Importance of the phase-proportion on superplastic ductility of the eutectic alloys

Abstract: In the wire arc additive manufacturing (WAAM) process, the flow behavior of the molten pool determines the formation accuracy and formation defects. Therefore, it is significant to understand the complex physical process of the molten pool behavior in the WAAM. A real-time X-ray direct observation method and volume of fluid method (VOF) were performed to study the flow in molten pool and liquid flow in the molten pool. X-ray was used to observe the liquid flow in the molten pool and the droplet transfer from the WAAM. A three-dimensional model of the molten pool and droplet was established based on the VOF method, and the temperature distribution and flow status of the molten pool were calculated. By controlling different wire feeding speeds, two different droplet transfer modes were observed by X-ray, which include globular transfer and bridging transfer. Compared with globular transfer, bridging transition has little effect on molten pool flow. The flow model during the deposition process is established; the x–z plane is divided into four regions according to the flow characteristics of different positions in the molten pool. The maximum velocity in the molten pool appears in the action area of plasma arc force, which is 0.277 m/s, which leads to the increase in melting depth and promotes the flow of molten metal.

Abstract: General physical and chemical constants X-ray analysis of metallic material Crystallography Crystal chemistry Metallurgically important minerals Thermochemical data Physical properties of molton salts Metallography Equilibrium diagrams Gas-metal systems Diffusion in metals General physical properties Elastic properties, damping capacity and shape memory alloys Temperature measurement and thermoelectric properties Radiating properties of metals Electron emission Electrical properties Magnetic materials and their properties Mechanical testing Mechanical properties of metals and alloys Sintered materials Lubricants Friction and wear Casting alloys and foundry data Engineering ceramics and refractory materials Fuels Heat treatment Metal cutting and forming Corrosion Electroplating and metal finishing Welding Soldering and brazing Vapour deposited coatings and thermal spraying Superplasticity Metal-matrix composites Non-conventional and emerging metallic minerals modelling and simulation supporting technologies for the processing of metals and alloys.

Abstract: An experiment has been designed to check a previously proposed equivalence of the effects of changes in strain rate and in temperature upon the stress‐strain relation in metals. It is found that this equivalence is valid for the typical steels investigated. The behavior of these steels at very high rates of deformation may, therefore, be obtained by tests at moderate rates of deformation performed at low temperatures. The results of such tests are described. Aside from changing the isothermal stress‐strain relation, an increase of strain rate tends to change the conditions from isothermal to adiabatic. It is found that at low temperatures, the adiabatic stress‐strain relation in the plastic range is radically different from the isothermal, having an initial negative rather than a positive slope. This initial negative slope renders unstable homogeneous plastic deformation.

Abstract: An analysis is made of the normal tractions acting on grain boundaries in a solid with a perfectly regular hexagonal grain structure deforming via diffusional creep. Restrictions are placed on the allowable diffusion paths solely by requiring that the normal stresses on opposite sides of a grain boundary be identical. It is shown that a model for grain switching recently proposed by Ashby and Verrall is inconsistent with this requirement. The problem of grain boundary diffusional flow is solved by treating grains as elastically rigid, and the solution, which agrees with earlier results in the limit of small strains, provides an explicit description of the equilibrium boundary traction distribution during steady state flow. This solution suggests that grain neighbor switching can occur in single phase materials only when grain boundary migration occurs. In two phase materials it is expected that diffusional creep will give rise to a grain switching process in which a grain of one phase wedges between and separates two grains of the other phase.

Abstract: Current models describing dislocations by-passing particles by climb do not satisfactorily account for the creep deformation of alloys containing high particle volume fractions such as nickel-base superalloys. An alternative approach involving cooperative climb over groups of particles leads to a resistance to deformation, rather than a threshold stress, that is insensitive to the particle size but which depends strongly on applied stress. Detailed calculations have been carried out for the nickel-base superalloy IN738LC and these are in close agreement with measurements of the friction stress. The theoretical conclusions are generally compatible with the creep behaviour of nickel-base superalloys.