Dinda, G. P., Dasgupta, A. K., Bhattacharya, S., Natu, H., Dutta, B., and Mazumder, J.
Metallurgical and Materials Transactions A. May 2013, Vol. 44 Issue 5, p2233, 10 p.
Alloys, Rapid prototyping, Transmission electron microscopes, and Computer-aided design
Direct metal deposition (DMD) technology is a laser-aided rapid prototyping method that can be used to fabricate near net shape components from their CAD files. In the present study, a series of Al-Si samples have been deposited by DMD in order to optimize the laser deposition parameters to produce high quality deposit with minimum porosity and maximum deposition rate. This paper presents the microstructural evolution of the as-deposited Al 4047 sample produced with optimized process parameters. Optical, scanning, and transmission electron microscopes have been employed to characterize the microstructure of the deposit. The electron backscattered diffraction method was used to investigate the grain size distribution, grain boundary misorientation, and texture of the deposits. Metallographic investigation revealed that the microstructural morphology strongly varies with the location of the deposit. The layer boundaries consist of equiaxed Si particles distributed in the Al matrix. However, a systematic transition from columnar Al dendrites to equiaxed dendrites has been observed in each layer. The observed variation of the microstructure was correlated with the thermal history and local cooling rate of the melt pool.
Kernan, Brian D., Sachs, Emanuel M., Allen, Samuel M., Lorenz, Adam, Sachs, Christoph, Raffenbeul, Lukas, and Pettavino, Alberto
Metallurgical and Materials Transactions A. Oct 2005, Vol. 36 Issue 10, p2815, 13 p.
The direct manufacture of metal parts by rapid prototyping (RP) often involves using a metal powder. Densification of the powder can be done either by sintering or infiltration. Infiltration avoids the shrinkage and distortion that typically accompanies sintering. However, in steels, the use of copper or bronze infiltrants limits the usefulness of parts because of the nonhomogeneous structure and properties. In this work, a conventional tool steel alloy has been made via homogeneous steel infiltration (HSI), a gated infiltration process that uses as the infiltrant a steel alloy with a lower melting point than the base powder. The infiltrant liquid uses carbon or silicon as a melting point depressant (MPD). Freeze-off of the steel infiltrant is avoided by infiltrating at a temperature at which some liquid is stable at chemical equilibrium. Examples of successful infiltrations using D2 tool steel as a target composition are shown. Mechanical properties (hardness and impact strength) following various heat treatments of the infiltrated D2 are compared with conventional wrought D2 tool steel and found to be very similar. The HSI is believed to be suitable to a wide variety of tool steels and stainless steels. Further, the process is applicable to the postprocessing of any suitable steel skeleton made by RP, as well as other powder metallurgy processes, such as metal injection molding.