Papers by Keyword: Alloying Effect

Abstract: The influence of chromium cast iron Cr8 treatment by Fe-45Si-6Mg-0,5REM modifier on the structure, phase transformation and heat resistance was studied experimentally.It is demonstrated that during modifying of chromium cast iron Cr8 the alloying effect takes place. The initial cast iron structure which consists of alloyed ferrite, carbide (Cr,Fe)₇C₃ and cementite (Fe,Cr)₃C is transformed as in the process of chromium alloying according to modifier consumption increase. At the modifier consumption of 0,15 % the mass quota of cementite (Fe,Cr)₃C decreases from 3,2 % to zero, and the mass quota of carbide (Cr,Fe)₇C₃ increases from 20 % up to 30 %.

Abstract: The effect of Ti addition on phase equilibria among Ni (A1), Ni3Al (L12) and Ni3V (D022) phases at 950 °C was investigated through TEM/EDS analysis on heat-treated alloys. The three-phase coexisting region of A1 + L12 + D022 was found to exist around the composition of Ni-4Al-19V (at. %) in the Ni-Al-V ternary system. With addition of Ti to the ternary system the three-phase coexisting region was shifted to the Ni-rich side. Ti partitioned most into the L12 phase and least into the A1 phase. These results suggest that the addition of Ti stabilizes the L12 and D022 phases against A1 phase, and raises the temperature of eutectoid reaction in the Ni3Al-Ni3V pseudo-binary system: A1 → L12 + D022.

Abstract: Hydrogen permeation and diffusivity in V1−xNbx alloys (x = 0.25, 0.5 and 0.75) were investigated over a temperature range between 573 and 673 K. The alloy sheets surface-coated with Pd (100 nm) by ion-beam sputtering technique were subjected to the hydrogen permeation measurement with hydrogen pressures less than 3000 Pa. It was found that the hydrogen permeation is strongly suppressed especially at low hydrogen pressures; the hydrogen permeation is considered to be controlled by some surface processes. The V0.50Nb0.50 alloy showed the largest permeability 1.4×10−8 mol H2 m−1s−1Pa−1/2 at 673 K which is larger than that for pure Pd. The diffusivity which was determined from the fitting of the permeation curve decreases with the alloy concentration at both the Nb- and V-rich sides and takes a minimum value at x=0.75. The hydrogen potential obtained by a first-principles calculation showed that V atoms act as trapping centers for hydrogen in the Nb matrix and Nb atoms act as anti-trapping centers in the V matrix.

Abstract: Microstructures and mechanical properties of Ni3Al based intermetallic alloys produced by vacuum arc melting and vacuum induction melting were investigated in terms of phase analysis using scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffractometer and tensile test machine. The duplex microstructural feature consisting of γ’ matrix phase and small intermetallic dispersoids was observed to be distributed over the whole microstructure in the Zr and/or Mo-added samples. From the SEM-EDS analysis of the alloys, it is clearly confirmed that the Mo is solved both into γ’ matrix phase and intermetallic phase while Zr has a role to form an intermetallic Ni5Zr phase for the entire alloys investigated. The ultimate tensile strength of the present alloy was superior to iron-based and Ni-based die materials especially in the high temperature region. The mechanical results obtained will be discussed in correlation with microstructural observations, phase analyses.

Abstract: Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.

Abstract: Employing the first principles discrete variational method(DVM), we investigated the electronic structure of LaNi5 hydrogen storage alloys containing various alloying elements, M=Mn,Fe,Co. The results showed that s electrons of H mainly interact with s electrons of hydride-non-forming element Ni, though hydride forming element La have stronger affinity to hydrogen atom. And alloying elements strengthened the bond between B-H, so decreased the capacity of doped-system.