Search

Precipitation of the secondary phase is a key factor that influences the strengthening effect of nickel-based superalloy. The precipitation behaviours of the M23C6 carbide and γ′-Ni3(Ti, Al) phase in Inconel 617B alloy aged at 700°C for different times were studied by scanning electron microscopy, transmission electron microscopy and atom probe tomography. Plate-like carbide nucleated in the interior of grain and irregular shape carbide precipitated at grain boundary respectively during the early stage of ageing. γ′ particle co-precipitated around carbide is a common microstructure feature during ageing for 5–160 h. After ageing for 160 h, γ′ phase is the main secondary phase. The carbide only distributes on the grain boundary, high density γ′ particle homogeneously distributes in the matrix after a longer ageing time. Elemental partitioning to the secondary phases and composition profiles across different phases was quantitatively analysed. Enrichments of Ti and Al at the carbide/γ interface are directly observed, which act as the nucleation site of γ′ particles during ageing. Enrichments of B, Si and Co at different interfaces are also detected. Based on the experimental results, the precipitation mechanisms of γ′ particles and carbide were discussed. [ABSTRACT FROM AUTHOR]

The post-heat treatment of laser powder bed fusion (LPBF) Sc-modified Al alloy is a remarkably necessary method to improve mechanical properties. In this work, the LPBF Al-Mn-Sc alloys with a high yield strength of 586 ± 4 MPa and excellent elongation of 14.5% were obtained by a novel and efficient non-isothermal aging (NIA) treatment at the heating rate of 2 °C/min from 30°C to 350°C. The precipitation behaviour and mechanical properties of the LPBF Al-Mn-Sc alloys after NIA treatment were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), hardness test as well as tensile test. The activation energy and Avrami exponent were calculated through DSC results with various heating rates. A non-isothermal aging kinetic model was applied to evaluate the NIA process referring to isothermal aging. The excellent mechanical property was analysed by revealing the strengthening mechanism of LPBF Al-Mn-Sc alloys after NIA. [ABSTRACT FROM AUTHOR]

We have investigated microstructure and orientation relationship (OR) of the?and?phases in an as-cast ingot and nodular bainite of Cu-14.9 at.% Sn alloy by using transmission electron microscopy. Proeutectoid?grains and surrounding?phase (prior?phase) possess well-defined (1?1?1)?//(1?1?0)?,OR, that is, Kurdjumov–Sach (K–S) OR, while these two phases formed by eutectoid decomposition exhibit some deviation from K–S OR. On the other hand, the?and?phases in nodular bainite exhibit (1?1?1)?//(1?1?0)?,, which is Nishiyama–Wassermann (N–W) OR, as well as K–S OR. The emergence and variations of these ORs between the?and?phases have been interpreted from the viewpoints of (i) matching of interplanar spacing of {1?1?1}?, {1?1?0}?and {6?6?0}?planes, (ii) minimum strain criteria based on the invariant line concept for K–S OR and (iii) correspondence of atomic positions in the relevant phases by employing the structural ledge concept for N–W OR. [ABSTRACT FROM AUTHOR]