Rapid solidification of zinc based alloys

This work presents an investigation into two areas : the development of zinc based brazing alloys for the joining of copper produced by the rapid solidification technique; the study of the development of microstructures in rapidly solidified dilute zinc alloys. A new model has been proposed, based on the present experimental results and the available data from the literature, to account for the ribbon formation mechanism. Within this model ribbon formation in melt spinning is mainly determined by the behaviour of the viscosity in undercooled melts. It has been shown that, contrary to previous studies, the present model can be used to predict the ribbon thickness of both crystalline and amorphous alloys, and the agreement with the measured values is excellent. The development of microstructures in dilute zinc alloys during rapid solidification has been studied by the deliberate addition of impurity elements. Significant differences in structures are observed between the dilute zinc alloys and high purity zinc. The high purity zinc exhibits a strong preferred orientation with the basal plane parallel to the ribbon surface. The severity of this texture markedly reduces with the formation of cellular substructures in dilute zinc alloys. The morphology of the cells depends on the type of impurity elements present. The presence of impurity elements which expand on solidification leads to the development of an eutectic-like structure consisting of regular lamellae. This requires reorientation of the basal plane and instability of the solid liquid interface during solidification. The instability conditions of the planar solid liquid interface during rapid solidification of these alloys have been examined by using the morphological stability criterion. A possible mechanism which accounts for the formation of unusual structures observed in rapidly solidified dilute zinc alloys has been proposed. The observed variety of microstructures of binary Zn-Mg alloys, and the structural transitions across the ribbon thickness have been reported. Comparisons are made between as-cast and rapidly solidified materials and the resulting structures have been described using a growth rate composition map. Rapidly solidified eutectic and hypereutectic alloys show a tendency to form an amorphous phase. A total of more than 50 zinc based alloys have been investigated for the development of brazing filler metal. Alloys have been examined, and their compositions optimized, in terms of their spreading and wetting abilities and brazing performances to obtain a suitable candidate. Based on the experimental results it has been suggested that Zn-Mg alloys could be used for the joining of copper. They exhibit a lower surface tension, a lower density and comparable mechanical properties to high temperature high strength silver based brazing alloys

İRİ HACİMLİ CAMSI/NANOKRİSTAL MALZEMELER: CAMSI YAPI ÇELİKLERİ

İRİ HACİMLİ CAMSI/NANOKRİSTAL MALZEMELER: CAMSI YAPI ÇELİKLER

Amorf/Camsı Çeliklerin Sert Kaplama Malzemesi olarak Kullanımının Araştırılması

Önerilen bu proje, yüksek mukavemet, sertlik, aşınma direnci ve korozyon direnci gibi üstün servis performans değerlerine gereksinim duyulan sanayii ve mühendislik uygulamaları için katma değeri yüksek, ekonomik, çevreye duyarlı, daha uzun ömürlü ve performans yükseltme amaç ve hedeflerine yönelik olarak yeni nesil Amorf/Camsı Çeliklerin Üretimi ve Kaplama Malzemesi olarak Kullanımının araştırılmasını amaçlamaktadır.İri hacimli amorf/camsı çelikler (İHCÇ) dünyada oldukça yeni bir teknoloji olup, ülkemizde herhangi bir kullanım alanı ve uygulaması henüz bulunmamaktadır. Ancak, sahip oldukları üstün ve sıradışı özellikler dikkate alındığında, birçok farklı sektörde ve alanda bu malzemeden yararlanılması şüphesizdir. Bu anlamda değerlendirildiğinde önerilen projenin temel hedefi, proje kapsamında tasarlanarak atık malzemeler ile ekonomik olarak üretimi gerçekleştirilecek olan üstün özellikli amorf/camsı çelik malzemelerin, çeşitli sanayii ve mühendislik uygulamalarında yaygın bir şekilde kullanılan geleneksel malzemelerin üzerine kaplanarak servis performans ve ömürlerinin arttırılması yönünde olacaktır. Amaçlanan performans hedefleri arasında yüksek mukavemet, karbon ve paslanmaz çeliklerin neredeyse 3-4 katı sertlik değerleri (~1000 Hv), yüksek kırılma dayanımı (~3000 MPa) ve yüksek elastik geriniminin yanısıra çok daha üstün korozyon direnci ve düzgün, pürüzsüz dış görünüm ve yüzey sayılabilir

Solidification microstructures and carbides morphology in rapidly solidified Fe-Al-Cr-C alloys

The combined effects of alloying additions and heat treatment on the evolution and development of the microstructures of Fe3Al-based Fe-Al-Cr-C alloys produced by melt suction processing have been examined. Particular emphasis has been placed on the distribution and morphology of carbides in rapidly solidified Fe3Al-based intermetallics. The results suggest that the formation of intrinsically hard and brittle Fe3AlC and Cr7C3 type carbides depends on the alloying content. These carbides tend to form preferentially along the grain boundaries where more continuous and coarse networks are observed, especially for alloys having higher Cr and C content. These networks are fragmented as a result of heat treatment at 1200 degrees C and subsequent air cooling and quenching

DESIGN AND DEVELOPMENT OF HEUSLER ALLOYS FOR MAGNETIC REFRIGERATION APPLICATIONS

Cooling systems are used in houses, cars, hospitals, defence systems and many other such areas. However, the gases (chlorofluorocarbons and hydrochlorofluorocarbons) present in today's refrigerant systems are harmful to the environment and cause global warming. Moreover, today's cooling technology is expensive and low efficiency technology. Therefore, new and cost-effective with higher energy efficiencies cooling systems have begun to be developed to eliminate the use of these harmful gases. Among them, magnetic refrigeration has attracted increasing interest in the materials research communities because of its higher cooling efficiency and environmentally friendliness. Full Heusler alloys are magnetic ternary intermetallic compounds with the L2(1)-type crystal structure. Typically, these alloys undergo a low temperature martensitic transformation (austenite martensite), a magnetic transformation (ferromagnetic paramagnetic) and relatively high temperature atomic ordering (order order and order disorder) transformations. After the discovery of the ferromagnetic shape memory (FSM) and giant magnetocaloric effects (GMCE) in Ni-Mn-Ga alloy, Ni-Mn based Heusler alloys have received considerable attention due to their unique magnetic and structural properties. In this present study compositional dependence of structural and magnetic properties of off-stoichiometric Ni-rich Ni-Mn-Ga Heusler alloys have been investigated, in order to determine an alloy composition where a coupled magneto -structural transformation occurs and to measure the MCE near this temperature. Structural and magnetic properties of Ni-Mn-Ga Heusler alloy system were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) measurements