توليد و مشخصه يابي آلياژ نانو ساختار FeCo آلايش يافته با نيوبيوم و كامپوزيت آن باذرات WC به روش آلياژ سازي مكانيكي

چكيده انگليسي :

97 Fabrication and characterization of nanostructure FeCo Nb alloys and their reinforcement with WC by mechanical alloying K Saeidi Email adress k saidi@ma iut ac ir Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree MSc Language FarsiSupervisors name Ahmad Monshi Professor a monshi@cc iut ac irAli Saidi Professor a saidi@cc iut ac irAbstractIron cobalt alloys are the most important soft magentic materials which exhibit unique magnetic propertiessuch as high magnetic saturation high curie temperature and low magnetic loss and therefore are widely usedin different industrial applications such as electric motors information storage telecomunications highpower transformators and recently in areospace industries Although FeCo alloys are famous due to theirmagnetic properties their application in different industries have drawn some attention to their mechanicalproperties as well The formability of FeCo alloy is very low and so is not suitable for fabrication of magneticparts by any deformation process such as rolling or extrusion This mechanical property formability can beimproved by addition of small amount of alloying elements such as V Nb Ni and Cr The strength hardnessand wear resistance of these alloys may also be improved by reinforcement with hard ceramic particles Themain challenge in this respect is to maintain the magnetic properties when the mechanical properties areimproved So in this research work production of FeCo Nb alloys and their reinforcement with WC particleswas investigated using mechanical alloying technique Elemental Fe Co Nb and WC powders were used asstarting materials and the products FeCo Nb alloy and FeCo Nb WC were characterized for their magneticproperties namely magnetic saturation and coercivity using a Vibrating Sample Magnetometer VSM Phasetransformation microstructural characteristics were studied by X ray Diffraction XRD Scaning ElectronMicroscope SEM The results indicated that a phase transformation for Cobalt from fcc to hcp occurred atthe first three hours of milling This was followed by dissolution of Co in Fe and a nearly complete FeCo Nbsolid solution was obtained after 10 hr milling Addition of WC to the starting powders resulted in a moreefficient milling such that the alloy formation took place at a shorter time 5 hr The SEM micrographs alsoindicated that a homogeneous composite with finely disstributed WC particles have been produced after 10hr milling Regarding the magnetic properties the results showed that addition of 2 wt Nb to FeCo alloyimproved the magnetic saturation and coercivity compared to the conventional FeCo and FeCo V alloys Reinforcement of FeCo Nb alloy with WC particles did not change the magnetic properties severely butincreased the microhardness from 470 Hv for FeCo Nb alloy to 850 Hv for FeCo Nb WC composite Annealing the composite powders at 500 C increased the magnetic saturation from 160 emu g to 180 emu gand also decreased the coercivity to about 20 Oe Annealing at higher temperatures 700 and 900 C declined the magnetic properties due to formation of an antimagnetic phase called the Eta phase Fe6W6C By sintering the composite powders at 1000 C and 1200 C and in H2 atmosphere bulk specimens wereproduced The results showed that 1000 C was not sufficient for proper sintering while sintering at 1200 Cwas successful with less than18 porosity and a fine disspersion of WC particles in the FeCo Nb matrix Furthermore hardness of the sintered sample measured 720 Vikers and the magnetic saturation andcoercivity of this sample were measured 194 emu g and 39 Oe respectively Keywords Soft magnetic materials FeCo alloy magnetic properties Mechanical alloying composite nanostructure

سعيدي، كامران

توليد و مشخصه يابي آلياژ نانو ساختار FeCo آلايش يافته با نيوبيوم و كامپوزيت آن باذرات WC به روش آلياژ سازي مكانيكي

مواد مغناطيسي نرم , آهن-كبالت