Lars B Ekbom

Tungsten heavy alloy: deformation texture and recrystallization of tungsten particles

Abstract Sintered tungsten heavy alloy (90W, 7Ni, 3Fe) has been deformed in different ways and heat treated at 800–1100 °C. The texture and dislocation density of the tungsten particles were determined as well as the effect of the heat treatment on recovery and recrystallization. A 〈1 1 0〉 deformation texture of the tungsten particles was found using X-ray diffraction. Formation of dislocation cells and subgrains was found to occur during the heat treatment as well as recrystallization by grain boundary migration. A model for the recrystallization of particles by grain boundary motion in a deformed heavy alloy is presented.

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.

On solidification shrinkage of copper–lead and copper–tin–lead alloys

Abstract Solidification shrinkage is an important concept in achieving sound castings. In the present work solidification shrinkage was studied in copper–lead and copper–lead–tin alloys. A series of solidification experiments was performed under different cooling rates using a dilatometer which was developed for melting and solidification purposes. The volume change was measured during primary solidification and the monotectic reaction. In order to explain the volume-changing results, the sample macrostructures were studied to evaluate gas and shrinkage cavities which were formed during the solidification. Furthermore, the volume fraction of the primary phase during solidification was evaluated in the samples that were quenched from different temperatures below the liquidus temperature. A shrinkage model was used to explain the volume changes during solidification.

The distribution and influence of impurities in tungsten heavy metals

Abstract Tungsten heavy metals are particle composites produced by liquid phase sintering. The ductility of the alloy is sensitive to impurities and heat treatments, some impurities being concentrated in the interphase boundaries. Such elements include phosphorous and sulphur but also oxides of aluminium and silicon. Even small amounts of oxygen, carbon and hydrogen can also be deleterious. Ion microprobe analysis, SIMS, has been used to determine the distribution of alloying elements and impurities. The relationship between the content of different elements in the particles and in the matrix has also been determined.

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 ...