Abstract: The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel
has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the
milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the
(XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and
Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L
stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.
Abstract: It is discussed the difference between the magnetic reversal mechanisms: i) coherent
rotation, ii) nucleation, iii) unpinning of domain walls. The main argument to suggest pinning as
the coercivity mechanism of Sm(CoFeCuZr)z magnets is the low initial susceptibility of
magnetization curves of thermally demagnetized magnets. However, coherent rotation also implies
in low initial susceptibility, since the grain size of the magnets is near the single domain particle
size. It is unlikely that pinning could be the coercivity mechanism in this case, since the anisotropy
field of Sm2Co17 phase is 65 kOe, whereas the coercivity of magnets can be higher than 40 kOe.
Such coercive field of 60% of the anisotropy field indicates coherent rotation as mechanism. A
model for describing the abnormal coercivity behavior in Sm(CoFeCuZr)z magnets is proposed.
Abstract: ZnO has received great attention in many applications due to its electronic and
optical properties. We report on the preparation of ZnO and gallium-containing ZnO
(ZnO:Ga) nanoparticles by the precipitation method. The nanoparticles have the wurtzite
structure and a high crystallinity. Gallium ions are present as Ga3+, as evidenced by the
binding energies through XPS. Porosity and surface area of the powder increased under
increasing gallium level, explained by the smaller particle size of ZnO:Ga samples compared
with ZnO. The estimated optical band gap of ZnO was 3.2 eV, comparable to ZnO:Ga.
Abstract: The corrosion resistance of 17-4PH stainless steel obtained by powder injection
molding (PIM) was investigated in a phosphate buffer solution (PBS) that simulates
physiological solution and compared with that of 17-4PH steel obtained by conventional
metallurgy. The corrosion resistance was investigated by electrochemical techniques for
different immersion times. The cytotoxicity of both types of 17-4PH steel was also
investigated using a minimum Eagle’s medium (MEM). The MEM solution is a type of cell
culture medium, which simulates physiological fluids. The cytotoxicity assay was carried out
by neutral red uptake methodology utilizing NCTC L929 cell line from ATCC bank and none
of the steels showed cytotoxic effects. The resulting extracts obtained by immersion of the
steel samples in MEM were analyzed by neutron activation analysis and the results indicated
liberation of chromium and cobalt as corrosion products but in very low amounts. The
electrochemical evaluation of both steels indicated that they are passive in PBS but presented
susceptibility to pitting. The 17-4PH PIM steel was slightly more susceptible to pitting than
that fabricated by conventional metallurgy due to its inherent porosity.
Abstract: The use of titanium and its alloy as biomaterial is increasing due to their low
modulus, superior biocompatibility and enhanced corrosion resistance when compared to
more conventional stainless steel and cobalt-based alloys. Ti-13Nb-13Zr is a titanium alloy
specifically developed for surgical implants. In this work, highly porous titanium foams, with
porosities above from 50%, are reached using an efficient powder metallurgical process,
which includes the introduction of a selected spacer into the starting powders. Samples were
produced by mixing of initial metallic powders followed by uniaxial and cold isostatic
pressing with subsequent densification by sintering. The samples presented a Widmanstättenlike
microstructure in an open cellular morphology with pore size between 200-500 μm.
Abstract: Thermomechanical and electrical properties of zirconia-based ceramics have led to
a wide range of advanced and engineering ceramic applications like solid electrolyte in
oxygen sensors, fuel cells and furnace elements and its low thermal conductivity has allowed
its use for thermal barrier coatings for aerospace engine components. A comparison
between CoNiCrAlY bond coat and zirconia plasma sprayed coatings on creep tests of the
Ti-6Al-4V alloy was studied. The material used was commercial Ti-6Al-4V alloy. 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. Constant load creep tests were
conducted on a standard creep machine in air on coated samples, at stress levels of 520
MPa at 500°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Results
indicate that the creep resistance of the ceramic coating was greater than metallic coating.
Abstract: Porosity and pore size are critical features for biomaterial scaffolds as they play an
essential role in bone formation and bone ingrowth in vivo. Therefore, techniques for
scaffolds evaluation are of great importance for their design and processing. Porous titanium
has been used for grafts and implant coatings as it allows the mechanical interlocking of the
pores and bone. In this study, porous titanium samples were manufactured by powder
metallurgy. The porosity quantification was assessed by optical quantitative metallographic
analysis, and non-destructive gamma-ray transmission and X-ray microtomography
techniques, in order to compare their efficacy for porosity evaluation. Pore morphology and
surface topography were characterized via scanning electron microscopy. These techniques
have demonstrated to be suitable for titanium scaffolds evaluation, and micro-CT was the one
that allowed the three-dimensional porosity assessment.
Abstract: Fine magnetic powder has been produced using the hydrogenation
disproportionation desorption and recombination (HDDR) process. The first goal of this work
involved an investigation of a range of disproportionation/desorption temperatures between
800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy.
The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum
disproportionation temperature for achieving high anisotropy was 820°C. The influence of the
reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR
powders and magnets has been shown. A second stage of this study involved the
characterization, for each temperature, of the HDDR processed powder using X-ray
diffraction analysis. Samples of the HDDR material have been studied by synchrotron
radiation powder diffraction using the Rietveld method for cell refinement, phase
quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has
also been employed to reveal the morphology of the HDDR powder.