Please use this identifier to cite or link to this item: http://prr.hec.gov.pk/jspui/handle/123456789/15514
Title: Preparation and Characterization of Some New Invar Alloys
Authors: Ahmad Khan, Sajjad
Keywords: Physical Sciences
Physics
Issue Date: 2020
Publisher: Bahauddin Zakariya University Multan
Abstract: Fe65Ni35 alloy exhibits low thermal expansion as well as unique physical and magnetic properties. These alloys are known as invar. The work in hand was an effort to incorporate ternary addition of transition metals (Cu, Pd) to Fe65Ni35 alloys for subsequent investigation of invar effect ( low coefficient of thermal expansion, magnetic and electrical properties etc.). Two series of Fe65Ni35-xMx ( M=Cu, Pd and x=0.0, 0.2, 0.6, 1, 1.4, 1.8 at.%) bulk alloys were prepared by arc-melting technique. The invar effect has been studied in these alloys and the results have been compared with those for classical invar alloy. One series of Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8) nano-crystalline alloys was also prepared by chemical reduction method. The invar effect was investigated and the results has been then compared with those of classical binary invar alloy. Furthermore, bulk Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4 at.%) alloys were irradiated by He+2 ions at various fluences. Studies were carried out on pre- and post-irradiated samples and the results were compared with binary Fe65Ni35 invar alloy. Experimental techniques such as X-ray diffraction, optical microscopy, differential scanning calorimetry, scanning electron microscopy, vibrating sample magnetometry, superconducting quantum interference and Pelletron accelerator for He+2 ion irradiation were used to study the structure, crystallites size, coefficient of thermal expansion, magnetization, magnetic susceptibility, Curie temperature, electrical and thermal conductivity. X-ray diffraction experiments on series of bulk Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. %) and Fe65Ni35-xPdx (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. %) as well as nano structured Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. %) alloys showed that all samples were single ii phase and had face-centered cubic (f.c.c) structure. This was finally confirmed by optical microscopy and electron probe microanalysis. The lattice parameters were found to depend strongly on Cu & Pd contents in these alloys. The effect of temperature on the lattice parameters was studied by utilizing in-situ X-ray diffraction technique. It was seen that the lattice parameters almost remained unchanged in ternary alloys in the temperature range from room temperature to 500 ˚C. The results showed that the temperature range for invar effect enhanced with ternary addition (Cu and Pd) as compared to the conventional binary invar alloy. High temperature X-ray diffraction was performed on both series of Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) and Fe65Ni35-xPdx (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) alloys, to measure the coefficient of thermal expansion in the temperature range from room temperature to 500 ˚C. The temperature range in case of classical binary invar alloy is from room temperature to 200 ˚C. Ternary addition of Cu to binary classical invar alloy enhanced this range up to 250 ˚C, whereas, addition of Pd resulted in increasing this range up to 300 ˚C, which was one of the objectives of the research in hand. Owing to increased temperature range with low coefficient of thermal expansion, these alloys are potential candidates for various scientific and technological applications. In-situ X-ray diffraction data was further utilized for determination of Debye characteristic temperature and mean square amplitude of vibration. The analysis showed that the Debye characteristic temperature and mean square amplitude of vibrations remained approximately unchanged up to 250 ˚C and 300 ˚C for Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. % ) alloys and Fe65Ni35-xPdx (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at . % ) alloys, respectively. The results confirmed that the investigated ternary alloys have better invar characteristics as compared to the conventional binary invar alloy i.e. Fe65Ni35. iii Binary invar alloy has low electrical and thermal conductivity. The electrical and thermal conductivity is found to increase by the addition of Cu, which is due to the fact that Cu has low electrical resistivity. A reverse trend was observed for Fe65Ni35-xPdx (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) alloys owing to the fact that Pd has higher electrical resistivity as compared to Cu. The electrical and thermal conductivity of Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. %) nano-crystalline alloys increased as compared to binary nano-crystalline Fe65Ni35 invar alloy. The magnetic properties of bulk Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at. %) and Fe65Ni35-xPdx (x= 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) alloys were studied. It was found that the magnetic properties i.e. magnetization and Curie temperature are increased by ternary additions. The magnetization increased from 96 emu/g in binary (x=0.0) to 133 emu/g for ternary alloy (x= 1.8 at. %). A similar behavior was observed for Curie temperatures. Ternary addition of Cu resulted in enhancement of Curie temperature to a maximum of 50 ˚C (at x=1.8 at. %). In the same way, the ternary addition of Pd resulted in the enhancement of Curie temperature to 100 ˚C (at x=1.8 at. %). The magnetic properties of ternary Fe65Ni35-xCux (x= 0, 0.2, 0.6, 1, 1.4 at. %) alloys are increased with ion irradiation. The He+2 ions with 2 MeV energy with a fluence of 1×1013, 1×1014, 5×1014, 1×1015 and 5×1015cm-2 were used. The temperature dependence of magnetization of unirradiated and irradiated alloys and the Curie temperature of the alloys increases with both the Cu addition and ion fluences. A comparative study shows that the effect of irradiation with increasing ion fluence is more pronounced than the Cu addition. The f.c.c structure was also investigated after ion irradiation which was found to remain unchanged. However, the reflections become broader with ion fluence, which may be attributed to lattice fluctuations i.e. the crystal defects. iv Fe65Ni35-xCux ( x= 0, 0.2, 0.6, 1, 1.4 and 1.8 at.%) nano-crystalline alloys made by chemical reduction method were studied through different techniques. The X-ray diffraction analysis revealed the formation of face centered cubic (f.c.c) structure. The lattice parameter and the crystallite size of these alloys were determined. The particle size was estimated from scanning electron microscopy which decreased by the incorporation of Cu and found to be in the range of 24-40 nm. The addition of Cu in these alloys appreciably enhanced the saturation magnetization and results in an increase from 99 emu/g for the binary alloy to 123 emu/g for ternary alloys prepared by chemical reduction method.
Gov't Doc #: 20630
URI: http://prr.hec.gov.pk/jspui/handle/123456789/15514
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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