Devitrification kinetics and phase selection mechanisms in Cu-Zr metallic glasses
Başlık çevirisi mevcut değil.
- Tez No: 400270
- Danışmanlar: PROF. RALPH E. NAPOLİTANO
- Tez Türü: Doktora
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2010
- Dil: İngilizce
- Üniversite: Iowa State University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Malzeme Bilimi ve Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 187
Özet
Özet yok.
Özet (Çeviri)
Metallic glasses have been a promising class of materials since their discovery in the1960s. Indeed, remarkable chemical, mechanical and physical properties have attractedconsiderable attention, and several excellent reviews are available. Moreover, the specialgroup of glass forming alloys known as the bulk metallic glasses (BMG) become amorphoussolids even at relatively low cooling rates, allowing them to be cast in large cross sections,opening the scope of potential applications to include bulk forms and net shape structuralapplications. Recent studies have been reported for new bulk metallic glasses produced withlower cooling rates, from 0.1 to several hundred K/s. Some of the application products ofBMGs include sporting goods, high performance springs and medical devices. Several rapidsolidification techniques, including melt-spinning, atomization and surface melting havebeen developed to produce amorphous alloys. The aim of all these methods is to solidify theliquid phase rapidly enough to suppress the nucleation and growth of crystalline phases.Furthermore, the production of amorphous/crystalline composite (ACC) materials by partialcrystallization of amorphous precursor has recently given rise to materials that provide bettermechanical and magnetic properties than the monolithic amorphous or crystalline alloys. Inaddition, these advances illustrate the broad untapped potential of using the glassy state as anintermediate stage in the processing of new materials and nanostructures. These advancesunderlie the necessity of investigations on prediction and control of phase stability andmicrostructural dynamics during both solidification and devitrification processes.This research presented in this dissertation is mainly focused on Cu-Zr and Cu-Zr-Alalloy systems. The Cu-Zr binary system has high glass forming ability in a widecompositional range (35-70 at.% Cu). Thereby, Cu-Zr based alloys have attracted muchviattention according to fundamental research on the behaviors of glass forming alloys. Furthermotivation arising from the application of this system as a basis for many BMGs and ACCmaterials; the Cu-Zr system warrants this attention and offers great potential for thedevelopment of new materials. However, the prediction and control of microstructuralevolution during devitrification remains challenging because of the complex devitrificationbehavior of the Cu-Zr binary alloy which is arising from the competition of metastable andstable phases and diversity of crystal structures. This dissertation details a systematicfundamental investigation into the mechanisms and kinetics of the various crystallizationtransformation processes involved in the overall devitrification response of Cu-Zr and Cu-Zr-Al glasses. Various isothermal and nonisothermal treatments are employed, and the structuralresponse is characterized using bulk X-ray and thermal analysis methods as well as nanoscalemicroscopic analysis methods, revealing structural and chemical details down to theatomic-scale.By carefully combining techniques such as differential scanning calorimetry (DSC),in-situ synchrotron high energy X-ray diffraction (HEXRD), and transmission electronmicroscopy (TEM) to quantify the characterization transformations, this research hasuncovered numerous details concerning the atomistic mechanisms of crystallization and hasprovided much new understanding related to the dominant phases, the overall reactionsequences, and the rate-controlling mechanisms. As such this work represents a substantialstep forward in understanding these transformations and provides a clear framework forfurther progress toward ultimate application of controlled devitrification processing for theproduction of new materials with remarkable properties.
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