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Li K.,Tianjin University | Dong Z.,Tianjin University | Dong Z.,Materials Research Institute for Energy Equipment | Liu Y.,Tianjin University | Zhang L.,Tianjin University
Smart Materials and Structures | Year: 2013

A nominally new Fe-16Mn-5Si-10Cr-4Ni-1(V, N) (mass %) alloy containing V and N has been developed aiming to precipitate VN particles without training. Transmission electron microscope (TEM) observations have indicated that VN preferentially precipitated on the top of stacking faults and act as nucleation sites for the γ (FCC) →ε phase (hcp) transformation. VN plays a key role in improving the thermo-mechanical properties. The results showed that shape memory properties could be remarkably improved by pre-deformation at room temperature before aging or deformation at low temperature after aging treatment. 44% shape recovery and 440 MP shape recovery stress were achieved when heating to 160°C after the initial 4% strain at RT. Nearly perfect shape recovery (90%) and shape recovery stress (500 Mpa) have been achieved when the alloy was 4% deformed at -45 °C followed by heating up to 225 °C. Moreover, no relaxation phenomena were found when the tested samples were cooled to room temperature. All of these results suggested the possible practical applications of Fe-Mn-Si SMAs, especially in smart civil engineering. © 2013 IOP Publishing Ltd. Source

Qin X.-M.,Northeastern University China | Qin X.-M.,Materials Research Institute for Energy Equipment | Di H.-S.,Northeastern University China | Chen L.-Q.,Northeastern University China | And 2 more authors.
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2012

Tensile deformation behavior and microstructural evolution of Fe-23Mn-2Al-0.2C TWIP steel after solution treatment were studied and the deformation mechanism was discussed. The results show that as increase of the solution temperature, grain size of the steel gradually increases, its yield strength and tensile strength decrease, while plasticity increases. The product of strength and plasticity first increases and then decreases with the temperature increase from 700°C to 1100°C, and reaches the peak value at 900°C. Deformation behavior with three stages was observed for the steel solution-treated at high solution temperatures. While at low temperature, there exist only two stages in the deformation behavior for the dependence of strain hardening rate on true strain. With increasing the grain size, more deformation twins are observed in the deformed steel and the effect of twining induced plasticity (TWIP) increases. Source

Guo Q.,Tianjin University | Dong Z.,Tianjin University | Dong Z.,Materials Research Institute for Energy Equipment | Liu Z.,Tianjin University | And 2 more authors.
Materials Science and Technology (United Kingdom) | Year: 2014

The effects of aging on the precipitation of the second phase and the shape memory effect (SME) of an Fe-Mn-Si-Cr-Ni based alloy containing V and N elements (0·9 wt-%) have been investigated. The results showed that VN particles, precipitated during aging, could improve the shape recovery ratio to 56%, compared with that of only 25% for the solution treated samples when the V and N bearing alloy was aged for 24 h. It was further confirmed by X-ray diffraction that the fitting relationship between shape recovery and martensite content is practically in agreement with linearity. Electron microscopic observation has shown that aging treatment gives rise to an increasing amount of VN precipitates, among which the small ones uniformly precipitated inside grains but would aggregate and grew quite remarkably to be large ones at the grain boundaries. These large particles do not appear to have much negative effects on the SME, whereas it is the fine nanosize VN particles inside grains that are the key factor to act as preferential nucleation sites for martensite, improving the SME. © 2014 Institute of Materials, Minerals and Mining. Source

Wu Y.,Materials Research Institute for Energy Equipment | Nie Y.-H.,Materials Research Institute for Energy Equipment | Zhao S.,Materials Research Institute for Energy Equipment | Bai Y.-G.,Materials Research Institute for Energy Equipment | And 3 more authors.
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2015

Nickel-based superalloy modified 617 ingots for 700℃ ultra-supercritical turbine rotor were prepared by vacuum-induction-melting and electroslag-remelting, and the as-cast microstructure of the alloy after homogenization heat treatment was investigated by SEM analysis. The results show that the major microstructural features of the as-cast alloy are identified to be the presence of marked elements segregations, especially Mo and Ti segregating within dendrites, and inter-and intragranular carbides. After homogenization the elements segregation are almost eliminated and carbides both within dendrites and along grain boundary dissolve to some extent. The research also shows that the homogenization microstructure of the alloy 617 is mainly controlled by the diffusion of Mo, and the appropriate homogenization process for this alloy is heating at 1180-1200℃ for over 24 h. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved. Source

Liu H.,Materials Research Institute for Energy Equipment | Zhang X.,Materials Research Institute for Energy Equipment | Li L.,Materials Research Institute for Energy Equipment
Jinshu Rechuli/Heat Treatment of Metals | Year: 2013

Heat treatment of stainless steel clad plate made by hot rolled bonding was studied. The microstructure was analyzed by OM, interfacial adhesion and mechanical properties before and after heat treatment were investigated. Corrosion resistance of the stainless steel clad plate was also evaluated. The results show that, after hot rolled bonding, the microstructure of the base carbon steel consists of ferrite and pearlite with low strength, and the corrosion resistance of the clad stainless steel is poor. By rapid cooling after hot rolling, its strength increases, but the ductility obviously decreases because much of martensite and bainite formed in the carbon steel. The ductility of the base carbon steel after tempering can remarkably be improved, but still not satisfy the demand for use. After the treatment of rapid cooling plus slow cooling, the microstructure of the carbon steel consists of fine ferrite, bainite and a small amount of pearlite, and the mechanical properties of the clad plate can meet the requirement. After this heat treatment, the shear strength of the stainless steel clad plate can be over 380 MPa, the bonding of the interface is satisfied. Meanwhile the corrosion rate of the clad stainless steel is only 2 g/(m2·h), compared with the corrosion rate 36.2 g/(m2·h) as hot rolled. Therefore, the optimized heat treatment process for the plate should be rapid cooling from high temperature after hot rolling (about 1000°C), and successively slow cooling at low temperature (about 500°C). Source

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