Tuba Yener

A process control method for the electric current-activated/assisted sintering system based on the container-consumed power and temperature estimation

In this paper, the current, voltage and temperature of the container of an electric current-activated/assisted sintering (ECAS) system are measured and recorded with respect to time during the sintering process. By post-processing of the recorded data, the power and thermal energy of the system container are calculated. Interpretation of the measured and post-processed data has provided a criterion: It has been found that the dissipated electrical power in quasi-steady state is almost equal to the power conducted from the container to the copper bars throughout the stiffs and the convection and radiation powers are negligible compared to the conducted power. Therefore, the container-stored thermal energy or the container surface temperature can be estimated from the dissipated electrical power with the values of the container heat capacitance and the stiff thermal resistances without the need for a temperature measurement equipment. If the thermal energy or the temperature required to make the samples has a known/required minimum value and if this amount of the thermal energy is provided to the sample, the sample production process can be stopped. In this study, for an actual implemented design, we suggest that ECAS current and voltages should be continuously measured in real time and the process is automatically terminated when the calculated steady-state container temperature becomes equal to the required container temperature. Therefore, a standard procedure for material production in ECAS system is provided to automate sample production and the performance of the produced samples is guaranteed.

Memristor-based timing circuit

Memristor has been proposed as the fourth missing fundamental circuit element in 1971. This new circuit element has a charge controlled resistance, saturation mechanism and zero-crossing hysteresis loop which cannot be mimicked by previously known circuit elements. It is a promising candidate for both digital and analog electric circuit applications. In this work, a memristor based timer circuit is proposed. Concept of the circuit is presented and its analysis is done. Simulation of the timer is done using the linear drift model of the TiO2 memristor and the result is compared to the analytical calculations.

Rapid Synthesis of Metallic Reinforced in Situ Intermetallic Composites in Ti-Al-Nb System via Resistive Sintering

Abstract Intermetallics are known as a group of materials that draws attention with their features such as ordered structure, high temperature resistance, high hardness and low density. In this paper, it is aimed to obtain intermetallic matrix composites and also to maintain some ductile Nb and Ti metallic phase by using 99.5% purity, 35-44 μm particle size titanium, niobium and aluminium powders in one step via recently developed powder metallurgy processing technique - Electric current activated/assisted sintering system (ECAS). In this way, metallic reinforced intermetallic matrix composites were produced. Dominant phases of TiAl3 and NbAl3 which were the first compounds formed between peritectic reaction of solid titanium, niobium and molten aluminum in Ti-Al-Nb system during 10, 30 and 90 s for 2000 A current and 1.5-2.0 voltage were detected by XRD and SEM-EDS analysis. Hardness values of the test samples were measured by Vickers indentation technique and it was detected that the hardnesses of intermetallic phases as 411 HVN whereas ductile metallic phase as 120 HVN.

Effect of Double Stage Nitriding on 34CrAlNi7-10 Nitriding Steel

In this study, effect of double stage gas nitriding of 34CrAlNi7-10 steel was analyzed. Nitriding processes were carried out in two stages. in the first stage, samples were nitridied at 500 ◦C for 10 h and then in second stage nitriding process was continued at 530 and 550 ◦C for 20 h. During both stages, the nitrogen activity on surface was controlled by the nitriding potential, which is a thermodynamical control parameter for controlled gas nitriding process. The nitriding potential was kept constant, at value of 10, during the first stage and was varied in the range of 3.2–0.2, for both nitriding temperatures, in the second stage. The presence of nitrides, formed on the surface of test materials was determined by XRD analysis technique. The morphology of nitrided layer was studied by optical microscopy. The microhardness of the surfaces of nitrided samples in HV1 was between 955 and 1029. The measurements have shown that the thickness of the compound layer (white layer) has varied between 6.85–23.90 μm and that the growth of the white layer and microhardness gradient were strongly affected by the nitriding potential and the temperature. Diffusion depths as Nht(HV) for Vickers Hardness were determined and compared.