Characterization of Martensitic Transformation, Microstructure and a Kinetic Study of Ti-based High Temperature Shape Memory Alloy

Abstract

High temperature shape memory alloys (HTSMAs) are widely used in many fiels such as industry, biomedical, aerospace, etc. In order to expand the usage areas of these alloys, it is necessary to improve the materials, especially the martensitic transformation temperatures should be controlled. Third elements are often added to the material to control the martensitic transformation temperature. Ti-12V-8Al (wt. %) alloy, which is prepared for use in aircraft engines in the aviation industry, is a good choice due to its low density. In this study, Ti-12V-8Al (wt. %) alloy was prepared with the help of arc-melting technique. The martensite-austenite transformation temperatures, phase formations, microstructure of Ti-12V-8Al (wt. %) alloy were examined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM) respectively. In the DSC test, it was determined that the martensitic transformation temperature reduced according as the heating rate of the alloy. In XRD and SEM measurements, it was observed that the alloy has α″ martensitic phases as well as some β austenite phases. Thermal activation energies of the alloy were founded by Kissinger and Ozawa techniques. It was concluded that the activation energy amounts computed by these two techniques are parallel to each other.

Keywords

• Activation energy
• High temperature shape memory alloys
• Martensitic transformation

Ti-temelli Yüksek Sıcaklık Şekil Hafızalı Alaşımının Martensitik Dönüşüm, Mikroyapı Karakterizasyonu ve Kinetik Çalışması

Abstract

Yüksek sıcaklık şekil hafızalı alaşımlar (YSŞHA) endüstri, biyomedikal, havacılık vb. gibi birçok alanda yaygın olarak kullanılmaktadır. Bu alaşımların kullanım alanlarını genişletmek için malzemelerin iyileştirilmesi, özellikle martensitik dönüşüm sıcaklıklarının kontrol edilmesi gerekmektedir. Martensitik dönüşüm sıcaklığını kontrol etmek için malzemeye genellikle üçüncü elementler eklenir. Havacılık sektöründe uçak motorlarında kullanılmak üzere hazırlanan Ti-12V-8Al (ağ. %) alaşımı düşük yoğunluğu nedeniyle iyi bir seçimdir. Bu çalışmada, Ti-12V-8Al (ağ. %) alaşımı ark-eritme tekniği kullanılarak hazırlanmıştır. Ti-12V-8Al (ağ. %) alaşımının martensit-ostenit dönüşüm sıcaklıkları, faz oluşumları, mikro yapısı sırasıyla diferansiyel taramalı kalorimetri (DSC), X-ışını kırınımı (XRD), taramalı elektron mikroskobu (SEM) ve optik mikroskop (OM) ile incelenmiştir. DSC testinde alaşımın ısıtma hızına bağlı olarak martensitik dönüşüm sıcaklığının azaldığı tespit edilmiştir. XRD ve SEM ölçümlerinde alaşımın α″ martensitik fazlarının yanı sıra bazı β ostenit fazlarına da sahip olduğu gözlenmiştir. Alaşımın termal aktivasyon enerjileri Kissinger ve Ozawa yöntemleri ile bulunmuştur. Bu iki yöntemle hesaplanan aktivasyon enerjisi değerlerinin birbirine yakın olduğu sonucuna varılmıştır.

Keywords

• aktivasyon enerjisi
• martensitik dönüşüm
• yüksek sıcaklık şekil hafızalı alaşımlar

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