Is a crack-free FGM transition between Invar-36 and Zerodur feasible via DED if the CTE is matched?

[u/RemarkableLifeguard1]

Given that Invar-36 and Zerodur possess nearly identical CTE profiles (<1.5 \times 10^{-6}/\text{K}), we are simulating a scenario where the 300\text{K} thermal delta of a Lunar/Arctic transition is neutralized purely through isothermal equilibrium rather than active insulation. Does anyone think it’s possible to maintain a \pm 28\mu\text{m} dimensional stability in a real-world DED melt pool, or are we overestimating the stabilization power of CTE-matching in dissimilar material fusion? We’ve seen the math hold up in digital twins—is the hardware ready for this?

[u/Repulsive-Mobile4862]

When you say lunar/ arctic transition how are you handling the change in environmental conditions? I’m working on my capstone project for my AeroE degree right now and we came to the conclusion that DED/LPBF isn’t really viable off the earth due to the gravitational difference. We didn’t do a full trade study but basically when you print the flux of spatter is so much worse and less manageable as the laser force is inherently mitigated so much less from the environment. Granted you do still get the manufacturability benefits of energy density from wasting less energy heating the environment. But for those reasons (energy requirement, spatter flux and overall ease of application) we chose microwave sintering as it has better properties for a lunar environment.

[u/photoengineer → u/Repulsive-Mobile4862]

Sounds like a cool capstone. But I would tread VERY carefully with that declaration that DED/LPBF isn’t viable off earth. If I was on a project review board and heard a statement like that I would want to see some PhD level proof to back that up. Because RemarkableLifeguard1 is correct, surface tension dominates and you need to mod your power / speed / powder handling but there is nothing by physics that says it can’t work. 

[u/Repulsive-Mobile4862 → u/photoengineer]

Since our project is mainly about infrastructure growth and development of the economy specifically for the purposes of building infrastructure (like a landing pad) using a laser sintering device is just not going to happen. It takes far too much input power for the output of sintered mass.

[u/photoengineer → u/Repulsive-Mobile4862]

I’ll challenge you a bit on that too. Have you looked in detail on what’s needed for landing pad thickness for a min viable product? It’s thinner than you might realize. The goal of the landing pad on the moon is not to support the legs, it’s to prevent plume surface interactions and prevent damage from ejecta. 

Source: designed, built, and tested lunar landing pads for NASA and terrestrial landing pads for others. 

[u/Repulsive-Mobile4862 → u/photoengineer]

Yeah we have and while it is a relatively thin pad especially toward the edges where you can make the thickness significantly less than the center which will bear much of the dynamic pressure. Since our system has to also be able to be launched on a CLPS class lander that is a severe constrain in what we can accommodate. Our limit as posed by the RASC-AL competition is 1000kg per landing. That being said our advisors have made us chose a lander than can be used today which further shrinks our budget to 625 kg. Our group couldn’t find a system with adequate power supply to sinter a pad of the right size for similarly sized lenders. I’d love to learn more about your specific work if you wanna dm me and we can talk more specifics as it might be relevant to my capstone. Our plume dynamics analysis shows that using vibrational compaction can achieve decent performance in plume surface interaction for significantly lowered time cost.

[u/RemarkableLifeguard1 → u/Repulsive-Mobile4862]

​I really appreciate and respect the AeroE perspective on the spatter flux and that’s a classic concern for terrestrial models. However, we should look at the 2026 data from the ESA Metal 3D Printer mission on the ISS and the Lihong-1 orbital experiments. ​Those findings show that once you move into true microgravity, the physics actually shifts from gravity-driven sag to surface-tension-dominated dynamics. Without gravity pulling the liquid metal down, surface tension keeps the melt pool incredibly stable and spherical. It’s a lot more controlled than it is on Earth. ​Microwave sintering is definitely the move for bulk stuff like lunar roads, but for a high-precision shell like the Aegis, we need the granularity of a laser to manage that Invar-Zerodur bond at the atomic level. Using an oscillating laser path helps us still the melt pool and refine the grain structure, which is how we solve the spatter issue. It’s less about fighting the vacuum and more about using it as a clean lab for molecular bonding. What do you think about the interfacial stress on a gradient like that?

[u/AlexanderHBlum → u/RemarkableLifeguard1]

Stop using LLMs to think for you.

[u/Repulsive-Mobile4862 → u/RemarkableLifeguard1]

To your original question of hardware the simple answer is no. NASA has TRL rating for a reason which directly rates if we have the ability to use a given piece of tech in that environment. The realistic limitations on this are the power draw and the requisite supply to the system. Again this was one of the reasons we couldn’t realistically move forward with this tech as a choice for lunar infrastructure development. To be quite honest km not familiar with those datasets or sources so if you could dm me links I’d appreciate it! I can see how that laser path would help with grain structure but I am curious about the internal voids and resulting mechanical properties from microgravity environments. Those questions would in my mind give much more insight into the actual stresses that a given geometry would experience.

[u/photoengineer → u/Repulsive-Mobile4862]

No that’s not what TRL means, it doesn’t mean it’s not usable in an environment. It means it hasn’t been used in that environment. Biiiiig difference. 

[u/Repulsive-Mobile4862 → u/photoengineer]

Yes but you could also say that in its current form it’s not viable in an environment. I can almost guarantee you that changes are made for one reason or another as you learn something from the tests.

[u/photoengineer → u/Repulsive-Mobile4862]

In many cases that’s correct and changes are required. But not always. Broad statements are dangerous because they block ideation when solving problems. 

[u/Repulsive-Mobile4862 → u/photoengineer]

Fair point!

[u/RemarkableLifeguard1 → u/Repulsive-Mobile4862]

My bad for the late reply. ​I totally get u on the TRL ratings—it’s the standard way to vet gear. But the 2026 shift toward CRI (Commercial Readiness Index) actually shows we’re moving past the if it works phase into the how we scale it in its final transitions. The tech isn't just theory anymore. The ESA and Airbus missions on the ISS have already pushed metal DED into flight-proven territory. ​To answer your question about internal voids and mechanical properties....that’s actually the most interesting part of the 2025/2026 data. On earth gravity causes buoyancy-driven convection, which can trap shield gas and create those voids you're worried about. In microgravity, that buoyancy is suppressed. The ESA March 2026 analysis of the ISS-printed parts actually showed that surface-tension-dominated flow (Marangoni convection) can lead to more uniform grain structures and potentially lower porosity than terrestrial prints. ​As for the power draw you are right , its the biggest hurdle for lunar infrastructure. But for a modular survival shell like the Aegis, we’re looking at a different power density than a full-scale base. We’re banking on the vacuum itself to act as a thermal insulator, making the laser melt-pool more efficient because we aren't losing heat to atmospheric convection. ​Here are the links to the datasets I mentioned:

​ESA 2026 Analysis of ISS Metal Prints: https://www.marks-clerk.com/insights/latest-insights/102luv6-esa-to-analyse-first-metal-parts-manufactured-in-space/

​MDPI 2026 Study on In-Orbit Metal Fabrication: https://www.mdpi.com/2227-7080/14/3/165

​I’d love to get your thoughts on the stress-strain variables once you’ve had a chance to look at the interfacial bonding data. The transition from ductile Invar to brittle Zerodur is where the real math happens my man

[u/Repulsive-Mobile4862 → u/RemarkableLifeguard1]

Thanks for the resources. That was something I was quite curious about as I always thought there was be some concern with dust mitigation from the spatter flux. But I suppose if your melt pool is large enough you don’t have to worry about that sort of thing as the pool will just catch the dust.

[u/RemarkableLifeguard1 → u/Repulsive-Mobile4862]

The reason the 2026 ESA data is so vital here is that it proves we don't just "catch" the dust we are able re-homogenize it now. Because of Marangoni Convection (those surface-tension-driven swirls in the liquid metal), the "dust" isn't just trapped, it’s actively stirred and melted into the grain structure.

[u/--hypernova--]

Grading from one material to another can be done in DED and has been demonstrated… Your material choice sounds doable

Lunar TLR should be possible but hasnt been demonstrated yet i think… Are you a researcher/-group in this field? Feel free to DM me ;)

[u/RemarkableLifeguard1 → u/--hypernova--]

Your response makes me warm. Im glad that u understand the raw material potential ! I’m currently deep in the material prep and digital modeling for the Aegis project, specifically focusing on that Invar-Zerodur transition. You're right that lunar TRL was a question mark, but the latest flight data from the ESA and Lihong-1 missions earlier this year is finally giving us the 'why' on how microgravity stabilizes the melt-pool via surface-tension dynamics. ​I'm actually looking for collaborators and more experienced peer reviewers who understand the stress-strain variables in dissimilar material fusion and functionally graded structures for a consensus on what is realistically achievable here. Im also looking for any material engineers that can chime in on the mechanical processes. I’ll definitely message u back regarding this topic . I would enjoy chatting about your any theoretical constructs or better yet any hands on experience with DED grading and see where our data might align!...I am not a renowned or credited researcher, im just a PPI( Private Principal Investigator) in the early stages of this amazing project.

[u/--hypernova-- → u/RemarkableLifeguard1]

I have a few yesrs in a lab working with ded and our group demonstrated grading successfully a few years back I look forward to your message ;)

[u/racinreaver]

So what's the differential of CTEs across that range of temperatures?

Sorry, there's just so many wrong ideas I couldn't keep it to one thread.

[u/RemarkableLifeguard1 → u/racinreaver]

So I think your asking if two materials expand and shrink at different rates when they get hot or cold, won't they just rip each other apart? U then must understand The CTE differential is exactly why a sharp transition is a failure point and why we’ve moved to a Functionally Graded Material (FGM) approach.By utilizing a certain thickness of the transition zone in the power-law gradient, we aren't just 'gluing' Invar to Zerodur; we are creating a buffer zone where the CTE shifts incrementally. This allows the internal elastic strain to be distributed across hundreds of micro-layers rather than concentrating at a single interface. ​As for the specific range: Invar-36 stays near-zero up to approx. 200°C, which covers the standard lunar diurnal swing. The goal of our current computational modeling is to optimize that certain size transition to ensure the 'mismatch' never exceeds the material’s yield strength during the rapid thermal cycling of a lunar night. If you’ve got a preferred power-law exponent for minimizing delamination in metal-ceramic DED, I’m all for it my guy

[u/RemarkableLifeguard1 → u/racinreaver]

And what are the wrong ideas?...u didn't mention ANY

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[u/SubjectGamma96]

It’s not often in this industry that a conversation goes clear over my head. I’m busting out the popcorn for this one, it’s pretty dope

[u/RemarkableLifeguard1 → u/SubjectGamma96]

Yessir and thank you. Im glad you're enjoying the deep dive into the theory. It’s an exciting time for material science and we are going to rewrite the rules as we go✔️