Features of strengthening of welded seams by balls in a magnetic field at repair of fan blades and compressor from titanium alloys

Abstract

Objective. Investigate the effect of hardening by balls in a magnetic field on the fatigue strength (endurance limit) of welds in titanium alloys.Research methods. The studies were carried out on samples of VT3-1 titanium alloy manufactured using a technology close to the technology of manufacturing the blades. The endurance limit of welded specimens without hardening and welded treated with balls in a magnetic field was determined by the accelerated method based on N = 2×107 cycles, followed by recalculation using the coefficient α = 0,8 to the base N = 108 cycles [3]. The tests were carried out so that the axis of the weld was in the zone of maximum stress. Fractographic studies were performed on a STEMI 2000-C microscope from KARL ZEISS. Hardness measurements were carried out on a LECO LM-248AT microhardness meter equipped with an automatic hardness measurement system AMN-43 in accordance with [6].Obtained results. An analysis of the results shows that treating with balls in a magnetic field increases the endurance limit of welded samples by 19 %. Damage during fatigue tests of the original welded and welded, hardened by balls in the magnetic field of the samples, occurs at the location of the weld. In the heat-affected zone, characterized by a decrease in mechanical properties, no damage during fatigue testing was detected. A fracto-graphic analysis of the destroyed samples showed that the fractures are fatigue-like, fracture occurs by a brittle mechanism. A distinctive feature is the presence of pores with a diameter of 0,05 to0,15 mm, in most cases they are located in the area of the fracture focus.Scientific novelty. It was found that hardening by balls in a magnetic field leads to an increase in the fatigue strength of welds. In welding seams, pores may form during welding of titanium alloy parts. When the seam is located in the zone of action of the highest stresses, the pores can help reduce fatigue strength.Practical value. It was established that processing by balls in a magnetic field does not lead to embrittlement of the weld and increases the fatigue strength of welded samples, which allows considering the hardening by balls in a magnetic field as applied to the repair of critical parts of a gas turbine engine, including fan blades.