EFFECT OF AGING TIME ON PHASE TRANSFORMATION, MICROSTRUCTURE AND HARDNESS OF Co-Cr-Mo ALLOYS

Yıl 2019, Cilt: 7 Sayı: 1, 146 - 153, 01.03.2019

Mehmet Yıldırım Ali Keleş

https://doi.org/10.15317/Scitech.2019.188

Öz

The effect of heat-treatment on phase
relationships, microstructures and hardness of Co-Cr-Mo alloys were
investigated in detail. The samples were produced by investment casting
technique and subsequently solutionized (1240 °C for 4 h) and aged (720 °C for
2, 4, 8 and 16 h). Phase analysis of the samples were performed via X-ray
diffraction analysis, microstructural examination were done by light optical
and scanning electron microscopy. The microstructures of as-cast and short-time
(2 and 4 h) aged samples were composed of FCC γ-Co matrix phase and fine M₂₃C₆
(where M= Co, Cr and Mo) precipitates. Increasing the aging time to 8 and 16 h
led to partial transformation of FCC γ-Co matrix phase into HCP ε-Co phase. The
volume fraction of ε-Co phase increased with increasing aging time. Moreover,
hardness of the Co-Cr-Mo samples were significantly enhanced with formation of
ε-Co phase.

Anahtar Kelimeler

Co-Cr-Mo alloys, Hardness, Microstructure

Yaşlandırma Süresinin Co-Cr-Mo Alaşımlarının Faz Dönüşümleri, Mikroyapıları ve Sertliğine Etkisi

Öz

Bu
çalışmada, ısıl işlemin Co-Cr-Mo
alaşımlarının faz ilişkileri, mikroyapıları ve sertliklerine etkisi detaylı
biçimde incelenmiştir. Alaşım
hassas döküm yöntemiyle üretilmiş, takiben çözeltiye alma (1240 °C’de 4 saat) ve
yaşlandırma (720 °C’de 2, 4, 8 ve 16 saat) ısıl işlemi uygulanmıştır. Numunelerin faz
analizleri X-ışınları kırınım yöntemiyle, mikroyapıları ise optik ve taramalı
elektron mikrokobisi yöntemleriyle incelenmiştir. Dökülmüş haldeki ve kısa süre
(2 ve 4 saat) yaşlandırılmış numunelerin mikroyapıları YMK kristal yapısına
sahip γ-Co matris fazı ve M₂₃C₆ (M= Co, Cr ve Mo) tipi
ince karbür çökeltilerinden meydana gelmektedir. Artan yaşlandırma süresi ile
birlikte γ-Co matris fazı kısmen ε-Co fazına dönüşmüştür. ε-Co fazının miktarı
artan yaşlandırma süresi ile artmıştır. Ayrıca, ε-Co fazının oluşumu alaşımın
sertliğini önemli ölçüde arttırmıştır.

Anahtar Kelimeler

Co-Cr-Mo alaşımları, Mikroyapı, Sertlik

Kaynakça

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