Massachusetts Institute of Technology

Samuel M Allen

Emanuel Michael Sachs

Adam M Lorenz

Steven P Michaels

Helen J Yoo

Constantinos Hadjiloucas

Brian D Kernan

A steel powder metal skeleton is infiltrated with an infiltrant composition similar to the skeleton, with an additional agent that depresses the melting point of the infiltrant relative to the skeleton. Infiltration is driven primarily by capillary pressure. The powder and infiltrant compositions differ primarily only in a higher concentration of a melting point depressant agent 'MPD' in the infiltrant. Carbon (C) and silicon (Si) and several other elements can be elements in an MPD, either alone or in combination. Certain steel target compositions are such that a complementary infiltrant, and skeleton can be chosen such that a skeleton will remain solid at an infiltration temperature at which the infiltrant can be melted and fully infiltrated, and further where there is a persistent two phase field, with a liquid phase that is large enough (greater than 7% vol, and typically between 20 and 40 vol %) so that flow can be maintained without choke off from diffusional solidification. The solid and the liquid phases remaining after any diffusional solidification have different compositions, with a bulk composition of the target. Typically the difference is slight, and the full part is substantially homogeneous. Heat treating, such as austenitizing, quenching, or slow cooling and tempering, can improve homogeneity and mechanical properties. The MPD can have a relatively high diffusivity and solubility in the skeleton. Methods of designing systems of target, skeleton and infiltrant compositions and infiltration temperature are disclosed.

Infiltrating a powder metal skeleton by a similar alloy with depressed melting point exploiting a persistent liquid phase at equilibrium, suitable for fabricating steel parts

An infiltrant is used to fill a metal powder skeleton. The infiltrant is similar in composition to the base powder, but contains a melting point depressant. The infiltrant will quickly fill the powder skeleton, then as the melting point depressant diffuses into the base powder, the liquid will undergo solidification and the material will eventually homogenize. This process allows more accurate control of dimensions in large parts with uniform or homogeneous microstructure or bulk properties.

Infiltration of a powder metal skeleton of similar materials using melting point depressant

In infiltrating a porous metal skeleton an infiltrant composition is used similar to that of the powder skeleton, but with the addition of a melting point depressant. The infiltrant quickly fills the skeleton. As the melting point depressant diffuses into the base powder, the liquid may undergo diffusional solidification and the material eventually homogenizes. Maintaining the infiltrant at a liquidus composition for the infiltration temperature typically ensures that the bulk composition or properties will remain uniform throughout the part, particularly in the direction of infiltration. Success of such an infiltration is enhanced by effective means of maintaining the molten infiltrant at a liquidus composition. It is also beneficial, in some cases, for the time scale of the infiltration to be much faster than the time scale of the diffusion of the melting point depressant and the subsequent solidification and homogenization. The relative rates of infiltration and diffusion/solidification rate are significantly impacted by the choice of materials system. Other factors also influence these rates. They include: selection of powder size (diameter), shape, surface roughness, and size distribution, feeding liquid from different locations, liquid feeder channels, smoothing of the part surface with fine powder and affecting infiltrant fluid properties. Various material systems are also disclosed, as are methods of designing a process of infiltrating a part, including binary and ternary and higher component systems. Homogeneous composition may be achieved using these techniques, particularly along the direction of infiltration.

Techniques for infiltration of a powder metal skeleton by a similar alloy with melting point depressed

Parts made from powder use a material that originates from a salt to bind powder particles together. The salt may be provided dissolved in a solution, as molten salt, or as a dry powder. The figure is an electron micrograph of a cross section of a silver nitrate bound product with a skeleton of steel powder.

Metal and ceramic containing parts produced from powder using binders derived from salt

Processes for providing enhanced thermal properties of tooling, particularly metal and metal/ceramic molds, made by solid free form fabrication techniques, such as the three dimensional printing process, and the tooling made by these processes are disclosed. The methods of enhancing thermal properties include incorporating integral contour coolant channels into the mold, adding surface textures to the coolant channels, creating high thermal conductivity paths between the surfaces and the coolant channels, and creating low thermal inertia regions in the mold.

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Jamaica Plain, MA, United States of America

Samuel M Allen