The Influence of Duty Cycle on Plasma Nitriding

Abstract

Different surface hardening methods are applied to improve the microstructure of machine parts, increase wear resistance, provide resistance to corrosion and extend fatigue life. Plasma nitriding process is widely used in the industry due to the precise control of the hardened layers obtained and the various advantages it offers compared to other hardening techniques. In this research, DC plasma nitriding and pulsed plasma nitriding with 75% and 50% duty cycles were applied to AISI 5115 steel in a 50% H2+50% N2 gas mixture environment at 500 ºC for 5 hours. The phase properties of plasma nitrided samples were examined by XRD and optical microscope. Surface hardness was determined by microhardness measurements. As a result of metallographic examinations, it was observed that a white layer was formed and the layer thickness decreased with the decrease in duty cycle. As a result of X-ray examinations, Fe3N, Fe4N phases were formed with DC plasma nitriding and in the study carried out with 50% duty cycle, α-Fe and Fe3O4 phases were observed on the surface in addition to these phases. As a result of microhardness examinations, it was determined that there was an increase of approximately 3-5 times in surface hardness depending on the process.

Keywords

• AISI 5115 Steel
• Plasma nitriding
• Duty cycle
• Microhardness

Görev Döngüsünün (Duty Cycle) Plazma Nitrürleme Üzerindeki Etkisi

Öz

Makine parçalarının mikro yapısını iyileştirmek, aşınmaya karşı dayanıklılığını artırmak, korozyona karşı direnç kazandırmak ve yorulma ömrünü uzatmak için farklı yüzey sertleştirme yöntemleri uygulanmaktadır. Plazma nitrürleme işlemi, elde edilen sertleşmiş tabakaların hassas bir şekilde kontrol edilebilmesi ve diğer sertleştirme tekniklerine kıyasla sunduğu çeşitli avantajlar sayesinde endüstride geniş çapta kullanılmaktadır. Bu araştırmada AISI 5115 çeliğine %50 H2+%50 N2 gaz karışımı ortamında 500 ºC sıcaklıkta 5 saat süreyle DC plazma nitrürleme, %75 ve %50 görev döngüsü ile darbeli (puls) plazma nitrürleme işlemi uygulanmıştır. Plazma nitrürlenmiş numunelerin faz özellikleri XRD ve optik mikroskop ile incelenmiştir. Mikrosertlik ölçümleri ile yüzey sertlikleri belirlenmiştir. Metalografik incelemeler sonucunda beyaz tabakanın oluştuğu, görev döngüsünün azalmasıyla tabaka kalınlığının azaldığı görülmüştür. X-ışınları incelemeleri sonucunda DC plazma nitrürleme ile Fe3N, Fe4N fazlarının oluştuğu %50 görev döngüsü ile yapılan çalışmada ise bu fazlara ek olarak yüzeyde α-Fe ve Fe3O4 fazları görülmüştür. Mikrosertlik incelemeleri sonucunda yüzey sertliğinde işleme bağlı olarak yaklaşık 3-5 kat artış olduğu tespit edilmiştir. 93B1

Anahtar Kelimeler

• 5115 çeliği
• Plazma nitrürleme
• Görev Döngüsü
• Mikrosertlik

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