Papers by Keyword: Vanadium Alloy

Abstract: The determination method for analyzing trace copper in vanadium alloy by flame atomic absorption spectrometry was investigated in the paper. The sample digestion method, digestion acidity, determination conditions, matrix interferences, method precision, recovery of standard addition were investigated in detail. The method precision in RSD% was 8.6%, and the average recoveries of standard addition were from 93.9% to 95.6%. The experimental results indicated that the proposed method for determination of trace copper in vanadium alloy was simple, fast, accurate, and easy to operate, which was suitable for quality control of vanadium alloy.

Abstract: In this work the static and dynamic properties of vanadium alloy V-5Cr-5Ti over a wide range of temperature from 20 to 1000 degree at strain rates ranged from 10-4/s~103/s were studied experimentally under uniaxial quasi-static tension with MTS universal testing machine, uniaxial dynamic compression and tension with split Hopkinson bar system with temperature control. The stress-strain curves of V-5Cr-5Ti at various temperatures and various strain rates were obtained. Experimental data show that V-5Cr-5Ti behaves strain-rate sensitive and temperature dependent, for instance the material parameters yield stress, tensile strength and failure strain. And fracture mode of the material is also dependent on strain-rate and temperature. Based on experimental data the temperature-rate-dependent constitutive relations were established in the form of Johnson-Cook and Cowper-Symonds models which are widely used in numerical simulation of dynamic processes of structures under impact loading. The material microstructures and failure modes were analyzed using optical microscope, TEM etc, and results shows that the yield stress and strength are increased with strain rate. The brittle-ductile transition strain-rate is from 101/s to102/s.

Abstract: V-4Cr-4Ti alloy is an attractive candidate low activation structural material for nuclear fusion reactors. The properties of V-4Cr-4Ti during its operation strongly depend on initial microstructure, especially size and density of Ti-rich precipitates and their interaction with dislocations. This paper focuses on the effects of the precipitate states and other microstructural variables on mechanical properties of V-4Cr-4Ti alloys and the potential methods to improve the properties by microstructural control, based on Transmission Electron Microscopy.

Abstract: In this work the static and dynamic tensile properties of vanadium alloy V-5Cr-5Ti were investigated at strain rates ranged from 3.3x10-5/s to 1.2x102/s. The material microstructures were analyzed using optical microscope, SEM, TEM, XRD and EDS. Results show that the yield strength a increases with strain rate. The brittle-ductile transition strain-rate is about 101/s to102/s. At room temperature the tensile fracture at a low strain rate occurs via mixed modes of microvoid aggregating and transgranular cracking; at high strain rate the fracture occurs via a brittle mode. The analysis by TEM, XRD and EDX shows the existence of lath martensite, and on there exits precipitate phase of Ti(O,C, N) in grain boundaries.

Abstract: In this work, LS-DYNA program was adopted to simulate the loading process of Vanadium Alloy specimen conducted on the Split Hopkinson Pressure Bar (SHPB) in two dimensions. Based on the Johnson-Cook material constitutive relation and criterion of Johnson-Cook failure, the initiation, propagation process of an adiabatic shear band (ASB) and the corresponding distribution of temperature field in the vanadium alloy V-5Cr-5Ti hat-shaped specimen are analyzed. The field of stress, strain and temperature in the tip of an ASB, and the spread speed, the width as well as the type of the ASB are all studied. It is shown that the formation of the ASB is related to the loading velocity and the size of the hat-shaped specimen. And formation of mircocracks and their interlinkage are primary shearing failure mechanism of hat-shaped specimen.

Abstract: Vanadium alloys in the composition range around V-4Cr-4Ti have been proposed as candidate materials for fusion reactor applications and structures. These applications will require detailed characterization of constitutive and fracture properties. This study is aimed at understanding the basic constitutive and fracture mechanisms in vanadium alloys. Understanding of the basic constitutive and fracture mechanisms is achieved through a series of mechanical tests. These test results are combined with quantitative models of the underlying macro- and micromechanics. In addition to these experimental studies, finite element analysis (FEA) techniques are used to determine stress and strain fields to verify the constitutive law used in the fracture specimens.

Abstract: A V-4Cr-4Ti alloy and pure V were oxidized in flowing argon for 0.5-8h and subsequently annealed in vacuum for 16h at 973K. The oxygen of 1000-9000ppm was introduced into the V-alloys with little nitrogen, where oxygen was concentrated in region near the surface. By the annealing, oxygen was homogeneously diffused into depth of 150µm. The diffusion depth of oxygen in V-4Cr-4Ti is much smaller than that of pure V, because of Ti-O precipitates formed as oxygen trap. The study indicated that it is feasible to control oxygen level and distribute in the surface region of the vanadium alloys.