Ni-ti sistemindeki Farklı Bileşimlerin Mekanik Alaşımlama Yöntemi İle Toz Halde Sentezi ve Sinter Sonrası Karakterizasyonu

Abstract

Ni-Ti SİSTEMİNDEKİ FARKLI BİLEŞİMLERİN MEKANİK ALAŞIMLAMA YÖNTEMİ İLE TOZ HALDE SENTEZİ ve SİNTER SONRASI KARAKTERİZASYONU ÖZET Bu çalışma kapsamında Ni-Ti ikili denge diyagramı üzerindeki farklı bileşimler başlangıç Ni ve Ti tozlarından hareketle karıştırma suretiyle hazırlanmış ve mekanik alaşımlanmıştır. Bu bağlamda B1, B2, B3, B4, B5 isimleri verilmiş olan ve sırasıyla 35Ni-65Ti, 45Ni-55Ti, 50Ni-50Ni, 55Ni-45Ti, 75Ni-25Ti bileşimlerini temsil eden bileşimler incelenmiştir.İlgili bileşimlerin mekanik alaşımlanma çalışmalarında mekanik alaşımlama zamanı,mekanik alaşımlanmış tozların preslenmesi esnasında basınç gibi parametreler değişken olarak çalışılmıştır. Mekanik alaşımlanan tozlardan hareketle toz metalurjisi adımları uygulanarak sinterlenmemiş numuneler hazırlanmıştır. Gerek toz halde gerekse sinter sonrası karakterizasyon aşamaları uygulanmıştır. Bu bağlamda partikül boyut, yoğunluk ölçümleri ile faz analizleri ve SEM incelemeleri yapılmıştır. Çalışmaya 35Ni-65Ti bileşimine ait bölgeden başlanmıştır. Bu bileşimi atomik olarak karşılayacak miktarda tozlar mekanik olarak 1, 2, 4, 8 saat süre ile mekanik alaşımlanarak elde edilen tozlar karakterize edilmiştir. Sonraki aşamada bu tozlar preslenip sinterlenerek karakterizasyon işlemleri tekrarlanmıştır. Sonraki aşamada 45Ni-55Ti bileşimine ait tozlar mekanik alaşımlama yöntemi ile elde edilip karakterize edilmiştir. Elde edilen tozlar üzerinde mekanik alaşımlama zamanın etkisi incelenmiştir. Aynı bileşime ait tozlar farklı basınçlarda preslenerek sinterlenmiş ve farklı preslenme basınçlarının mekanik alaşımlanmış numuneler üzerindeki etkileri incelenmiştir. Üzerinde en fazla çalışılan bileşim ise Şekil Bellek Olayı ve Süperelastik özelliğinin olduğu 50Ni-50Ti bileşimi olmuştur. Burada; 50Ni-50Ti bileşiminde 100-200-300-400-500 MPa’da preslenmiş numunelerde artan basıncın faz değişimlerine etkisi çalışılmıştır. Bununla birlikte numuneler 300 MPa’da preslenerek artan mekanik alaşımlamalarda (1, 2, 4, 8, 12 saat) faz farklılıklarını tespit edilmeye çalışılmıştır. Mekanik alaşımlama süresi ve basınç sabit tutularak (4 saat ve 500 MPa) başlangıç tozlarına farklı miktarlarda mekanik alaşımlanmış tozlar katılarak faz değişimleri incelenmiştir. Mekanik alaşımlama zamanının faz değişimlerine etkisini ölçmek amacıyla tozlar 5dk’dan başlanarak 12 saate kadar mekanik alaşımlanmış ve 500 MPa’da preslenip karakterize edilmişlerdir. Sinter ortamının faz değişimi ve oksidasyon üzerine etkilelerini görmek amacıyla 4 saat mekanik alaşımlanmış tozlar 500 MPa’da preslenip, dilatometre, tüp fırın ve yüksek sıcaklık fırınlarında sinterlenmiş ve elde edilen numuneler karakterize edilmiştir. Ni-Ti bileşimlerinde R-fazı üretme yeteneğine sahip nikelce zengin 55Ni-45Ti bileşimine ait tozlar mekanik alaşımlama ile elde edilmiştir. Karakterizasyon işlemlerinin ardından farklı basınçlarda preslenip sinterlenerek tekrar karakterizasyon işlemlerine tabii tutulmuşlardır. Son olarak B5 olarak isimlendirilmiş olan 75Ni-25Ti bileşimine ait tozlar mekanik alaşımlama yöntemiyle elde edilip analizleri yapılmış ve preslenerek sinterlenmiştir. Sinterlenen numuneler yine diğer bileşimlerde olduğu gibi karakterize edilmişlerdir. Çalışmanın son bölümünde tüm bu verilerden elde edilen sonuçlar tartışılmış ve mekanik alaşımlama yöntemi ile elde edilen nikel titanyum bileşimleri ile ilgili öneriler sunulmuştur.

POWDER STATE SYNTHESIS OF DIFFERENT COMPOSITIONS IN NI-TI SYSTEM VIA MECHANICAL ALLOYING AND THEIR CHARACTERIZATION AFTER SINTERING Summary General applied practice for the production of alloys in Ni-Ti system involves advanced casting operations. On the other hand, there have been some efforts to produce these materials via PIM. It can be seen three different intermetallic regions in binary nickel-titanium phase diagram. There are three intermetallic compouds occur in these regions. The first of these compound is Ti2Ni intermetallic alloy that is candidate of one of the hydrogen storege materials. The second is Ni3Ti and occurs in nickel-rich regiongs and it can be used for hardenning martensitic stainless steel via forming eta precipitates phase. But there is one content existing which is starting from atomic % 49 nickel content and extending to atomic % 55 nickel content. In those ranges , there can be obtained extraordinary properties. Therefore, those ranges and regions are the most extensively studied by researchers. NiTi intermetallics exhibit unique Shape Memory Effect (SME) and Psudoelasticity (PE) in this range. These features are widely used in medical and industrial areas and put these materials to the class of smart materials. This study based on mechanical alloying whether in order to obtain intermetallic phases or not and also aimed at which phases occur before and after sintering, amount of phase quantities, parameters that affect this phases, shape memory and psudoelasticity behavior and finally mechanical properties are investigated. In order to produce Nickel-Titanium alloys, there has been two major way. One of the method is casting and the other is sintering. First we use mechanical alloyning method to produce the powder of nickel-titanium. On the other hand there are some difficulties to reaching exact composition during the solidification and control of desired microstructure is not a easy task. Mechanical alloying (MA) is a solid-state powder processing technique involving repeated cold welding, fracturing, and re-welding of powder particles in a high-energy ball mill. Originally developed to produce oxide dispersionstrengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or pre-alloyed powders. Indeed, mechanical alloying is a subsidary of Powder Metalurgy (PM) that is the process of blending fine powdered materials, pressing them into a desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process generally consists of four basic steps: powder manufacture, powder blending, compacting, and sintering which is a method for making objects from powder, by heating the material in a sintering furnace below its melting point (solid state sintering) until its particlesadhere to each other. Compacting is generally performed at room temperature, and the elevated-temperature process of sintering is usually conducted at atmospheric pressure. Optional secondary processing often follows to obtain special properties or enhanced precision. The use of powder metal technology bypasses the need to manufacture the resulting products by metal removal processes, thereby reducing costs. Regarding information about thesis purpose and also a general overview about nickel-titanium alloys is given in the first part of the thesis. In the second part of the thesis, powder metallurgy and mechanical alloying that is main methods abovementioned are described in this section. Martensitic phase transformation, shape memory mechanism, one way shape memory effect, two way spape memory effect, shape memory effect, psudoelasticity phonemenon, physical and mechanical properties of nickel-titanium are expressed in the third chapter the thesis. Also intermetallics, nickel titanium intelmetallics compounds and related literature review are introduced. In the fourth chapter of the thesisequipments and standarts used during experimental and characterization studiesareintroduced. In the fifth section of the thesis, production of powder of the intermetallic compound Ti2Ni and its powder particle size, density, XRD, SEM images and EDS analysis are introduced. After sintering the same characterization studies have been performed like powders and its results has been shared this chapter. In the same section, the composition of 45Ni-55Ti region is worked and mentioned about time and forming phases relationship which is occured during the mechanical alloying prosess. In addition, the effect of pressing pressure were examined in sintered samples of 45Ni-55Ti. The most extensively studied composition was 50Ni-50Ti which has uniqe shape memory effect and psudoelasticity properties. Here, the spicemens whose composition is 50Ni-50Ti and at whom pressed under 100, 200, 300, 400, 500 MPa are studied and the increased pressure causes the phase change whether or not is elicited. Additionally, all samples were pressed at 300 MPa and mechanically alloying different alloying time (1, 2, 4, 8, 12 hours) in order to to determine phase differences were studied. In the same section, mechanical alloying time and the pressure is kept constant (4 hours and 500 MPa). Thus, in order to evaluate whether such phase changes may ocur or not, starting powders and mechanical alloyed powders were mixed with different amounts. In another study, in order to measure mechanical alloying time on the effect of the phase changes whether or not, powders are mechanically alloyed from 5 min up to 12 hours and then pressed at constant 500 MPa presures. In different studies, ın order to evaluate phase changes and positive or negative impacts of sintering environment on the oxidation, powders are mechanically alloyed 4 hours and pressed under 500 MPa pressures, finally sintered three different sintering media in order of dilatometer furnace, quartz tube furnace and Linn high tempreture furnace. Also in this section, 55Ni-45Ti phase composition was studied which is capeble of producing R-phase in nickel-titanium system. Both powders and sintered samples of 55Ni-45Ti has been worked with different parameters and gained some information about this range. Finally, 75Ni-25Ti range and its intelmetallic compound was studied and obtain some information about it. Final section, the results obtained from all these data which were obtained from mechanical alloying and after sintering is disscused and recommendations related nickel- titanium intermetallics are presented .