Materials Science Forum Vols. 675-677

Abstract: Cemented carbide YG30 and steel 1045 were welded with various Ni-Fe-C filling alloys via the Cemented carbide YG30 and steel 1045 were welded with various Ni-Fe-C filling alloys via the tungsten-inert-gas (TIG) arc welding. η phase formation at the welding joints was investigated via scanning electronic microscope (SEM), transmission electronic microscope (TEM) coupled with selected diffraction, and electron probe microanalysis methods. η phases in three different morphologies were identified and they appeared to form in different mechanisms. The η phase formed at the heat-affected zone (HAZ) exhibited a similar size to that of WC particles and its formation was mainly attributed to the inter diffusion among W, C and Fe, Co, Ni in solid-state γ phase. The large-size η phase near the interface between YG30 and weld bead was due to the coarsening of tiny η grains in the liquid weld bead. The small-size η phase was formed via precipitation from the γ phase during cooling. The η phase formation could be controlled by optimization of C and/or Ni concentration in the filling alloys.

Abstract: A new high strength and high toughness Ti-alloy, Ti-63, was designed via the CALPHAD approach using a thermodynamic database including elements Ti-Al-Cr-Mo-O-Si-Sn- V-Zr. Good combinations of strength, ductility and fracture toughness, with the values of tensile strength Rm > 1200 MPa, elongation A > 10%, reduction of area Z > 20% and fracture toughness KIC ≈ 80 MPa·m1/2, were achieved for the Ti-63 alloy after optimized heat treatment process.

Abstract: In this paper, a 2-D nonlinear thermo-mechanical coupled finite element model was developed to simulate the vacuum hot bulge forming process of rotor-can with the aid of finite element software MSC.Marc. Thermal physical and mechanical properties of materials vary with temperature in the model. In addition, the effects of high temperature creep properties of materials on the vacuum hot bulge forming process of rotor-can were considered. The temperature field, the stress-strain field and the displacement field of rotor-can during vacuum hot bulge forming process were calculated. This work is beneficial to understand the vacuum hot bulge forming process of rotor-can and lays a good foundation for future work.

Abstract: Movement behavior of AISI 316L stainless steel powder under hot isostatic pressing (HIP) were investigated using finite element analysis (FEA). The analysis, which was based on the porous metal yield criterion, was carried out in the FEA program. Density distributions, deformations and displacements of compact were discussed. The evolution of displacement for some typical positions in the compact was also studied in this paper. The calculation results show that thermal expansion plays an important role at the early stage of HIP. There are large displacements for powder compact during the ramp stage and the early holding stage in the HIP cycle. Correspondingly, the improvement of densification increases significantly. Simulation results for the shape change and average density of a sample were also compared with experiment.

Abstract: The temperature and strain distributions of the mockup composed of Cu-alloy with distinct structural material (SS316L and China Low Activation martensitic steel (CLAM)) were calculated and analyzed, based on a high heat flux (HHF) test recently reported with heat flux of 3.2MW/m². The calculated temperature and strain results in the first wall (FW), in which SS316L is as the structural material, showed good agreement with HHF test. By substituting CLAM steel for SS316L the contrast analysis indicates that the thermo-mechanical property for CLAM steel is better than that of SS316 at the same condition. Furthermore, the temperature and strain distributions of the FW were calculated under the condition of normal ITER operation: the surface heat flux is about 0.5MW/m² and volumetric heating due to neutron radiation is on the order of 15~20 MW/m².

Abstract: Vacuum hot bulge forming (VHBF) is becoming an increasingly important manufacturing process for titanium alloy cylindrical workpiece in the aerospace industries. Finite element simulation is an essential tool for the specification of process parameters. In this paper, a two-dimensional nonlinear thermo-mechanical couple FE model was established. Numerical simulation of vacuum hot bulge forming of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC.Marc. The effects of process parameter on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece was analyzed by numerical simulation. The proposed an optimized vacuum hot bulge forming process parameters and die size. And the corresponding experiments were carried out. The simulated results agreed well with the experimental results.

Abstract: Using finite element analysis software of COSMAP, a three-dimensional elastic-plastic finite element model of linear friction welding (LFW) process of Ti6Al4V alloy was established. Based on metallo-thermo-mechanical theory relevant to describing the coupled fields of metallic structure, temperature and stress–strain, the temperature fields, phase transformation and stress fields during the LFW process were investigated in numerical simulation. Moreover, the validation experiment was carried out. The results showed that the simulation results of temperature，phase transformation and the residual stress were in good agreement with the experimental ones, which proved the numerical simulation to be reliable.

Abstract: The simulation of magnesium plasticity at the microscopic and mesoscopic scale using space and time-discretized statics and dynamics dislocation was carried out. The complexity of discrete dislocation models dues to the fact that the mechanical interaction of ensembles of such defects is with an elastic nature, and therefore involves long-range interactions. The motion of dislocations or dislocation segments in their respective glide planes are usually described by assuming simple phenomenological viscous flows laws. The formulation of the dislocation dynamics is obtained by the Newton’s Second Law of motion for each dislocation or dislocation segment. The evolution of the dislocation position is obtained by simple difference algorithms.

Abstract: A two-dimensional modified cellular automaton (CA) model was developed to simulate the dynamic recrystallization (DRX) behaviour during thermo-mechanical processing. It provides a link for multiscale modeling to bridge the mesoscopic dislocation activities with the macroscopic mechanical properties. This model is applied to investigate the effect of initial grain sizes on DRX process in commercial pure copper. The simulated results indicate that the stable size of recrystallized grain is independent on initial grain sizes. However, the percentage of DRX is not only related to the thermo-mechanical parameters, but also influenced by the initial microstructure. It is concluded that larger initial grain sizes promote a delay in the DRX occur on commercial pure copper. The calculated results compare well with the limited number of experimental observations and theoretical conclusions.

Abstract: Developing large scale modelling of oxide surfaces as well as of interfaces formed upon various deposits (oxide, metal, nanoclusters) is of great importance to get prediction on functional material properties under different conditions and in interpreting experiments. We recently developed a new variable-charge model in which the covalent energy is described in the framework of the second-moment approximation of the tight-binding scheme. This model is applied here to the study of the low index rutile TiO2 surfaces. The surface energies, the atomic relaxations and the charge transfer at the (110), (100) and (001) surfaces are calculated and the results compared well, for the first time, with DFT calculations, performed both with GGA and hybrid B3LYP functional.