Abstract
This research studied Ti-6Al-4V alloy behavior with two (2) different microstructure subjected to nitrogen addition by PIII treatment, with and without sample heating, under cyclic load. PIII conditions, at 390 °C, were DC voltage of 9.5 kV, frequency of 1.5 kHz and pulse of 40 μs. PIII conditions, with sample heating at 800 °C, were 7 kV, 0.4 kHz and 30 μs. Axial fatigue tests were performed on untreated and treated samples for resistance to fatigue comparison. The untreated Ti-6Al-4V had an annealed microstructure, PIII treatment at 390 °C resulted in a microstructure that has no nitride layer or diffusion zone. In the PIII treatment at 800 °C, the microstructure presented nitride layer and diffusion zone. Resistance to fatigue decreased with PIII treatments in both temperatures. At 390 °C, the treatment created deformation regions and cracks on surface due to nitrogen implantation that formed solid solution with titanium and imposed lattice strains on the crystal lattice. At 800 °C, bulk ductility decrease, increasing of αTi proportion in microstructure due to α case formation and the presence of a ceramic layer dropped fatigue resistance of Ti-6A-4V alloy.
Highlights
Industry applies titanium alloys in the biomedical, petrochemical, automotive and aeronautical field
Annealed Ti6Al4V alloy was subjected to Plasma immersion ion implantation (PIII) treatment at 800 °C and had the microstructure changed during the treatment
This study reported the results involving untreated and PIII treated Ti-6AL-4V alloy, at different work temperatures, and submitted to axial fatigue loading
Summary
Industry applies titanium alloys in the biomedical, petrochemical, automotive and aeronautical field. The aeronautical industry accounts for about 80% of all worldwide titanium demand and is, the main application field, being Ti-6Al-4V alloy the most used of the titanium alloy family. Titanium alloys have the highest specific resistance among structural materials, which means that they are as light as aluminum alloys and mechanical resistant as microalloyed steel [1,2,3,4]. Even though the applied stress is below the yield strength (σys), these components may fail due to fatigue. This failure mode involves nucleation, crack propagation stages and subsequent catastrophic failure (including materials that exhibit ductile behavior). Among the aspects that change fatigue life, surface characteristics are critical because, in most cases, crack nucleation starts at the surface [5, 6]
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