Indigenisation of Copper-Chromium-Zirconium-Titanium Alloy for Cryo and Semi-Cryo engines- A Success Story
Copper Alloy (Cu-0.5Cr-0.05Ti-0.05Zr) is an important and vital item required for cryogenic/semi-cryogenic engines for the realisation of thrust chamber inner shell and injector face plates of Cryogenic Upper Stage (CUS) engine for GSLV Mk-II, CE20 engine for GSLV Mk-III and Semi-Cryo (SC) stage. This is also required for the Steering Engines (SE) of CUS engine, Gas generator of CUS & CE20 engines, injectors, pre-burner and pyro components of SC engine.
These projects require Copper Alloy plates, rods and forgings of various dimensions. For plates, thickness requirement range from 12 mm to 18 mm and width of 850 mm. Rods and forgings of this alloy are also required with diameters ranging from 30 mm upto 300 mm.
Indigenisation efforts were made through NFTDC, Hyderabad for CUS, CE20 and SC. Melt capacity was augmented to 1000 kg and plate rolling mill capable of 1500 mm width was established for meeting the project requirements. All required products using this alloy have been successfully realized for CUS, CE20 and Semi-Cryo projects. The hot test of the CUS engine using this copper alloy for 200 sec in the nominal and 13% uprated thrust regime was carried out at IPRC, Mahendragiri. This engine will power the cryogenic stage of GSLV Mk-II, which is scheduled to launch GSAT-7A in November this year.
Process Flow: Cast ingots from the melt furnace are made into skinned ingots weighing 375 to 400 kg. These are converted into as forged plates which gets further forged to skinned plates ready for rolling. Plates of required size are generated through hot rolling process.
The major challenges faced in the endeavor are:
- Optimisation of chemical composition and the melting practice to achieve the designed chemistry and mechanical properties at ambient and high temperatures.
- Optimisation of press forging to avoid defects in UT for higher width plates leading to considerable increase in the yield.
- Achieving fine grains by optimizing heat treatment from 9800 C for 10 min. to 7500C for 20 min.
- Ultrasonic Trasducer (UT) – Normal beam with TR probe and Angle beam scanning with Class A acceptance criteria.
- Bend tests on samples from plates subjected to annealing at 7500C for 20 min. followed by air cooling ensuring formability.
- Benefits of the indigenization include:
- Very cost effective compared to import.
- Self-reliance through establishment of facilities at M/s. NFTDC, Hyderabad which is the second known processing unit globally for production of aerospace quality Cu-Cr-Zr-Ti alloy.
- Low establishment costs
- Refurbishment route of available facilities adopted
- Rolling mill components designed and realized through various units within India and integrated at NFTDC
- Existing melt furnace coils at NFTDC were modified to increase the melt capacity to 1000kg