Anders Eliasson

Penetration of tungsten grain boundaries by a liquid W-Ni-Fe matrix

Abstract The penetration of saturated Ni-Fe melts into grain boundaries of pure tungsten has been experimentally analysed. The penetration rate was much faster in cold-worked tungsten than in annealed samples. A new model where the driving force for flow of the penetrating liquid was combined by diffusion has been derived. The theory is compared with experimental data.

Liquid Ni–Fe penetration and recrystallisation in tungsten

Melt penetration in grain boundaries of solid tungsten has been investigated. Solid tungsten rods have been exposed to a nickel-iron melt saturated with tungsten and the penetration depth and the s ...

Liquid phase sintering of tungsten composites in space: Results of tests performed in Texus

Abstract Tungsten-nickel-iron composites are commersially fabricated from powders by liquid phase sintering. They consist of almost spherical tungsten particles in a matrix of nickel-iron-tungsten. A way to contribute to the understanding of the sintering mechanism and the mechanical properties is to study composites with a low amount of tungsten particles. Depending on the great difference in density between the particles and the matrix, this can only be done under microgravity. A primary sintering test of the tungsten composite was done in space using the Texus 10 modul. Prealloys were fabricated from metal powder mixtures, which were hot isostatic pressed. Liquid phase sintering of the two tungsten composites under microgravity has shown that the particles are evenly distributed and that no segregation occured due to convection. Despite an uneven distribution of the particles in the preformed specimens and the short melting period the patricle distribution has become even. Compared to short time sintering tests made on four alloys in the laboratory, the growth and separation of the particles was fast.

Tungsten grain separation during initial stage of liquid phase sintering

Abstract The initial stage, the first few seconds of liquid phase sintering has been investigated in experiments using a tungsten heavy alloy with low tungsten content. The heavy alloy has been melted in a temperature gradient for short periods, ∼9 s in an ellipsoid mirror furnace. During the liquid phase sintering at about 1470°C, a penetration followed by a remarkably rapid separation and dispersion of the tungsten grains by the molten matrix occur. The suggested explanation for this grain separation and dispersion is based on the effect of composition gradients in the liquid matrix and a theory based on interagglomerate melt swelling due to a Kirkendall effect.

Prediction of particle size for water atomised metal powders: parameter study

Abstract This work aims to investigate how some significant atomising parameters influence the mass median particle size d50 of water atomised metal powders. More specifically, these were water pressure, melt flowrate, water jet angle, liquid metal viscosity and surface tension. Existing models for the prediction of d50 during water atomisation were reviewed. The selected models were fitted and compared with atomising experiments of liquid iron containing 0·5–4·4%C. Experimental results and model calculations were used in a parameter study to investigate how the different parameters influenced d50. The effect on d50 was large for the water pressure, medium for the viscosity and low for the melt flowrate and surface tension. Model calculations indicate that the jet angle has a large effect on d50, which should be verified by additional studies. The model proposed by Bergquist (B. Bergquist: Powder Metall., 1999, 42, 331–343) showed the best agreement with the current experimental data.

Flow pattern in ingot during mould filling and its impact on inclusion removal

Abstract A two-dimensional non-steady state computational fluid dynamic model was employed to gain a basic understanding of the flow in the ingot during casting. The surface velocity was found to be affected by the inlet angle and was found to vary with the casting level. The information of surface velocity was related to the probability of the inclusion removal. Water model experiments were also conducted to help the understanding. The model calculation revealed the same trends as the results of water model experiments. Both computational fluid dynamic data and the physical modelling showed that the inlet angle of 5° currently used in the industry was a good alternative regarding inclusion removal. The present work suggests strongly that the melting shop should try to obtain a liquid or semiliquid film at as early stage as possible in ingot casting.

On the dendritic growth and microsegregation in Ni-base superalloys IN718, IN625 and IN939

Directional Solidification and Quenching (DSQ) has been used to analyse the solidification, segregation and precipitation behaviour of the Ni-base alloys IN718, IN625 and IN939. The microsegregation in the primary solidified gamma-phase was analysed by Energy Dispersive Spectroscopy (EDS) and were mainly found to be Nb for alloy IN718 and Ti for alloy IN939. The microsegregation behaviour were analysed by numerical back diffusion models and it was found that the diffusion rate in the samples was higher than expected from the theory. A suggested explanation was that this was an effect of the formation of lattice defects during the solidification process. The coarsening process that occurs during the further cooling of the samples is proved to be by the mechanism of back diffusion i.e. the smaller secondary dendrite arms grow together with the thicker ones into a plate.

Liquid phase sintering of tungsten composites under microgravity: Influence of liquid/particle surface energy

Tungsten-nickel-iron heavy metals are fabricated from powders by liquid phase sintering. A study of the sintering mechanism of heavy metals with a low amount of tungsten particles can, depending on ...