Indian Developments in Materials for Military Aero Engines

The Indian aircraft industry is still in its nascent stages of growth. Hindustan Aeronautics Limited (HAL) is the only significant player, manufacturing aircraft and engines, albeit under license production. Even so, most of the materials and material technologies have been sourced from the original manufacturers (OEMs) of the engines and aircraft.

In the recent past, a number of new material technologies have been recently introduced which are required in the production of Sukhoi aircraft (Su-30) and its engine (AL31FP). Kaveri, the proposed engine for LCA Tejas is the only programme which aims to design and develop indigenous engine and also to develop indigenous capabilities in the areas of materials and manufacturing technologies. In a sense, the development of indigenous material technologies in India is linked to Kaveri programme. Assessment of materials and manufacturing technologies presented here is largely based on the Kaveri experience in which many industries and research laboratories are participating. GTRE is also developing a smaller engine called “laghu Shakti.”

Primary mill products

Most of the primary alloys used in gas turbines are being manufactured at Mishra Dhatu Nigam (MIDHANI), Hyderabad. MIDHANI has been successful in indigenous development and manufacture of various mill products of several grades of super-alloys, Titanium alloys and steels. In addition MIDHANI also produces several Russian grades of steels, Titanium alloys and super-alloys. Some of the most important alloys produced at MIDHANI are:

Space & Missiles – MDN-250, Ti-64, Ti-15-3,
Kaveri Engine – Su-718, CM247LC, Su-263, Ti-29A (834), Ti-64, GTM900, BS-347,
LCA – 17- 4PH, 15- 5PH,
MIG series – AE961W, AE646M, A286, BT-9,
Sukhoi-30 – BT-20, BT-18
Infrastructural constraints have restricted MIDHANI to expand its range to newer alloys such as 720Li and large diameter products in nickel base super-alloys which are required for turbine and compressor discs and large casings of engine. Thankfully the facilities at MIDHANI are being upgraded and these upgrades are expected to enhance its capabilities in this area.

Forgings

The Foundry and Forge (F&F) plant of HAL has the capacity to produce rings, blocker forgings, closed die forgings and precision forgings in a wide variety of Al, Mg, Cu alloys and steels.

Its association with the Kaveri Engine programme has resulted in HAL’s F&F plant to develop the technologies to manufacture a large number of ring, open die forgings and blade forgings in various grades of super-alloys and Titanium alloys. Some of the important forgings include ring rolled products in super-alloys – Su-718 and Su-263, Titanium alloys – Ti64 and Ti685, and steels – S-80 and E16NCD 13. In addition HAL’s F&F plant has demonstrated the capability to produce complex airfoil forgings for compressor blades and vanes in Su718, Ti64 and GTM900.

The other benefactor of the Kaveri Engine programme is this regards has been the Steel Industrial forgings Limited (SIFL), Trichur, which has also developed small closed die forgings in Ti6A14V and 718 for Kaveri engine.

The turbine’s Discs are the most critical components in a gas turbine. These have to be manufactured to very strict specifications of mechanical properties, macro-structure, micro-structure and integrity. A collaborative programme between Bharat Forge Limited, (BFL), Pune, Project Office (Materials), Defence (Materials) and CRI (M) has resulted in the successful development of all the three Kaveri fan discs using the Ti64 alloy. The discs were made using indigenous forging stock of requisite specification produced at MIDHANI.

Castings

The DMRL has successfully developed complex airfoil castings for the Kaveri turbine using the Nickel base alloy CM247LC. The castings are hollow with internal cooling channels and have to meet very stringent dimensional, micro-structural, chemical and porosity requirements. This is one of the most complex processing steps, each requiring a very strict control. The DS castings have been qualified by airworthiness agencies (CEMILAC) for use in Kaveri engine. Recently, vaccume diffusion brazing process for tip and root of HPY blade of Kaveri engine has been developed in collaboration with Godrej and Boyce, Mumbai.


The DMRL has also developed the jet fuel starter castings for the LCA Tejas as well as the castings for the Adour engine (used in the Jaguar). The technology developed at DMRL is currently being transferred to HAL, Koraput. HAL has investment casting facilities although so far it has been manufacturing only equiaxed castings of Russian grade super-alloys. Recently, HAL (Koraput) has also developed shroud castings in CM247LC and 718 alloys for Kaveri engine and these castings have been qualified by CEMILAC. HAL has also acquired capability to manufacture DS and single crystal castings of turbine airfoils for Sukhoi aircraft engine AL31FP.

The development of Platinum-Aluminide coatings and thermal barrier coatings (TBC) are also in progress at DMRL in association with ARCI, Hyderabad.

Advanced materials and Processes

DMRL has been working on Titanium-Aluminides (TiAl) and has developed alloy compositions with adequate ductility. Compressor blades of a α2-Ti3Al TiAl alloy have been forged at HAL (F&F). DMRL has also demonstrated processing of TiAl alloys by isothermal forging route to get equiaxed structure of α2 + γ. Development of discs in Titanium alloys Ti26A (Ti685) for Adour and Kaveri engine has been carried out at DMRL. The near-isothermal forging process along with extensive use of modelling and simulation has been used at DMRL to optimise the process. Discs in Ti26A alloys for Adour engines will soon be produced in larger numbers by MIDHANI employing the DMRL infrastructure and technology with appropriate augmentation of the infrastructure required for the production batches.

Recently, DMRL has also carried out development of disc and integral shaft forgings for the Kaveri engine using the Ti834, which is a new Titanium alloy developed for use at 600 degree C. While many important technologies have been developed for gas turbines, some of these technologies developed cannot be said to have attained a maturity level typical of production environments. This has been largely due to the small volumes and only a few batches of components that have been produced so far. Also some of the materials’ technologies already employed routinely in gas turbines in western countries are still not indigenously available. The most important of these are:

Single crystal alloys and castings for turbine airfoils,
Blisk Technology for compressor discs both in titanium alloys and super alloys,
Inertia welding for engine parts such as compressor drums,
Large diameter forging stock, large width plates and sheets in super alloys and titanium alloys,
Super-alloy discs for compressor and turbine.
Many of these have not been attempted due to non-availability of the required equipment/ infrastructure, for example large capacity press to forge discs using the super-alloys or inertia welding facilities. In addition there are several gaps in knowledge and in the understanding of various aspects of materials and processes which need to be developed for efficient exploration of materials technologies.

Looking Forward

Despite the relatively small size of aerospace industry in India, the future growth prospects of this sector in a fast emerging economy make it imperative that critical gaps in technologies are filled. It may require augmentation of infrastructure on the one hand and generation of knowledge and acquisition of expertise and highly skilled human resources on the other. Some of the core technologies and critical facilities that need to be established are:

Large forge capacity, large billet capacity,
Inertia welding and linear friction welding,
Augmentation of investment castings – DS and single crystal,
Composites – fibre C/SiC, etc.,
Facilities for testing both the materials as well as the components,
Life prediction technologies,
EBPVD for TBC,
Advanced machining such as creep feed grinding,
EDM/laser drilling, laser peening Ultrasonic peening, electro-chemical machining, etc.,
Advanced inspection and NDT such as phased array ultrasonic, 3D x-ray tomography in production environment
Notwithstanding the augmentation of infrastructure, it is equally essential to integrate design, materials and manufacturing capabilities available within the country to evolve indigenous solutions for problems unique to our environment. It may be possible to overcome certain manufacturing limitations by smart design. In addition to infrastructure requirements, capability to design processes, techniques, tools and acceptance criterion will play an important role in indigenous development of engine and its components with satisfactory performance.