengthening (1 wt.% tungsten [W])—to clarify their contrasting influence on crack evolution, microstructural development, and mechanical response under identical LPBF processing conditions. All compositions were fabricated using a single set of optimized parameters to isolate compositional effects from processing variations. Optical microscopy revealed that TiN addition increased both crack density and porosity, whereas W addition reduced crack density and improved densification relative to the pristine alloy. Electron backscatter diffraction showed similar columnar grain structures across all conditions with weak global texture, although localized orientation sharpening was observed in the vicinity of crack networks. Differential scanning calorimetry indicated that TiN broadened the melting/solidification range, while W shifted transformation temperatures slightly upward and produced more gradual thermal transitions. Room-temperature tensile testing demonstrated that TiN significantly reduced tensile strength and ductility, whereas W preserved a predominantly ductile response with properties comparable to those of the pristine alloy. These findings highlight the fundamentally different microstructural and mechanical consequences of ceramic versus solid-solution additions in LPBF IN939 and provide guidance on compositional strategies for mitigating crack susceptibility in additively manufactured Ni-based superalloys.