Carlos Eugênio Foerster

Nanomechanical and nanotribological properties of bioactive titanium surfaces prepared by alkali treatment.

Alkali-heat treatment (AHT) is a simple and practical method to make titanium surfaces bioactive. Hydroxyapatite nucleates on Ti when in contact with body fluids due to the presence of a thin sodium titanate film produced by the AHT. This method was proposed more than a decade ago and it has been widely investigated at varied scopes. However, there is still little information about the mechanical properties of this film. In this work, the tribo-mechanical behavior of films produced by alkali treatment (AT) and AHT on Ti is investigated using instrumented indentation technique. The films were also characterized by TF-XRD, SEM, EDS and in vitro bioactivity tests. Analytical methods were employed to obtain the mechanical properties of the film from instrumented indentation data. The heat treatment subsequent to the alkaline processing increased the film elastic modulus from 1.7 GPa to 2.8 GPa, the hardness from 12 MPa to 20 MPa and the critical load for scratch test from 1.5 mN to 5.5 mN. Despite the overall improvement in the film bioactivity and tribo-mechanical behavior, the AHT elastic modulus is only 2% of the pristine Ti whereas hardness is less than 1%. This information must be considered for implant design purposes.

A method to measure fracture toughness using indentation in REBa2Cu3O7-δ superconductor single crystals

A method is proposed to estimate indentation fracture toughness based on the critical load for crack nucleation calculated by the derivative of the loading curve. This method is applied to REBa2Cu3O7-δ superconductor single crystals based on xenotime, where is difficult to observe well defined radial crack lengths due to its lamellar structure. The indentation fracture toughness agrees well with that obtained from the traditional method based on radial crack propagation. The proposed procedure is an alternative technique to estimate indentation fracture toughness without the necessity of measuring radial cracks lengths while keeping the advantages of the traditional method.

Mechanical properties of highly oriented FeSe0.5Te0.5 superconductor

We have synthesized highly oriented samples of the superconducting compound FeSe0.5Te0.5 and investigated its mechanical properties. These samples were characterized by scanning electron microscopy (SEM) with energy-dispersive analysis, x-ray diffraction, and electrical resistivity. The measured critical temperature is TC~ 14.5 K. Hardness and elastic modulus on the ab- and a(b)c-plane were obtained by instrumented indentation. The samples’ morphology consists of plate-like crystals with a lamellar structure. Two phases were observed with a typically eutectic microstructure composed by white and gray lamellas when observed with SEM using backscattered electrons. The white phase is richer in Te and poorer in Se than the gray phase. No significant differences in hardness and elastic modulus were observed between ab- and a(b)c-planes. Hardness profiles indicated values in the range 0.6–0.8 GPa at deep tip penetration depths, while the elastic modulus showed values in between 20–25 GPa. Cracking was occasiona...

Low‐temperature iron‐nitride phase transformations induced by ion bombardment

We show that for the Fe–N system the combined use of ion irradiation and thermal annealing can lower the temperature for a given phase transformation. By Ar bombarding N‐implanted Fe samples at 250 and 300 °C, we have induced the e‐Fe2N⇒e‐Fe2+xN+e‐Fe3.2N and the e‐Fe2N⇒e‐Fe3N+γ′‐Fe4N phase transformations, respectively. These temperatures are 50 °C lower than the ones needed to produce the same transformations by thermal annealing.

Mechanical and Tribological Properties of LDX2101 Duplex Stainless Steel Submitted to Glow Discharge Ion Nitriding

In this paper, the mechanical and tribological properties of LDX2101 duplex stainless steel submitted to glow discharge (GD) nitriding and conventional ion beam nitrogen implantation (II) are reported. Different combinations of rich and poor nitrogen/hydrogen atmospheres and working GD temperatures are employed. Nitrogen II at room temperature and 350°C was performed at different energies and fluences in order to obtain a plateau distribution around 27 at.% until a depth of 400 nm. X-ray diffraction investigation indicated that the poor nitrogen atmosphere in GD processes is more efficient to produce expanded austenite and nitride precipitates at all temperatures. Nitrogen II, even at high temperature, produced only expanded austenite. The hardness of the nitrided surface region is about 18 GPa compared to ~ 3.3 GPa of the pristine condition. Wear resistance can be improved by one order of magnitude, independent of the GD nitrogen/hydrogen atmosphere, even at 300°C, where only expanded austenite is present.

Influence of Ar bombardment on the thermal behavior of nitrides produced by N implantation into Fe

The effects of Ar bombardment and thermal annealing on nitrides produced by N implantation in Fe were studied using conversion electron Mossbauer spectroscopy (CEMS). The results show that the Ar bombardment affects the thermal behavior of the nitrides, raising their temperature of dissolution. In addition it is shown that this retention temperature depends strongly on the thermal history of the (nitride-Ar) complexes formed as a consequence of the implantation process.

Kr and N implantations in a stainless steel AISI304L: thermal evolution

Abstract The evolution of nitrides produced by N-implantation of stainless steel samples previously bombarded with Kr and annealed up to temperature corresponding to 0.5 of the melting point is studied. Transmission electron microscopy shows the size evolution of the bubbles. The dependence of the bubbles on the nitride evolution is established by conversion electron Mossbauer spectroscopy and a retention of e-(Fe,Cr,Ni) 2 + x N up to 400°C was observed. Between 450 °C and 650 °C the presence of a magnetic field characteristic of the α-Fe phase was observed. The evolution of the N-profile was obtained by nuclear reaction analysis.

Modification of the thermal behavior of nitrides induced by Ar bombardment in a nitrogen implanted iron

It is known that nitrides obtained by N implantation into Fe are stable only up to 400°C. In the present work we report results where we show that Ar bombardment of nitrides changes significantly not only the retention and thermal behavior of the nitrides, but also their characteristics. We have produced the nitrides by N implantation into Fe. Then, we have bombarded the precipitates with Ar and subsequently submitted the samples to thermal annealings between 200 and 530°C. We observed that for increasing Ar bombarding fluences, there is an increase not only in the amount of retained nitrides but also in the retention temperature which goes up to 500°C.