Study of heat-treatment regimens influence on structure and phase composition of disc forgings for «Blisk» made of alloy VT8-1

Аuthors

Istrakova A. R.^*, Kashapov O. S., Kalashnikov V. S.

All-Russian Scientific Research Institute of Aviation Materials. State Research Center of the Russian Federation, 17, Radio str., Moscow, 105005, Russia

*e-mail: Nasty.77@list.ru

Abstract

The main purpose of the materials research in the aerospace industry is to improve the structure reliability while reducing the weight. Heat-resistance titanium alloys with a density of about 4,5 g/cm3 can facilitate engine weight, but titanium and its alloys have polymorphism, which limits the application temperature of the alloys in 0.6 times then polymorphous transformation temperature. A heat resistant titanium alloys can continuously operate at temperature of 500 550 °С, depending on the chemical composition of the alloy, the process conditions of heat and deformation processing. Discs and the compressor blades made of titanium alloys where used in aircraft gas turbine engines. Further reduce of weight of the engine can be achieved by replacing the classical design of the compressor stage with removable blades by blisks.

This article examines the impact of different modes of annealing on structure, phase composition and mechanical properties of the samples of punching blisks. Raising the temperature in the first heating stage at ten degrees Celsius and lowering the heating temperature in the second step of annealing from 590 to 550 °C reduces the volume fraction of primary á -phase and 50% in batch annealing to 2025% reduction in the thickness of the secondary plates á — phase and increase the length of the interphase boundaries. Using transmission electron microscopy it was found that when adjusted mode annealing at interphase boundaries silicide particles are not detected. By increasing the efficiency of solid- solution and precipitation hardening is provided by increasing: the strength of 120 MPa at room temperature and 70110 MPa at elevated; rupture strength at 500 °C at 75 MPa; low cycle fatigue at 20 °C for 20 MPa high cycle fatigue at 20 °C at 30 MPa. At the same time, due to changes in the structure and phase composition, sensitivity to stress concentrators during the impact test is reduced.

Keywords:

heat treatment, titanium alloys, structure, high-temperature strength, creep rupture strength, fatigue

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