ÖzetBu çalışmada AISI 5140 ve AISI 420 çelikleri 1123, 1173 ve 1223 K sıcaklıklarında2,4 ve 6 saat süreyle kutu borlama yöntemi ile borlanmıştır. Deneyler sonucunda, çelik yüzeylerinde oluşan borür tabakalarının morfolojisi optik mikroskobu ile incelenmiştir. Sertlik değerleri, mikro-sertlik cihazı ile ölçülmüş ve tabaka üzerinde oluşturulan fazlar XRD yöntemi ile belirlenmiştir. XRD analizinde FeB, Fe 2 B, CrB ve MnB fazlarının borür tabakasının üzerinde oluştuğu görülmüştür. Sonuç olarak, borlanmış çeliklerde elde edilen borür tabakasının kalınlık değerleri, borlama süresi ve sıcaklığın artmasıyla artığı görülmüştür. Buna ek olarak, borür tabakasının kalınlık değerleri çeliklerin kimyasal bileşimine bağlı olarak değişmiştir. AbstractIn this study, AISI 5140 steel and AISI 420 stainless steel were pack borided at 1123, 1173 and 1223 K for retention times of 2, 4 and 6 h. The morphology of the boride layers formed on the steel surfaces as a result of the experiments was investigated by optical microscopy. The hardness values were measured by a micro-hardness device and the phases formed on the layer were determined by the XRD method. The XRD analysis revealed that FeB, Fe 2 B, CrB and MnB phases had formed on the boride layer. The results indicate that the boride layer thickness in all the steel samples had an incres as a function of incresing boriding time and temperature. In addition, the boride layer thickness values changed depending on the chemical composition of the steels. While the original hardness values of AISI 5140 and AISI 420 steels were 265 HV 0,05 and 340 HV 0,05 respectively, as a result of boriding, they increased up to 1843 HV 0,05 and 1972 HV 0,05 . Activation energies (Q) of borided AISI 5140 steel and AISI 420 stainless steel used in the current study were determined as 194.951 and 206.161 kJ/mol, respectively. The growth kinetics of the boride layers forming on the AISI 5140 steel and AISI 420 steels and thickness of boride layers were also investigated. The adhesion properties of the boride layer were analyzed by performing the Daimler-Benz Rockwell-C adhesion method. According to the adhesion test results, the adhesion resistance of the boride layer decreased with the increase in the boriding temperature and time.

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CoWB based composites were produced by annealing Ni33.6Co23.2Zr0.5Ta4W23.7B15 bulk metallic glass above the crystallization temperature. The effect of annealing on the microstructure of the composites was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Microhardness (Hv) and indentation fracture toughness (KC) of the composites were also measured. Microstructural examinations revealed that the first precipitated phase as a result of annealing is a nickel solid solution. As the annealing time is increased, the CoWB and the nickel solid solution begins to precipitate. If the annealing time is increased further, the CoWB remains stable, while the nickel solid solution transforms into the Ni3Ta. The microhardness of the as-cast alloy was determined to be 1190 HV. As a result of annealing, composites with a microhardness of around 1400 HV were obtained due to the precipitation of CoWB. KC of the composite with the maximum hardness was determined to be ~3 MPa.m1/2. The effect of microstructure on the mechanical properties of the composites is discussed.

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