Materials systems for low shrinkage metal skeletons in three dimensional printing

Three Dimensional Printing (3DP) is a process for the rapid fabrication of three dimensional parts directly from computer models. A solid object is created by printing a sequence of two dimensional layers. The creation of each layer involves the spreading of a thin layer of powdered material followed by the selective joining of powder in the layer by printing binder material. In the current process, metal skeletons are produced by printing a polymeric binder into stainless steel powder. Subsequent heat treatments de-bind and lightly sinter the printed skeletons which are then infiltrated with a molten metal alloy to make a final part. The growth of the necks during the sintering step causes a shrinkage of the part which, in general, is not uniform and has a certain amount of error associated with it. With this method, the magnitude of the shrinkage is 1.5% and the uncertainty is 0.2%. The 3DP process can compensate for predicted shrinkage by beginning with a larger part. However, the uncertainty in the amount of shrinkage causes loss of dimensional control of the parts. Therefore, there is a need to improve the dimensional control of metal parts produced by 3D Printing. The current work investigates the reduction of the average shrinkage by eliminating the sintering in the base powder. The concept under investigation is an alternative method of forming the skeleton where metallic necks are formed from material printed in a binder slurry. The material in the binder is a <3[mu]m fine slurry of a 1) metal and activator, 2) nickel braze, or 3) a eutectic metalloid. In category 1), one promising binder slurry for tungsten skeletons is 1[mu]m W with 0.5wt% lpmNi, which achieved 68.5±6.3% density and 26.6±2.3% linear shrinkage at 1200°C, 1 hour. Two <5[mu]m powders, W with wt%:13Ni,4.9Fe,3Co and W with wt%:13Ni,4.9Fe,3Co,0.06B, were more than 90% dense under the same conditions. In category 2), a 66[mu]m Mo skeleton with a 9wt% Nickel Phosphorus binder (wt%: 11P) had a linear shrinkage of 0.02+0.18 and a 31 [mu]m Mo skeleton with this binder shrank 0.30±0.17%, both at 1025°C for 1 hour. These shrinkages are comparable to those of a reference AgNO3 salt binder (0.35±0.01% and 0.14±0.03%, respectively), though the uncertainties are much higher. In category 3), AuGe was selected from a set of criteria for experiments. Investigation of a 66[mu]m Mo skeleton with 2vol% 30-100[mu]m AuGe fired at 700°C for 1 hour show that fracture occurs at the Mo and Mo-AuGe interface rather than in the necks themselves. This is due to Ge diffusion into the Mo powder.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• Buttz, Diana (Diana Christine), 1978-

Advisor dc:contributor.advisor

• Emanuel M. Sachs.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8913

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8913