S-allümina (Saffil) takviyeli ZA 12 esaslı kompozit malzemelerin infiltrasyon yöntemi ile üretim ve özelliklerinin incelenmesi
S-allümina (Saffil) takviyeli ZA 12 esaslı kompozit malzemelerin infiltrasyon yöntemi ile üretim ve özelliklerinin incelenmesi
Dosyalar
Tarih
1993
Yazarlar
Kurnaz, Süleyman Can
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
İTÜ Fen Bilimleri Enstitüsü
Özet
Bu çal açmada, çinko-al ümı nyum esalı ZA12 al açımı nı n mekanik özelliklerinin geliştirilmesi ve mukavemet/ağırlık. oranının yükseltilmesi amacıyla, bu alaşımın, değişik nacım oranlarındaki "SAFFÎL" ticari ismi ile bilmen, S^Al zOs yapısına sahip fiberler ile takviyesi amaçlanmıştır. Bu nedenle, ilk önce özgün bir tasarımla i nf i 1 tras yon cihazı geliştirilmiş, daha sonra malzemelerin üretimine geçilmiştir. Malzemelerin üretiminde 5-Aİ203 yapısına sahip fiberlerin düzl emsel olarak gelişigüzel dağılmış hal de bul unduğu 1 OOxl O mm boyut 1 ar ı ndak i ön bi çi m ver ı i - mı ş disk şeklindeki p>reformlar kullanılmıştır. Vakum altındaki sistem içinde bulunan % 10, 15, 20 ve 3ö fiber hacim oranlarına sahip pref or mi ara, O. 1, O. 2, O. 5, 1, 2 ve 3 MPa basınçları ile sıvı ZA12 infiltre edilmiş ve kompozit malzemeler üretilmiştir, üretilen malzemeler üzerinde, yoğunluk tayini yapılmış ve buna bağlı olarak basmç-inf il trasyon ilişkileri belirlenmiş ve daha sonra sertlik, çekme, ve aşınma gibi mekanik incelemeler ile metalografik çalışmalar yapılmıştır. Genel olarak, artan saffil hacırn oranı ile üretilen kompozitlerin yoğunluklarının doğrusal olarak azaldığı bulunmuştur. Ayrıca, basınç miktarının artması ile preformlarm dolma oranının arttığı fakat, basınç sabit tutulduğunda artan saffil hacim oranı ile dolma oranın azaldığı' görülmüştür. Buna bağlı olarak, pref or mi ar i çın kritik i nf il trasyon basıncı tespit edilmiştir. Mekanik deneylerde kullanılan numuneler,, minimum porozite içeren, 3 MPa basınç kullanarak elde edilen kompozi ti erden alın mıştır. Kompozitlerin Brinel sertlik değerlerinin fiber lere dik ve paralel kesitlerde yaklaşık aynı olduğu ve artan saffil hacirn oranının artması ile doğrusal arttığı bulunmuştur. Kompozitlerin çekme mukavemeti ve 'a uzama ları ise artan fiber hacim oranı ile azalmıştır. ZAİ 2 alaşımı ve fiberlere dik yönde kesitlerden alınan numune ler üzerinde, 10N ve 30N yükler kullanarak yapılan sür tünme aşınma deneyleri sonucu ise, saf ZAİ 2 alaşımının aşınma miktarının %10 saffil takviyesi ile önemli ölçüde azaldığı, ancak bu hacim oranının üzerindeki takviyelerin aşınma miktarının daha fazla azaltılmasında çok fazla etkili olmadığı görülmüştür. Buna karşılık, genel olarak kompozit malzemelerin artan yük ile aşınma miktarının arttığı bulunmuş, fakat bu aşınma oranlarındaki artışın, saf ZAİ 2 ve %10 fiber hacimli kompozit malzemeler için birbirine yaklaşık olarak eşit olduğu, daha fazla hacı- oranlarında fiber içeren diğer kompozi ti erde ise daha ir ol d uğu bul unmu^ t ur.
In recent years, there has been an enormous interest in metal matrix composites (MMCs > because of their attrac tive physical and mechanical properties, such as high specific modulus, strength, and retention of properties at moderately elevated high temperatures. MMCs combine metal i c properties (ductility and toughness > with ceramic properties (high strength and high rnodulus> leading to greater strength in shear and compression and higher service teperature capabilities. Interest in MMCs for aerospace, automotive and other structural applications has increased over the last five years as a result of availability of relatively inexpensive reinforcement, and the development of various processing routes which result in reproducible rnicrostructures and properties. MMCs encompasses a very broad class of materials which can be subdivided into three main groups; particulate, whisker or short fibre and continuous fibre reinforced metals. Although MMCs reinforced with continuous fibre provides the greatest improvement in properties, the main thrust of the commercialisation of metal composites has been with the use of particulate reinforcement. This is due mainly to the relative ease of production of particulate reinforced MMCs compared with the difficulty in processing continuous fibre composites. For the production of particulate reinforced composite it is relatively easy to process large quantities of the material by conventional manufacturing methods, such as casting and extrusion. The particles are mixed with the molten aluminum and the composite material can then be processed by conventional means. With these production methods the volume fraction is limited to approximately 20% due to increase of the metal viscosity that occurs on the addition of the reinforcing particles.Whisker and short fibre composites can be manufactured either by incorporation of the reinforcement material into the melt or by the production of a fibre preform which can then be infiltrated with molten metal, as in squeeze casting and pressure infiltration process. In melt mixing the level of reinforcement is once again restricted in the liquid metal by the increase in viscosity. In the infiltration of preforms it is restricted as a result of the mabilty of randomly oriented fibres to achive a packing density higher than O. 35 volume fraction. Other manufacturing processes that are used for discontinuous and particulate reinforcement include powder metallurgy and plasma cospray deposition. Both have considerable drawbacks. The mechanical forces involved during powder processing result in consi.dera.ble fibre damage and the plasma cospray deposition has a low productivity and is severely limited by shape/size consi der ati ons. There are two main routes for production of short fibre MMCs. These are squeeze casting and pressure infiltration process. Squeeze casting was the first manufacturing method that gave the possibility of a one shot process combined with high producibility rates. The main drawback of this process is that the engineering required to cope with the high process pressures involved result in a size and shape limitation and the mechanical forces involved result in severe fibre damage. Pressure infiltration process is also a route for high qual typroduction of net shape components using gas pressure to force molten metal into a previouslly manufactured preform. The advantage of this process over squeeze casting is that die cavity and the pressure vessel can be evacuated, which greatly increases the quality of material produced. The development of alumina based short fibre such as I.C.I. 's saffil fibre and its incorporation in aluminum alloys by these techniques has lead to its industrial application in areas where high temperature, strength and resistance to thermal fatique are important criteria. Such fibres are connected to solid preforms by suspansion in an aqueous medium, which indudes a binder such as sodium silicate, corpareted by infiltration and pressing or centr i fuji ng followed by drying and firing. These fibres in the preform are usually two dimensional andrandom in orientation. These preforms can be located in a die cavity for selective reinforcement specific areas. The most carnrnon metal matrix material used in industrial application of MMCs is aluminum alloys, although considerable interest is also being shown in titanium and magnesium and, to lesser extent, copper, lead and iron. The concentration of effort on aluminum alloys stems, from its uniqe combination of good corossion resistance, low density and excellent mechanical properties However new materials, such as new zinc- aluminum based ZA alloys, with superior properties to the above communly used alloys in many aspect would also be a good substitutes as a matrix material for many applications.
In recent years, there has been an enormous interest in metal matrix composites (MMCs > because of their attrac tive physical and mechanical properties, such as high specific modulus, strength, and retention of properties at moderately elevated high temperatures. MMCs combine metal i c properties (ductility and toughness > with ceramic properties (high strength and high rnodulus> leading to greater strength in shear and compression and higher service teperature capabilities. Interest in MMCs for aerospace, automotive and other structural applications has increased over the last five years as a result of availability of relatively inexpensive reinforcement, and the development of various processing routes which result in reproducible rnicrostructures and properties. MMCs encompasses a very broad class of materials which can be subdivided into three main groups; particulate, whisker or short fibre and continuous fibre reinforced metals. Although MMCs reinforced with continuous fibre provides the greatest improvement in properties, the main thrust of the commercialisation of metal composites has been with the use of particulate reinforcement. This is due mainly to the relative ease of production of particulate reinforced MMCs compared with the difficulty in processing continuous fibre composites. For the production of particulate reinforced composite it is relatively easy to process large quantities of the material by conventional manufacturing methods, such as casting and extrusion. The particles are mixed with the molten aluminum and the composite material can then be processed by conventional means. With these production methods the volume fraction is limited to approximately 20% due to increase of the metal viscosity that occurs on the addition of the reinforcing particles.Whisker and short fibre composites can be manufactured either by incorporation of the reinforcement material into the melt or by the production of a fibre preform which can then be infiltrated with molten metal, as in squeeze casting and pressure infiltration process. In melt mixing the level of reinforcement is once again restricted in the liquid metal by the increase in viscosity. In the infiltration of preforms it is restricted as a result of the mabilty of randomly oriented fibres to achive a packing density higher than O. 35 volume fraction. Other manufacturing processes that are used for discontinuous and particulate reinforcement include powder metallurgy and plasma cospray deposition. Both have considerable drawbacks. The mechanical forces involved during powder processing result in consi.dera.ble fibre damage and the plasma cospray deposition has a low productivity and is severely limited by shape/size consi der ati ons. There are two main routes for production of short fibre MMCs. These are squeeze casting and pressure infiltration process. Squeeze casting was the first manufacturing method that gave the possibility of a one shot process combined with high producibility rates. The main drawback of this process is that the engineering required to cope with the high process pressures involved result in a size and shape limitation and the mechanical forces involved result in severe fibre damage. Pressure infiltration process is also a route for high qual typroduction of net shape components using gas pressure to force molten metal into a previouslly manufactured preform. The advantage of this process over squeeze casting is that die cavity and the pressure vessel can be evacuated, which greatly increases the quality of material produced. The development of alumina based short fibre such as I.C.I. 's saffil fibre and its incorporation in aluminum alloys by these techniques has lead to its industrial application in areas where high temperature, strength and resistance to thermal fatique are important criteria. Such fibres are connected to solid preforms by suspansion in an aqueous medium, which indudes a binder such as sodium silicate, corpareted by infiltration and pressing or centr i fuji ng followed by drying and firing. These fibres in the preform are usually two dimensional andrandom in orientation. These preforms can be located in a die cavity for selective reinforcement specific areas. The most carnrnon metal matrix material used in industrial application of MMCs is aluminum alloys, although considerable interest is also being shown in titanium and magnesium and, to lesser extent, copper, lead and iron. The concentration of effort on aluminum alloys stems, from its uniqe combination of good corossion resistance, low density and excellent mechanical properties However new materials, such as new zinc- aluminum based ZA alloys, with superior properties to the above communly used alloys in many aspect would also be a good substitutes as a matrix material for many applications.
Açıklama
Tez (Yüksek Lisans)-- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1993
Anahtar kelimeler
kompozit malzemeler,
composite materials,
infiltrasyon,
infiltration