Physical and Morphological Properties of Hard- Soft Ferrite Functionally Graded Materials

Functionally graded materials (FGMs), with ceramic –ceramic constituents are fabricated using powder technology techniques. In this work three different sets of FGMs samples were designed in to 3 layers, 5 layers and 7 layers. The ceramic constituents were represented by hard ferrite (Barium ferrite) and soft ferrite (lithium ferrite). All samples sintered at constant temperature at 1100C for 2 hrs. and characterized by FESEM. Some physical properties were measured for fabricated FGMs include apparent density, bulk density, porosity, shrinkage and hardness. The results indicated that the density increase with the increase the number of layer. Lateral shrinkage is one of the important parameter for estimating the quality of component gradation in an FGM structure. The Vickers hardness show higher value at FGM7, Finally the FESEM images showed a gradation in microstructure within the system from platelike structure for the hard ferrite to spherical structure for the soft ferrite.


Introduction
In the previous couple of years, the usage of ceramic materials has amazingly expanded in various applications in view of the particular properties of these materials in examination with metals and polymers. The gainful qualities of ceramic materials are hardness, inflexibility, grating durability and low thickness. Ceramics are a sort of materials by and large characterized as "inorganic, nonmetallic solids". They have the colossal degree of motivation behind every single known material. The most recent decades have seen the advancement of the tremendous capability of practical earthenware production in light of interesting dielectric, ferroelectric, piezoelectric, pyro-electric, ferromagnetic, magneto-resistive, ionical, electronical, superconducting, electrooptical, and gas-detecting properties. Similar logical extensions additionally have occurred in auxiliary ceramic. Thermal, chemical, and mechanical steadiness of numerous oxide and nonoxide mixes have put the reason for improved handling, which prompted an upgraded level of microstructure outline and flaw control. This has progressively directed in at no other time seen improvements in mechanical conduct and in the precision of the properties of parts and devices [1]. Ferrites are categorized mainly into three sets with various crystal types. They are spinel, Garnets and Magneto-plumbite. Spinel ferrites have a cubic structure with general equation MO Fe2O3, where M is a divalent metal particle, similar to Mn, Ni, Fe, Co, Mg, and so forth. Garnets have a complex cubic structure having a general equation M3Fe5O12. The third sort, magneto-plumbite, has a hexagonal structure with general recipe MO. Fe12O18. The most critical in the arrangement of magneto plumbite is barium ferrite BaO Fe12O18, which is a hard ferrite [2]. The quick advancement of new high innovation requests an ever increasing number of new materials with various uncommon attributes or capacities. Under some serious boundaries, for example, super high temperature, conventional materials may not serve. Another material idea, practically evaluated materials (FGMs), has been proposed to meet the prerequisite which typically incorporate diverse material constituents, for example, ceramic and metal. FGMs have received significant attention in many engineering applications since they were first outlined in 1980s. They are composite materials, microscopically inhomogeneous, in which the mechanical properties change smoothly and continuously from one surface to the other. Compared with classical laminated composite materials, FGMs supply outstanding thermo-mechanical performances under given loading conditions. FGMs can be utilized to enhance creep behavior, fracture toughness of machine tools, wear resistance, oxidation resistance of high temperature aerospace and automotive components and so on . [3] (Jaworska, et.al.2006) Studied functionally graded cermets. Materials were acquired using free sintering at vacuum and the high temperature-high weight sintering system. Practically evaluated cermets have greater amount of hard stage in the surface layer and lower cooperation of this stage in the body outline. FGMs were set up by the layers pressing operation and the diffusive statement operation. Material with 55 wt.% of TiC and 45 wt.% of (Ni,Mo) was incorporated. The stage's structure of this material was analyzed. (Shabana,et.al.2006) Modeling the development of stress because of differential shrinkage in powderprocessed functionally graded metal-ceramic composites during pressureless sintering. This model can be used to decide helpful shrinkage rates and slope structures for a given segment geometry that will restrict the part from breaking amid pressureless sintering by adjusting the advancement of quality, which should be a power law capacity of the porosity, with the improvement of stress. To estimate this model, the powder blend is evaluated as a three-stage material including voids, metal particles, and artistic particles. A micromechanical thermal elastic-viscoplastic constitutive model is then proposed to show the thermomechanical conduct of the composite microstructure. According to the above literature reviewing, it's clear that the fabrication of hard ferrite\lithium ferrite functionally graded materials is a very new area for investigation that based on using graded ceramic materials.
The aim of this work is Fabrication a functionally graded materials (FGMs) from hard ferrite and soft ferrite materials in three different set of multiples layers and then studying the physical and morphological properties of the system.

Preparation of Hard/ Soft Functionally Graded Material
The start material used to fabricate FGM sample were Nano barium ferrite and Nano lithium ferrite, are weighted in the proportions as shown in Table  (1). The formation of a discrete layered graded structure at first requires mixing of the base materials to appropriate composite powder composition. The FGM structure consists of the two base materials on either end of the specimen, with the desired compositional gradient layered between the two as shown in Fig. (1). The FGM system are composed of (3, 5, and 7) layers with thickness (4.5, 8, and 12) mm, respectively. The weight of FGM layer will measured by sensitive balance , the constituents powder were arranged according to the volume fraction of layer starting from lithium ferrite to barium ferrite as mentioned in table (1), After that compacting practice were done under 20000 Mpa load pressure. Each sample was subjected to sintering under temperature of 1100 o C for 2 hr. The sintering heating cycle including a slow heating rate with 5 °C∕ min, (see Fig. 2). All sintering practices were carried out by using electric furnace.

Physical Properties 3.1.1 Density and Porosity
The (bulk and apparent) density for FGM sample are shown in Fig. (3). Porosity for FGM system was also shown in Fig. (4). the variation of density between the different FGM sample with (3, 5, 7) layer which shown slightly an increase of density with the increase the number of layer; the reason behind such improvement is related to high densification, high homogeneity and good blending between the layer of FGMs [7]. The

Lateral Shrinkage
Lateral shrinkage is one of the important parameter for estimating the quality of component gradation in a FGM structure. Figure (5) illustrates the effect of change of the percentages among the layers versus the number of layers of the sample sintered at 1100 o C for 2 hours. Shrinkage showed an increase in FGM7 as compared with FGM3 and FGM5. The linear shrinkage obtained was an appropriate indicator of the functionality of the design.

Micro Hardness Test
Microhardness test was carried out to study the gradient of the mechanical property along the FGMs thickness. In spite of the fact that the phenomenon of hardness is in general is purely a surface property, which represents its resistance to indentation, but in numerous cases the value of surface hardness may be safely used to indication of the state of compactness and integrity of the bulk. The Vickers micro hardness value of FGM sample (3, 5, and 7) layers after sintering practices is presented in Figs. (6), (7) and (8) respectively. It is clear that as the Barium ferrite percentage increased; the hardness is increased. (FGM 3) seems to give graded hardness properties. Also it can be noted that the (FGM 7) layer 7 (100% BaM) and layer 1 (100% LiM) has the higher value of Vickers hardness as compared with (FGM3) and (FGM5) due to increment of density and compacting load.

FE-Scanning Electron Microscopy (FESEM) Analysis
Field emission Scanning electron microscope (FESEM) is used to visualize the microstructure of functionally graded materials by scanning with high energy electron beams.    Fig.(10a) the grain morphology appear totally plate -like shape which is clearly indicated the formation of barium ferrite. Barium hexaferrite nanoparticles with plate-like morphology is the best for the electromagnetic wave absorption application [9]. Also for the composite layer SEM images show the grain microstructure as a combination of spherical and plate like structure which is an evidence for the gradation in FGMs samples and resulting in properties variation.

Conclusions
Functionally graded BaM/LiM specimens have been fabricated at three different set of layer (3, 5 and 7) by powder metallurgy. Characterization of fabricated FGMs was carried out by FESEM which revealed gradation in microstructure from platelike structure (hard ferrite) to spherical structure (soft ferrite). The result of density indicate the high homogeneity and good blending between the layers of FGM led to increasing of density. The Vickers hardness showed higher value at FGM7 layer 7.