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The evolution of η phase and its effect on the tensile properties at 700 °C in 718Plus superalloy after three solution (at 940 °C for 1 h) and single aging (at 870 °C for 25 h, 50 h and 100 h) heat treatments, were investigated. The results showed that there were several various morphologies of η phase in 718Plus samples. As aging time increased, the volume fraction of needle-like/plate-like increased continuously from 5.32%, 7.78% to 29.52%, while the volume of granular/short rod-like η phase firstly increased from 0.46% to 0.68% then decreased to 0.56%. The high temperature tensile properties were affected by η phases with various morphologies. With aging time increasing, the ultimate tensile strength was obviously improved from 797.11 MPa to 860.57 MPa, which could be attributed to a certain number of plate-like/needle-like η phases at the grain boundaries which could hinder the dislocations motion near the grain boundaries. And the elongation weakly increased firstly from 16.84% to 18.76% and then decreased to 18%, which was closely related to granular/short-rod η phases. Enhancing tensile strength and acceptable ductility could be obtained by morphology control of η phase applying SA heat treatments in the study: promoting the simultaneous precipitation of an appropriate amount of plate-like/needle-like η phases and a small amount of granular/short rod-like η phases. • The morphologies of η phases found in studied 718Plus superalloy samples are plate-like/needle-like, granular/short rod-like. • With aging time extending, the volume fraction of needle-like/plate-like increased, resulting in improving tensile strength. • By applying SA aging heat treatments, an enhancing tensile strength could be obtained by morphology control of η phase [ABSTRACT FROM AUTHOR]

Allvac 718Plus alloy is a newly-developed Ni-based superalloy with excellent thermal stability and mechanical performance at elevated temperatures up to 704 °C. The precipitation behavior of the rapidly-solidified Allvac 718Plus superalloy during aging is systematically investigated in this work. The microstructure evolutions of the strengthening γ' phase and the γ'/γ″ co-precipitates during aging are examined. During aging, the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″ occur and then disappear due to the dissolution of γ″ phase, which is promoted by the δ precipitation. On the contrary, the "triplet" γ'/γ″/γ' forms and remains after aging, resulting from the low diffusion rate of solute atoms through the spheroidal γ' precipitates. The lamellar δ-Ni 3 Nb phase occurs at grain boundaries. Its size and content increase with the prolongation of aging time. After long-term thermal exposure, the hexagonal η phase forms at the δ-γ interface due to the variations of local chemical composition, and then the tetragonal Cr-rich σ phase nucleates adjacent to the δ and η particles because of the segregation of Cr atoms rejected from the δ and η particles. • The rapidly-solidified γ-matrix of 718Plus is obtained with a supersaturated solid solution and a high density of defects. • The dissolution of ellipsoidal γ″ results in the disappearance of the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″. • The "triplet" γ'/γ″/γ' is remained due to the low diffusion rate of solute atoms through the spheroidal γ' precipitates. • The lamellar δ forms first and the η and σ phases successively nucleate at the δ-γ interface after long-time thermal exposure. [ABSTRACT FROM AUTHOR]

The microstructure and corrosion behavior of Al–10%Mg 2 Si alloy after heat treatment are investigated. For Al–10%Mg 2 Si in 3.5 wt.% NaCl solution, corrosion of α -Al phase initiates in (Al + Mg 2 Si) binary eutectic zones with electrochemical polarity change of Mg 2 Si phase, and expands along the eutectic Mg 2 Si precipitates. After heat treatment, eutectic Mg 2 Si transforms from long flakes and rods to short fibers, disks and spheroidized particles. The transformation of eutectic Mg 2 Si phase suppresses the rapid expansion of corrosion pits, which leads to enhancing the corrosion resistance of Al–10%Mg 2 Si alloy. [ABSTRACT FROM AUTHOR]

The precipitation of η phase during the solution treatments of Allvac 718Plus was investigated in this study. The results showed that there was free-γ′ zone appearing around η phase which was consistent with the hexagonal η-Ni 3 (Al/Ti) 0.5 Nb 0.5 after heat treatments. The granular η phase was found to be the transition of the plate-like η phase and have no pinning effect against the grain boundary, while the plate-like η phase has a pinning effect on the grain boundary and leads to the formation of serrated grain boundaries. With the solution temperature increasing, the size and fraction of η phase were observed to increase and then decrease with the morphology changing from granular to plate-like and then to granular. With the solution time prolonging, the fraction and size of η phase were increased, and the η phase formed in a cellular mode and then grow in a Widmanstätten morphology into the grain with its morphology changing from the dominant granular/plate-like to Widmanstättan structure. It was found that the increase in room temperature microhardness with the solution time changing from 6 h to 24 h was caused by the formation of Widmanstätten η phase. • The granular η phase is the transition of the plate-like η phase,having no pinning effect against the grain boundary. • The content and morphology of η phase changes with the solution temperature increasing. • The η phase forms in a cellular mode and then grow in a Widmanstätten morphology with the solution time prolonging. • The increase in microhardness with the solution time from 6 h to 24 h is closely related to the Widmanstätten η phase. [ABSTRACT FROM AUTHOR]

Microalloying of an Al-15%Mg 2 Si alloy (wt%) with 1%Cu produced an enhanced age-hardening response, increasing peak hardness and ultimate tensile strength due to a modified precipitation process. The solid solubility of Cu in Al-15%Mg 2 Si alloy effectively promotes the formation of the high number density of Guinier-Preston-Bagaryasky (GPB) zones combined with S precipitates. It suppresses β′ and β″ formation during ageing at 200 °C. Consequently, Al-15%Mg 2 Si-1%Cu alloy with the high density of GPB zones and S phase exhibited high peak hardness (121 HVN) and ultimate tensile strength (284 MPa), 42.4% and 49.5% higher than that of the Al-15%Mg 2 Si alloy, respectively. • The addition of 1% Cu in Al-15%Mg 2 Si alloy has a significant influence on precipitation during ageing at 200 °C. • Cu addition promotes the formation of GPB zones and S phase, instead of β′ and β″ precipitates. • The high number density of GPB zones and S phase produces an enhanced age-hardening response. [ABSTRACT FROM AUTHOR]