Fe-B esaslı sert dolgu elektrot alaşımının özellikleri üzerine W, Nb ve Cr ilavesinin etkisinin araştırılması
Investigation of the effect of added W, Nb and Cr on the properties of Fe-B based hard filler electrode alloy
Yazar: ORHAN AKYILDIZ
Danışman: PROF. DR. UĞUR ŞEN
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Metalurji ve Malzeme Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Sert yüzey alaşımlama, ağır, agresif ve aşındırıcı ortamlarda çalışan iş parçalarının yüzey performanslarını geliştirmek amacıyla uygulanan bir yüzey işlemidir. Bu yöntemde alaşım, altlığın sünekliği ve tokluğunda önemli bir kayıp olmaksızın sertliği ve aşınma direncini artırmak amacıyla kaynak yoluyla yumuşak bir malzemenin (genellikle düşük veya orta karbonlu çelikler) yüzeyine homojen olarak kaplanır. Bu yöntem sayesinde malzemelerin aşınma ve korozyon gibi malzeme kayıplarına neden olan zararlardan etkilenmesi azaltılarak malzeme ömrü önemli ölçüde artırılabilmekte, ekonomik kayıplar azaltılmakta, bakım onarım masrafları düşürülmekte, işçilik giderleri azaltılmakta ve aşınan parçaların değişimi sırasında üretime ara verme, makinelerin durdurulması gibi zaman kayıpları minimize edilmektedir. Bu yöntem, bütün bu sayılan kayıplar düşünüldüğünde çok büyük bir ekonomik kazanç sağlamaktadır. Bu amaçla, bu çalışma kapsamında üretilen ve çalışılan Fe-B esaslı sert yüzey alaşımları özellikleri bakımından önemli ve umut vaat edici sonuçlar sunmuştur. Yine bu çalışmada, Fe-B esaslı sert yüzey alaşımlara, W, Nb ve Cr  ilavesinin özellikler üzerine ne gibi etkiler yapacağı araştırılmıştır. Ayrıca, önceden bileşimi belirlenen Fe-B alaşım tozu, ferro-alaşımlar kullanılarak ve içerisine değişik oranlarda W, Nb ve Cr elementleri yine ferro-tungsten, ferro-niyobyum ve ferro-krom tozlar kullanılarak ilave edilmiştir. Elde edilen karışım önce halkalı değirmende öğütülerek alaşım tozu haline getirilmiştir. Daha sonra, bu alaşım tozlarının içerisine fuluşpat, kuvars, alginatlar, camsuyu gibi ilaveler yapılarak toz karışımı kalıpta şekil almasını kolaylaştıracak plastik bir hale getirilmiştir. Önceden hazırlanmış kalıplara tel çubuk elektrotlar yerleştirildikten sonra hazırlanan plastik karışım presle kalıp içerisine enjekte edilerek çubuğun etrafı kaplanmıştır. Kurutma ve pişirme işlemleri ile üretilmiş olan elektrotlar, klasik örtülü elektrot kaynak yöntemiyle AISI 1020 çelik altlık plaka üzerine alaşımlama yapılmıştır. Üretilen plakalar içerdikleri W, Nb ve Cr miktarına bağlı olarak, metalografik olarak hazırlanarak, optik ve taramalı electron mikroskoplarında incelenmiştir. Yine X-ışınları difraksiyon analizi ile oluşan intermetalik bileşikler tespit edilmiştir. Mikro ve makro sertlik ölçümleri yapılmıştır. Ayrıca ball on disk tekniği ile sert aşındırıcı bilyeye karşı aşınma deneyleri yapılmıştır. Böylelikle üretilen yüzey alaşımının performansları ölçülerek muadilleri ile karşılaştırılmıştır.

Abstract:
Hard surface treatments are surface treatments applied to increase the surface performance of heavy, aggressive and abrasive workpieces. In this method, the alloy is homogeneously coated with a soft material (usually low- or medium-carbon steels) by welding in order to increase durability and wear resistance without significant loss in the ductility and toughness of the substrate. Thanks to this method, the lifespan can be increased significantly by reducing the losses that cause material losses such as wear and tear, economic losses are reduced, maintenance and repair interruptions are reduced, labor costs are reduced, and the time such as interrupting production and stopping machines during wear and tear is minimized. This method provides a huge economic gain when all these losses are considered. For this purpose, the Fe-B based hard surface alloys produced and studied within the scope of this study have provided important and promising results in terms of their properties. However, the effects of W, Nb and Cr addition on the properties of these effective Fe-B based hard surface alloys were investigated. Additionally, distribution was recorded through Fe-B alloy powder, ferro-alloys and into which W, Nb and Cr elements were added in divided proportions to ferro-tungsten, ferro-niobium and ferro-chromium powders. The resulting mixtures are first ground in a ring mill and turned into alloy powder. Then, the powder mixture containing additions such as phlushpar, quartz, alginates and glass water into these alloy powders was made plastic in the mold to facilitate shape. After the wire rod electrodes were glued to the created molds, the molds were combined with the prepared plastic press and their frames were covered. Electrodes equipped with drying and baking processes are alloyed on AISI 1020 steel base plate by classical coated electrode welding method. The produced plates are prepared metallographically and listed in optical and scanning electron microscopes, depending on the amount of W, Nb and Cr they contain. However, intermetallic images formed by X-ray diffraction analysis were detected. Micro and macro measurements were made. Additionally, wear experiments were carried out against hard abrasive balls using ball disc technology. In this way, the performances of the produced surface alloy were measured and compared with their counterparts.
When the layers of the produced hard surface alloy coatings are examined, there is usually a homogeneous phase distribution in their microstructures. A compatible transition between the coating layer and the steel substrate was determined by the interface investigations.
The microstructures of the produced hard surface coatings were investigated and the following results were observed.
As a result of the microstructure investigations of the Fe-B surface alloy, α-Fe and Fe2B phases were detected in the coating layer. On the other hand, in Fe-W-B based coatings, it was determined that FeWB phase is present in addition to α-Fe and Fe2B phases. Two different regions were detected in the microstructure of the Fe17B3-based coating, which does not contain W in its structure and has an atomic B content of 15%. This composition has a sub-eutectic microstructure. MAP analysis and XRD analyzes show that this eutectic structure consists of α-Fe+Fe2B phases.
When the microstructure of the Fe16WB3 based coating is examined, a microstructure consisting of dark gray, eutectic and white regions is observed. When the white area was examined, it was determined that there was intense W together with Fe and B. FeWB phase was detected in the coatings containing W, and it is understood that the white region consists of this phase. When the dark gray region was examined, Fe and W were detected. Here, it is seen that the intensity of the Fe element is intense. Therefore, this region is thought to be composed of the α-Fe phase. When the eutectic region was examined, Fe, B and partially W elements were detected. Considering the Fe2B phase determined in XRD, it was understood that this eutectic structure consisted of α-Fe+Fe2B.
When the Fe15W2B3 coating is examined, it is seen that the microstructure consists of two regions. When the white colored eutectic structure was examined, W, Fe, B and C elements were determined and it was determined that this structure consisted of α-Fe+FeW(B,C) phase. When the dark region is examined, Fe element is intensely found. Therefore, it has been determined that this region consists of α-Fe.
In the Fe-Nb-B coating layers, α-Fe, Fe2B and NbFeB phases were detected as a result of XRD investigations. It has been observed that the microstructure of this alloy consists of three regions as light gray, dark gray and white. The light gray areas are composed of primary α-Fe phase. NbFeB phases were formed as white block structures at their grain boundaries. In dark gray areas, α-Fe+Fe2B eutectic occurred. It was observed that the ratio of NbFeB phase in the microstructure increased with the increase of Nb content in the Fe-Nb-B based coating layer.
When the X-rays of Fe-Cr-B based hard surface alloys were examined, α-Fe, Cr2B and BFe2 phases were detected. It has been determined that the microstructure of this coating group consists of a sub-eutectic alloy. This system is composed of primary α-Fe phase and α-Fe+M2B(M= Fe, Cr) eutectic.
α-Fe, W2FeB2, NbFeB, Fe2B, NbB2, Fe23B6, W2B5, Cr2B, and NbC phases were determined by XRD analysis of Fe-W-Nb-Cr based hard surface alloys. The structure of the coating consists of light gray, dark gray and white regions. Light gray areas are primary α-Fe and dark gray areas are composed of α-Fe+M2B eutectic structure. Again, complex carboboride phases were detected in the eutectic region. The white regions were found to be rich in tungsten and it was determined that these regions were composed of W2FeB2 phases.
When the micro and macro hardness tests of the produced hard surface alloys were examined, the following results were obtained.
The effect of 5% and 10% W additions to the Fe-B base composition on the hardness was investigated. It was determined that the microhardness values of the Fe-W-B based hard surface coating layer were between 470-756 HV values. Considering the Fe-B base composition, as a result of the row hardness tests, the microhardness values of the coating layers increased significantly with the increase of 5% and 10% W addition in this system. In this system, the highest hardness was observed in the composition with 10% W addition. When the hard surface alloying macrohardness values are examined, it varies between 32-43 HRC, and in this test, the highest HRC hardness value was obtained from the coating with 10% W ratio.
The effect of 5% and 10% Nb addition to Fe-B base composition on hardness was investigated. It was determined that the microhardness values of the Fe-Nb-B based hard surface coating layer were between 330-427 HV values. As a result of the row hardness tests, 5% and 10% Nb added to the Fe-B base composition gave approximately the same microhardness values in this system. When the hard surface alloying macrohardness values are examined, it varies between 30-32 HRC, where the highest hardness value of 32 HRC was obtained from the hard surface alloy with 10% Nb added.
The effect of 5% and 10% Cr addition to Fe-B base composition on hardness was investigated. It was determined that the microhardness values of the Fe-Cr-B based hard surface coating layer were 426-653 HV values. As a result of row hardness tests, it was observed that the addition of 5% and 10% Cr to the Fe-B base system increased the hardness, respectively. Here, the highest hardness value was observed in the composition with 10% Cr addition. When the hard surface alloying macrohardness values are examined, it varies between 41-50 HRC, where the highest hardness value of 50 HRC was obtained from the hard alloy with 10% Cr added.