الفهرس 
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Abstract
The present work mainly covers studying the essence of adding TiO2 nanoparticles on the structural and mechanical properties of Al- 4 wt.% Ag alloy. Three topics are discussed:
1)Studying the effect of TiO2 nanoparticles addition on structural characteristics of Al- 4 wt.% Ag alloy.
2)Studying the effect of strain rate ε• and testing temperatures T on the stress-strain characteristics of Al- 4 wt.% Ag alloy and Al- 4 wt.% Ag-0.1wt.% TiO2 alloy wire samples.
3)Studying creep characteristics of the two alloys. The experimental results were investigated under different levels of stress and temperature.
In the first topic, Studying the structure evolutions of both Al- 4 wt.% Ag alloy and Al- 4 wt.% Ag-0.1wt.% TiO2alloy were discussed (XRD). The results showed that the values of the lattice parameter ao reached maximum value at the deformation peak (maximum lattice strain). The addition of 0.1wt.% nano-sized TiO2 particles to Al-4wt.% Ag alloy cause the disappearance hard phases of AlAg3 and Ag2Al (hcp) (inter-metallic compounds) as shown in X-ray diffraction patterns and appear AlTi phase (tetragonal)which is less hardening than the hcp phase..
In the second topic, stress-strain tests for Al- 4 wt.% Ag and Al- 4 wt.% Ag-0.1wt.% TiO2 alloys were performed under the effect of different strain rates ε• ranged from 3 x 10-4 to 9x 10-4 s-1 at different testing temperatures T in the range of 603 to 663 K. The results showed that increasing strain rates and decreasing the testing temperatures resulted in increasing the hardening parameters ultimate tensile stress UTS, yield stress y , fracture stress f , time of fracture tf and work hardening coefficient χ and decreasing the softening parameters strain fracture εf and dislocation slip distance L. Also the existence of the nano-sized TiO2 particles resulted in decreasing the hardening parameters ultimate tensile stress UTS, yield stress y , fracture stress f , time of fracture tf and work hardening coefficient χ and increasing the softening parameters strain fracture εf and dislocation slip distance L.
The lower values of the hardening parameters and higher values of the softening parameters of the ternary alloy (alloy B) than those of the binary alloy (alloy A) under the same deformation temperature , because the addition of 0.1wt.% nano-sized TiO2 particles to Al-4wt.% Ag alloy cause a disappearance of the hard phases AlAg3 and Ag2Al (hcp) (inter-metallic compounds) as shown in X-ray diffraction patterns and appear AlTi phase which leads to freeing more numbers of Ag atoms that move through the material.
In the thrid topic, tensile creep tests of the Al- 4 wt.% Ag and Al- 4 wt.% Ag-0.1wt.% TiO2 alloys were carried out at the temperatures ranging from 603 to 663K under effect of different applied stresses ranged for 12.75 to 15.3 MPa. It can be noticed that isothermal creep curves of both alloys showed a monotonic shift towards higher strains and lower fracture times with increasing testing temperature and/or applied stress. Moreover, the level of creep strain for Al-4wt.% Ag alloy ( alloy A) is generally lower than that of Al- 4 wt.% Ag-0.1wt.% TiO2 (alloy B ) under the same testing conditions. Creep parameters were found to be increased with increasing temperature and addition of TiO2 nanoparticles. It is also seen that under the same test conditions alloy A yields lower (steady state) creep rate ε•st compared with those of alloy B. This means that alloy B have more creep life time while retaining more creep resistance.
Steady state creep parameters ε.st and m of both alloys were found to increase with increasing the deformation temperature. Their values for both alloys exhibited a discontinuity at 633 K. These observations represent two deformation regions, the low and high temperature region below and above the transition temperature.
The present results yield activation energies of mean values 130 and 125 KJ/mole for alloys A and B respectively at low temperature region, which are in agreement with the activation energy for solute diffusion of Ag in Aluminum this would indicate that the rate controlling process is associated with viscous drag of dislocations by Ag atoms during glide.
The values 135 and 130 KJ/mole for activation energy of alloys A and B respectively for high temperature region, consistent with the activation energy of the grain boundary diffusion of Al atoms.