Papers by Keyword: Secondary Phase

Abstract: This paper deals with the martensitic transformation and functional properties in the quenched single crystals of the Co₃₅Ni₃₅Al₂₈Fe₂ medium-entropy alloy, oriented along the [001]_B2-direction. The microstructure and chemical composition of the single crystals have been studied in detail using transmission and scanning electron microscopy. The {111}_L10 martensite twins up to 10-20 nm width and γ/γ′-phase precipitations larger than 100 μm are detected. The thermoelastic B2-L1₀ martensitic transformation upon stress-free cooling/heating in single crystals of Co₃₅Ni₃₅Al₂₈Fe₂ alloy is characterized by the accumulation of elastic energy, which is the driving force of the reverse martensitic transformation, and the low dissipation energy. The reverse transformation starts at lower temperatures than the forward transformation M_s>A_s. The regularities of the stress-induced B2-L1₀ martensitic transformation change due to an increase in the contribution of the dissipated energy and M_s^σ<A_s^σ. There is shape memory effect with the reversible strain (3.2±0.3)% and high temperature superelasticity with the reversible strain (3.3±0.3)% in the temperature range from 323 K to ≥548 K in the [001]_B2-oriented single crystals. These crystals withstand stress up to 1200 MPa in compression without destruction.

Abstract: The microstructure and segregation of 7N01 aluminum alloy microalloyed with Er and Zr before and after homogenization process at 470 °C for 24 h have been investigated using transmission electron microscope (TEM), and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS) and transmission electron detecter (STEM). SEM images and EDS line scan results showed that there were dendritic segregation of Mg and Zn and micron-sized primary phases along dendrites in the as-cast alloy. The primary phases were mainly Al₂Mg₃Zn₃ containing Al, Zn, Mg and Mn. And a small amount of primary phases were the particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr. After homogenization at 470°C for 24 h, dendritic segregation of Mg and Zn was eliminated, Al₂Mg₃Zn₃ and the particles containing Al, Zn, Mg and Mn were basically dissolved. The particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr remained. Meanwhile, TEM and STEM images showed that a large number of secondary phases appeared after the homogenization, which were mainly distributed in the inter-dendrite area. EDS results showed that the block-shaped and rod-shaped phases with the width of 10-70 nm and length of 100-500 nm were the particles containing Al, Cr and Mn or Al, Mg, Cr and Mn, and the ellipsoid secondary phase with the size of 50-100 nm was MgZn₂.

Abstract: The Al-Cu-Mg alloy is a precipitation-strengthening alloy, which is traditionally dissolving lots of secondary phase and precipitating in subsequent aging process, thus having been applied to aerospace and automobile industry due to its low density and high strength. However, the high temperature and long operating time needed for the dissolution of secondary phase consume numerous energy. In this work, rapid dissolution of secondary phase in cold-rolling Al-Cu-Mg alloy was achieved by coupling treatment of thermal field and pulsed electric current. The energy consumption for dissolving secondary phasewas reduced from 495°C operating 1h to 450°C operating several minutes. Therefore, the coupling treatment of thermal field and pulsed electric current significantly improves the dissolving rate and decreases the energy consumption.

Abstract: Secondary phase carbides in term of type and morphology are considered as the most challenge facing the applications of hot work tool steel. AISI H13 tool steel is one of the most applicable hot work tool steel grades. M₂₃C₆, M₆C and MC are the common secondary carbides that are forming throughout the martensite matrix of H13 tool steel. In this research, nanoinoculant silicon nitride was added to the molten H13 tool steel to act as an inoculant for the secondary carbide categories through ladle treatment process. By using OM and SEM, it was observed that nanoinoculant has the great impact in the nucleation of secondary carbides into fine shape, in particular M₂₃C₆ type. In addition, mechanical tests proved that the nucleation of secondary carbides promotes the mechanical properties of hot work H13 tool steel to its ultimate. Impact toughness of the inoculated H13 tool steel was observed with higher value than that was done at the ordinary H13 tool steel. At the meantime, wear resistance of inoculated H13 tool steel was multiplied two times higher than as delivered H13 tool steel.

Abstract: Unfavorable secondary phases like binaries and ternaries are often observed in synthesizing Cu₂ZnSnSe₄ (CZTSe) quaternary crystal due to its narrow phase space, which strongly limits the performance of Kesterite solar cells. To identify the growth parameters against the stability of these secondary phases, we systematically studied the growth process of Sn-Se binaries and Cu-Sn-Se ternaries using co-evaporation method. We found that the compositions of Sn-related binary and ternary phases were strongly dependent on the substrate temperature and Se flux during deposition, which will be helpful in designing formation paths for quaternary system. Growth temperature of CZTSe higher than 490 °C will make the thin film free of Cu₂SnSe₃ phase. Our experiments also suggest that formation pathways in the Cu₂SnSe₃-ZnSe pseudobinary phase diagram at a slightly lower substrate temperature deserve more experimental and theoretical considerations because of its easier composition control.

Abstract: The Pr₂O₃ doped SnO₂ dense ceramic was prepared by co-precipitation method and further sintering. Through the micrograph of the cross-sectional microstructure of the electrodes, the sintering process was analyzed and discussed. Results showed that the solid phase sintering was exhibited at the early stage; when sintering was kept going on, the instant liquid phase could be emerged due to the rich dopants in the grain boundary. Finally, there would be much secondary phase existe as the concentration of dopants reached to a certain value.

Abstract: The influence of ZnO and Nb₂O₅ additions on the sinterability, microstructure and microwave dielectric properties of (Mg_0.95Ca_0.05)TiO₃ (abbreviated as 95MCT hereafter) ceramic is investigated. XRD patterns indicate that MgTi₂O₅ secondary phase can be effectively suppressed by ZnO and Nb₂O₅ additions, which is beneficial for improving the microwave dielectric properties. Appropriate amount of Nb₂O₅ addition can effectively improve the Qf value of 95MCT ceramic, which is suggested to be ascribed to the reduced oxygen vacancies. When the ZnO: Nb₂O₅ mole ratio is 1.5 and the co-doping content is 0.25wt%, the optimal microwave dielectric properties can be obtained Qf=72730GHz(6.8GHz), ε_r=20.29 and τ_f=-6.84ppm/°C and the sintering temperature of 95MCT is lowered from 1400°C to 1320°C.

Abstract: Sublimation-recrystallization processes occurring during PVT are investigated from the viewpoint of quasi-equilibrium phase transitions of SiC. In addition to the elemental reaction processes of PVT, other phenomena such as silicon droplet formation and in-situ etching are also discussed based upon the Si-C binary phase diagram, and possible mechanisms are proposed.

Abstract: With development of theory on microalloy in steel, now there are trends of adding microalloy in many kinds of steels, making the production and application of microalloy-steel enlarge. The second phase in microalloy-steel is significant for quality of casting. During the periods of continuous casting, conveying and heating, different process may affect precipitation and dissolution behaviors of casting according to different heating profile, further affect state of precipitation and distribution of secondary phase. In this paper, secondary phase in micro-alloy steel J55 were studied. Results show that some secondary phase particulars in micro-alloy steel J55 steel distribute along the austenitic grain boundaries when the temperature of slab is below 805°C in roller conveying; The distribution of secondary phase particulars in different thermal history slab are comparatively similar after heating; Al, Ti, C and N elements which dissolute in J55 steel has the feature of austenitic grain boundary segregation.

Abstract: The effect of adding Al2O3 to the PZT-PMN solid solution material for use for ceramic resonator was investigated. It has been found that when the amount of Al2O3 added to PZT-PMN is 0.3　wt% or below, it exists inside the crystal lattice as Al3+ ion and increases the stability of oscillation frequency over application of heat (heat resistance). It has been found that when more than 0.3　wt% of Al2O3 is added, the Al3+ ion that remained undoped will exist at grain boundary as secondary phase, and increase the strength.