Densification of a powder-metal skeleton by transient liquid-phase infiltration

Abstract

Transient liquid-phase infiltration (TLI) is a new method for densifying a powder-metal skeleton that produces a final part of homogeneous composition without significant dimensional change, offering advantages over traditional infiltration and full-density sintering. Fabrication of direct metal parts with complex geometry is possible using TLI in conjunction with solid freeform fabrication (SFF) processes such as three-dimensional printing, which produce net-shape powder-metal skeletons directly from computer-aided design models. The TLI method uses an infiltrant material similar in composition to the skeleton, but also containing a melting-point depressant (MPD), which allows the liquid metal to fill the skeleton void space and later facilitates homogenization. The materials requirements for such a system are discussed, and four experimental material systems were developed with final compositions of approximately Ni-40 wt pct Cu, Ni-4 wt pct Si, Fe-3 wt pct Si, and Fe-12 wt pct Cr-1 wt pct C, with copper, silicon, and carbon serving as the MPDs. Infiltration techniques include gating the introduction of liquid, saturating the melt to prevent erosion, and controlling variations in bulk composition along the infiltration path. Infiltration lengths exceeded 200 mm in the two nickel systems and exceeded 100 mm in the two iron systems. After infiltration, various heat treatments were conducted and mechanical properties were tested, including the tensile, hardness, and impact strength.

Liquid-phase Infiltration of Thermal Sintered Skeletons by Low-temperature Gold Eutectic Alloys

“…From their interpretation and by extrapolation from similar processes, like standard infiltration and TLI, the dominating material properties influencing the product quality will be inferred. Small pores have been found in most samples and may be due to close porosity or to insufficient capillary infiltration or freeze off [8] [9], if present. Freeze off is caused by diffusional solidification of the infiltrant, resulting into early choke-off of the infiltrant supply.…”

“…The infiltration of a molten metal into a metal powder matrix is driven by capillary force, which mainly depends on the relative surface tension between infiltrant and powder surface and on the skeleton voids size [7] [8]. This relative surface tension also depends on the powder surface type (surface texture, presence of oxides, thermal treatments, etc.)…”

“…In addition to a limited material choice, parts are heterogeneous; -Transient Liquid-phase Infiltration (TLI), capillary induced infiltration of the powder skeleton using an infiltrant similar to the powder material containing a melting point depressant, usually some common alloying element. This technique facilitates homogenization after the liquid metal fills the void space; This work is derived from current research on TLI [8,9], which has shown the benefits and drawbacks of element diffusion between phases, and on Three Dimensional Printing [10] The beneficial properties of eutectics are well known, but only a few literature can be found on infiltration by eutectic alloys, particularly regarding gold [13]. The process described in Figure 1 is based on capillary infiltration of the skeleton made of a pure base material by an infiltrant alloy with the composition of a lowtemperature eutectic [14].…”

Additive Manufacturing: Post Processing Methods and Challenges

“…Binder jetting or three-dimensional printing (3DP) process employs a powder-based material and a liquid based binder that acts as an adhesive between the consecutively laid layers. For fabrication of homogenous parts, larger particles having bigger pores and lower surface per unit volume are employed [36]. The porosity levels of this technique are higher as compared to SLS or SLM.…”

Inspeção por digitalização em aplicações de prototipagem rapida na medicina

“…Figura 5.53 -Densificação de um esqueleto de substrato metálico por fase líquida transiente de infiltração (a) diagrama de fase de equilíbrio genérica com a nomenclatura dos componentes do sistema TLI para uma temperatura de infiltração, Ti e (b) ilustração esquemática dos principais estágios da fase líquida transiente de infiltração(Sachs et al 2004b) …”