Demir-karbon sisteminin mekanik alaşımlama tekniği ile üretim süreçlerinin incelenmesi ve karakterizasyonu
The study and characterization of mechanical alloying of iron-carbon systems
- Tez No: 39819
- Danışmanlar: DOÇ.DR. M. LÜTFİ ÖVEÇOĞLU
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Demir-karbon sistemi, Mekanik alaşımlama tekniği, Iron-carbon systems, Mechanical alloying technique
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Sunulan yüksek lisans tez çalışmasında, geleneksel toz metalürji yöntemiyle üretilemeyen yüksek karbonlu demir-karbon ikili sisteminin mekanik alaşımlama yöntemiyle üretilmesi, üretim şartlarının belirlenmesi ve işlem parametrelerinin ürüne etkileri incelenmiştir. Bu amaçla, Szegvari atritöründe gerçekleştirilen deneysel çalışmalarda ilk olarak optimum deney şartlarının belirlenmesi için bir ön deneysel çalışma gerçekleştirildi. Bu ön deneylerde en uygun deney şartları belirlendikten sonra gerçekleştirilen deneysel çalışmada karbon miktarlarım ve öğütme sürelerinin etkilerini incelemek amacıyla üç farklı karbon içeriğinde ve üç farklı öğütme sürelerinde mekanik alaşımlama işlemi gerçekleştirildi. Farklı öğütme sürelerinde ve karbon miktarlarında mekanik alaşımlanmış tozların x-ışınları difraksiyonu ile faz oluşumları tesbit edildi. Daha sonra alaşımlanmış tozlar, tek eksenli preslerle direngen kalıplarda silindirik şekillerde kompaktlandılar. Bu kompaktların sinterlenmesi sürekli tipteki bir konveyör fırınında gerçekleşti. Daha sonra sinterlenen numunelerin karakterizasyon çalışmaları yapıldı. Yoğunluk ölçümleri, optik mikroskop, taramalı elektron mikroskobu ve bu cihaza bağlı nokta analizleri ile mikroyapısal incelemeler ve mikro sertlik değerlerinin ölçülmesiyle de mekanik özelliklerin karakterizasyonu çalışmaları yapıldı.
Özet (Çeviri)
THE STUDY AND CHARACTERIZATION OF MECHANICAL ALLOYING OF IRON- CARBON SYSTEM SUMMARY Powder metallurgy (P/M) has the distinction of being at the same time one of the oldest and one of the most modern methods known for the production of metal parts. Powder metallurgy can be dated back to prehistoric time. In prehistoric time, powder metallurgy techniques were used to process metals with melting points above these attainable by means of existed technology. Development of this techniques probably began with iron in the form of sponge produced by reduction of iron oxide in charcoal fired furnaces. After that this sponge iron was forged into solid iron. Powder materials were first press-bonded in the early 1800's in a manner similar to tahat employed today. It was in the 1900's that the process was really first used commercially with the development of the porous bronze bushing and the related techniques for mass production. During the period between 1900 and 1920's (World War I), developments on powder metallurgy technology advanced through modern developments such as infiltration techniques, porous materials, iron powder cores, permanent magnets. After World War II powder metallurgy developed in the field of automative industry making the use of iron and copper powders in the large tonnages. Selflubricatrng bearings and steel components which are made by the use of iron andcopper powders became the dominant powder metallurgy products throuh the 1940 and 1950's. Due to low sintering temperatures and net design features P/M is a capital intensive technology offering economies in materials, labor and energy. In addition, the major advantages of powder metallurgy techniques with respect to ingot metallurgy are the elimination of segregations and ensuring of a fully homogeneous, fine-grained, pore- free and high alloy structure. Because of this advantages P/M products are widely used in the field of automobiles, washing machines, refrigerator and air conditioning compressors, bicycles and lawnmowers. Farm machinery and industrial hydraulic equipment are large users. Data processing equipment, office copiers, postage meters and similar machines may actually have more than a hundred P/M parts designed into them. For the outdoorsman, the fishing reel, firearm, tape decks and phonograph turntables also utilize components made by powder metallurgy. The P/M production process can be looked at as consisting of three basic steps : i) powder preparation, ii) powder consolidation and iii) sintering. In the powder preparation step, raw powders having the desired size and shape distribution and the other characteristics are blended with lubricants such as zinc stearate or a stearate derivative and alloying additives which are weighted carefully. The purpose of such a lubricant is to facilitate ejection of the compact from the tooling and to prevent scoring of the punches, dies and core rods. Blending is carried out in a special device for enough duration to ensure a homogeneous mix. Mixing, usually done in double cone blenders in lot sizes ranging from a few hundred to tens of thousands of tons, is carefully controlled. The mixed powder is compacted within a rigid die to the desired shape and size. Compaction is done to consolidate and densify the loose powder into a“green”compact of sufficient strength and density. The compacting or briquetting operation is accomplished in specially designed mechanical or hydraulic presses. Compaction pressures may range from 50 to 500 tons per square cm. Compression ratio - the ratio ofthe volume of loose powder to the volume of the compact made from it - vary considerably depending upon the characteristics of the raw materials used. The last of the three basic operations is sintering. The compacted parts are heated at a temperature about one third below the melting point of the principal constituent in a protective atmosphere, this is termed sintering. Standard sintering temperatures for iron and steel parts are in the range of 1120°C, although this may vary from a few degrees lower to 100 to 150°C higher. In this stage true chemical bonding of the particles and recrytallization across the particle interfaces take place. Protective sintering atmosphere is used to cleanse the compact and to prevent any undesirable reaction between the compacts and its environment. The strength and the integrity of the part greatly increases as a result of this step. After the sintering, most parts are ready for service. However some secondery operations may be necessary which include: repressing, impregnation, machining, infiltration, plating, steam treating, heat treating, brazing and welding. Ferrous powder metallurgy is the largest and economically most important sector of the conventional P/M business. All materials are added as weight percentages, and they can include graphite, copper, nickel, chromium, molibdenium etc. Graphite additions, however, are very important as an industrial material in the region of carbon content lower than that of eutectic. In powder metallurgy, the limitation on the production for higher carbon concentrations is attributable to the difficulty in alloy formation because of the sublimation of carbon. The solid state reaction by mechanical alloying (MA) process makes it possible to produce the high carbon alloys. Mechanical alloying (MA) is an alternative powder metallurgy technique for the production of composite metal powders. Mechanical alloying is the intimate mixing, on an atomic scale, of constituents that results from intense mechanical working in a high- intensity mill of apowder mixture. It utilizes various types of milling machines in which a blend of different powders (elemental, prealloyed, intermetallic etc) is subjected to highly energetic compressive forces. By repeated fracture and cold welding of the constituent powder particles, it is possible to make alloys from normally immiscible components. Mechanical alloying was first developed for the production of complex oxide dispersion-strengthened alloys by INCO company in 1960's. Alloying by melting of metals with significantly different melting points may presents considerable problems,, which may be overcome by mechanical alloying, as it is a solid state process. An advantages of mechanical alloying over many other techniques is that it is solid state technique and consequently problems associated with melting and solidification (such as segregation or large differences in melting points) are bypassed. Since mechanical alloying results in a very fine mix initial constituents, heating of the resulting powder enables the formation of very fine grained and homogeneous compounds, similar to those produced by the other powder metallurgy techniques, through a process of enhanced solid state diffusion. In this disertation work, the metallographic structure change and process parameters, in the mechanical alloying process, of Fe-C alloy produced by atritor milling were investigated. To determine optimum process parameters, initial experimental studies were done. In the light of these preworks, the formation of various phases depending on carbon concentration and processing time were investigated. Elemental powders of iron (average size, 72 #m) and graphite (average size, 42 fim) were used as starting materials. MA of Fe-C alloys which is prepared in various carbon contents were performed by the use of atritor mill at aball to powder ratio of 7:1 and a speed of 600 rev mhr1. The batch was opened after every several hours processing and a small amount of sample was removed for X-ray diffractometry using Cu ka radiation and particle size analyzes. The MA Fe-C alloys were pressed into cylindrical form using uniaxial press and cold isostatic press. Consolidated powder was sintered in the atmosphere controlled(dissociated ammonia) sintering furnace at 1080°C. After the sintering, density measurements of compacted samples were done according to Archimed principle. The metallografic structure of sintered compacts was observed by optic and scanning electron microscope (SEM) equipped with an energy dispersive microanalysis system (EDS). After that, microhardness values of sintered compacts were measured. As a result of this studies, MA Fe-C alloys was achieved. During MA process, phase transformation of iron carbide was observed. Due to this carbide phases, MA Fe-C alloys have greater microhardness values than the conventional powder metallurgy Fe-C alloys.
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