Mikoyan Gurevich MiG 25 foxbat interceptor

The Mikoyan-Gurevich MiG-25 is a supersonic interceptor and reconnaissance aircraft that was among the fastest military aircraft to enter service. It was designed by the Soviet Union's Mikoyan-Gurevich bureau. The first prototype flew in 1964, and the aircraft entered service in 1970. It has an operational top speed of Mach 2.83 (Mach 3.2 is possible but at risk of significant damage to the engines), and features a powerful radar and four air-to-air missiles. Because of the thermal stresses incurred in flight above Mach 2, the Mikoyan-Gurevich OKB had difficulties choosing what materials to use for the aircraft.

They had to use E-2 heat-resistant Plexiglas for the canopy, and high-strength stainless steel for the wings and fuselage. Using titanium rather than steel would have been ideal, but it was expensive and difficult to work with.

The problem of cracks in welded titanium structures with thin walls could not be solved, so the heavier nickel steel was used instead. It cost far less than titanium and allowed for welding, along with heat resistant seals. The MiG-25 was constructed from 80% nickel steel alloy, 11% aluminium, and 9% titanium.The steel components were formed by a combination of spot welding, automatic machine welding and hand arc welding methods