| At present, high strength stainless steel and less titanium alloy are using in mechanical moving parts and structural materials of the spacecraft. The usage amount of stainless steel is limited as its high density. The titanium alloy has the lower density and high strength-to-weight ratio, however, it is not perfect too, due to its low hardness and poor abrasive resistance. A new kind of zirconium-titanium alloys47Zr45Ti5A13V with high strength-to-weight ratio which has been synthesized recently is believed to have great engineering potential used as structural material of spacecraft exposed to space environment. Its tensile strength is1638MPa, and density which is5.11g/cm3is2/3of the steel. However, its space applicability has rarely reported, and the further research should be carried out. Therefore, In order to provide associated parameters of47Zr45Ti5A13V for further use in the future spacecraft, this dissertation takes orbital debris as it background, focus properties of shock compression, hypervelocity impact and high pressures of47Zr45Ti5A13V.First of all, shock-wave compression experiments under30-200GPa were carried out by impacting a target with a hypervelocity flyer plate launched by a two-stage light gas gun. Three impact methods were employed to study the Hugoniot curve, i.e. symmetrical impact method, asymmetric impact method and reverse impact method. The shock wave velocity Us in the specimens was measured using electrical probe technique, and the particle velocity up behind the shock front was calculated by the impedance-match method. The relationship between Us and up can be described linearly by:Us=4.324(±0.035)+1.177(±0.012) up. From the linear relationship between shock wave velocity Us and particle velocity up, there was no detective phase transitions occurred from30to200GPa. In order to understand the phase transition under0-30GPa whether occurred or not, we calculated the Hugoniot using additive principle based on assumption that there were no phase transition and chemical reaction occurred. The calculated Us-up are compared with the experimental data, the larger deviations between experimental and calculated data obvious shows that the pressure-induced phase transitions occurred. We prefer that α'β phase transition occurs below30GPa, and between30and200GPa the β with bcc structure remain stable.Based on the shock-wave compression experimental data, the Gruneisen parameter γ=1.277(ρ0/ρ), the bulk modulus at zero pressure B0s=97.96GPa and its first pressure derivative B0s=3.68were obtained. The Debye temperature (?)=305K was obtained by Lindemann empirical formula. The P-V-T equation of state for47Zr45Ti5A13V was given out using Vinet equation of state to descript the cold curve and the Debye model for thermal contributions.The simulated orbital debris hypervelocity impact experiments for47Zr45Ti5A13V alloy were conducted by laser driven plate flyer technique. Single and repeatedly impact experiments were employed to this study. The (?)=1mm aluminum miniflyers with two different sizes were launched to2-7km/s:5μm and8μm thickness, respectively. There was a crater appeared after impact, however, the outline of crater was not obvious, due to smaller weight of aluminum miniflyers. The deepness (h) of craters was measured by surface profilometer, and the relationship between h and velocity of miniflyers (D) could be described linearly by:h8μm,=-11.715+5.530D and h5μm=-0.410+1.118D respectively. The relationship between h and impact frequency N for miniflyers at2.5and5.7km/s could also be described linearly by:h2.5=0.675+2.397N, h5.7=8.861+10.826N, respectively. From the results, it was concluded that the damage degrees of repeated impact were less than those of the first time.The shock pressures and temperatures of hypervelocity impact were obtained based on the results of shock-wave experiments. The critical impact velocity (4.163-5.683km/s) for Rotational Dynamic Recrystallization was calculated by two methods, which named temperature rise and grain refinement dynamics. However, for all the single impact, there were no fine grain been occurred, and the fine grain only appeared at bottom of carter which formed after repeated impact at hypervelocity. It could be explained by that initial grains were not be broken by not enough dislocation and twins, due to smaller plastic deformation caused by single impact. In addition, this dissertation had investigated the bottom of carter by using transmission electron microscope. The results show that there is no β'ω phase transition which is observed in titanium alloys occurred under hypervelocity impact, although the process of impacting is similar to quenching. It is demonstrate that the47Zr45Ti5A13V alloy shows excellent stability of phase composition and mechanical properties under hypervelocity impact. In order to study the properties of each phases for the47Zr45Ti5A13V alloy, this paper investigated the phase transition, structural, elastic and thermodynamics properties of Ti2Zr which was the matrix for47Zr45Ti5A13V alloy by using the first-principles pseudopotential method based on density functional theory. The third-order Birch-Murnaghan equation of state (EOS) was obtained by fitted the energy-volume (E-V) data. We calculated the enthalpy of α-Ti2Zr, β-Ti2Zr and ω-Ti2Zr under0～100GPa, and found the common tangent to determine the equilibrium phase transition pressure. It is shown that β-phase becomes dominantly stable along with the pressure further increases, the ω'β transition occurs at25.4～29.1GPa, and the phase transition pressure is51.3～94.7GPa for ω'β. The quasi-harmonic Debye model was used to investigate the thermodynamic properties of α-Ti2Zr and ω-TiZr. The Debye temperature, heat capacity and thermal expansion coefficient as a function of pressure and temperature were obtained.Finally, elastic constants and their pressure dependence of α-Ti2Zr and ω-Ti2Zr were obtained using the static finite strain technique. According to an empirically relationship to predict ductile and brittle behavior of solids bases on elastic constants, by the ratio R=G/B. It is clear that the co-Ti2Zr in greater brittleness than α-Ti2Zr whether pressure loads or not. This result consists with difference charge density contour which shows that Ti combine with the three nearest neighbours form a graphite-like net structure lead to greater brittleness. The results of electronic density of state and Mulliken population analysis at equilibrium geometries under pressure shows that pressure-induce sp-d electron transfer, and eventual transforms to the β-phase under high pressures.In summary, in order to assess the suitability of a new kind of alloys use in spacecraft in space debris environment, this dissertation studies the dynamic response properties and performance of47Zr45Ti5A13V alloy under hypervelocity impact by using experiments combine with theoretical calculation. This study provides associated parameter and theoretical guidance of47Zr45Ti5A13V for future spacecraft. |
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