Ultra-Sünek YMK Tek Kristalli Bir Alaşımda Kırılma Davranışının İncelenmesi

Abstract

Tek kristalli konsantre alaşım sisteminin çekme deformasyonu davranışı, kırılma yüzeyi davranışının yönelim bağımlılığını ortaya koymak amacıyla [111], [110] ve [100] olmak üzere üç kristalografik yönelim boyunca oda sıcaklığında sistematik olarak incelenmiştir. Önceki çalışmalar, tüm yönelimlerde başlangıçtaki pekleşme davranışının dislokasyon aracılı kayma tarafından kontrol edildiğini göstermiştir. Bununla birlikte, [111] ve [110] yönelimli kristallerde deformasyonun ilerlemesi, mekanik ikizlerin kademeli oluşumu da dahil olmak üzere karmaşık, deformasyonla indüklenen mikroyapısal bir evrimle birlikte gerçekleşmektedir. Bu mekanizmaların etkileşimi, deformasyon pekleşmesinde ve toplam plastik şekil değiştirme kapasitesinde belirgin bir artışa yol açmaktadır. Ayrıca, bu yönelimlerde ikizlenmenin gecikmeli aktivasyonu ek bir pekleşme aşaması oluşturarak deformasyon lokalizasyonunu etkin biçimde baskılamakta ve homojen plastik deformasyon rejimini genişletmektedir. Taramalı elektron mikroskobu (SEM) analizleri dikkat çekici bir karşıtlığı ortaya koymaktadır: en düşük sünekliği gösteren [100] yönelimli numuneler sünek kırılma modu ile hasara uğrarken, daha sünek olan [111] ve [110] yönelimli kristaller gevrek kırılmaya özgü özellikler sergilemektedir. İlk bakışta çelişkili görünen bu davranış, [111] ve [110] yönelimli kristallerde boyun verme kararsızlığına karşı artan stabilite dikkate alınarak açıklanabilir; bu stabilite, daha yüksek seviyelere kadar şekil değiştirme birikimini mümkün kılmakta ve nihayetinde gevrek kırılmaya yol açmaktadır.

Keywords

• Kırılma yüzeyi
• Yönelim bağımlılığı
• Kayma–ikizlenme etkileşimi

Investigation of Fracture Behavior in an Ultra-Ductile FCC Single-Crystal Alloy

Abstract

The tensile deformation behavior of a single-crystalline multi-principal alloy system was systematically investigated at room temperature along three crystallographic orientations [111], [110], and [100] to elucidate the orientation dependence of the fracture surface behavior. Previous studies demonstrated that the initial hardening response in the [100]-oriented crystal is governed by dislocation-mediated deformation. However, the tensile response in the [111]- and [110]-oriented crystals is accompanied by the progressive formation of mechanical twins and multi-slip activation. The interplay of these mechanisms results in a pronounced enhancement in strain hardening and overall plastic deformability. Moreover, the secondary or tertiary twinning activation in these orientations contributes an additional hardening stage, effectively suppressing strain localization and extending the regime of uniform plastic deformation. Scanning electron microscopy (SEM) analysis reveals an apparent paradox: while the [100]-oriented specimens, which exhibit the lowest ductility, fail via a ductile fracture mode, the more ductile [111]- and [110]-oriented crystals display features characteristic of brittle fracture. This seemingly contradictory behavior is rationalized by considering the enhanced stability against necking in the [111]- and [110]-oriented crystals, which promotes strain accumulation to higher levels and ultimately leads to brittle fracture.

Keywords

• Fracture surface
• Orientation Dependence
• Slip–twinning interaction

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