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Fe‐based heat‐resistant A286 superalloy is an age‐hardened austenitic stainless steel. Age‐hardening is greatly affected by TiC particles and η‐Ni3Ti phases. Herein, the evolution of TiC and η (hcp‐Ni3Ti) precipitations is investigated in six different A286 alloys with simultaneous variations of C and Ti contents, such as 0.00C–2.38Ti, 0.02C–2.46Ti, 0.04C–2.54Ti, 0.05C–2.58Ti, 0.06C–2.62Ti, and 0.08C–2.69Ti wt%. During microstructure evolution from solutioning state (900 °C for 2 h) to aging state (720 °Cfor 16 h), nodular/needle‐like TiC (fcc) and platelet lamellar structures of eta (η (hcp‐Ni3Ti)) phases are observed in the austenitic matrix of superalloys. Statistical analysis of TiC and eta phases after microstructural examination indicates that mean size goes up to 3.3 and 6.8 μm2 in 0.08C–2.69Ti wt% alloy, respectively. Yield strength and ultimate tensile strength are increased from 350 to 510 MPa and 530 to 650 MPa as a result of the strengthening mechanism of TiC from 0.00C–2.38Ti to 0.08C–2.69Ti wt% alloys, respectively. However, precipitation of these phases leads to brittleness of the alloys and elongation decreases from 20% to 12% with the increment of these phases. The strengthening mechanism is explained by stress–strain curves and fracture topography. [ABSTRACT FROM AUTHOR]

The role of coherency strain at the matrix/precipitate interface toward hardening of bulk polycrystalline "ceramic alloys" has been established here. Formation of "near ideal" bulk polycrystalline ceramic microstructure characterized by the presence of uniformly distributed coherent "ultra‐fine" MgCr2O4 particles (size: ~25 nm) within matrix (MgO) grains was achieved via solid‐state precipitation during aging treatment of bulk supersaturated MgO–Cr2O3 solid solutions (formed during pressureless sintering in air, followed by fast cooling). The as‐aged MgO–MgCr2O4 "ceramic alloys" exhibited hardness increment by ~73% over that of phase pure bulk MgO upon aging for just 10 hours at 1000°C in air. Evidences toward the presence of significant coherency strains across the MgO/MgCr2O4 coherent interfaces were obtained with transmission electron microscopy. Analysis based on hardening mechanisms and comparisons with MgO–MgFe2O4 system, having lesser hardening due to lower misfit strain at MgO/MgFe2O4 coherent interfaces (despite greater content of second‐phase particles), confirm the dominant role of coherency strains toward hardness enhancement in "ceramic alloys." [ABSTRACT FROM AUTHOR]

The current study explores the feasibility of artificial aging treatment to aluminium alloy 6061 hybrid composites reinforced with graphite and fine granite particulates to suit structural applications. Aging at 100 °C retrieved a better response of the hybrid composites as compared to that at 150 °C in terms of peak hardness and strength. Among the five different stir-cast compositions, the composition of aluminium 6061 with 2 wt. % graphite and 4 wt. % granite showed enhanced mechanical properties than that of the base alloy as well as mono reinforcement type composites which was attribued to the formation of rod-shaped β-Mg2Si precipitates. [ABSTRACT FROM AUTHOR]

The influence of low-temperature preaging on the artificial age-hardening of a aluminum alloy 6063 (Al–0.72Mg–0.42Si) has been investigated in this study. The precipitation behaviors of samples of the alloy were analyzed using differential scanning calorimetry as well as by measuring the electrical resistivity, and confirmed by microstructure observation using transmission electron microscopy. Tensile tests were performed to determine the mechanical properties of the samples. The results indicate that GP zones (I) are formed in the aluminum alloy 6063 at 0–30°C during a long preaging period. The formation of GP zones (I) will retard the precipitation of the intermediate β′ phase during artificial aging and will result in decrease in the strength of the alloy after the artificial aging process. Increasing either the preaging temperature or the holding period will significantly decrease the strength after artificial aging. The results indicate that GP zones (II) are formed in the Al alloy 6063 at a preaging temperature of 40–70°C but this has no influence on age-hardening after artificial aging, even for a long period. Increasing either the preaging temperature or the holding period will significantly increase the strength after artificial aging. However, for preaging at −10°C, the negative effect on age-hardening is still not clear and should be investigated in the future. [ABSTRACT FROM AUTHOR]

New Mg–Y–Gd–Mn alloys, strengthened by a dense fine scale precipitation, have been recently designed for structural applications up to 523 K. The qualitative small-angle X-ray scattering study presented here enlightens the mechanical properties at high temperature of these alloys. Small Guinier–Preston zones have been evidenced in alloys maintained at room temperature after quenching. The metastable phases, studied in parallel using high-resolution transmission electron microscopy and responsible for the good mechanical properties, are difficult to quantify completely owing to their complex microstructure of interconnected globular and faceted precipitates. [ABSTRACT FROM AUTHOR]