The properties of alloy parts can be adjusted conveniently if alloy element powders are used for manufacturing alloy parts by indirect selective laser sintering, but no research has been reported on this so far. In this paper several composite powders have been obtained by blending pure Fe, Cu and graphite powders, which have been used to produce green parts by indirect selective laser sintering. Cu infiltrated Fe–Cu–C alloy was manufactured after green parts had been degreased, high temperature sintered and infiltrated. Contents of composite powders, post-processing of green parts, microstructures and mechanical property of alloys were investigated. The results indicate that: Cu and C can diffuse into γ-Fe when green parts are being sintered at high temperature; the microstructures of alloy are composed of a large quantity of eutectoid structures mixtures of Fe–C and Fe–Cu at room temperature besides a coarse structure; the eutectoid structure varies regionally owing to the inhomogeneous concentr...

Investigation into manufacturing Fe–Cu–C alloy parts through indirect selective laser sintering

In ferrous powder metallurgy, copper and graphite are used as common alloying elements. Copper melts at low temperature compared to iron and forms liquid which promote interparticle bond formation. However, it also results in compact swelling. To negate this, graphite is used as an additive. This study examines the influence of copper and graphite addition on the densification, dimensional changes, and mechanical properties of iron compacts sintered at 1120°C. These properties have been correlated with the microstructure.

Effect of copper and graphite addition on sinterability of iron

The effect of alloying additions, such as copper, carbon, and molybdenum with carbonyl iron powder, on the densification behavior, microstructural evolution, and mechanical properties of spark plasma sintered (SPS) compacts have been investigated in this work. The sintering temperature, pressure, and time during SPS were 1120°C, 30 MPa, and 5 min, respectively. Fe–2Cu–0.8C–0.6Mo was found to exhibit the highest density, hardness, and also tensile strength among all the compositions attempted. The microstructural examination of fractured surfaces of the sintered samples revealed the evidence of a mixed mode of fracture in all the alloy compositions.

Microstructural Evolution of Iron Based Alloys Produced by Spark Plasma Sintering Method

Fabrication of structures with fine features has been a challenge and has required sophisticated equipment. In the current work, the use of a cost-effective method, PIM (powder injection molding) was evaluated to fabricate structures with fine features such as sharp edges with dimension in microns. The selected component consisted of micro features of two steps having a cross-section dimension of 0.6×0.07 mm and 0.6×0.06 mm. In order to achieve good mechanical properties coupled with wear resistance, an M2 tool steel material was selected. The mould tip region with two-step micro features was fabricated using into multi-mould pieces to ensure the edge sharpness of the two-step micro features in the mould cavity and to create an air vent to release the entrapped gas at the moulding stage. The moulded samples were first debound and then sintered at different temperatures. The results of actual sintering at 1,244, 1,252, 1,260, and 1,280°C were analyzed, since transition to liquid phase sintering occurs in this region. Visual observation, microstructural analysis and hardness distribution were carried out on the samples sintering at different temperatures. Incomplete sintering occurred at 1,244°C while at 1,252°C distortion of the samples was identified. Sintering at 1,260°C yielded parts with good integrity and strength and a further increase of sintering temperature deteriorated the characteristics. Five samples were chosen randomly from three batches of 100 pieces for a pilot production scale. Their dimensional flatness was measured and the result showed that flatness less than ±0.3% can be achieved under optimized sintering temperature of 1,260°C ± 0.3°C. This means that the M2 tool steel component with micro features can be possibly produced by PIM process in mass production.

Studies on the fabrication of tool steel components with micro-features by PIM

Carbon – Copper – Iron

The driving force for sintering in the Fe-Cu-C system induced by the gap in carbon concentration between iron particles, and the driving force arising from differences in surface curvature, have been evaluated quantitatively. It is shown that the former is at least one order of magnitude larger than the surface curvature effect. Under the influence of the driving force of carbon, a semipermeable layer of liquid capper forms which prevents carbon diffusion, but which allows iron to be transported between particles, thereby enhancing sintering. This pehnomenon appears to control copper-growth of the ferrous compact. Neck formation in a columnar structure is shown to be an example of liquid boundary migration in which particle coalescence occurs.

H. Kuroki

Papers

Solution-reprecipitation mechanism in Fe-Cu-C during liquid phase sintering