Casper van der Eijk

Reduction of Mixtures of Ni‐Oxide and Ti‐Oxide Powder in a Natural Gas Containing Atmosphere

Natural gas has been used as reductant in the production of iron for several decades. Recently, the use of natural gas as reductant for other metals has been drawing attention because of the low price of natural gas, as well as the reduction of CO2 emissions compared to the use of coke and coal. In this work, the reduction of a mixture of Ti- and Ni-oxides by natural gas has been studied. Within the Ni-Ti system, the intermetallic compound Ni3 Ti is thermodynamically the most stable one. Therefore, powders of Ni-oxide and Ti-oxides were mixed in an atomic ratio of three to one and subsequently pelletized. Reduction was performed in a TGA furnace at constant temperature with varying reducing gas atmospheres.

Effect of Micro-voids on Plasticity in NiTi-alloys

Recent experimental investigations have indicated that commercial NiTi superelastic alloys consist of particles and inclusions which can nucleate micro-voids. Almost no study on the effect of micro-voids has been carried out in the literature. In this study the effect of micro-voids and plasticity on the behaviour of a superelastic NiTi-alloy has been investigated. Axisymmetric unit cell models with different micro-void volume fractions have been analysed subjected to various stress triaxiality states. It is shown that the onset of plasticity is located at the void edge as the maximum stress initially occurs at this position. The finite element results indicate that the existence of micro-voids can reduce the re-centring capabilities in NiTi-alloys and that this effect should be taken into consideration of constitutive equations.