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In this experimental investigation, the effect of adding limited contents of yttrium oxide Y2O3 (0.02-0.5 % wt), zirconium oxide ZrO2 (0.1-0.5% wt), and aluminum oxide Al2O3 (0.5-3% wt) on the mechanical and microstructure properties of the tungsten heavy alloy (90W-7Ni-3Fe %wt).Elemental powders and oxide additives were mixed for 120 min. Green compact in the form of standard tensile and impact specimens were fabricated by applying uniaxial compaction under 200 MPa. Finally the specimens were sintered at 1480oC for 90 min under vacuum atmosphere. It was found that the addition of yttrium oxides in the order of 0.02-0.04% wt provides the highest improvements of both tensile strength and impact toughness. Moreover the addition of aluminum oxides in the order of 1% wt has strong effect in enhancing only the tensile strength, while the impact toughness is sensibly reduced. The addition of zirconium oxide in the non-stabilized form up to 0.5%wt reduces significantly the tensile properties. Furthermore, the addition of yttrium and zirconium oxides in the indicated ranges has no significant effect on the sintered density of compacts .On the other hand; the addition of aluminum oxides slightly reduces this density. Introduction Tungsten heavy alloys, containing from 88 to 97% wt tungsten as a base ingredient having BCC structure and a binding matrix of Ni-Fe having FCC structure are widely uses in many application like kinetic energy penetrator, air to air rocket nozzles and armor plating. That is due to their very strong inter-atomic bonding, high mechanical properties, low heat conductivity, low thermal expansion, and high corrosion resistance[1, 2]. In order to achieve as high kinetic energy as possible for kinetic energy penetrators, high density materials are required. Only there are two important candidate materials which can satisfy this high density requirement, they are depleted uranium (DU), and tungsten heavy alloys. DU alloys are currently the most widely used and favored materials for log rod kinetic energy penetrators. This is essentially attributed to the high density, and elevated mechanical properties, in addition to the self-sharpening phenomenon that results from the adiabatic shear that generally occurs during material deformation at high strain rates[3]. Because of the increasing environmental concerns due to contamination, resulting from residual radiation, intensive efforts were done to find suitable substitutes for these alloys. In the last decades, extensive researches were carried out to improve the penetration and ballistic properties of tungsten heavy alloys to be the appropriate substitute of DU alloys. * eng.roma27@hotmail.com † Egyptian Armed Forces, Egypt. Paper: ASAT-15-110-MS 2 Tungsten heavy alloys are manufactured only by powder metallurgy technique, due to the very high melting temperature of tungsten. Tungsten heavy alloys contain W with some combinations of Ni, Fe, Co, or Cu. After mixing and compaction, these elemental powders are liquid phase sintered mostly at temperature above 1450oC. Liquid phase sintering is usually done under hydrogen, argon or vacuum atmospheres[4, 5]. To enhance the mechanical and the ballistic characteristics of tungsten heavy alloys, there are several approaches, the first, by modifying the composition either by optimizing the proportions of tungsten and the other matrix ingredients (Ni, Fe, ...etc.) or by Adding different types of oxides, like yttrium oxides[6-8], aluminum oxides[9] and zirconium oxides[6]. The second, by optimizing the processing parameters (compaction pressure, sintering temperature, time, and atmosphere). The third approach, by post thermal and mechanical treatments. In this work, the effect of addition of minor amounts of different ceramic oxides on the mechanical and structure properties will be the main concern. Jing-lian [7], studied the effect of adding dispersed yttrium oxide(Y2O3) from 0.02%wt to 0.08%wt to the same tungsten heavy alloy (90W-7Ni-3Fe in %wt), fabricated by the mechanical alloying (MA) process, the powder was then pressed and sintered under H2 atmosphere. The results showed that a maximum tensile strength of about 1000 MPa and elongation of about 30.8% can be obtained. Lee et al. [6], investigated the properties of mechanically alloyed oxide dispersion strengthened tungsten heavy alloy 94W-4.8NI-1.2Fe %wt (Ni/Fe weight ratio 4:1), by adding partially stabilized zirconium (PSZ) up to 0.5%wt. The alloy was liquid phase sintered under hydrogen atmosphere. The results confirm that the yield strength and ultimate tensile strength were moderately increased, while elongation was severely decreased. Demirkan et al. [9], investigated a high tungsten mechanically alloyed composition containing 1%wt Ni and up to 2%wt Al2O3 uniaxially pressed and sintered under Ar and H2 atmospheres. They reported that a remarkable grain refining took place and a sensible increase of ultimate tensile strength and hardness are recorded. Experimental Work A heavy tungsten alloy having the composition 90%wt W, 7%wt Ni, and 3%wt Fe was chosen, as a base alloy, to evaluate the effect of limited additions of yttrium oxide (Y2O3) from 0.02%wt to 0.5%wt, zirconium oxide (ZrO2) from 0.1%wt to 0.5%wt, and aluminum oxide (Al2O3) from 0.5%wt to 3%wt, on the mechanical and structure properties of this alloy. The characteristics of the elemental and oxide powders are given in Table 1, and the morphologies of the different powders are illustrated in Fig. 1. The different mixtures with the prescribed basic composition and additives, together with 0.5%wt paraffin wax were mixed in a planetary mixer for 120min.The mixtures were consolidated into green compacts in the form of a standard tensile and impact specimens using uniaxial pressing under 200MPa. The compacted specimens were then liquid phase sintered, in vacuum, at a temperature of 1480oC for 90min.the regime of the applied sintering cycle is shown in Fig.2 .Density of the obtained sintered specimens was measured by Archimedes water immersion technique. Tensile test was carried out using Instorn tensile test machine type 8032 with loading rate control 8 kN\min. Impact test was carried out using Galdbini charpy pendulum impact testing machine. Hardness values where measured by Rockwell hardness testing machine. The fractures and microstructures of the different specimens were obtained using scanning electron microscope (SEM) type Seo 202. Paper: ASAT-15-110-MS 3 Table 1: Characteristics of the elemental and the oxide powders

Effect of Limited Additions of Y2O3, ZrO2 andAl2O3 on the Mechanical and Microstructure Characteristics of Tungsten Heavy Alloys