Účinky prostředí na spolehlivost superslitin na bázi niklu

Abstract

This work deals with the effects of hydrogen on mechanical properties of nickel based superalloys IN 738 LC in a tensile test. Tensile specimens were treated for 4 hours by HIP technology at 1 190 °C and 175 MPa for the purpose of reducing the amount of casting defects in the structure and to avoid premature cracking of the samples. Half set of samples was heat treated in flowing hydrogen gas at 800 °C for 4 hours followed by cooling to 400 °C and then by water quenching. Results of tensile tests that were carried out at strain of 0,025 s-1, showed that hydrogen effect led to increasing yield strength and decreasing ultimate tensile strength. Hydrogen quantity in the structure of nickel based superalloy samples was deteremined by means of LECO RH600 analyzer. Fracture surfaces of tensile tested specimens were observed using scanning elektron microscopy. Hydrogen dissolved in the structure of hydrogenated samples contributed to the embrittlement of the alloy. The study was completed with the structure phase analysis of superalloys using EDS microanalysis and HV 0,2 microhardness measurements.