L.H. Chown

Hot-deformation behaviour of α+β Ti-Al-V-Fe experimental alloys

To reduce the cost of metallic alloys the first approach considered is to substitute expensive alloying elements with inexpensive elements that fulfil similar functions. The second approach is to optimise the microstructure and mechanical properties of the alloys by adjusting processing conditions. Iron, a cheap β-stabilising element in titanium alloys, was added to partially substitute vanadium in experimental Ti-6Al-xV-yFe alloys (where x = 1-4, y = 0-3 and x+y = 4). Unlike other studies where vanadium was totally replaced by iron, in this work partial substitution of V by 1-3 wt % Fe was made to limit the possibility of forming intermetallic phases in the alloys. The experimental alloys were produced by vacuum arc melting and the small ingots were machined to produce plane strain compression samples for hot isothermal testing on a Gleeble 3500. The tests were done at a temperature of 900°C, strain rate of 1s−1 and total strains of 0.6 and 1.2, under plane strain conditions. The microstructures of the as-cast and deformed samples were analysed using optical and scanning electron microscopy (SEM) to assess the deformation mechanisms. The flow stress curves showed that the as-cast Ti-6Al-4V had a higher resistance to deformation than the iron-added experimental alloys. The amount of total strain had a significant effect on the flow behaviour of the alloys. Microscopy showed that deformation bands were more prominent in the deformed Ti-6Al-4V alloy than in the deformed Ti-Al-V-Fe alloys. SEM images revealed rotation and bending of α-laths in the deformed experimental Ti-Al-V-Fe alloys. The low resistance to deformation observed in the experimental alloys at 900°C was sensitive to the higher ratio of iron to vanadium.To reduce the cost of metallic alloys the first approach considered is to substitute expensive alloying elements with inexpensive elements that fulfil similar functions. The second approach is to optimise the microstructure and mechanical properties of the alloys by adjusting processing conditions. Iron, a cheap β-stabilising element in titanium alloys, was added to partially substitute vanadium in experimental Ti-6Al-xV-yFe alloys (where x = 1-4, y = 0-3 and x+y = 4). Unlike other studies where vanadium was totally replaced by iron, in this work partial substitution of V by 1-3 wt % Fe was made to limit the possibility of forming intermetallic phases in the alloys. The experimental alloys were produced by vacuum arc melting and the small ingots were machined to produce plane strain compression samples for hot isothermal testing on a Gleeble 3500. The tests were done at a temperature of 900°C, strain rate of 1s−1 and total strains of 0.6 and 1.2, under plane strain conditions. The microstructures of the a...

Hot tensile behaviour in silicon-killed boron microalloyed steels

Low carbon steel for drawing and cold heading applications should have low strength, high ductility and low strain ageing rates. To achieve this, nitrogen must be removed from solid solution, which can be done by low additions of boron. A wire producer had been experiencing occasional problems with severe cracking on silicon-killed, boron steel billets during continuous casting, but the solution was not obvious. Samples from four billets, each from different casts, were removed for analysis and testing. The tested steel compositions were within the specification limits, with boron to nitrogen ratios of 0.40-1.19. Hot ductility testing was performed on a Gleeble 1500 using parameters approximating the capabilities of this particular billet caster. The steel specimens were subjected to in situ melting, then cooled at a rate of 2 C.s−1 to temperatures in the range 750-1250°C, where they were then pulled to failure at a strain rate of 8x10−4 s−1. In this work, it was found that both the boron to nitrogen rati...

Corrosion behaviour of Al-Fe-Ti-V medium entropy alloy

Alloys containing up to four multi-principal elements in equiatomic ratios are referred to as medium entropy alloys (MEA). These alloys have attracted the interest of many researchers due to the superior mechanical properties it offers over the traditional alloys. The design approach of MEA often results to simple solid solution with either body centered cubic; face centered cubic structures or both. As the consideration for introducing the alloys into several engineering application increases, there have been efforts to study the corrosion behaviour of these alloys. Previous reports have shown that some of these alloys are more susceptible to corrosion when compared with traditional alloys due to lack of protective passive film. In this research, we have developed AlFeTiV medium entropy alloys containing two elements (Ti and Al) that readily passivate when exposed to corrosive solutions. The alloys were produced in vacuum arc furnace purged with high purity argon. Open circuit potential and potentiodynamic polarisation tests were used to evaluate the corrosion behaviour of the as-cast AlFeTiV alloy in 3.5 wt% NaCl and 1 M H2SO4. The corrosion performance of the alloy was compared with Ti-6Al-4V alloy tested under similar conditions. The results show that unlike in Ti-6Al-4V alloy, the open circuit potential of the AlFeTiV alloy move towards the negative values in both 3.5 wt% NaCl and 1 M H2SO4 solutions indicating that self-activation occurred rapidly on immersion. Anodic polarisation of the alloys showed that AlFeTiV alloy exhibited a narrow range of passivity in both solutions. In addition, the alloys exhibited lower Ecorr and higher Icorr when compared with traditional Ti-6Al-4V alloy. The traditional Ti-6Al-4V alloy showed superior corrosion resistant to the AlFeTiV alloy in both 3.5 wt.% NaCl and 1 M H2SO4 solutions.