Densification behaviour of pure copper processed through cold pressing and binder jetting under different atmospheres

Abstract

Purpose Binder jetting is a promising route to produce complex copper components for electronic/thermal applications. This paper aims to lay a framework for determining the effects of sintering parameters on the final microstructure of copper parts fabricated through binder jetting. Design/methodology/approach The knowledge gained from well-established powder metallurgy processes was leveraged to study the densification behaviour of a fine high-purity copper powder (D50 of 3.4 µm) processed via binder jetting, by performing dilatometry and microstructural characterization. The effects of sintering parameters on densification of samples obtained with a commercial water-based binder were also explored. Findings Sintering started at lower temperature in cold-pressed (∼680 °C) than in binder jetted parts (∼900 °C), because the strain energy introduced by powder compression reduces the sintering activation energy. Vacuum sintering promoted pore closure, resulting in greater and more uniform densification than sintering in argon, as argon pressure stabilizes the residual porosity. About 6.9% residual porosity was obtained with air sintering in the presence of graphite, promoting solid-state diffusion by copper oxide reduction. Originality/value This paper reports the first systematic characterization of the thermal events occurring during solid-state sintering of high-purity copper under different atmospheres. The results can be used to optimize the sintering parameters for the manufacturing of complex copper components through binder jetting.

Additive Manufacturing of Pure Copper: Technologies and Applications

“…Feedstock powders with an average size exceeding 20 μm are normally preferred in binder jetting because their relatively low tendency to agglomerate facilitates the spreading operation [25]. However, the development of vibrating devices for powder sieving and dispensing has enabled the use of finer powders with an average size lower than 5 μm [26,27] for improved resolution and densification. Bimodal mixtures also showed the potential to improve powder flowability and reduce part shrinkage upon sintering, because particles with different sizes can tightly pack and result in high green part density [28].…”

“…Both the surface oxide layer and the large interparticle distance hamper neck formation and growth between neighboring powder particles by solid-state diffusion [25,29]. In addition, carbon residues may result from incomplete combustion of the polymeric binder during the debinding stage [27], and uneven sintering may occur between the outer and the core regions of the parts due to temperature gradients along the material thickness. Indeed, the rapid stiffening of the outer zones exposed to a higher temperature may hinder inward shrinkage, thus leaving a central volume with a high residual porosity [27].…”

“…In addition, carbon residues may result from incomplete combustion of the polymeric binder during the debinding stage [27], and uneven sintering may occur between the outer and the core regions of the parts due to temperature gradients along the material thickness. Indeed, the rapid stiffening of the outer zones exposed to a higher temperature may hinder inward shrinkage, thus leaving a central volume with a high residual porosity [27]. Therefore, the sintering parameters need to be carefully adjusted in terms of sintering atmosphere, heating ramp, peak temperature, and sintering time to minimize the residual porosity and carbon impurities, which adversely affect the mechanical, thermal, and electrical properties of the final parts [30,31].…”

“…In binder jetting, the powder in the bed is further subjected to oxidation during the curing stage [27], which is normally carried out in the air. In the case of copper, oxidation is additionally promoted when a water-based binder is employed, as copper is highly sensitive to moisture.…”

Effect of Process Parameters on the Performance of Drop-On-Demand 3D Inkjet Printing: Geometrical-Based Modeling and Experimental Validation

“…As of today, AM includes seven main technologies which can be divided into three subcategories, including material extrusion, powder bed fusion and material jetting [14,15]. A subsection of the latter category is inkjet printing (IJP), an advanced technology based on conventional inkjet printing which is found in many households and offices.…”