Plasma immersion ion implantation (PIII) influence on Ti-6Al-4V alloy: Frequency effect

The plasma immersion ion implantation treatment (PIII) acts to increase mechanical resistance with solid solution formation, new phases and defects inclusion, besides chemical and residual stress profile modification. Ti-6Al-4V alloy presents poor tribological properties and high affinity with interstitial elements, such as nitrogen and oxygen, this makes it more reactive at high temperatures. This paper aims to study Ti-6Al-4V alloy fatigue behavior subjected to nitrogen addition by plasma immersion ion implantation. It was investigated the frequency parameter influence on fatigue resistance. Ti-6Al-4V alloy was PIII treated with voltage equal to 9.5 kV, frequencies varying between 1000 and 1500 Hz and submitted to axial fatigue tests. Axial fatigue tests were performed, at room temperature and R = 0.1. Ti-6Al-4V alloy fatigue results were supported by Weibull statistics analysis. Ti-6Al-4V alloy microstructural analysis showed equiaxed alpha + beta grains. Weibull analysis at untreated condition presented m values greater than 1, indicating reliability and uniformity. For a lifetime of 10(7) cycles, fatigue resistance was equal to 829 MPa for untreated condition, 644, 767 and 417 MPa, for f = 1000, 1200 and 1500 Hz, respectively. The nitrogen-based compounds were detected only at the condition where f = 1200 Hz. Thus, the combination of PIII treatment parameters, when f = 1200 Hz, hindered crack nucleation and increasing fatigue resistance of treated Ti-6Al-4V alloy when compared with the other two treatment conditions.