Advanced Materials Research Vols. 887-888

Abstract: K4169 is the Nickel-base superalloy that is the most widely used in the turbine components. The article selects three kinds of etching solution to corrode, in order to achieve the purpose that studies on its morphology. Etchant1 is the mixed solution of 15mlHCl, 10mlAcetic acid, 5mlHNO₃ and 2drop glycerin. Etchant2 is the mixed solution of 3ml glycerin, 3mlHCl, 1ml HNO₃. Etchant 3 is the mixed solution of 20mlHNO₃, 60mlHCl. The results showed that we can mainly observe strengthened phase γ'' (Ni₃ (Ti, Al)) and matrix γ (Fe-Ni-Cr) phase with etchant1 to corrode. Using the etchant2 to corrode, we can clearly see its dendrite structure. Using the etchant3 to corrode, we can obverse its grain boundary that includes white inter-metallic compounds. We also respectively discussed the K4169 morphology when magnifications are 200times and 500times.

Abstract: A Ni-7.2at%Ti alloy was prepared and the d-electron occupancy of Ni was measured from electron energy loss spectroscopy (EELS) of nickel. The results showed that the white-line intensity of Ni EELS and the d-electron occupancy of Ni in Ni-7.2at%Ti alloy did not change significantly relative to pure Ni.

Abstract: The microstructure and properties of Cu-7.5Ni-5Sn alloy after homogenization treatment was investigated. The research results show that homogenization treatment can obviously eliminate dendritic segregation in Cu-7.5Ni-5Sn alloy. The temperature of homogenization annealing has a great influence than the effect of holding time. The ingots of Cu-7.5Ni-5Sn alloy which were homogenization treated at 780°C for 24 hours can be rolled up to 30% deformation by cold-rolling. Some tiny white matter is still remaining in dendrite boundary, but atom fraction of Ni and Sn of the dendritic segregation is decreased by 12.04% and 4.73% respectively compare with casting state. The electrical conductivity and Brinell hardness of Cu-7.5Ni-5Sn alloy homogenization treated at 800°C for 24 hours is 12.8%IACS and 132Hv, and increases 18.5% and 29.9% respectively.

Abstract: The structure stability, mechanical properties and electronic structures of B2 phase FeAl intermetallic compounds and FeAl ternary alloys containing V, Cr or Ni were investigated using first-principles density functional theory calculations. Several models are established. The total energies, cohesive energies, lattice constants, elastic constants, density of states, and the charge densities of Fe₈Al₈ and Fe₈XAl₇ ( X=V, Cr, Ni ) are calculated. The stable crystal structures of alloy systems are determined due to the cohesive energy results. The calculated lattice contants of Fe-Al-X ( X= V, Cr, Ni) were found to be related to the atomic radii of the alloy elements. The calculation and analysis of the elastic constants showed that ductility of FeAl alloys was improved by the addition of V, Cr or Ni, the improvement was the highest when Cr was used. The order of the ductility was as follows: Fe₈CrAl₇ > Fe₈NiAl₇ > Fe₈VAl₇ > Fe₈Al₈. The results of electronic structure analysis showed that FeAl were brittle, mainly due to the orbital hybridization of the s, p and d state electron of Fe and the s and p state electrons of Al, showing typical characteristics of a valence bond. Micro-mechanism for improving ductility of FeAl is that d orbital electron of alloying element is maily involved in hybridization of FeAl, alloying element V, Cr and Ni decrease the directional property in bonding of FeAl.

Abstract: The boronizing experiments on the surface of Ti-6Al-4V (TC4) titanium alloys were based on solid powder method. Different additives were added into the boronizing agent. The morphologies of surface layers on titanium alloys were observed in scanning electron microscopy (SEM). The phase compositions of boronized layers were analyzed by X-ray diffraction (XRD). The wear resistance properties of boronized TC4 were determined by the friction and wear testing machine. The results showed that all the boronized layers were composed of TiB₂ and TiB dual phases.When 5%Fe₃O₄ was added into the boronizing agent, the boride layer contained more TiB₂ compound and was thicker than those with the addition of 5%Na₂B₄O₇.

Abstract: The structures and optical performances of TiO₂ doped with 4^th periodic transition metal ions were investigated in this paper. The characterization results of X-ray photoelectron spectroscopy and X-ray diffraction showed that the transition metal ions existed in oxidative states, and composites formed because of the reaction between doped metal ions and TiO₂. The absorption spectroscopy of TiO₂ doped with zinc was mainly in ultraviolet region, close to that of the pure TiO₂. While for TiO₂ doped with other transition metal ions including V, Cr, Mn, Fe, Co, Ni and Cu ions, the absorption spectroscopies covered ultraviolet region and visible light region, much broader than that of the pure TiO₂.

Abstract: Conventional hot compression deformation and water quenching experiments were applied to investigate the evolution of austenite grain structures before the initiation of dynamic recrystallization. The experimental results reveal an interesting phenomenon that dynamic strain induced boundary migration can lower dislocation density and coarsen austenite grains. The results show that dynamic recovery is not the only way to decrease dislocation density, the mechanism of which for dynamic recovery is related to dislocations climb and annihilation, resulting in the formation of sub-grains and regular sub-boundaries. However, the mechanism of decreasing dislocation density for dynamic strain induced boundary migration is different from dynamic recovery. Therefore, dynamic strain induced boundary migration should be another softening mechanism before the initiation of dynamic recrystallization.

Abstract: Residual stresses developed after quenching of high-strength aluminum alloy ultra-thick plates have an important effect on the quality and reliability of parts, and should be reduction to meet the requirement. In this investigation, numerical techniques of SIMUFACT software are used to simulate residual stresses in quenched 340mm×127mm×124mm Al-Zn-Mg-Cu high-strength aluminum alloy ultra-thick plate, and the results have been verified. On the basis of verified simulation parameters, residual stresses in quenched 4000mm×720mm×285mm ultra-thick plate and their reduction through single-side cold compression method were simulated by SIMUFACT software. After quenching, the value of maximum tension stress located at the interior center of the plate is 200MPa, and the value of maximum compression stress located on the surface of the plate is-169MPa. Through analysis of single-side cold compression processes, it can be concluded that more than 90% quenching residual stresses can be reduced by 1% upsetting ratio and 75% feed of the top die. Residual stresses after compression can be reduced down to the range of-25~9MPa. Mean residual stress values of simulation after compression are identical to the XRD testing data.

Abstract: Objective: To evaluate the influence of three pattern materials on the marginal fitness of Co-Cr alloy inner crown of porcelain fused to metal (PFM) endocrown. Method: Standard molar abutments mould with 90°shoulder, 6°convergens, 5.0mm occlusal-gingival height, and 15.0mm neck diameter were made of stainless steel. Three kinds of pattern materials, including Inlay wax (group A), Casting Pattern resin (group B), and Pattern Resin (group C), were used to fabricate the pattern of Co-Cr alloy inner crown of PFM endocrown. The fitness of the inner crown finished was evaluated. T test was used for statistical analysis. Results: The means of marginal gaps between inner crown and abutment shoulder made of three pattern materials were 55.9μm for group A, 37.1μm for group B, 63.1μm for group C respectively. There were statistically significance among the 3 groups (P< 0. 05). Conclusion: As a pattern material, Casting Pattern resin is suitable for fabrication of Co-Cr alloy inner crown of porcelain fused to metal endocrown.

Abstract: Thermally stimulated current (TSC) is a simple and effective test technique to study the thermal activated charge, electron trap and activation energy of dielectric and semiconducting materials. It is well known that the addition of glass frits can improve the degradation property of ZnO varistors. An activation energy of 0.45 eV has been found on the ZnO varistors with/without glass frits after the DC degradation by using TSC method. The tested quantity of thermal activated charges, Q_TSC, may represent the numbers of migrated zinc interstitials. ZnO visitors doped with glass frits have less Q_TSC. Experiment indicates that TSC test is a convenient method to evaluate the degradation behavior of ZnO varistors.