Gaz enjeksiyon ve elementel karbon ilavesi yöntemleri ile tic takviyeli alüminyum matrisli kompozit üretimi
Başlık çevirisi mevcut değil.
- Tez No: 75047
- Danışmanlar: PROF. DR. H. ERMAN TULGAR
- Tez Türü: Doktora
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Malzeme Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 125
Özet
Otomotiv ve havacılık sektöründeki gelişmeler, düşük yoğunluklu, yüksek mukavemetli aşınmaya karşı dirençli ve bu özelliklerini yüksek sıcaklıkta koruyan malzemelere ihtiyaç duyulacağını göstermektedir. Bu düşünceden yola çıkılarak, bu çalışmada Al-Ti mastır alaşımı kullanılarak TiC takviyeli alüminyum matrisli kompozit malzemenin üretimi gerçekleştirilmiştir. Diğer klasik kompozit üretim proseslerine göre üstün yanlan bulunan, takviye fazın ergiyik metal içerisinde çekirdeklendiği (In-Situ Production) yöntemlerden gaz enjeksiyon ve elementel karbon ilavesi üretim yöntemleri olarak seçilmiştir. Gaz enjeksiyon yöntemi ile TiC takviyeli alüminyum matrisli kompozit üretiminde, karbonlu gazın (CHU) infiltrasyon reaksiyonu vakum indiksiyon fırınında gerçekleştirilmiştir. Alaşım saf alümina pota içerisinde ergitildikten sonra taşıyıcı argon gazı ile karbon kaynağı olan metan gazı Al-Ti ergiyiği içine gönderilmiştir. Elementel karbon ilavesi ile TiC takviyeli alüminyum matrisli kompozit üretiminde Al-Ti alaşımının ergitme işlemi içerisi saf alümina ile sıvanmış grafit potada indiksiyon firını kullanılarak gerçekleştirilmiştir. Ergiyik sıcaklığı AI3Tİ fazının tamamen çözünmesine imkan veren 1200 °C olarak seçilmiştir. Bu sıcaklıkta, ergiyik içinde bulunan AbTi'un tamamen çözünmesi için yaklaşık 30 dakika beklenmiştir. Daha sonra nemi uçurulmak için 850 °C da 1 saat ön ısıtılmış ortalama tane boyutu 10-20 um olan karbon l'er gramlık paketler halinde alüminyum folyoya sarılarak ergiyik içerisine ilave edilmiştir. Karbon ilavesinden sonra titanyum ile elementel karbon arasındaki reaksiyonu gerçekleşebilmesi için uygun sıcaklıklara çıkılmış ve bu sıcaklıklarda reaksiyonun tamamlanması için yeterli süre beklenmiştir. 1200 °C sıcaklık, 0.4 1/dak. gaz akış hızında 90 dakikalık reaksiyon süresi sonucu elde edilen üründe yapı içerisinde TiC'ün yanı sıra AI3Tİ fazıda bulunduğu tesbit edilmiştir. 1200 °C sıcaklık, 0.4 1/dak. gaz akış hızında 120 dakikalık reaksiyon süresi sonucu elde edilen üründe yapı içerisinde AI3Tİ iğneciklerinin tamamen yok olduğu ve boyutu ~ 1 um olan TiC partiküllerinin bulunduğu saptanmıştır. Al+%4Ti, Al+%5Ti ve Al+%6Ti alaşımlarında yapılan inceleme sonucunda 1300°C sıcaklıkta ve %30 fazla karbon ilavesinde ve 15 dak.'lık bekleme süresinde Al3Ti fazının tamamının 1 um ve altı boyuta sahip TiC'e dönüştüğü tesbit edilmiştir. TiC takviyeli alüminyum matrisli kompozitlerin kırılma özelliklerini belirlemek amacı ile kırılma yüzeylerinde metalografik inceleme yapılmıştır. Karbon ilave edilmemiş Al+%4Ti alaşımında gevrek kırılma meydana geldiği tesbit edilmiştir. AI3Tİ ve TiC fazlarının birlikte bulunduğu numunede yapılan metalografik inceleme sonucunda bazı bölgelerin sünek bazı bölgelerin ise gevrek davranış gösterdiği tesbit edilmiştir. Sünek kırılmanın olduğu bölgelerde TiC fazı bulunurken gevrek kırılmanın olduğu bölgelerde TiC fazına rastlanmamıştır. TiC oluşumunun tamamlandığı numunelerde sünek kırılmanın meydana geldiğini tesbit edilmiştir. 1 um ve altı boyuta sahip TiC partikülleri ve matris arasında ayrılma gözlenmemiştir. Matris ile TiC partikülleri arasında çok iyi arayüzey bağlanması olduğu belirlenmiştir. 2 um ve üzeri boyuta sahip partiller ile matris arasında ayrılma olduğu tesbit edilmiştir.
Özet (Çeviri)
. During the past decade, specific materials property requirements for advanced aerospace, automotive and other structural applications have escalated where conventional alloy systems are no longer suitable. The development of materials with minimum specific gravity, high structural strength at the highest possible temperature and the capability of withstanding oxidative hot corrosion is a major goal of materials science for high technology engine and aerospace applications. Therefore attempts have been made to enhance the material properties via a reinforcing ceramic second phase of higher strength and stiffness. Various materials such as oxides carbides, and nitrides have been investigated for improving the properties of the monolithic metals. The reinforcing phase and the metal matrix are combined by various processing techniques such as powder metallurgy, preform infiltration, spray deposition, casting technologies, i.e squeeze casting, rheocasting and compocasting. These artificial composites have resulted in the realisation of strength and modules goals, however rarely have the composites been economically viable. Additionally these processes also have problems such as interface reactions leading to undesirable products, thermodynamic and mechanical incompatibility, internal stresses owing to the mismatch of coefficients of thermal expansion of the various phases. In the last decade, new in situ fabrication technologies have been developed for processing metal and ceramic matrix composites. Simply stated, in situ processes involve a chemical reaction resulting in the formation of a thermodynamically stablereinforcing ceramic phase. Some of these technologies include DIMOXT, XDT, SHS and reactive gas infiltration. In-situ production of metal matrix composites (MMCs) can produce a new class of naturally stable composites for advanced structural and wear applications. Conventional mechanical mixtures of whiskers, fibers, or particles and matrices (i.e., synthetic MMCs) are often not thermodynamically stable. The in-situ processes for nonferrous and intermetallic systems eliminate interface incompatibility of matrices with reinforcements by creating more thermodynamically stable reinforcements based on their nucleation and growth from the parent matrix phase. By controlling the melt (i.e., matrix alloy design) and reaction gas chemistry, a hierarchical range of carbides, nitrides, oxides, borides, and even suicides can be generated. Using knowledge of local mixing characteristics and by suitable selection of the two reacting phases, their concentrations, and their reactivities, the size and size distribution of the carbide and nitride phases can be controlled. Dual-phase reinforcements and graded reinforcements also may be produced via multicomponent gas chemistry and novel processing routes. The reactions can be categorised generically, in terms of the starting phases, as gas-liquid, liquid-solid, liquid-liquid, etc. One of the major, fundamental scientific challenges lies in controlling the materials synthesis through optimised reaction kinetics and interfacial design. Commercial application of these technologies requires an understanding of several keys processing steps. It is important to be able to control the microstructure and consider processing and near-net-shape production capabilities. The incorporation of these in-situ formed reinforcements into an ambient -and elevated- temperature alloy system offers the advantage of increasing the modules and strength of the base alloy while still maintaining a relatively low volume fraction to preserve the fracture toughness and elongation. Another benefit is improved elevated temperature performance. Materials property requirements for advanced aerospace, land transportation, and wear application have escalated such that conventional nonferrous alloy systems and synthetic MMCs may not be suitable or cost-effective in some applications.Therefore, cost-effective enhancement of the performance of monolithic metallic materials by in-situ or natural reinforcements with a high-strength/high-stiffness second phase is required. The processing microstructure mechanical properties of artificial particulate reinforced MMCs have been evaluated for more than two decades, but the concept of in-situ MMCs has only recently been exploited for commercial wear and high- performance applications. Refractory metals, stable carbides (eg. SiC, B4C), nitrides (Si3N4), A1N), borides, oxides (AI2O3, SİO2), sulphides, intermetallics, silicide, and silicates are all possible candidates for reinforcing phases in a range of engineered composite materials. Since refractory metal compounds such as carbides, nitrides, borides, silicide and oxides are known to be extremely hard and to keep their strength at elevated temperatures, in addition to their high melting point. The formation kinetics and the compatibility of these compounds with candidate matrix alloys must be considered. Potential reinforcing particulates include TiC, TaC, B4C, SiC, Sİ3N4, and BN in several conventional alloys or higher-temperature intermetallic-matrix systems. Liquid-gas reaction processing involves the formation of thermodynamically stable refractory compounds in a nonferrous alloy matrix (eg. Al, Cu, Mg, Ni, or Ti). The reinforcing phase is the product of a gas-liquid reaction caused by the injection of gas into a reactive liquid metal. The rapid reaction between the solute alloying elements and the nonmetal-bearing gas refractory dispersion in the matrix alloy. The flow diagram given in Fig.l illustrates the chronological sequence of events occurring during the gas injection process. Step A is the initial stage in which the carbonaceous gas, ie. CH4, undergoes decomposition within the liquid met. Step B indicates the various reaction paths and products that may form. Depending on alloy chemistry, either AI4C3 or TiC or a mixture of both may form. Step C outlines the possible (solute state or liquid solution-precipitation process) reaction paths for the formation of TiC.Step A, GâADeeöftiposttiûit Teaıperai»F&& CoslpOsMöıı Stop H“ ftiiaelian Psödöcte J”ai4C: Rate Time, Msaix 4*-3 TiC AI4C3 + TiC SfcuC:PGSs$ \ 1 Solid State C + AMS««Ai*TEIC Liquid Solution Âî-Tl-£~Al-HrtC Step 13; XoMfi&aktti Vdft Figure 1. Illustration of the chronological sequence of events occurring during processing. The developments in the automotive and aerospace applications, point to the importance of materials which have high strength, low density and wear resistance properties which are also protected at high temperatures (>250 °C). In this study, TiC reinforced aluminium matrix composite material was produced by using Al-Ti master alloy. Gas injection and addition of elemental carbon methods are used in preference to other classical composite production methods among the in-situ production processes. In the production of TiC reinforced aluminium matrix composites by gas injection, infiltration reaction of CH4 was let to take place in vacuum induction furnace. After the melting of aluminium alloy, metan gas as source of carbon together with argon gas was injected in the Al-Ti solution.In the production of TiC reinforced aluminium matrix composites by the elemental carbon addition, Al-Ti alloys were melted in graphite crucible cover with pure alumina by using induction furnace. The melting temperature was 1200 °C which was an ideal solving temperature for AI3Tİ phases. At this temperature, in order to solve AI3Tİ, after duration of 30 min carbon which was wrapped by an aluminium foil was dried at 850°C for 1 hour and added in to the solution in the form of packages containing 1 gram carbon having 10- 20 um particle size. After the addition of carbon, in order the reaction to take place between titanium and elemental carbon the reaction temperature was increased to an appropriate level and reaction time was chosen accordingly. At the end of the reaction which took place at 1200 °C, both of TiC and AI3Tİ phases were identified at 0.4 1/sec flow rate for 90 seconds reaction time. However, Al3Ti needles disappeared and TiC particles were observed at the end of 120 sec reaction time at the same reaction temperature and flow rate. At the end of the investigation with Al+%4Ti, Al+%5Ti and Al+%6Ti alloys conducted at 1300°C with 30% extra carbon addition AI3T1 phase was completely chanced to TiC with grain size 1 um or below. The cracking surface of the TiC reinforced aluminium matrix composites was inspected by metallographic studies to determine the cracking behaviour. A brittle cracking character was observed for the sample of Al+%4Ti alloy without carbon addition. The samples containing AI3Tİ and TiC phases together showed a brittle cracking behaviour in some areas and ductile cracking behaviour in others. TiC phase was present in the ductile cracking areas and not present in the brittle cracking areas. When TiC formation was copmleted the cracking surface showed ductile cracking behaviour. Disconnection between the phases of Ti particle and matrix was not visible for the particles having lum or below grain size. Otherwise, the disconnection between the TiC particles and the matrix was visible for the particles having grain size of 2 um or above
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