Susan Draper performs microstructural analysis of metals and determines where fractures have occurred and propagated. Draper is currently characterizing electron-beam-melted, additive-manufactured titanium-6 aluminum-4 vanadium, a titanium alloy. Her team is currently working with the rocket and missile propulsion manufacturer Aerojet Rockdyne to improve the RL10 rocket engine.
NASA Tech Briefs: What is the current project that you're working on?
Susan Draper: I am working on a US Air force-funded project. We are working with Aerojet Rockdyne to improve the RL10 rocket engine, using additive manufacturing. Also, in-house, we’re doing an in-depth characterization of electron-beam-melted titanium-6 aluminum-4 vanadium to eventually be used in a gimbal structure.
NTB: What are the exciting possibilities for this type of manufacturing method? What are the possibilities with additive manufacturing?
Draper: 3D printing is exceptional for complex parts, where the part would require, say, a large block of material and then require the machining out of all of the internal passages and internal parts of it — possibly having brazed pieces attached to it like the gimbal does. The gimbal is basically a hollowed cone, but with additive manufacture, you don’t have to start with a block of material. You just build the part as the shape is required. All the brazed-on pieces can be built right on as it’s printing.
NTB: What can these 3D-printed metals withstand? What have your tests shown?
Draper: So far we’ve tested this material under cryogenic to 300 ⁰F testing, using low-cycle fatigue, tensile testing, high-cycle fatigue, fatigue crack growth, and fracture toughness. And all the properties so far are showing properties equivalent to or better than conventionally manufactured material.
NTB: Why is that?
Draper: The microstructure of this has been characterized extensively, and it has very few flaws. The microstructure is very fine, compared to conventionally manufactured material. For any application, you want to make sure that it has the properties to withstand what the structure is designed to do. In this case, it’s a gimbal. While I’m not a gimbal designer, I know that it has to have the properties at least equivalent to what would be in a conventionally manufactured material.
NTB: Do you see the applications especially for in-space manufacturing? Outside of space? Where do you think it will be most valuable?
Draper: Certainly for in-space manufacturing, it would be very convenient as something breaks up on a space station; you would just manufacture the part as needed. But it also is ideal for lots of different aerospace applications – anything with a complex shape that needs a lot of machining, brazing, or welding. Some parts can only be made by additive manufacturing. Say you have a combustor liner that has an internal cooling passage. That can’t always be machined in, but it can be manufactured in using 3D printing. 3D printing would also be great for making parts for retired engines, where the parts are no longer in production, but you can go and make one part much cheaper than you could fabricate one single part using conventional manufacturing.
NTB: Are you working exclusively with one type of material? What’s the range?
Draper: My project is exclusively on electron-beam-melted titanium-6 aluminum-4 vanadium, which is a very common titanium alloy. It’s a metal. Here at Glenn we have other projects working on copper alloy. There is quite a large group working on polymer additive manufacturing. We’re doing some super-alloy feasibility studies of additive manufacturing. We have a number of projects going on.
NTB: What’s next with the additive manufacturing project?
Draper: We have to complete all of our testing, analyze all the fracture surfaces, write a report, and put it into a journal. This will be key, because a lot of the properties that have been generated so far in these materials have not been put into public domain. Most of it is generated by companies, and they don’t publish their results. All these results will be publicly published.
NTB: Can you take me through the testing process?
Draper: We had these parts, coupons, manufactured to close any porosity. Then, they were machined into the different test coupons that were required. We did all our cryogenic testing using a supplier, since we don’t have that capability here. We have extensive material characterization facilities here, and we’ve done all the high-cycle fatigue, where we cycle the coupon at 20 Hz, and go from 100,000 cycles to 10 million cycles and determine at what stress it breaks. The process is similar for low-cycle fatigue, but at lower frequencies and shorter cycle times. Tensile testing is simply picking [the metal] up until it breaks in a simple tensile load.
NTB: What is a typical day for you, and what kinds of work are you doing?
Draper: I have done most of the microstructural analysis, looking at the microstructure using a scanning electron microscope and optical microscope. We have a large team working on this, and I oversee the mechanical testing, the manufacturing, and also the performing of all the fractography. So after the samples are broken, I look at the fracture surfaces and determine where the initiation of the fracture occurred and how it propagated.
NTB: And how big is this team?
Draper: We probably have about 6 people working on it, not full-time but part-time.
NTB: What is the most exciting part of your work?
Draper: It’s been very fun to see this project from start to finish, knowing that it’s going into a part, to see how it’s fabricated. In the first few tests, we were very excited to see that it had the properties equivalent to what a conventionally manufactured Ti-64 part would have.
NTB: What do you mean by conventional manufacturing, and how has you work improved upon that method?
Draper: Ti-64 is a cast-and-wrought alloy, so you would cast and forge it into a disc or some type of shape, and then you would have to machine out the parts. It would be a very large piece of material. We made each of these materials nearly net shape.
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