Bülent BOSTAN, Ekrem Emre ELVERİŞLİ, Sinan AKSÖZ, Gülizar ALTINIŞIK

Önalaşımlı NiTi ŞBA Tozlarında B19 – R – B2 ve B19 – B2 Dönüşümlerine Sıcaklık ve Deformasyonun Etkileri

Çalışmada, önalaşımlı NiTi şekil bellekli alaşım (ŞBA) tozlarına 25°C, 100°C, 200°Csıcaklıklarda ve farklı yükleme oranlarında (800MPa, 1300MPa, 1600MPa, 1800MPa, 2000MPa,2500MPa), deformasyon işlemleri uygulanmıştır. NiTi ŞBA tozlarına uygulanan farklı preslemeoranlarının etkilerini tespit edebilmek için ise; DSC, XRD analizleri yapılmıştır. Ayrıca hamtozların optik mikroskop görüntüleri incelenmiştir.25ºC’de uygulanan presleme neticesinde yapıda B19 → R ve R → B2 çift fazlı dönüşümügörülürken, 100°C’de ve 200°C’de uygulanan presleme sonrası yapıda yalnızca B19 → B2dönüşümü görülmüştür. Numunelerin XRD analizleri incelendiğinde ise, ham tozlarda görülenB2 (östenit) fazları deformasyon oranına bağlı olarak pik şiddetleri düşmeye başlamış, en düşükB2 piki en yüksek deformasyon oranında tespit edilmiştir. XRD pik şiddetindeki düşüşün nedeniise artan deformasyon oranına bağlı olarak, östenit pikinin şiddetinin azalması ve martenzit pikşiddetlerinin ise oluşmaya başlaması olarak söylenebilir.

Effects of Temperature and Deformation on B19- R - B2 and B19 - B2 Transformation in Prealloyed NiTi SMA Powders

In this study, prealloyed NiTi shape memory alloy (SMA) powders have been deformed at 25°C, 100°C, 200°C and different loading rates (800MPa, 1300MPa, 1600MPa, 1800MPa, 2000MPa, 2500MPa). In order to determine the effects of different pressing rates on NiTi SBA powder, DSC, XRD analyzes were performed. Furthermore, optical microscope images of raw powders were examined. B19 → R and R → B2 multi-stage transformation peaks were observed in the structure at 25ºC, whereas only B19 → B2 a single-stage transformation peaks were observed after pressing at 100°C and 200°C. When the XRD analysis of the samples was examined, the peak intensities of the B2 (austenite) phases in the raw powders were decreased due to the deformation rate, and the lowest B2 intensities were found at the highest deformation rate. The reason for the decrease in XRD peak intensity can be attributed to the decrease in the severity of the austenite peak and the onset the increasing of martensite peak intensities, depending on the increasing rate of deformation.

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