In this study, Zn-reinforced Mg matrix composite materials were produced via powder metallurgy by exposing them to ball milling at varying mechanical milling times. Following ball milling, the powders were cold-pressed under 600 MPa to obtain green compacts. The sintering process was carried out in a tube furnace under an argon atmosphere at 500 °C for 120 min. The effects of different milling times (2 h, 4 h, and 8 h) on particle and grain size, as well as the influence of sintering temperature and time on the microstructure, were investigated through SEM analysis. Phase evolution and changes in crystal planes occurring after ball milling were revealed by XRD analysis. SEM images show that Zn particles were homogeneously distributed within the matrix after 8 h of milling. Furthermore, it can be clearly stated that the highest hardness values were obtained from the samples produced after 8 h of milling. The sample group with the highest density, least mass loss, and lowest degradation rate was obtained from materials produced from 4 h ball milled powders. The intermetallic phase formed in the powder structure after 8 h of milling tends to reduce density and corrosion properties. The findings reveal that the addition of these alloys to pure Mg clearly enhances its hardness and density, while also imparting superior corrosion resistance. These combined improvements suggest that the developed materials hold strong potential for application in biomedical and clinical environments, where both mechanical strength and corrosion resistance are critical.

2,25Cr-1Mo steel is extensively used at elevated temperature structural applications in fossil fire power plants for steam pipes, nozzle chambers and petrochemical industry for hydrocracking unit due to its excellent creep resistance and good redundant to oxidation. Also they should have acceptable weldability and toughness. The steels are supplied in quenched and tempered condition and their welded components are subjected to post-weld heat treatment (PWHT). Tempering process is carried out at 690-710°C to improve toughness properties. However they are sensitive to reheat cracking and temper embrittlement. To measure temper embrittlement of the steels and their weld metal, temper embrittlement factor and formula (J factor - Watanabe and X formula- Bruscato) are used. Step cooling heat treatment is also applied to determine temper embrittlement. In this study, toughness properties of Cr Mo (W) steels were reviewed. Also transition temperature curves of 2,25Cr-1Mo steel and its weld metal were constructed before and after step cool heat treatment as experimental study. While 2,25Cr-1Mo steel as base metal was supplied, all weld metal samples were produced in Gedik Welding Company. Hardness measurements and microstructure evaluation were also carried out.

As internal combustion engine (ICE) systems are increasingly exposed to severe thermal and oxidative environments, the oxidation resistance and structural integrity of exhaust valve materials have become critical for maintaining long-term engine reliability and efficiency. This study presents a comparative evaluation of the cyclic oxidation behavior of two candidate valve steels, 1.4718 (ferritic stainless steel) and 1.4871 (austenitic stainless steel), under service-temperature conditions. The specimens were exposed to repeated oxidation at 550 °C, 650 °C and 750 °C for 25 cycles in ambient air. The surface and cross-sectional morphologies of the oxide layers were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to investigate oxide scale composition, thickness, and growth characteristics. The oxidation behavior of both alloys proceeded in two distinct stages: an initial phase marked by accelerated oxidation, followed by a slower, more stable growth period. The extent of oxidation intensified with increasing temperature. The 1.4718 alloy developed relatively porous but compositionally stable oxide layers consisting primarily of Fe- and Cr-based spinels such as FeCr₂O₄ and Cr₂SiO₄. In contrast, the 1.4871 alloy formed a dense, adherent, dual-layered oxide scale composed of an outer Mn₂O₃-rich layer and an inner Cr₂O₃-rich layer, attributable to its high Mn and Cr content. The results underscore the critical influence of elemental composition, particularly Cr, Mn and Si, on oxide scale stability and spallation resistance, demonstrating the superior cyclic oxidation resistance of the 1.4871 alloy and its potential suitability for exhaust valve applications in thermally aggressive environments.

AA7075 alüminyum alaşımı endüstride yaygın olarak kullanılmaktadır. Bu alaşımların yüksek sıcaklık mukavemetleri, aşınma dirençleri gibi özellikler bazı durumlarda yeterli olamamaktadır. Alaşımlara takviye elemanları ilave edilerek üretilen metal matrisli kompozit malzemeler ile bu eksiklik giderilmeye çalışılmaktadır. Bu çalışma kapsamında AA7075 alüminyum alaşımına, mekanik alaşımlama yöntemi ile nano boyutta Al2O3 toz takviyesi yapılmıştır. Mekanik alaşımla yöntemi farklı sürelerde (0, 1 ve 5 sa) uygulanmış ve elde edilen tozlar önce 500 MPa da soğuk presleme işlemine tabi tutulmuş sonrasında 500°C de 25 MPa basınç altında 20 dakika boyunca sıcak preste numuneler üretilmiştir. Üretimi gerçekleştirilen numunelerin sertlik, yoğunluk ve mikroyapı analizleri için metalografik numune hazırlama işlemleri gerçekleştirilmiştir. Öncelikle numuneler sırasıyla 600-2000’lik zımparalar yardımı ile zımparalanmış, hemen sonrasında 6 ve 0,5 µm alümina solisyon ile parlatma işlemi tamamlanmıştır. Parlatma işleminden sonra numuneler, uygun bileşimlerde hazırlanan Modifiye Keller solüsyonu ile dağlanmıştır. Dağlanmış numunelerin mikroyapıları optik mikroskop ile incelenmiştir Numunelerin mikroyapıları incelendiğinde mekanik alaşımlama işlemine tabi tutulmadan üretilen numunede daha büyük taneler göze çarparken artan mekanik alaşımlama süresi ile daha ince taneli yapıların oluştuğu görülmüştür. Mekanik alaşımlama süresinin sertlik ve yoğunluk üzerindeki etkileri incelemek amacı ile yoğunluk ölçümleri Arşimet prensibi ile sertlik ölçümleri ise, Brinell sertlik ölçme yöntemi kullanılarak gerçekleştirilmiştir. Yapılan analizler sonucunda en yüksek yoğunluk değeri (2,81 gr/cm3 ) 1 saat mekanik alaşımlanmış alaşımda elde edilmiştir. En yüksek sertlik değeri (237,2 HB) ise 5 saat mekanik alaşımlanmış alaşımda elde edilmiştir.

This paper investigates the cyclic oxidation behavior of the Inconel 718 (IN-718) superalloy at elevated temperatures, combining experimental measurements with thermodynamic predictions using Thermo-Calc. Samples were exposed to 25 oxidation cycles at 550 °C, 650 °C, and 750 °C, with each cycle consisting of a 1-hour exposure followed by cooling to ambient conditions. Mass change and microstructural analyses revealed the development of protective oxide scales, while thermodynamic calculations provided insight into phase stability and oxidation mechanisms. Mass change results revealed a rapid initial oxidation stage, followed by a slower, quasi-steady-state regime, with the total mass gain increasing with temperature and peaking at 750 °C. While the oxidation kinetics increased parabolically at 650 °C and 750 °C, deviations observed at 550 °C were attributed to limited atomic diffusion. X-ray diffraction (XRD) analyses confirmed the formation of NiO as the primary oxide along with minor Cr2O3 at higher temperatures. Surface examinations employing scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed a distinct bilayer oxide at 750 °C, consisting of a thin Al2O3 inner layer beneath a dense NiCr2O4 outer layer. X-ray photoelectron spectroscopy (XPS) confirmed the chemical states of Ni, Cr, and O, indicating the coexistence of NiO and NiCr2O4 phases. These outcomes demonstrate the importance of the diffusion-controlled bilayer oxide in providing enhanced oxidation resistance at elevated temperatures. The study offers valuable insights into oxide scale development and elemental distribution, contributing to the optimized design of nickel-based superalloys for elevated-temperature applications.