Titanium alloy powder preparation for selective laser sintering

Abstract

Selective laser sintering (SLS) is a solid freeform fabrication process whereby a part is built layerwise by scanning a powder bed. The processability of metal powder varies depending on the state of the powder prior to SLS. A powder thermal pre‐treatment was developed which involved degassing the powder at an elevated temperature in a vacuum. Without powder thermal pre‐treatment, the powder may flow poorly and may “ball” or form molten clumps during the laser exposure rather than wetting into the present and previous layer. These effects result in SLS parts with poor surface finish, mechanical properties and density. The purpose of this study was to identify for titanium alloy powder the mechanisms responsible for the improvements obtained after powder thermal pre‐treatment and to optimize the thermal excursion.

Physical Aspects of Process Control in Selective Laser Sintering of Metals

“…As-received powders are known to harbor moisture, organics, adsorbed gases, oxide and nitride films on particle surfaces depending on the production method and shelf life. [20] These contaminants not only inhibit successful wetting and densification of the melted powder but also degrade mechanical properties of the consolidated product. Therefore, processing under high vacuum (<10 ±5 Torr) or under ultra high purity inert environments is necessary for successful direct SLS of high performance metals.…”

Selective laser sintering: A qualitative and objective approach

“…25 Prior to performing the SLS process, the sinterability of powders can be improved (cleaned or degassed) by thermal pre-treatment. 58 …”

Powder Densification Maps in Selective Laser Sintering

“…The density achieved for a particular set of processing conditions was measured by gas pycnometry or Archimedes' method and compared to the value predicted by the HIP maps. Powder was placed in borosilicate glass, evacuated to at least 5x10 ±5 torr, degassed at 350C for a minimum of 24 h to remove the majority of surface adsorbed gases as well as some species dissolved within the powder, [11] and the glass tube was sealed prior to HIP. The glass capsules were processed in an ABB QIH-3 HIP system equipped with a graphite heating element.…”