In his BEng Individual Project for 2020-21, Jacob Round discovers the potential benefits of Co-Sintering of Metal and Ceramic materials.
This research explores sintering behaviours and key aspects of the sintering process and technologies that may enable or already utilise co-sintering.
3D Matters Limited in collaboration with Aston University’s College of Engineering and Physical Sciences investigated the potential for co-sintering two materials with different properties and explore the future product development opportunities of multi-material 3D structures. As an example manufacturing components with integrated cabling could be advantageous.
Currently the main obstacle is the difficulty of co-sintering. This is the process of sintering two materials together as a component. Commonly this is with one material being a metal and the other a ceramic. This become possible if a second material, ideally a metal, can be present during the sintering of the first material.
Machining and manufacture come at great cost in time and money and require specialists. Additive manufacture (AM) or 3D printing (3DP) has been bringing manufacturing to households and industry alike. 3DP has been developed to use a variety of materials from plastics all the way through to metal. In addition ceramic materials can be 3D printed.
One way metals or ceramics are printed is by mixing the material as a fine powder into a plastic filament so it can be printed in the same way plastics are. Once the shape is formed the plastic is melted or dissolved using solvents. The part is then sintered to improve mechanical properties. Sintering is a heat treatment process that upon heating starts densification making the material stronger than it was previously. This process is the same as firing clay in a kiln.
Theoretical simulation was conducted using Ansys Workbench to explore variables on the sintering process. The intention to see if it is possible to demonstrate co-sintering between two materials that have different properties.
The simulation approach aimed at the key factors that can influence the likelihood of co-sintering. This can be modelled on software. The three main factors considered were heat rate, metal insert selection (ceramic will remain the same) and geometry.
All experiments used alumina at a 96% purity. Only consideration was given to the sintering of the ceramic with a conductor present in the furnace instead of requiring sintering both materials. This may be a starting point for future work.
Using the material properties of tungsten, copper, SS316 and alumina a set of experiments were designed to look at all the combinations as efficiently as possible. In addition, test pieces where the whole of the metal insert is encased with a ceramic were used. The theory being tested; that an increased layer of ceramic to protect the metal temperature from heating will improve the chances of co-sintering and would yield more promising results.
The heat rate was applied as heat flux to every exposed surface to simulate a constant heat load from a furnace. This was done using a thermal transient study in Ansys Workbench version 2020 R2. Temperature was recorded using various temperature probes placed around the part. Data was collected from all of these key points at 300 second intervals for the duration of the sinter. Each simulation started with the 54000 (s) duration to be in the same region of time as the material sinter times. This varied based on heat flux applied. Any simulation which took longer than the proposed time to sinter had simulation length increased proportionally to keep each time step at 300 seconds for however long was required.
Two key criteria were used to determine the success of these experiments. First metal insert melting temperature. Secondly the sinter temperature of the ceramic. The success of co-sintering will be assessed as follows: any metal that melts before the ceramic reaches sinter temperature will be considered a failure. If not, co-sintered consideration was given to the difference between the two key temperatures to judge how close co-sintering was.
In conclusion, the research explored the sintering process and its variables including how 3D printing adds a level of complexity to the sinter process. Current technologies that utilise co-sintering and their approaches to this problem were also considered.
By simulation, using Ansys Workbench three key factors that will have an impact on the ability to co-sinter; heat rate, material and part shape all have some bearing on the likelihood of co-sintering. Currently only metals with properties that can survive the high sinter temperatures are suitable for co-sintering.
No evidence was found that supported the idea that co-sintering is possible by part design alone. With shape and heat rate influencing the likelihood of co-sintering, but not enough to counter the differences in material sintering temperature.
Data also showed trends that favoured the chances of co-sintering. Lower thermal conductivity materials had an increased chance of co-sintering. It also showed that the metal insert did improve temperature distribution through the part and speed up sintering but that this did not favour co-sintering. Smaller shapes were better than larger shapes due to more concentrated heat flux per unit area. High heat rates were superior to lower heat rates for co-sintering. Equally it was also proven that using ceramic as an insulator did not work as well as expected.
Of all of the experiments which were not co-sintered the data did show favouring circumstances for each factor. However, these differences were only marginal improvements and may offer future points of discussion but do not show any likelihood for co-sintering for 316L and Copper at the moment.
Moving forward data proves that co-sintering is feasible with any material that has a melting point in excess of the ceramic sinter temperature which opens avenues for other material combinations. Materials that meet this criteria have large potential in future areas of manufacture.
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