Laser engineering net shaping (LENS) is one of the representative processes of directed energy deposition (DED) in which a moving heat source having high-intensity melts and fuses metal powders together to print parts. The complex and nonuniform thermal gradients during the laser heating and cooling cycles in the LENS process directly affect the microstructural characteristics, and thereby the ultimate mechanical properties of fabricated parts. Therefore, prediction of microstructure evolution during the LENS process is of paramount importance. The objective of this study is to present a thermo-microstructural model for predicting microstructure evolution during the LENS process of Ti-6Al-4V. First, a detailed transient thermal finite element (FE) model is developed and validated for a sample LENS process. Then, a density type microstructural model which enables calculation of the α-phase fractions (i.e., Widmanstätten colony and basketweave α-phase fractions), β-phase fraction, and alpha lath widths during LENS process is developed and coupled to the thermal model. The microstructural algorithm is first verified by comparing the phase fraction results with the results presented in the literature for a given thermal history data. Second, the average lath width values calculated using the model are compared with the experimentally measured counterparts, where a reasonable agreement is achieved in both cases.

In this study, copper oxide (CuO) nanostructures were successfully prepared by adding EG (ethylene glycol) and PEG (4000, 8000) (polyethylene glycol) via an in-situ chemical precipitation method. EG and PEG (4000, 8000) were effective for changing the particular size of CuO and we examined the effects of drying type such as freeze drying, muffle and horizontal furnace on the size of CuO nanostructure. The structure, morphology and elemental analysis of CuO nanostructure were analyzed by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Also, the CuO nanostructures showed excellent electrical conductivity by the changing of PEG’s molecular weight and drying processes.

In this study, using the Materials Calculator software program, the pseudo binary phase diagrams (i.e. isoplethal maps) of high chromium white cast irons (~19% in weight) with different molybdenum contents were simulated. In order to test the accuracy of the calculated phase diagrams, the transformation temperatures read from the diagrams at certain compositions were compared with the phase transformation temperatures measured using Differential Scanning Calorimetry (DSC) analysis of the samples produced by casting in the same composition followed by slow cooling. With the same purpose, low temperature phases read from the phase diagrams were compared with the crystalline phases determined by X-Ray Diffraction (XRD) of the casted samples. Simulated diagrams predicted an increase in the amount of secondary M 23 C 6 carbides with increasing molybdenum content. The validity of this prediction was tested by determining the phase distribution and phase compositions in the casted samples by means of metallographic examinations and Scanning Electron Microscopy (SEM)-Energy Dispersive Spectroscopy (EDS) analyzes. When the hardness values of the samples were taken into consideration, it was seen that the hardness increased from 44.90 to 51.05 HRC with a 1% increase in Mo content and a corresponding increase in the amount of secondary carbides without any heat treatments. Results show that theoretical predictions and experimental measurements are in accord and estimating phase equilibria in multi-component systems is of practical importance.

In this study, corrosion behavior of low carbon steels containing low boron in acidic and saltwater medium was investigated. Boron is an alloying element particularly used to improve the mechanical properties of steels. In order to determine the effects of boron addition on corrosion behavior, boron free, 15, 20 and 100 ppm boron containing SAE 1020 steels were examined. Corrosion tests were performed in a solution of 0.1 M sulfuric acid solution (H 2 SO 4) and 0.1 M sodium chloride (NaCl) solution. Result of electrochemical corrosion test by potentiodynamic method showed that the corrosion rate increased with boron addition and these steels have better corrosion resistance in saltwater medium than in acidic medium. ÖZET Bu çalışmada çok düşük oranlarda bor içeren az karbonlu çeliklerin asidik ve tuzlu ortamlardaki korozyon davranışları incelenmiştir. Bor, çeliklerin özellikle mekanik özelliklerini geliştirmek için kullanılan bir alaşım elementidir. Az karbonlu çeliklerde düşük oranlardaki bor ilavesinin korozyon davranışına etkilerini belirlemek için bor içermeyen ve 15 ppm, 20 ppm ve 100 ppm bor içeren SAE 1020 çelikleri kullanılmıştır. Korozyon testleri 0,1 M sülfürik asit (H 2 SO 4) çözeltisi ve 0,1 M sodyumklorür (NaCl) çözeltisinde yapılmıştır. Potansiyodinamik yöntemin kullanıldığı elektrokimyasal korozyon testleri sonucunda bu çeliklere alaşım elementi olarak bor ilavesi ile korozyon hızının bir miktar arttığı, bu çeliklerin tuzlu ortamda asidik ortama göre daha iyi korozyon dayanımı sergilediği belirlenmiştir.