Advanced Materials Research Vols. 89-91

Abstract: An Al-5.1%Mg-2.1%Li-0.17%Sc-0.08%Zr (in mass%) alloy designated as 1421 Al was subjected to equal channel angular extrusion (ECAE) with rectangular shape of channels up to fixed true strains of ~4 and ~8 at a temperature of 325oC. This processing provided the formation of uniform recrystallized structures with micron scale average grain size. The 1421 Al after ECAE processing and in initial hot extruded condition was subjected to solution treatment followed by oil quenching and subsequent ageing. Fine grained structure evolved under ECAE remains essentially unchanged under solution treatment. However, this structure affects significantly the precipitation sequence during ageing. Relationships between microstructure and service mechanical properties are considered.

Abstract: The multiple precipitation behavior of NbC and Cu particles in martensitic structure was investigated by using 0.05C-0.46Nb-2Cu-1.5Mn steel (NbC-Cu steel). Additionally, 0.05C-0.45Nb-2Mn steel (NbC steel) and 2Cu-5Mn steel (Cu steel) were also prepared to examine the respective precipitation behaviors of NbC and Cu. Aging treatment at 873K after quenching revealed that these steels exhibit typical age hardening. Comparing the NbC steel and Cu steel in the precipitation rate, the Cu precipitated much faster than the NbC. On the other hand, the peak hardness in NbC-Cu steel is higher than that by the respective precipitations in NbC steel and Cu steel. Besides, the aging time for the peak hardness in NbC-Cu steel was between those in NbC steel and Cu steel. This suggests that the NbC and Cu particles were separately precipitated within martensite matrix and each of them contributed to the hardening in NbC-Cu steel. As a result of TEM investigation for crystallographic characteristics of the precipitates, the NbC and Cu particles had different crystallographic orientation relationship with tempered martensite matrix: Baker-Nutting relationship for NbC particle and Kurdjumov-Sachs relationship for Cu particle.

Abstract: Implanting a spinal fixture using metallic rods is one of the effective treatments for spinal diseases. Because cyclic bending stress is loaded on the implant rods when patients move their upper bodies in daily life, bending fatigue properties are important for the implant rod. Further, the implant rods are bended plastically into a curved shape of spine by hand in a surgical operation. In that case, keeping shape is important, namely bending spring back properties are important factors. On the other hand, a biomedical β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (mass %) alloy (TNTZ), has been developed by the authors. Currently, this alloy are investigated to be applied to the above mentioned implant rod practically. Therefore, four-point bending fatigue and three point-bending spring back properties of TNTZ subjected various heat treatments were examined in this study. TNTZ rods were subjected to solution treatment, and then some of them were subjected to aging treatment at 673 K or 723 K for 259.2 ks, followed by water quenching. Then, four-point bending fatigue and three-point bending spring back tests were carried out on TNTZ rods subjected to the various heat treatments mentioned above. The bending fatigue strength at 2.5 million cycles in the high cycle fatigue region are not much different among any TNTZ rod. However, the bending fatigue strength of the Ti-6Al-4V ELI (Ti64) rod exceeds the fatigue strengths of every TNTZ rods in both low and high cycle fatigue regions. On the other hand, the lower spring back, which is a favorable property, was obtained for some TNTZ rod than Ti64 rod.

Abstract: Due to Plasticity induced Transformation in metastable β-Ti-10V-2Fe-3Al (wt.%) alloy (PiTTi) upon deformation, a noticeable improvement in mechanical properties is observed. Among the main factors controlling such effect are the β grain size and its composition. Such phase transforms into martensite upon quenching. Its martensite start temperature (Ms) varies in accordance with its composition. Following Ghosh and Olson’s theory, a thermodynamics based model to predict the compositional dependence of the Ms temperature is developed, and successfully validated for Ti-X (X = Fe, Cr, Mo, V, Nb, Zr and Al) binary alloys. The model has been used to design new alloys displaying a tailored PiTTi effect.

Abstract: Magnetic nanoparticles have been used extensively as drug delivery materials in recent years [1,2]. The present research goal is to treat bone diseases (such as osteoporosis and infection) by using surface modified magnetic nanoparticles. Magnetite (Fe3O4) and maghemite (Fe2O3) were synthesized and coated with calcium phosphate (CaP). The resulting nanoparticles were treated hydrothermally to change the crystalline properties of CaP. Nanoparticles were characterized via transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). TEM was also used to study the uptake of nanoparticles into osteoblasts (OB) and bacteria. OB proliferation experiments were conducted after 1, 3 and 5 days in the presence of the various iron oxide nanoparticles alone and CaP coated iron oxide magnetic nanoparticles. OB proliferation experiments were also conducted after 1, 3 and 5 days in the presence of various concentrations of CaP coated nanoparticles to examine a possible concentration dependent trend on OB density. Staph epidermidis were incubated with different doses of Fe3O4 to determine the effect of these nanoparticles on bacteria activity. Results of this in vitro study demonstrated greater OB functions and inhibited bacteria functions in the presence of select magnetic nanoparticles. In summary, the results of this study showed that magnetic nanoparticles should be further studied for various orthopedic applications.

Abstract: In this study, authors investigated the effect of horn tip geometry on the mechanical properties of a joint ultrasonically welded between a mild steel sheet and an aluminum alloy sheet. Two types of weld tips with the different contact face geometries were employed. One type of a tip has a cylindrical contact face without knurl. The other type of a tip has flat contact face with knurl. The main results obtained in this study are as follows. Authors successfully welded the mild steel sheet to the aluminum alloy sheet using both of the weld tips. However, the strength of the joint welded by the tip with cylindrical geometry was higher than that welded by the flat tip with knurl under the same welding condition, and the strength of the joint by the tip with cylindrical geometry was twice larger than that by the flat tip with knurl under the optimal welding condition. The strength of the joint increased with increasing the welding time and the clamping force, and showed the maximum under the reasonable welding condition. Excessively long welding time and large clamping force damaged the workpiece surface contacted the horn side tip, resulting in the decrease of the joint strength. It was possible to improve the joint strength using commercially pure aluminum foil with suitable thickness as insert metal.

Abstract: A new software was developed for the X-ray stress analysis of textured materials, especially useful in the case of thin films and coating. Literature data for a sputtered Cu thin film were used as a test case. Good agreement with the published results was found considering a grain interaction mechanism based on the combination of four models (Ruess/Voigt/Vook-Witt/inverse Vook-Witt). A similar value for the in-plane residual stress was obtained by the Eshelby-Kröner model, by optimizing the grain aspect-ratio. Main features and numerical/graphic output are briefly discussed.

Abstract: Indirect Template Magnetic Field Assisted Assembly (IT-MFAA), a parallel processing technique, is presented. IT-MFAA is designed to assemble devices onto substrates through a versatile and scalable methodology, which is capable of adjusting to manufacturing situations and producing 100% yields with error correction. This paper discusses existing serial and parallel techniques and compares them to IT-MFAA. It demonstrates that IT-MFAA circumvents drawbacks present in other techniques, and outlines a model of IT-MFAA.

Abstract: In this contribution, two experimental techniques to study the dynamic shear behaviour of metals are presented and applied to Ti-6Al-4V. For bulk materials hat-shaped specimens are subjected to a high-strain-rate load in a split Hopkinson compression bar set-up. For sheet materials a purpose-developed, novel shear specimen geometry, is loaded in a Hopkinson tensile bar set-up. The value of both techniques to assess the dynamic material behaviour is discussed. The experiments are optimized by means of numerical simulations. Digital image correlation is used to extract the specimen deformation from high speed camera recordings. It is shown that the dynamic behaviour, including fracture of Ti-6Al-4V differs considerably from the static behaviour. Both experimental techniques gain complementary information.

Abstract: Objective of this study is to develop simulation for predicting mechanical properties of Ti-6Al-4V alloy. Rockwell Hardness (HRC), Ultimate tensile strength (UTS) and elongation (ε) are predicted by using Neural Network (NN) with multilayer feedforward architecture. The input of simulations are chemical compositions of Ti-alloy at room temperature. The data of the mechanical properties which are reported by other researchers are used for the NN training and Gradient Descent (GD) and Lavenberg Marquardt (LM) are applied as methods of learning algorithms. The results of training by both methods are compared in order to obtain high performance of output criteria which are determined by a Normalized Root Mean Square Error (NRMSE). is used to determine the performance of output criteria. In training, the NRMSE output calculated by GD algorithm show that HRC, UTS and ε are 0.024, 0.0717 and 0.1375 respectively, while LM algorithm for HRC, UTS and ε are 0.0207, 0.0689 and 0.1150, respectively. The NRMSE predicted output of GD algorithm for HRC, UTS, and ε are 0.0658, 0.0338 and 0.2994, while LM algorithm for HRC, UTS and ε are 0.0371, 0.1192 and 0.5487 respectively. In training, values of NRMSE calculated by LM algorithm is smaller than GD algorithm. These results suggest that LM algorithm shows excellent ability for training, however the GD method is more appropriate for the training algorithm in order to obtain a high performance of output criteria. It can be concluded that the NN can be applied for predicting mechanical properties of Ti-6Al-4V alloys.