Natural Communication: Oxide Dispersion Enhancement for High Performance 3D Printing of Pure Copper

The laser additive manufacturing technology of pure copper (Cu) with complex geometric shapes has opened up vast opportunities for the development of microelectronic and telecommunications functional devices. However, laser forming of high-density pure copper remains a challenge.

Recently, the forefront of additive manufacturing technology has noticed a joint report by the University of Hong Kong, The Chinese University of Hong Kong, and the University of Southern California on a simple method of oxide dispersion strengthening (ODS). The article was published in the internationally renowned journal Nature Communications, titled "Oxide dispersion enabled laser additive manufacturing of high-resolution copper".

This method starts with oxygen assisted atomization, introducing ultrafine copper oxide nanoparticles into pure Cu powder raw materials. These nanoscale dispersants not only improve laser absorption and melt viscosity, but also promote dynamic wetting behavior. ODS Cu can achieve a yield strength of approximately 450 MPa and an elongation of about 12%, while maintaining high conductivity. And the research team also printed a microstructured terahertz antenna using ODS Cu material, which increased the signal strength by 2.5 times compared to traditional 3D printed pure copper antennas.

The research team first introduced the ODS method of introducing oxide nanoparticles into Cu powder by precisely controlling the oxide content, and observed the internal and external morphology of the prepared powder.

Preparation process and internal and external morphology characteristics of ODS powder

Afterwards, the research team observed the microstructure of the printed state of ODS Cu, and the results showed that there were many equiaxed grains ranging from hundreds of nanometers to tens of micrometers in the internal structure of ODS Cu. Its average grain size is approximately 4 microns, which is half of the average grain size (-8 microns) printed using pure Cu and copper.

Metallographic structure, EBSD and TEM microstructure of ODS CU printed state

In order to achieve finer printing features of materials through PBF-LB technology, the melt pool should be controlled as narrow as possible. Traditional methods typically achieve this by reducing laser energy input. However, in the process of pure copper printing, low energy input often leads to the formation of various printing defects, including holes, cracks, unmelted powder, and poor adhesion to the front layer. 

Therefore, it is necessary to find a suitable energy input to ensure the density and surface quality of pure copper printing. Based on this, the research team compared the morphology characteristics of the melt pool side printed by ODS CU and pure CU, and the results showed that under the same energy input, ODS Cu samples have a narrower melt pool structure, finer melt channels, and better surface quality.

Comparison of Molten Pool Morphology between ODS CU and Traditional CU Printing and Observation of Molten Paths

At the same time, the research team also conducted theoretical simulations on the high-density printing melt pool of ODS CU, including melt pool depth, liquid flow rate, thermophysical properties, laser absorption rate, viscosity and contact angle, as well as the dynamic wetting behavior of ODS Cu. The results indicate that the key factors for high-density molding of ODS CU are narrower melt pool, more stable melt pool, and less powder adhesion/sintering during the printing process.

The research team simulated the depth of the melt pool, liquid flow rate, and thermophysical properties of ODS printing

Afterwards, the research team compared the mechanical and electrical properties of ODS CU and pure CU printed state. The thermal conductivity of pure copper is approximately 390W/m · K (about 96% IACS). The conductivity and thermal conductivity of the ODS Cu sample were measured to be -320W/m · K (-80% IACS), respectively. Compared with the results printed using traditional copper powder, the high conductivity of ODS Cu is only slightly sacrificed, mainly due to the extremely low solubility of oxygen in copper.

Mechanical and Electrical Properties of ODS CU and Pure CU Printed States

Finally, the research team used ODSCu to print terahertz emission array antennas as an application case, and the results showed that the lattice of ODS Cu had a yield strength three times higher than that of pure Cu lattice, while the weight was reduced by 30%. This indicates that ODS Cu is more advantageous for manufacturing thin-walled structures of different heights without the need for mechanical processing or post-treatment, and can eliminate the high cost and defect rate caused by traditional methods.

ODS Cu lattice exhibits three times higher yield strength than pure Cu lattice, while reducing weight by 30%

In summary, the research team has achieved high-density molding in the field of pure copper laser additive manufacturing by using an innovative oxide dispersion strengthening (ODS) method. Significantly improved the stability of the melt pool and material mechanical properties, while maintaining high conductivity of 80% IACS. The signal strength of the microstructure terahertz antenna printed based on this technology has increased by 2.5 times, verifying its practicality in precision functional devices. This work provides a new idea for laser forming of high-strength and high conductivity copper based materials, which is conducive to promoting the low-cost and high-performance manufacturing of complex devices in the fields of microelectronics and communication.

Source: Yangtze River Delta Laser Alliance