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is the U.S. subsidiary of Azista Industries (Hyderabad, India), a diversified conglomerate with roots in (Ahmedabad, founded in 2014) and (Hyderabad, founded in 2020). The company’s U.S. operations, based in Raleigh, North Carolina, are focused on expanding partnerships and domestic capabilities in support of both defense and commercial aerospace markets. “Azista Composites is India’s partner for hypersonic technologies,” says Jairam Chintalapati, business development manager for Azista USA.

The company supplies a variety of high-temperature materials to global markets. These include bismaleimide (BMI), cyanate ester and hot-melt phenolic prepregs and phthalonitrile (PN) resins and prepreg.

These are also offered as pre-ceramic polymer systems, part of its portfolio enabling ceramic matrix composite (CMC) materials and parts. This portfolio also includes PN and carbon foams, 3D woven and 2D stitched preforms, and a variety of process capabilities, including polymer impregnation and pyrolysis (PIP), liquid silicon infiltration (LSI), chemical vapor infiltration (CVI) — including a patented film boiling CVI process — as well as initial pyrolysis/graphitization and final machining for a complete process chain.  

“We have demonstrated our capability to make carbon/carbon [C/C] parts and also have systems to make silicon carbide [SiC] CMC as well,” says Chintalapati. Currently, these materials and parts are manufactured in India, but Azista USA is exploring domestic capabilities as it works to expand applications and partners in the U.S.

Hot-melt phenolic prepreg

Phenolic resins have a long history in fire-resistant and high-temperature composites, including automotive and aircraft interiors applications. “Phenolics have always been solvent-based resin systems, with a cure process that generates significant volatiles,” notes Chintalapati. Phenolic cure typically involves a condensation reaction where phenol and formaldehyde molecules link together, releasing water as the primary byproduct. This results in processing challenges, including how to minimize porosity in finished laminates.

“Azista has developed a solvent-free phenolic system, with a formulation that has close to 0% volatiles,” he adds. “It is processed in a way that is very close to addition polymerization, similar to epoxy. So, it is much easier to use, to make aircraft interior panels, for example, eliminating traditional porosity issues while retaining the good thermal and mechanical properties of phenolics.” The glass transition temperature (T_g) is around 160°C and typical cure is at 170°C.

Azista USA is supplying customers with hot-melt phenolic prepreg that handles more like an epoxy prepreg. It is safe to use, a nonhazardous material to transport and eliminates the extra precautions typically required to work with phenolics. Azista can also supply phenolic film that customers can use to impregnate their own fiber reinforcements.

“Another advantage of this prepreg is that we are able to make extremely thick ablative components without using a hydroclave,” says Chintalapati. A hydroclave is similar to an autoclave, but uses pressurized water instead of pressurized air and much higher pressure — typically 6.9 megapascals (1,000 psi) compared to 0.3-2.0 megapascals (50-300 psi) for autoclaves — which produces high-quality, void-free, thick laminates. “These ablative components are typical in thermal protection systems [TPS] for space and defense applications,” he explains. “We are working on advancing this technology in a program with the Indian government.”

Phenolic resins are also a workhorse system when creating carbon fiber-reinforced polymer (CFRP) composites that are then graphitized to form C/C composites for brake pads and discs, rocket nozzles, radomes and other spacecraft structures, for example. We’ll come back to this in a minute.

PN prepreg

Another key material that Azista USA offers is PN, a thermoset composite matrix said to provide not only the fire resistance of phenolics, but also the excellent heat resistance and mechanical properties of polyimide (PI) resin, plus the machinability and low water absorption of cyanate ester. “PN was originally developed by the U.S. Navy in the 1980s,” says Chintalapati, “but today, we are one of only two or three players in the global market providing commercial-grade PN resin systems, which offer the highest temperature resistance in thermoset polymers. Ours is designed to have a T_g of 435°C with long-duration in-service capability of 350-400°C.”

He notes these resins meet MIL-STD-2031, which outlines the stringent fire, smoke and toxicity requirements for composites used on submarines.

“Our PN also has good dielectric properties for high-temperature radomes,” says Chintalapati. “We are offering prepreg as well as liquid resin for resin transfer molding [RTM] and infusion processes. The resin has a viscosity of 75 centipoise at its cure temperature of 180-200°C. We have found use cases around aircraft engines and have worked in a project to replace titanium engine pylon parts with PN composites.”

What about PN’s traditional downside of brittleness? “It can be an issue at room temperature,” Chintalapati concedes. “For certain applications, we use optimized cure cycles or add fillers to help avoid microcracking.”

Work with NLR

The (NLR), headquartered in Amsterdam, with significant composites capabilities also in Marknesse, has also worked with Azista’s PN resins. In one project, NLR had already demonstrated the feasibility of manufacturing high-quality PI laminates using a powder coated semipreg and wanted to use the same approach for PN.

“Similar to the PI resin, the Azista PN is solid at room temperature and can be ground down to powder and applied on the dry reinforcement,” explains Ronald Klomp, R&D engineer composites at NLR. “Using this approach, we manufactured the dry semipregs and manufactured test laminates with up to 24 plies as well as a manufacturing demonstrator component. The low initial cure temperature of the Azista PN allows the use of standard autoclave bagging and also 3D printed tooling. We presented the results of this work at SAMPE Belfast 2024.”

The 3D printed tooling came into play in 2023, when NLR completed its work on the Clean Aviation project . With the objective to design and manufacture a high-performance, low-cost and lightweight nacelle structure for next-generation tilt-rotor aircraft, a complex-shaped scale model of a nacelle structure was vacuum-injected with BMI resin using a 3D printed tool. Klomp notes the tool was printed using a CEAD (Delft, Netherlands) 3D printer and Dahltram tooling resin from (Springfield, Tenn., U.S. and Luxembourg). This tool was then used to cure an eight-ply carbon fiber-reinforced PN component made with the Azista resin. “An ultrasound C-scan of the cured part showed that the laminate had good quality,” says Klomp.

“NLR has continued further investigation and development of PN composites,” he continues, which includes flexure and interlaminar shear strength (ILSS) testing at elevated temperatures (320°C).

“PN resins are known to be quite brittle and a key aspect in the development of high-quality laminates seems to be tuning the post-cure cycle to avoid premature microcracking,” explains Klomp. “NLR is investigating the use of this specific resin for various high-temperature applications and also intends to investigate the fire performance of this resin, which has a proven high char yield.” He notes that NLR has performed in-house thermogravimetric analysis (TGA) tests to 900°C to confirm this and that it is also investigating the potential of graphene-modified PN resin, including manufacture of several test laminates as part of the ongoing .

Converting polymers to CMC parts

The phenolic and PN materials that Azista USA is offering are being used not only for CFRP and other fiber-reinforced polymer composites, but also to create pre-ceramic preforms that are then pyrolized and densified into CMC. Although phenolic, with a char yield of ~60 wt%, is the traditional pre-ceramic resin matrix used for C/C composites, PN offers a char yield of 72%.

“This enables us to reduce densification cycles from five to three,” says Chintalapati. Here, he is talking about creating C/C using the PIP process, where high char content resin is used to infiltrate a fiber preform at room temperature and is then pyrolized at high temperatures (e.g., 900°C). However, to reach the required density and lack of porosity in the final CMC, infiltration and pyrolysis must be repeated as many as 10 times. Chintalapati is noting that by using PN, Azista has been able to produce C/C parts with only three densification cycles.

“And the microstructure of the resulting C/C is very close to that obtained using CVI,” adds Chintalapati. CVI was one of the first processes used to create CMC and involves injecting a reactive gas like methane (CH₄) into a reactor at high temperatures, resulting in the formation of a carbon matrix — an SiC matrix is also possible depending on the gas used — all through the porous preform, eventually building a dense CMC. Although CVI is an extremely slow process, taking weeks to months, it does avoid problems associated with liquid processes such as microcracking and damage to fibers. Traditionally, PIP and other liquid processes have produced a less dense and pure matrix compared to CVI. Thus, Azista’s ability to use PN to achieve a CVI-like microstructure in C/C but with a much faster and less expensive process is indeed very interesting.

Azista also converts PN into a porous foam used to produce composite parts and can do this with its other high-temperature resin systems, for example, using its hot-melt phenolic to produce carbon foams. 

Chintalapati points to a CMC cylinder made with PN foam and carbon fiber/PN prepreg.  This lightweight part (0.3 grams/cubic centimeter) measures 300 × 300 millimeters with a thickness of 20 millimeters. “This was made to demonstrate our CMC capabilities,” says Chintalapati. “We used PN foam and two plies of carbon fiber/PN prepreg for the skins. There were bonded together using PN that we formulated as an adhesive. We then cured the layup in a mold at 180-200°C followed by a 2-hour freestanding post-cure at up to 350°C. We then converted into a C/C using a carbonization furnace at 1000-1200C.” Azista is currently performing tests on these and other C/C parts, he adds.

Azista has also developed a polycarbosilane polymer used as a precursor for SiC matrix. “We have a formulation that produces SiC matrix composites and a high molecular weight variant for making SiC fibers,” says Chantalapati. “We currently have four variants and are looking for partners to help us evaluate these materials.” Polycarbosilane has been available in the U.S. for decades from Starfire Systems (Glenville, N.Y.). “The advantage we offer is that we can tailor the polymer chemistry according to the needs and end goal of the user,” notes Chantalapati.

Full CMC process chain

The full process chain that Azista has developed for CMC parts can start with design capabilities, including FEA and thermo-structural analysis. It then produces a wide rage of raw materials, as discussed above. “Thanks to our sister companies, we have a huge amount of infrastructure to produce resin systems and control purity levels to 99.9% purity,” says Chintalapati. “And we also custom formulate and tailor resins.”

“We have also invested in equipment, from prepreg and towpreg manufacturing, to RTM presses, autoclaves, filament winding machines and ovens,” he continues. “We have a needle punch machine to produce 2.5D and stitched preforms, as well as a carbonization furnace, graphitization furnace and our LSI and CVI equipment. Thus, we have everything under one roof, which significantly streamlines our parts production and development.” For CMC, these have mostly been used for small products and internal R&D, admits Chintalapati, “but now that we have characterized our materials and processes, we are scaling via programs with the Indian government. We are continuing to invest and have already set up large-scale equipment, including ICVI and carbonization, capable of processing C/C components up to 3 meters in dimension for aerospace and defense applications.”

Regarding the current concerns about security, Chintalapati points out that part designs do not have to be transmitted. “We can produce 3D blocks or shapes and send those to the U.S. for machining into parts.”

Film boiling CVI

Film boiling CVI is a CMC production technology that Azista has developed in-house. “It increases the densification rate for CVI,” explains Chintalapati. “For example, a typical rate for isothermal CVI is 0.015 millimeter/hour, but film boiling CVI can achieve densification at 1.5 millimeters/hour. With this 100-times increase, we were able to the reduce cycle time for manufacturing high-quality C/C by about 10 times.”

Azista also found using film boiling CVI produces a quite different microstructure and coefficient of thermal expansion compared to C/C made using traditional isothermal CVI. “Although this might not be optimal for all applications, we know the properties that are required or wanted for certain systems, and we can see there is an opportunity. We are in the process of completing a full characterization of CMC produced using film boiling CVI.”

Continued development, future growth

Azista Aerospace is manufacturing satellites at its Ahmedabad facility while Azista Composites has constructed two large facilities in Hyderabad. “The first one contains all of our R&D capabilities,” says Chintalapati. “The second facility is for parts production, including high-pressure, filament-wound hydrogen tanks and large polymer composite and CMC components.” So far, the facility has produced CFRP-skinned/aluminum honeycomb panels for satellites, CFRP pressure vessels and prostheses as well as carbon fiber/PN radomes, C/C rocket nozzles and jet vanes and carbon fiber/C-SiC brake discs.

Azista USA is actively expanding its presence in North America to support domestic partnerships, joint development programs, and U.S.-based manufacturing. With continued investment in advanced materials, scalable processing, and collaborative research, Azista is positioning itself as a global supplier of next-generation high-temperature composite solutions for aerospace, defense and space systems.