Levent Oncel

Ferrotitanium is widely used in alloying stainless steels to enhance their strength, corrosion resistance, and high-temperature resistance. Ferrotitanium’s advantages over pure titanium – such as better solubility in the liquid steel bath and lower cost – have made it the preferred choice in stainless steel alloying. In this study, it was aimed to produce ferrotitanium alloy through the metallothermic reduction of Fe₂O₃ and TiO₂. The system’s thermodynamic modeling was performed using HSC Chemistry 6.12 and FactSage 7.1. The experimental studies investigated the effect of using aluminum as a reductant with varying stoichiometries on the total metal recovery yield, hardness, and microstructure. Atomic absorption spectrometry (AAS), optical microscopy, scanning electron microscopy (SEM), X-ray fluorescence spectrometry (XRF), and hardness measurement techniques were employed in characterization studies. The results of the experimental studies showed that the highest metal recovery yields were obtained with 105 % stoichiometric aluminum as 97.9 % for Fe and 100 % for Ti.

Nitinol is the most widely used shape memory alloy in medical applications. In this study, the effect of different heat treatment conditions on the phase transformation characteristics of medical-grade nitinol was investigated. Nickel-rich nitinol wires containing 50.6% nickel with a diameter of 120 μm were used in the experimental studies. The nitinol wires were heat treated for 10 minutes at heat treatment temperatures between 540 and 570 °C. Then, nitinol wires were heat treated at a heat treatment temperature of 550 °C between 8 and 14 minutes. The austenitic and martensitic transition temperatures of these samples were measured using differential scanning calorimetry (DSC). In the experiments with 10 minutes of heat treatment time, transition temperatures decreased, and hysteresis increased with the increase in heat treatment temperature. This is related to the amount of precipitates in the structure. In the experiments carried out at 550 °C, transition temperatures decreased, and hysteresis increased with increasing heat treatment time. Experimental studies showed that the austenite finish (Af) temperature of all nitinol wire samples was below 37 °C, and they will exhibit superelasticity in the human body.

In this study, the production of ferromolybdenum (FeMo), which is an iron-based alloy, was carried out through the metallothermic reaction. This method was chosen due to its low cost, short process time and minimum energy need. Before the experiments, FactSage and HSC software were used for thermochemical modeling. Mill scale was used as a starting material in the experimental studies. Mill scale is waste material and it contains 70% iron by mass. MoO3 was used as the molybdenum source and aluminum was used as the reducing agent. Produced samples were characterized by Atomic Adsorption Spectrometry (AAS), X-Ray Fluorescence (XRF) and hardness tests (micro-Vickers). Initially, the effect of aluminum stoichiometry, which was used as a reductant, on FeMo efficiency was investigated. The closest result to the target alloy was achieved with the sample having 105% aluminum stoichiometry. Fe and Mo efficiencies were 95.16% and 97.21%, respectively. The effects of weight change on Fe and Mo efficiencies were investigated by using samples having 105% aluminum stoichiometry. It was observed that the closest result to the target alloy was achieved with a 75 g charge. Fe and Mo efficiencies were 99.10% and 97.98%, respectively. These were the highest efficiency values obtained in all experiments. The hardness values of samples were between 678 HV10 and 767 HV10. The highest hardness value was obtained in the alloy containing 100% stoichiometric aluminum. It was concluded that there was no significant difference in the hardness values of the samples due to the similarity in their chemical structures.