Papers by Author: R. Yilmaz

Abstract: In this study, AISI 420 martensitic stainless steels were welded by GTAW (gas tungsten arc welding) using ER 316L consumables. Pure argon, argon + 25% He and argon + 5% N2 were used as shielding gases. The obtained results indicated that shielding gases have some effect on the properties of the martensitic stainless steel weldments. The use of argon+5%N2 provides the highest tensile strength values and higher microhardness profile compared to the other shielding gas composition used.

Abstract: In this study, various ratios of ferro-molybdenum were added into low alloy distaloy steel powder and then the compacts were fabricated by powder metallurgy process. The effect of ferromolybdenum addition on the properties of these sintered materials such as density, microhardness and impact toughness were investigated. The results obtained from experimental works showed that ferro-molybdenum addition to the starting powder resulted in an increment in density and microhardness values. On the other hand, ferro-molybdenum addition has influence on impact toughness values of the sintered low alloy steel.

Abstract: In this study, the Clay – 220 mineral of Turkish origin from Kalemaden A.S., having a composition of the quarts, kaolinite, feldspar and the others with the weight percent of 36.20, 12.66, 48.03 and 3.11, respectively, was used as a raw material to investigate its transferability potential to a technological ceramic. The mineral was in the form of conglomerate rocks, which were prepared in the consecutive mineral processing procedures before taken it to the stage where carbothermal reduction - nitridation (CRN) was performed in an atmosphere controlled environment. Various process parameters, i.e., temperature, time and N2 – flow rate were tested in order to optimise the CRN process. SiAlON was formed at temperatures as low as 1300oC and its content increased with reaction temperature up to 1475oC. Above 1425oC, SiC becomes more predominant phase in the powdered product after CRN. Fine powders formed at temperature of 1350oC, which is the lowest value reported among the current literature, contain single crystalline phase of β-SiAlON. The results indicated that the best transformations and yield to the SiAlON ceramic were occurred on the previously prepared Clay – 220 samples in powder form that were processed at 1350oC for 6 hours with nitrogen flow rate of 1 lt/min.