Erosion resistance of refractory alloys modified by ion beams

Abstract The objective of the present research is the critical analysis of test results, dedicated to the effect of ion-beam irradiation conditions upon the sand particle erosion resistance of refractory alloys. Gas turbine engine compressor blades, produced with titanium alloys (VT9 and VT18U) as well as refractory steels (EP866sh and EP718ID) were used as the study objects. The ion implantation and irradiation of targets for the high-power pulsed ion beam were accomplished by means of Delta, Raduga-2 and Temp-M accelerators. The irradiation conditions were varied within the following ranges: B, N, C, La, Pd, Sm and Hf ion implantation — E  = 30–80 keV (ion energy), j  = 40–5·10 3  μA/cm 2 (ion current density), f  = 30 Hz (pulse frequency), D  = 10 16 –2  10 19  ion/cm 2 (irradiation dose); high-power pulsed ion-beam irradiation — ions of carbon (60–70%) and protons, E  = 250–300 keV, j  = 40–200 A/cm 2 , τ  = 50 ns (pulse duration), n  = 3–10 pulses (number of pulses). After irradiation some targets were subjected to vacuum annealing for 2 h at their service temperature. Erosion tests of initial and irradiated blades were performed in vacuum on the gas-dynamical branches with a sand load to 200 mg/mm 2 at the particle velocity of 200 m/s. The average size of the sand particles was equal to 80–120 μm. The target surface state prior to and after erosion tests was studied by Auger electron spectroscopy, scanning electron microscopy, transmission electron microscopy, optical metallography and X-ray structural analysis. The fracture surface was studied by optical and electron fractography. The test results showed that the erosion resistance of blades, subjected to the ion-beam irradiation with post-process vacuum annealing at the optimum conditions, could be increased by 20–200% depending on the type of implanted ion. This positive effect of ion-beam treatment on the erosion resistance of refractory alloy blades is evidently connected with strengthening the material in the surface layer with thickness of 1 μm (ion implantation) up to 10 μm (high-power pulsed ion-beam irradiation). Using electron fractography it was found, that the erosion resistance increase was associated both with the type change of craters created during beginning stages of the erosion tests and with the decrease of erosion rate due to the surface microrelief formed during the fracture incubation period (“start–inertial” mechanism of fracture).