Murat ÇELTEK, Sedat ŞENGÜL, Ünal DÖMEKELİ

Hızlı Soğutma Sürecinde Dörtlü Zr48Cu36Ag8Al8 İri Hacimli Metalik Camının Atomik Yapısının Gelişimi

Çalışmamızda Zr48Cu36Al8Ag8 dörtlü alaşımının atomik yapısı ve cam oluşturma süreci moleküler dinamik simülasyon ile gömülü atom metodu kullanılarak araştırıldı. Cam geçiş sürecini ve sıcaklığa bağlı atomik yapı gelişimini araştırmak için ortalama hacim-sıcaklık eğrisi, çiftler dağılım fonksiyonu (PDF) ve çift analiz metodu kullanıldı. 300 K’de hesaplanan toplam PDF, g(r), daha önce rapor edilen deneysel g(r) ile iyi bir uyum sağlamaktadır. Öte yandan ortalama hacim-sıcaklık grafiğinden yararlanılarak belirlenen cam geçiş sıcaklığı da deneysel değerlerle birbirlerine yakındır. Zr-Zr ve Cu-Cu çiftlerinin kısmi PDF'lerin pikleri sıcaklık düşüşüne bağlı olarak normal bir artış eğilimi gösterirken, Al-Al ve Ag-Ag çiftleri ise çok yüksek pikler üreterek anormal bir davranış sergilemektedir. Bu davranışın nedeninin simülasyon hücresindeki Al ve Ag atomlarının topaklanması olduğu görülmüştür. Sistemin mikro yapısı incelendiğinde ise kısa menzil düzenin göstergesi olan 1431, 1541 ve 1551 bağlı çiftlerinin bütün sıcaklıklarda baskın olduğu gözlenmiştir. Azalan sıcaklıkla birlikte özellikle ideal ikosahedral düzeni temsil eden 1551 bağlı çiftlerinin oranının artması sistemin kısa menzil düzeninin gelişerek artmaya devam ettiğini göstermektedir.

Anahtar Kelimeler:

İri hacimli metalik camlar, Moleküler dinamik simülasyon, Çiftler dağılım fonksiyonu, Topaklanma

The Evolution of Atomic Structure of the Zr48Cu36Ag8Al8 Bulk Metallic Glass in the Rapid Cooling Process

In our study, atomic structure and glass formation process of Zr48Cu36Al8Ag8 quaternary alloy was investigated by molecular dynamic simulation using embedded atom method. The average volume-temperature curve, the pair distribution function (PDF) and the pair analysis method were used to investigate the glass transition process and the atomic structure development depending on the temperature. The total PDF, g(r), calculated at 300 K is in good agreement with previously reported experimental g(r). On the other hand, the glass transition temperature determined by using the average volume-temperature graph is close to that achieved with experimental works. The peaks of the partial PDFs of the Zr-Zr and Cu-Cu pairs inhibit a normal upward trend due to the temperature drop, whereas the peaks of the Al-Al and Ag-Ag pairs exhibit an abnormal behavior by producing very high peaks. The reason for this behavior was the aggregation of Al and Ag atoms in the simulation cell. When the microstructure of the system was examined, it was observed that the 1431, 1541 and 1551 bonded pairs which are indicative of the short range order were dominant in all temperatures. The increase in the fraction of the 1551 bonded pairs, which represent the ideal icosahedral order together with the decreasing temperature, shows that the short range order of the system continues to develop and increase.

Keywords:

Bulk metallic glasses, Molecular dynamic simulation, Pair distribution function, Aggregation,

PDF

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