İÇTEN YANMALI MOTORLARDA ÖSTENİTİK EGZOZ SUPAPLARININ YÜKSEK SICAKLIK AŞINMA MEKANİZMALARININ TESPİTİ

Öz

Bu çalışmada 21-4N (%21 Cr, %9 Mn ve %3.88 Ni temel bileşenli alaşım) egzoz supap malzemesinin PL12 alaşımlı beyaz temper dökme demir baga malzemesi karşısında yüksek sıcaklıktaki aşınma davranışı incelenmiştir. Egzoz supap-baga ikilisinin aşınma testleri için özel olarak geliştirilmiş bir tribometre kullanılarak 25 ℃, 350 ℃, 550 ℃’de ve 20 N yük altında testler yapılmıştır. Yapısal ve termodinamik analizler ile 21-4N supap - PL12 baga ikilisinin ara yüzeyinde gerçekleşen yüksek sıcaklık aşınma mekanizması literatürde ilk kez incelenmiştir. Aşınma sırasında uygulanan lokal basınç ve sıcaklık artışı ile spinel oksit yapılardan oluşan, aşınmaya karşı koruyucu bir tabakanın 21-4N yüzeyinde oluştuğu görülmüştür. Bu oluşan tribofilm yüksek sıcaklıklarda 21-4N supap malzemesinin PL12 baga karşısında hacimsel aşınma kaybının azalmasına neden olmuştur. Ayrıca sıcaklığa bağlı oluşan/çözülen karbür ve karbonitrür fazları da termodinamik olarak hesaplanmıştır. Sıcaklık artışı ile pinin mukavemeti azalırken, 21-4N supap malzemesinin 900°C’ye kadar kararlılık gösteren çökelti fazlarından dolayı mekanik özelliklerini koruduğu ve aşınma direncinin arttırdığı tespit edilmiştir.

Anahtar Kelimeler

• Aşınma
• Supap
• Baga
• İçten Yanmalı Motor
• Östenitik

INVESTIGATION OF HIGH TEMPERATURE WEAR MECHANISMS OF AUSTENITIC EXHAUST VALVES IN INTERNAL COMBUSTION ENGINES

Öz

In this study, high temperature wear behaviour of 21-4N (%21Cr, %9Mn, %3.88 Ni based alloying elements) exhaust valve material against PL12 alloyed white cast iron seat insert material was investigated. The sliding wear tests were conducted at 25℃, 350℃, 550℃ and under 20N load using a high temperature tribometer which was designed for the wear tests of valve-seat insert couples. By means of structural and thermodynamic analysis, the high temperature wear mechanism that takes place at the interface of 21-4N-PL12 was investigated for the first time. It was determined that the spinel oxide structures formed a tribolayer on the surface 21-4N by the effects of local pressure and high temperature during the sliding. This causes a decrease in volumetric wear loss of 21-4N against PL12 at high temperatures. Additionally, the formed carbide and nitride phases were calculated thermodynamically. While the strength of pin decreases with increasing temperature, 21-4N maintains its mechanical properties and wear resistance increases since the precipitate phases are stable up to 900° C

Anahtar Kelimeler

• Wear
• Valve
• Valve Seat Insert
• Internal Combustion Engine
• Austenite

Kaynakça

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