Maria Margareth da Silva

Improvement of tribological properties of Ti6Al4V by nitrogen plasma immersion ion implantation

Plasma immersion nitrogen implantation of Ti6Al4V (TAV) alloy was carried out to improve the surface tribological properties of test samples for artificial heart valves. Our results show that a good implantation with nitrogen peak concentration of 40% was achieved but with only approximately 50 nm implanted layer, after 60 min of treatment. Longer treatments showed no improvement in the retained dose, probably due to sputtering effects. However, both significant reduction of friction coefficient and increase in hardness was seen even for such a shallow implantation. Furthermore, the hardness improvement extended to regions much deeper than the implanted layer. Improvements of the wear resistance of such nitrogen implanted Ti alloy is expected, increasing considerably the useful lifetime of components made of TAV which is finding widespread use in biomedical and aerospace applications.

Effects of Plasma Immersion Ion Implantation (PIII) of Nitrogen on Hardness, Composition and Corrosion Resistance of Ti-6Al-4V Alloy

Ti-6Al-4V samples have been treated by PIII processing at different temperatures (400-800 o C), treatment time (30-150 min) and plasma potential (100 and 420 V). Hardness measurements results showed an enhancement of the hardness for all implanted samples. XRD results detected the Ti2N phase and the best corrosion resistance was found for the samples processed at higher temperature and lower PIII time.

Comparative Study of Creep Resistance of a Ti-6Al-4V Alloy with Metallic and Ceramic Coatings

Titanium and its alloys are largely used for many industrial applications due to their high mechanical and corrosion resistance and low specific mass. Ti-6Al-4V alloy is the most used in aerospace industry and it is applied for the manufacturing of aircraft blades and steam turbines. This alloy has high affinity with oxygen which constrains its application at high temperatures due to creep resistance reduction. Methods to increase creep resistance of Ti-6Al-4V alloys includes the use of metallic coatings and its combination with ceramic thermal barrier coating deposition on the material surface. The aim of this work is to compare the creep behavior of Ti-6Al-4V alloy in three different conditions: uncoated, metallic coated, metallic + ceramic coated specimens. The metallic coating layer (CoNiCrAlY) and the ceramic coating (ZrO2 + 8wt%Y2O3) are both applied by plasma spray deposition technique. The specimens were submitted to constant load creep tests at 600oC and stress conditions of 125, 250 and 319MPa. Specimens of metallic + ceramic coating have presented higher creep resistance, longer lifetime and lower stationary creep rate when compared to uncoated and metallic coated specimens.

Evaluation of Creep Resistance and Superficial Study of Titanium Alloy Treated by PIII-N

The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. However, the high affinity to oxygen is one of the main factors that limit their application as a structural material at high temperatures. Materials with adequate behavior at high temperatures and in aggressive environments have become a scientific requirement for technological and economic reasons. The goal of this work is the roughness and creep studies of the Ti–6Al–4V alloy after treatment by the nitrogen Plasma Immersion Ion Implantation (PIII-N) process. The aim of this process is the improvement of the superficial mechanical properties of the Ti–6Al–4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests in 600 °C at 250 and 319 MPa. The techniques used in this work were Auger spectroscopy, Atomic Force microscopy (AFM), X ray, Raman spectroscopy and creep testing. The results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications.

Superficial Parameters Determination of the Ti-6Al-4V Alloy Submitted to PIII Treatment in Different Times of Implantation

The advancement of technology leads to the development of new materials improving their tribology properties. It can be noticed in different areas like aerospace industry, chemical and oil that need resistant material in high temperatures and aggressive environments. In this case, it is important to think in its tribological properties, like wear, oxidation, toughness, and hardness. An effective mean, economic and with easy application is the plasma immersion ion implantation (PIII) technique. In the case of difficult shapes, the material can be equally treated. In this work, the Ti-Al-4V alloy was submitted to PIII during 2 and 3 h. The comparative analysis to determine which of which time was more efficient related to the tribological improvement measured by Auger, X-ray diffraction and wear. It will be observed images by MEV of the alloy submitted to PIII treatment.

Comparation between Laser Surface Nitriding and Nitrogen Plasma Immersion Ion Implantation (N-PIII) on Creep Behavior of Ti-6Al-4V Alloy

Titanium alloys are widely used in machine building, aircraft manufacturing, medicine, motors, chemistry, and biomedicine due to their high strength-to-weight ratio, elasticity, corrosion resistance, and biocompatibility. In particular, Ti-6Al-4V containing (α + β) structure plays a very important role in aerospace industry in the manufacturing of components such as disks and blades for aircrafts turbines and structural forgings. However, one of the major factors limiting the life of titanium alloys in service is their degradation due to gaseous environments, in particular, to environments containing oxygen at elevated temperatures during long-term use. The sensitivity of titanium alloys to high-temperature exposure is a well-known phenomenon. When titanium alloys are heated to temperatures above approximately 800oC, oxygen, hydrogen and nitrogen can penetrate into them. The penetration of these elements increases hardness and brittleness while decreasing the toughness of the alloy. Laser surface nitriding is a technique used to modify the near-surface microstructure and/or composition by melting the surface using a high-power laser beam with reactive gas as a shrouding environment, forming a nitride layer on the surface of Ti–6Al–4V to improve the alloy’s tribological and mechanical properties. The results of laser gas nitriding of Ti–6Al–4V showed a significant increase of microhardness and enhanced erosion resistance significantly compared with untreated Ti–6Al–4V, since the nitride layer acts as a diffusion barrier for inward oxygen diffusion into the alloy, reducing the contribution of oxygen dissolution in the substrate to the total mass gain. Other important technique that was developed for the beneficial modification of surface sensitive properties is Nitrogen Plasma Immersion Ion Implantation N-PIII. A sample is immersed in plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. Enhancing of the hardness and wear process of the materials due to the N-enriched layer caused by diffusion of N in the sample at PIII process can be expected. Both techniques provide an improvement in the creep resistance. The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatments of laser nitriding and Nitrogen Plasma Immersion Ion Implantation N-PIII in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 oC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of laser nitriding and N-PIII was submitted to creep tests at 600 oC in the stress of 250 MPa and 319 MPa, under constant load mode. The creep parameters are determined and a comparative analysis is established with the results gotten from the alloy with both treatments. The laser nitrided has showed an improved creep behavior compared with the same alloy with N-PIII coating, with a reduction in the creep rate and increasing the creep lifetime.

Comparation between PIII Superficial and Ceramic Coating in Creep Test of Ti-6Al-4V Alloy

The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatment of PIII superficial treatment and ceramic coating in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190oC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treat-ment of PIII and ceramic coating was submitted to creep tests at 600°C and 250 and 319 MPa under constant load mode. In the PIII treatment the samples was put in a vacuum reactor (76x10-3 Pa) and implanted by nitrogen ions in time intervals between 15 and 120 minutes. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The obtained results suggest the ceramic coating on Ti-6Al-4V alloy improved its creep resistance.

Surface Modification of Ti6Al4V Alloy by Two Process: Immersion Ion Implantation and Plasma Jet

The present work was aimed to study the improvement of mechanical characteristics of the Ti6Al4V alloy surface, induced by ion nitriding process. The increase of hardness and other improvements of the Ti6Al4V alloy surface allow wider applicability of this material in several industrial areas, in particular, biocompatibility applications. One of the used processes was Plasma Immersion Ion Implantation (PIII), where the threedimensional samples can be homogeneously treated. In such technique, the target is surrounded by the plasma and then pulse biased to high negative voltage. Another technique studied in this article was the process of nitrogen plasma jet. In this case, a reactor of low plasma density is the source of an expansion gas through a constriction hole that separates the source chamber from the vacuum chamber, where the nitriding is processed. Physical and chemical characterizations of nitrided samples were carried out to formulate the correlations between superficial characteristics of the material and of the parameters of the ion nitriding process.