Electroless Ni-B Coating and Heat Treatment Application for Rail Fastener Elements

Yıl 2024, Sayı: 20, 67 - 78, 31.07.2024

Mustafa Dursunlar Zakir Taş

https://doi.org/10.47072/demiryolu.1471045

Öz

In recent years, the speed of rail system vehicles and the amount of load they carry have increased. This situation makes it difficult for urban and high-speed train lines to adapt to today's conditions. For this purpose, Zn-Al coating is generally used to increase the wear, corrosion and fatigue resistance of rail fasteners. Reasons such as Zn-Al coating not having sufficient hardness and wear resistance, zinc baths not being sustainable and environmentally friendly, and non-homogeneous coating thickness make Zn-Al coating disadvantageous. In this study, as an alternative to Zn-Al coating, SKL14 tension clamps were coated with electroless Ni-B and heat treated. In the examination of the coating surfaces, some scratches, pits and discontinuities were observed on the Zn-Al coating surfaces, while on the Ni-B coating surfaces, voids, pores, scratches, pits, discontinuities, flowing, blistering, flaking, cracking, capillary breaks, etc. were observed. No defects were observed. When examining the cross-sectional views of the coatings, it was observed that the Zn-Al coating thickness was not homogeneous and the average coating thickness was approximately 22.5µm, and that it did not adhere very well to the substrate material due to flaking, crust, discontinuity. No flaking, crusting or discontinuity was observed in Ni-B coatings, a homogeneous coating thickness was obtained and it was observed that it adhered very well to the substrate material, and the coating thickness was approximately 19.5 µm. As a result of the SEM analysis of the coating surfaces, a heterogeneous structure with roughness, cracks and voids was observed on the Zn-Al coating surface. The cauliflower form of Ni-B coatings, resulting from nodules that create irregular, textured and multi-layered clusters on the surface, was observed. It was observed that as a result of heat treatment, grain sizes decreased and grain boundaries became more distinct. This is explained by the fact that heat treatment increases the hardness and wear resistance of the coating. As a result, Ni-B coating and heat treatment have been successfully applied to tension clamps and represent a good alternative to Zn-Al coatings.

Anahtar Kelimeler

Railway, Rail, Rail Fastener, Tension Clamp, Ni-B Coating

Ray Bağlantı Elemanlarına Akımsız Ni-B Kaplama ve Isıl İşlem Uygulamaları

Öz

Son yıllarda raylı sistem araçlarının hızı ve taşıdığı yük miktarları artmıştır. Bu durum kent içi ve yüksek hızlı tren hatlarının günümüz koşullarına uyumunu zorlaştırmaktadır. Bu amaçla ray bağlantı elemanlarının aşınma, korozyon ve yorulma dayanımlarının artırılması için genellikle Zn-Al kaplanarak kullanılmaktadır. Zn-Al kaplamanın yeterli sertlik ve aşınma direncine sahip olmaması, çinko banyolarının sürdürülebilir ve çevreci olmaması, homojen olmayan kaplama kalınlığı gibi nedenler Zn-Al kaplamayı dezavantajlı kılmaktadır. Bu çalışmada Zn-Al kaplamaya alternatif olarak, SKL14 gergi kıskaçları akımsız Ni-B kaplanmış ve ısıl işlem uygulanmıştır. Kaplama yüzeylerinin incelenmesinde, Zn-Al kaplama yüzeylerinde bazı çizik, çukur ve süreksizlikler gözlemlenmiş olup, Ni-B kaplama yüzeylerinde ise boşluk, gözenek, çizik, çukur, süreksizlik, akma, kabarma, pullanma, çatlama, kılcal kırılma vb. herhangi bir kusur gözlemlenmemiştir. Kaplamaların kesitten görünüşlerinin incelemesinde, Zn-Al kaplama kalınlığının homojen olmadığı ve kaplama kalınlığının ortalama yaklaşık 22,5µm olduğu, atma, kabuk, süreksizlik ile altlık malzemeye çok iyi yapışmadığı gözlemlenmiştir. Ni-B kaplamalarda atma, kabuklanma ve süreksizlik gözlemlenmemiş olup, homojen bir kaplama kalınlığı elde edilmiş ve altlık malzemeye çok iyi bir şekilde yapıştığı, kaplama kalınlıklarının yaklaşık ise 19,5 µm olduğu gözlemlenmiştir. Kaplama yüzeylerinin SEM analizi sonucunda, Zn-Al kaplama yüzeyinde pürüz, çatlak ve boşlukların olduğu heterojen bir yapı gözlemlenmiştir. Ni-B kaplamaların ise yüzeyde düzensiz, dokulu ve çok katmanlı küme oluşmasını sağlayan nodüllerden kaynaklanan karnabahar formu gözlemlenmiştir. Isıl işlem sonucu, tane boyutlarının küçüldüğü ve tane sınırlarının daha belirgin hale geldiği gözlemlenmiştir. Bu durum, ısıl işlemin kaplamanın sertlik ve aşınma direncini artırmasıyla açıklanmaktadır. Sonuç olarak, gergi kıskaçlarına Ni-B kaplama ve ısıl işlem başarılı bir şekilde uygulanmış olup, Zn-Al kaplamalara iyi bir alternatif oluşturmaktadır.

Anahtar Kelimeler

Demiryolu, Ray, Ray Bağlantısı, Gergi Kıskacı, Ni-B Kaplama

Etik Beyan

Bu makalede bilimsel araştırma ve yayın etiğine uyulmuştur. Yazarlar çalışmaya eşit oranda katkı sağlamıştır.

Teşekkür

Bu çalışma Mustafa DURSUNLAR’ın doktora tez çalışmalarından türetilmiş olup, malzeme temini ve kaplamalar için Gürmak Demiryolu ve Bematek’e teşekkür ederiz.

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