ايمان جابر عبد الشيباني

The preparation of zirconia waste powder by sieving the powder, milling and after that characterization of the zirconia recycled zirconia powder by the particle size analyses, XRD and SEM. Then preparation of the presintered yttria-tetragonal polycrystall (3Y-TZP) blocks from the dental implant waste by different uniaxial pressures (75,100 and 145)MPa and different presintering temperature (950,1100) ºC. Then characterization of the yttria-tetragonal polycrystall (3Y-TZP) blocks by XRD ,SEM and EDS. The results showed (XRD) produce tetragonal phase with small amount of monoclinic phase of zirconia waste powder. While the results of the presintered zirconia (3Y-TZP) showed disappeared the monoclinic phase and remained only the tetragonal phase and therefore it is possible to reuse the waste dental implant zirconia powder from used blocks and can be milling by the (CAD/CAM) and the suitable presintering temperature to reuse the powder only 950ºC due to the similar properties to the commercial blocks.

In the current study, the effect of adding nano Al2O3 to 3 mol%Y2O3 stabilized tetragonal zirconia (3Y-TZP) prepared by precipitation method on the grain size and the mechanical properties was investigated. Different amount of nano Al2O3 (1.5 wt. % , 2.5 wt.% , 3.5 wt.% and 4.5 wt.%) have been added to (3Y-TZP). X-Ray diffraction (XRD) and scanning electron microscopy (SEM) was used to characterize both the prepared powder and the full dense ceramic composite. It has been found that ,the addition of nano Al2O3 have an influence on the densification process and lead to increase in both the apparent and bulk relative densities and recorded a 96.45% and 94.46 % respectively at 4.5 wt.%. The results also shows a decrease in grain size from 0.7 μm to 0.62 μm as the amount of nano Al2O3 vary from 0 wt.% to 4.5 wt.% due to the restricted of the grain boundary mobility via the effect of particle pinning. Also, the addition of nano Al2O3 have great effect on mechanical properties .The Vicker's microhardness and the flexural strength shown an increase as the nano Al2O3 amount increase and recorded 84.1201 HV, and 368.62 MPa maximum values respectively at 4.5 wt.% nano Al2O3 .

The aim of the present research is to study the effect tin content on wear rate of Al alloys. Mechanism wear behavior was studied by (pin on disc) technique under different conditions of applied loads(100-2500)g, constant sliding speed and time, steel disc hardness is 45 HRC. All alloys were prepared with different percent of tin(3,7,13,23,33 and 43)%, also the master alloy (Al-1Cu)was prepared by melting and pouring the molten metal in a metallic mold. Samples of different percentages of tin were investigated under as-cast in order to establish the metallurgical changes and wear. It was found that the tin addition to aluminum alloys decrease the wear rate and improves the wear properties. Also the Al- 43 % Sn alloy is the best alloy in wear resistant and friction coefficient, this is due to network distribution of Sn phase. The bonding between the tin and matrix was improved at higher tin content. The Al-13% Sn-1% Cu exhibited higher wear rate compare with other alloys tested under the same conditions. In high tin alloys the subsurface region does show plastic deformation having occurred in the direction of sliding. The wear rate of the alloys decrease with increasing Sn content and increases observably with increasing load.

Al-Sn alloys have a very long history to be used as bearing materials. These alloys provide a good combination of strength and surface properties. This study aimed to investigate solidification and mechanical behavior of Al-Sn alloy against both the molding conditions and tin content (20 % , 30 % , 40 % Sn). A metal mold with a different diameter was prepared to study the solidification rate; tribological experiments have been carried out by using a pin on disc machine to investigate the effect of the alloying element content and the molding conditions on the wear resistance and microstructure of the alloys. The results showed with the increasing of tin content the solidification time decreased, as also a decrease of the liquidus temperature was observed and then increased with increasing Sn %. However, decrease of both the ultimate tensile strength and the hardness is obtained by the increase of the tin content also the wear rate decrease with increase of tin content.

Solidification time is one of the very important parameters used for assessing the properties of the material. Aluminum casting alloys with tin as the major alloying elements are the most important commercial casting alloys because of their superior casting characteristics. This paper presents influence of different casting method on solidification time and mechanical properties of Al-(20%-40%) Sn alloys against both the molding conditions and tin content. Experimental investigation is carried out to measure the solidification time in cylindrical parts by using sand and die casting methods. The results showed different cooling rates and solidification times can produce substantial variation in the resulting structure and properties. However, decrease of both the ultimate tensile strength and the hardness is obtained by the increase of the tin content. For instance, die casting, which uses metal molds, has faster cooling and produces higher-strength castings than sand casting, which uses a more insulating mold material.

Compaction process was analyzed mathematically by predicting a steady-state mathematical model in order to give more description and understanding for the mechanism of this process. Numerical investigation has been carried out on axisymmetric cylindrical parts using the finite difference method with relaxation technique to examine the physical significance of constitutive model to produce the pressure gradients during compaction. The pressure distribution model is then typically coupled with empirical functions relating pressure and density to obtain a green density distribution at all nodes in the green compacts. The model has addressed the influence of frictional forces acting at the powder and die walls interfaces which dissipate the applied pressure throughout the compact. The effect of the compact geometry has a similar effect on the uniformity of green pressure and density distributions through the compact. It was found that a small aspect ratio resulted in a more uniform distribution than a higher aspect ratio. Therefore, the model seems to work better for the lower aspect ratio. The constitutive model predicts accurately the pressure and density distributions during compaction process.

The Al-Si alloys used in this investigation was prepared at the University of Kufa in the Metallurgy Laboratory. Heyper eutectic Al-Si alloys with compositions 15, 17, 19 wt% Si was quenched from the liquid state by using melt-spinning techniques. The as cast alloys and resulting ribbons were characterized using optical microscopy, scanning electron microscopy(SEM),X-ray diffraction (XRD) analysis, microhardness techniques and compared with their ingot alloys.Effects of chemical composition and quenching conditions on the variation in the microstructure were examined. Microstructural examinations revealed that microstructures of the melt-spun ribbons were very fine compared to their ingot alloys. The results microhardness value of the ribbons melt-spun alloy was measured as 82-200 kg/mm2 . The microhardness of as cast ingot and rapidly solidified ribbons approximately twice higher than those of original ingot alloy.

The melt spinning technique has been used in this study to produce rapidly solidified alloys in the simple binary Al-Sn alloys.Aluminum-5,15 and 25%Sn were prepared by as cast and melt spun technique. Optical microcopy,X-rays diffraction analysis and scanning electron with energy dispersive spectroscopy (EDS) were used to provide information about the difference in microstructure and phases of as cast and rapid solidified samples. In addition to hardness values of the ribbons and as cast ingots also measured. The results revealed that microstructure of the as cast alloys is formed from Sn particle spread in a continuous Al-rich matrix, moreover thin predendritic fine chill crystal zone at the wheel side with only Sn-rich phase particles, which develops into a region of disordered dendritic columnar grains. There is no solubility of Al in Sn or vice versa in thermal equilibrium diagram of aluminum-tin alloy system at room temperature; also, there is no intermediate phase formed between Al and Sn by conventional production processes. X-ray diffraction has ascertained the presence of the equilibrium phases for rapid solidified alloys. The hardness values of melt-spun alloys increase approximately twice higher than those of original ingot alloy.