The aim of this study is to clarify the effect of different concentrations of titanium dioxide nanoparticles (Nps) on the properties of two types of heat polymerized acrylic resin. The tested parameters were flexural strength, impact strength, and microhardness. The two types of acrylic resin used in this study were conventional unmodified (Implacryl, Vertex) and high impact heat polymerized acrylic resin (Vertex-Dental, Netherlands). Both types of acrylic resin were modified by using 1% and 5% TiO2 Nps powder. Specimen's dimensions were prepared according to the American Dental Association Specification No. 12. Three types of specimens were prepared: 1) flexural strength specimens 50 mm × 10 (±0.2) mm × 3 (±0.2) mm, 2) impact strength test specimens 60 mm × 6.0 mm × 4.0 mm, 3) microhardnesss specimens 25 mm × 10 mm × 3 (±0.2) mm. For each test 6 groups were prepared (each group containing 5 samples). Thirty specimens were prepared in each of the three tests, amounting to a total number of 90 specimens. Mechanical properties such as flexural strength (FS), impact strength and microhardness of the above mentioned specimens were determined using universal testing machine, Izod pendulum impact testing machine and Vickers microhardness tester, respectively. ISO Specification No. 1567 was followed in microhardness test. The data was collected and statistically analyzed. Flexural strength considerably decreased by increasing TiO2 concentration in both types of acrylic resin. Impact strength of the conventional acrylic resin modified by 1% of additives significantly increased. The microhardness is significantly increased by addition of 5% of TiO2 Nps. The Incorporation of TiO2 nanoparticles into acrylic resins can adversely affect its flexural strength. Meanwhile, the impact

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Semisolid casting using the cooling slope plate method (CSP) is known to refine the microstructure of hypereutectic aluminum alloys and enhance their mechanical properties. The current research investigates the combined effect of casting using the CSP and mechanical vibration of the mold on microstructure and wear behavior of A390 alloy. After pouring the alloy on the CSP, the mold (sand/ metallic) was vibrated mechanically at 50 Hz during filling and up to solidification. Conventional casting with the same mold vibration conditions was also done for comparison. During CSP casting with mechanical vibration of the mold, the crystal nucleus multiplication inhibits the grain growth, and the dendrite break-up takes place simultaneously, leading to refinement of the microstructure. The double effect of the shear force by melt flow and vibrational turbulence is responsible for fragmentation of the particles. This finding was more pronounced in case of using the sand mold. The quantitative measurements showed that the size of primary Si reduced from * 184 lm for the conventional casting in the sand mold without vibration to * 70 lm when the mold was vibrated and from * 30 lm in case of CSP down to * 20 lm when CSP was followed by mechanical vibration of the mold. However, applying the mechanical vibration after CSP in case of the metallic mold increased the size of primary Si from * 21 to 36 lm. Accordingly, the improvement in the hardness and wear resistance of the CSP samples due to vibration was more significant in case of using the sand mold.

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This study investigated the effect of heat treatment processes on the dry sliding wear resistance of the TC21 Ti-alloy at several levels of normal load and sliding speed. Response Surface Methodology (RSM) has been used as a design of the experiment procedure. OM and FESEM besides XRD analysis were used for results justification. Highest hardness of 49 HRC was recorded for WQ + Aging specimens due to the plenty of α″ which decomposed to αs and the more αs, while the lowest hardness of 36 HRC was reported for WQ specimens. The results revealed that specimens subjected to water quenching and aging (WQ + Aging) under extreme load and speed conditions (50 N and 3 m/s), possessed the poorest wear resistance although they had the highest hardness. While those left in the annealed condition revealed the highest wear resistance although they had much lower hardness when compared to other conditions. A mathematical polynomial model for wear resistance expressed in wear rate was developed, validated then used to get the optimum parameters.