Saif Haider Kayani

Equilibrium phases in precipitation-hardened superalloys are usually regarded as detrimental because they decorate grain boundaries and promote damage. Here, using laser powder bed fusion Inconel 718 as a model system, we examine how the equilibrium δ-Ni3Nb phase responds to spatial confinement during deformation. A three-dimensional Nb-rich cellular segregation network confines δ precipitates to nanoscale intragranular sites while preserving the γ′/γ″ strengthening framework. At 25 °C, dislocations penetrate confined δ precipitates through semi-coherent interface segments, shearing the precipitates and forming ordered planar faults. At 650 °C, repeated slip-band impingement together with interfacial incompatibility and elastic mismatch promotes bending-induced lattice disordering. Density functional theory and finite-element modeling support this mechanism. Consequently, the alloy retains tensile strengths of 1149–1195 MPa with elongations of 13.2–17.1% at 650 °C. These findings reveal a temperature-dependent deformation pathway of confined equilibrium δ precipitates in LPBF Inconel 718, in which interfacial coherency, slip-band impingement, and matrix–precipitate elastic mismatch jointly govern the precipitate-scale response.

Equilibrium phases in precipitation-hardened superalloys are usually regarded as detrimental because they decorate grain boundaries and promote damage. Here, using laser powder bed fusion Inconel 718 as a model system, we examine how the equilibrium δ-Ni3Nb phase responds to spatial confinement during deformation. A three-dimensional Nb-rich cellular segregation network confines δ precipitates to nanoscale intragranular sites while preserving the γ′/γ″ strengthening framework. At 25 °C, dislocations penetrate confined δ precipitates through semi-coherent interface segments, shearing the precipitates and forming ordered planar faults. At 650 °C, repeated slip-band impingement together with interfacial incompatibility and elastic mismatch promotes bending-induced lattice disordering. Density functional theory and finite-element modeling support this mechanism. Consequently, the alloy retains tensile strengths of 1149–1195 MPa with elongations of 13.2–17.1% at 650 °C. These findings reveal a temperature-dependent deformation pathway of confined equilibrium δ precipitates in LPBF Inconel 718, in which interfacial coherency, slip-band impingement, and matrix–precipitate elastic mismatch jointly govern the precipitate-scale response.

The strength of precipitation-hardened Al–Si–Mg alloys primarily derives from the nanoscale coherent β″ precipitates, which are the dominant contributors to strengthening under peak-aged conditions. Observing these nanoscale precipitates via TEM is particularly challenging due to their strict orientation relationship with the matrix and the subtle atomic number differences between Al, Si, and Mg. In this study, we investigate the precipitation behavior of a high-Si Al–Si–Mg alloy through a comprehensive and systematic microstructural analysis. We demonstrate that the key strengthening mechanism in the peak-aged alloy is the high number density of nanoscale β″ precipitates. The atomic structure of the β″ phase is revealed using HR-TEM, HAADF, and LAADF imaging along the < 010 > Al zone axis. HR-TEM provides clear reflections in the FFT, facilitating effective observation and identification of the β″ phase. Additionally, LAADF imaging proves particularly useful in resolving the atomic structure of the β″ phase. These precipitates display an eye-like morphology, with four Mg and Si atoms arranged in a rim and a central Mg/Al atom, forming a long-range ordered structure. This detailed characterization offers valuable insights into the contribution of β″ precipitates to the alloy’s age-hardening behavior.

Metallic materials are the workhorses of structural applications and remain central to modern engineering across energy, transportation, process equipment, and extreme-environment service

Metallic materials continue to attract significant interest for structural applications globally, ranging from high-performance sectors like aerospace and automotive industries to everyday household items