Materials Science Forum Vol. 1016

Abstract: A pure iron tape with cube orientation was fabricated by cold rolling and annealing. The orientation characteristics of the pure iron tape were evaluated using electron back-scattering diffraction (EBSD) analysis. The secondary recrystallized grains with cube orientation was formed on the tape surface for the pure iron tape. The coarse grains with a grain size of ca. 1mm were observed on the tape surface. The areal fraction of cube orientations with an angular deviation ≤ 20 ̊ amounts to ca. 81%.

Abstract: In order to quantitatively understand the residual strain distributions and benefits of engineering components following special technique treatment, such as Autofrettaging, Hot Isostatic Pressing (HIP) and Dissimilar Material Welding (DMW), the Neutron Diffraction Technique (NDT) has been employed recently to measure residual strain and stress distributions on following three cases of (a) Autofrettaged Aluminum 7075 high pressure vessels; (b) Hot Isostatic Pressed (HIPPED) heavy metals of tungsten clad in tantalum plate and (c) Dissimilar Material Welding (DMW) of 316L austenitic stainless steel and ferritic steel AS508 with Alloy 52 weld filler. This paper reports the recent research findings, including (a) NDT can identify optimal Autofrettage pressure level, by which load bearing capacity of the Autofrettaged pressure vessel increased by 215MPa; (b) NDT is able to reveal residual strains within heavy metals of Tungsten clad in Tantalum plate HIPPED and (c) NDT revealed a maximum residual tensile hoop stress value of about 494MPa in the interface between parent material SA508 and the weld seam. This is vital information for the post weld process and subsequent safe use of the dissimilar materials weld. Other researchers’ successful examples of working with NDT are also briefly reviewed. Future prospective of Engineering Materials Diffractometer (EMD) at CSNS is described too with a view to demonstrating the application and importance of NDT in revealing residual strain-stresses that are inevitable within engineering materials and engineering components following any manufacturing process.

Abstract: One of the applications of titanium in the dental field is a porcelain-fired-metal crown. It is made by firing porcelain multiple times with different composition of ceramics on a metallic abutment tooth. Regarding firing process to metallic abutment, a primer is generally required to be applied in advance of a porcelain firing and the opaque porcelain is applied to cover the metallic color of the abutment. By the way, our recent research shows that white oxide films formed on the Ti substrate have a color tone similar to opaque porcelain. Therefore, porcelain-fired-Ti samples replacing primer and opaque porcelain firing with the TiO2 oxide layer were fabricated and evaluated in this study. Color tone and peel strength were evaluated, and cross-sectional observation was observed by SEM and EPMA.

Abstract: Ti-Nb alloys in deionized water and Hanks' balanced salt solution were investigated at 310K using a ball-on-disc type frictional test machine with a ZrO2 ball counterface. In this study, besides the fretting wear behavior of Ti-Nb alloys was investigated, the relationship between the microstructure and mechanical properties of the Nb-added Ti alloy was investigated, and the relationship between the composition and hardness on the fretting wear of the alloy will be clarified from the results of the wear volume and surface analysis of wear track. The results obtained from the frictional test indicate that the dynamic coefficient of friction converged to a constant value with time variation. Also, wear volume in HBSS was smaller than in water, and wear volume of heat-treated became smaller than As-Rolled. Microstructural observations suggest the scars of adhesive wear were observed. Comparing each morphology, the ratio of the peeling part was more significant in Ti-Nb alloys, which have α+β than in Ti-Nb alloys, which have only β. Moreover, the results of Open circuit potentiometry indicate that the corrosion potential difference increased with wear. This is most likely due to the passive film was damaged. Besides, the corrosion potential difference of β-Ti-Nb alloy heat-treated with HBSS is small. It is assumed that there is an influence of HBSS besides the fine structure.

Abstract: In the most relevant technical β-titanium alloys, the extensive formation of the metastable ω-phase during common heat treatments has been a long-standing problem due to the deteriorating effect of this phase on the material properties. By means of dilatometry, the formation of the isothermal ω-phase has been investigated during ageing a Ti-21at.-%V-sample at 300 °C. A model has been developed, which allows to quantitatively correlate the maximum length changes appearing upon ageing to changes occurring at the microscopic scale, i.e. variations of the lattice constants, phase fractions and concentrations of vanadium in the phases appearing. The length change predicted by the model is in very good accordance with the data measured paving the way for further kinetic discussion and ultimately for deriving kinetic parameters.

Abstract: The hardness of AA 2024 is mainly dependent of the precipitation state in the material. This one will vary through the process of friction stir welding (FSW) which generates heat and deformations. The most important effect will be the thermal excursion which greatly affects the nature and the distribution of precipitates and so the mechanical properties of the material. Three Myhr & Grong-type submodels have been used in this study in order to simulate the variation of hardness in AA 2024-T3 FSW welds. These models allowed to simulate the hardening by growth of S-precipitates and the softening by coarsening and dissolution of GPB zones / co-clusters or S-precipitates. Finally, the natural ageing was taken into account following the Robson model. The complete model has been calibrated with isothermal data found in the literature and still has to be optimised. Nevertheless, preliminary results show the coherence of the model when performed on isothermal data. The model has been also applied to predict FSW hardness profiles that are compared to those found in the literature.

Abstract: In this study, we investigated the influence of the interaction between graphene and other materials as a basis for controlling the electronic structure of nanocarbon materials. First-principles calculations based on density functional theory (DFT) were performed on the optimized structure, adsorption energies and electronic states when copper and aluminum atoms were placed on graphene. As a result, we found that copper and aluminum are stable at the bridge and the hollow site, respectively. It was found that the adsorption energy of aluminum atom on graphene is larger than that of copper atom. It is considered that the difference in adsorption energy is caused by the difference in the dominant electron orbitals of the copper atom and the aluminum atom.

Abstract: The effect of ten different combinations with various amounts of niobium (0-0.6 wt.%) and chromium (1-4 wt.%) on weldability and mechanical properties of thermomechanically rolled and direct-quenched low-carbon (0.035 wt.%) microalloyed bainitic steel were investigated. Two compositions were alloyed with boron to increase the hardenability, and two with titanium to improve the toughness properties in heat affected zone. The target of the study was to produce steel with 700 MPa yield strength combined with good impact toughness. Coarse grained heat affected zone (CGHAZ) simulations were performed using the Gleeble 3800 thermomechanical simulator to evaluate the weldability of the investigated steels using cooling time from 800 °C to 500 °C (t_8/5) of 5 s and 15 s to simulate different heat inputs in actual welding procedure. Microstructures were characterized using light optical microscopy, and hardness profiles of simulated heat affected zones were determined as well as Charpy-V impact toughness at-40 °C and-60 °C. Shorter t_8/5 time (5 s) produced generally better impact toughness properties compared to longer t_8/5 -time (15 s). Steels with 4 % Cr had the highest impact energies. Generally, more softening occurred with longer t_8/5-time (15 s). However, Cr and Nb alloying decreased the amount of softening in the CGHAZ region, especially with longer t_8/5 -time. These results indicate that even with higher t_8/5 -time, it is possible to achieve strength properties equivalent to the base material in the CGHAZ region by Cr and Nb alloying.

Abstract: This paper presents an effective approach for the optimization of the semi-solid forging process of A356 Al-alloy based on the orthogonal array with the grey relational analysis and fuzzy logic analysis. Through the grey-fuzzy logic analysis, the optimization of complicated multiple performance characteristics can be converted into the optimization of a single grey-fuzzy reasoning grade. In this semi-solid forging process of A356 Al-alloy, the forging process parameters, namely the forging temperature, percent deformation, and die temperature are optimized with considerations of multiple performance characteristics including the tensile strength and hardness. The experimental results for the optimal setting have shown that the above performance characteristics in the semi-solid forging process of A356 Al-alloy can be improved effectively together through this approach.

Abstract: Heat-resistant Ti-Al-Nb-Zr alloys, which don’t contain Sn, have been designed to obtain good oxidation resistance above 600 °C. In addition, to design Ti alloys with best balance of creep and fatigue properties, prior β grain size which affects fatigue properties and lamellar microstructure which affects creep properties were controlled by heat treatment. In the present study, the effect of microstructure on creep properties of one of the alloys, i.e., Ti-7.5Al-4Nb-4Zr alloy, with the bimodal (B), the lamellar structures in small prior β grains (L_S), and the lamellar in large prior β grains (L_L) were investigated at 600 °C. The creep deformation mechanism for each microstructure was a power-law creep. However, the creep life varied depending on the microstructures. The longest creep life was obtained in L_S with prior β grain size of 90 μm and interlamellar spacing of approximately 10 μm, while the shortest creep life was obtained in L_L with prior β grain size of 550 μm and fine interlamellar spacing of less than 2~3 μm. This suggests that creep life is more affected by interlamellar spacing than by prior β grain size.