Mechanical Properties Of Vanadium Alloys Research Articles

The Influence of Thermomechanical Treatment Conditions on Characteristics of Structural-Phase Transformations and Level of Mechanical Properties of Vanadium Alloys of Different Systems

The data on the influence of thermomechanical treatment modes on characteristics of the short-term strength and plasticity of vanadium alloys of different systems (V–Ti–Cr, V–Zr–C, V–Cr–Zr, V–Cr–W–Zr, V–Cr–Ta–Zr) are generalized. It is shown that an application of a modified mode ensures an appreciable increase in the short-term strength at room temperature and elevated temperatures, while maintaining an acceptable plasticity. The principal mechanisms of metastable carbide transformations into oxicarbonitride phase particles with phase-forming elements participation and the conditions of their realization are discussed.

The effects of interstitial impurities on the mechanical properties of vanadium alloys: A first-principles study

This study aims to elucidate the effects of interstitial impurities on the mechanical properties of vanadium alloys investigated by means of the first-principles computations. For this purpose, we study the generalized stacking-fault energies and the ductility parameters in different slip system to evaluate the strengthening and ductility potentials of interstitial impurities in V alloys. The results show that the generalized stacking-fault energy values for two slip systems all increase significantly after adding C, O, and N impurities in comparison with pure V. Moreover, the impurities located in the slip plane greatly increase the generalized stacking-fault energy, suggesting that the impurity effect is localized. The calculations reveal a remarkably strong dependence of the USF energies on the impurities concentration. Though evaluating the generalized stacking-fault energies and the ductility parameters, we draw a conclusion that impurities not only strengthen the V alloys but also reduce their plasticity.

Effect of impurities on mechanical properties of vanadium alloys under liquid-lithium environment during neutron irradiation at HFIR

Vanadium alloys, including the highly purified V-4Cr-4Ti alloy, were irradiated in liquid lithium up to a damage level of 3.7dpa in the HFIR at 425°C and 598°C. Neutron irradiation caused an increase of the ductile–brittle transition temperature (DBTT) and irradiation hardening was observed. Adding titanium to the V-Cr alloys was effective for increasing irradiation hardening at 425°C. For highly purified (Zr-treated) V-4Cr-4Ti alloys the irradiation hardening was significantly reduced at both 425°C and 598°C. However, microstructural observations after the irradiation experiments showed that there was no significant difference in microstructure between the original and the highly purified specimens. It is suggested that the reduction of irradiation hardening in the highly purified V-4Cr-4Ti alloys was caused by the configuration and distribution of interstitial impurities in the neutron-irradiated specimen matrix. Controlling the impurities in V-4Cr-4Ti alloys has a very important effect for improving their mechanical properties that take place under neutron irradiation at around 400°C.

Effect of internal oxidation on the microstructure and mechanical properties of vanadium alloys

This paper presents a short review of previous studies on the internal oxidation of vanadium alloys performed by the authors. These have investigated how internal oxidation affects the thermal stability of the microstructure of Zr-containing vanadium alloys and the temperature dependence of the short-term strength and plasticity characteristics of these alloys. Methods for producing highly dispersed heterophase materials stable up to temperatures close to the melting point have been substantiated. It has been shown that these methods efficiently increase the recrystallization temperature (up to T ≈ 0.8 T m) for alloys subjected to internal oxidation in high-defect-density states. In combination with the high efficiency of precipitation hardening by ultrafine ZrO 2 particles, this provides a (1.5–2)-fold increase in short-term (including high-temperature, T ⩽ 1100 °C) strength of vanadium alloys while retaining good room temperature plasticity.

Varying temperature effects on mechanical properties of vanadium alloys during neutron irradiation

The varying temperature irradiation experiment in the HFIR was carried out in order to investigate the performance of vanadium alloys subject to temperature variation during operation. No significant differences of irradiation hardening between steady 340 °C irradiation and variable 225/340 °C irradiation could be seen in any alloys. In the case of the irradiation at 520 °C, the temperature variation to 360 °C influenced the formation process of voids in the unalloyed and dilute vanadium alloys compared to isothermal irradiation at 520 °C. It is contributed to the change of irradiation hardening behavior between steady irradiation and temperature variable irradiation at 520 °C. It could not be seen any effect of varying irradiation temperature in vanadium alloys containing >1 wt% titanium in this study. It is caused by the insensitivity of formation process of Ti(OCN) precipitates against the effect of irradiation temperature variation.

Effects of purity on high temperature mechanical properties of vanadium alloys

Creep tests of highly purified V–4Cr–4Ti alloy (NIFS-Heat) and V–10Cr–5Ti were examined using a purification technique of Zr heat treatment. The creep strain rate for highly purified specimens from the Zr-treatment was higher than for the original specimens. The effect of dynamic strain aging almost disappeared in the highly purified NIFS-Heat alloy containing less than 10 wppm oxygen. The result of the dissolution of precipitate bands and precipitates and removal of interstitial impurities was a decrease in the flow stress and ultimate tensile stress and a decrease of creep strength. These occurred at temperatures where the effect of dynamic strain aging can be seen in specimens containing above 170 wppm oxygen. The strain rate sensitivity parameters at a flow stress at 8% were negative even in highly purified NIFS-heat alloys, however their values were smaller than for specimens containing 150 wppm oxygen, and for data from previous work.

Microstructure control to improve mechanical properties of vanadium alloys for fusion applications

Powder metallurgy (P/M) methods including mechanical alloying (MA) treatment may be useful to improve both radiation resistance and high-temperature strength that are major concerns in the use of V–4Cr–4Ti for fusion reactor structural applications. For the P/M methods, however, there is a critical issue that solute oxygen and nitrogen contained in the starting powders and introduced through the fabrication processes cause a serious loss of ductility. In this paper, a process for microstructure control to solve the issue is proposed and applied to fabricate a vanadium alloy. The microstructures and mechanical properties of the fabricated alloy are also presented. It is shown that the proposed process is very effective in removing solute oxygen and nitrogen from the matrix resulting in a significant suppression of the ductility loss and that optimizing MA conditions will bring about further improvement in the ductility at low temperatures.

Mechanical properties of oxygen-injected vanadium alloy for application as structural component material for international thermonuclear experimental reactor

The effect of oxygen injection on the mechanical properties of vanadium alloys was investigated. Tensile testing of oxygen-containing and reference specimens were performed at temperatures up to 1000°C. Results show that, in general, oxygen decreases the ductility and increases the ultimate tensile stress. TEM investigation of alloy microstructures after mechanical testing was also performed. An attempt was made to relate quantitatively structural parameters (grain dimension size, density and distribution of secondary phases in grains and grain boundaries) to measured tensile properties. Fracture surfaces have been investigated as well.

Vanadium alloys for structural applications in fusion systems: a review of vanadium alloy mechanical and physical properties*1

The current knowledge is reviewed on (1) the effects of neutron irradiation on tensile strength and ductility, ductile-brittle transition temperature, creep, fatigue, and swelling of vanadium-base alloys, (2) the compatibility of vanadium-base alloys with liquid lithium, water, and helium environments, and (3) the effects of hydrogen and helium on the physical and mechanical properties of vanadium alloys that are potential candidates for structural materials applications in fusion systems. Also, physical and mechanical properties issues are identified that have not been adequately investigated in order to qualify a vanadium-base alloy for the structural material in experimental fusion devices and/or in fusion reactors.

The effects of exposure to sodium on the metallurgical and mechanical properties of vanadium alloys

Three vanadium alloys, VANSTAR-7 ∗ ∗ VANSTAR is a general term denoting a series of vanadium-base alloys developed by Westing-house Electric Corporation. , VANSTAR-9, and V-20Ti were examined after 500 and 1500 h exposure to sodium flowing at 5 ft/sec, and containing < 10 p.p.m. oxygen over the temperature range 675 °–800 °C. In all cases, weight gains were observed, but, the V-20Ti alloy gained approximately three times more weight than the VANSTAR alloys. The results appeared to fit the parabolic rate law, Δ/ dw 2 = K pt , and the observed weight gains were due to the transport and solution of nitrogen, carbon, and oxygen. The variation of the parabolic rate constant with temperature follows an Arrhenius-type relationship. Diffusion coefficients of 1·1 × 10 −11, 2·5 × 10 −12, and 2·5 × 10 −12 cm −2 sec −1 for nitrogen, carbon, and oxygen in the VANSTAR-9 alloy were calculated from analytical data. All alloys showed surface hardness increases due to interstitial absorption, and, in the case of the VANSTAR alloys, considerable hardening was observed away from the surface regions. The bend ductile-brittle transition temperatures were increased after corrosion, and considerable reductions were noted in room-temperature tensile ductility. However, after 1500 h exposure to sodium, samples of the VANSTAR alloys still retained more than adequate ductility at ~700 °C, for cladding applications.