Vanadium carbide is less dense, harder and tougher than tungsten carbide, and nickel is more corrosion resistant that cobalt. Replacing the binder with Ni should improve the corrosion resistance. Since there are eutectics with a wide range of compositions in the C-Ni-V system, this system has potential for wear resistant alloys with ~VC as the discrete hard phase and the nickel solid solution as the binder. The aim of this work was to ascertain if eutectic microstructures with vanadium carbides could be beneficial to wear resistance. Phase studies confirmed the wide range of the eutectic alloys, with VC + (Ni), VC + σ′, VC + (V) and graphite + (Ni) and different morphologies. Preliminary wear tests showed results comparable to WC-Co alloys.
The neutron diffraction technique was used to determine the residual stress field in welded compact tension specimens of the aluminium-lithium alloy AA 2095. The deep penetrating characteristic of neutrons was exploited to evaluate the through-thickness variation in residual stress. Moreover, insight into the redistribution of these stresses was gained by extending a fatigue crack through the residual stress field and re-examining the stress distribution. The specimen without a crack was found to have a high compressive stress (of the order of - 135MPa) ahead of the notch. This rose to a maximum tensile stress of about 50MPa, 22 mm from the notch, followed by a drop to negative values further ahead of the notch. It was observed that the magnitude of the stresses changed on moving into the thickness of the specimen. However, the form of the graph showing stress versus distance ahead of the notch remained unchanged. When fatigue cracks of different lengths were introduced, the magnitude of the stress close to the tip first increased with crack length, before decreasing and then rising again. Nevertheless, the form of the graph remained unchanged and the stress at the crack tip remained compressive. The paper concludes that any study of the response of a component to mechanical loading involving a residual stress field must take these factors (i.e. through-thickness stress variation and stress redistribution) into consideration.
The inaccessibility of commercial software has necessitated the development of low-cost, general-purpose finite element method (FEM) computer programs for structural analysis. Using the FEM program, the elastic, elastic-plastic, residual and service stresses and displacements in a closed ended, thick-walled cylinder under internal pressure were established. The displacement formulation was implemented and eight-noded brick isoparametric elements chosen. The frontal solution technique and the incremental theory of plasticity were used, as only limited computing facilities were available. The results were found to be in very good agreement with the through-thickness analytical values. The benefits of autofrettage were demonstrated and an optimum overstrain of 16% established for a cylinder with a thickness ratio of 2. The material economy achieved through autofrettage and the limitations imposed are illustrated. The FEM program could therefore be reliably used for other complex geometries and load conditions.
Twenty-three V-Ni-C alloys were produced and analysed in the as-cast condition, as well as after annealing at 1000°C for 1000 h. The phases were identified using SEM-EDX and XRD. The extensions of the binary phases were determined. The liquidus surface projection was derived from the overall compositions, primary phases and the solidification sequences. Four invariant reactions on solidification were found. The isothermal section at 1000°C was also derived, which included the * Ni 2 V 4 C ternary phase.
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