Marcela Lieblich

Mechanical properties of some PM aluminide and silicide reinforced 2124 aluminium matrix composites

Tensile properties of PM 2124 aluminium composites reinforced with Ni3Al, NiAl, Cr3Si and MoSi2 intermetallic powder particles have been investigated in tempering conditions T1 and T4. Intermetallics were produced by selfpropagated high-temperature synthesis and composite powders consolidated by extrusion. 2124/MoSi2 showed the highest thermal stability, and the best mechanical properties even after comparison with those of 2124/SiC composite after processing through the same route. 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Influence of extrusion temperature on the aging behavior of 6061Al-15vol%SiCw composites

It is known that some discontinuously reinforced metal matrix composites, MMCs, with precipitation hardenable matrices, like 6061Al with SiC whiskers or particles, show faster aging behavior than the unreinforced alloys. Regarding the influence of processing techniques on the aging behavior, some investigations have found acceleration on aging of materials consolidated by powder metallurgy (PM) with respect to materials consolidated by ingot metallurgy (IM). This was attributed to the higher presence of oxide inclusions in the PM than in the IM materials. For a given composite preparation technique, however, the influence of the processing variables on the aging response has been barely studied. In this work, the effect of extrusion temperature on the aging of 6061Al-15vol%SiC{sub w} composites processed by a powder metallurgy route is investigated. The results obtained in this research go deep into the influence of the dislocation density on both the accelerated aging and the increase in strength of composites. Whereas the effect of dislocation density on accelerated aging is well documented, its effect on the strength of MMCs is not yet clear.

Thermal stability of an AlNi3Al composite processed by powder metallurgy

Abstract The potential of Al Ni 3 Al composites for high-temperature applications, especially when friction is involved, is currently being explored. In this work, the thermal stability of an Al Ni 3 Al composite obtained by extrusion of Al and 5 vol% of spherical Ni3Al powder particles was investigated at temperatures up to 500 °C. The metal/intermetallic composite proved stable up to 300 °C. At higher temperatures, dissolution of Ni3Al particles occurred with formation of concentric layers of Al3Ni and Al3Ni2 phases. The amount of Ni aluminides for each annealing condition was determined by applying a specifically developed mathematical procedure. Dissolution of Ni3Al up to 500 °C was found to obey a parabolic-type law with an activation energy of 156 kJ mol−1. Activation energies for growth of Al3Ni2 and Al3Ni were 209 and 110 kJ mol−1, respectively, in agreement with the literature. The thermal stability shown by this composite makes it a good candidate for high-temperature applications up to 300 °C.

Microstructural characterization of P/M Ni3Al consolidated by HIP

Abstract Rapidly solidified powder of Ni 3 Al doped with boron was produced by inert gas atomization and consolidated by hot isostatic pressing (HIP). Morphology and microstructure of the powder were studied. From the particle morphology, it could be deduced that the solidification time was similar at least to the time necessary for complete fragmentation of the liquid. The powder showed a two-phase microstructure that was finer the smaller the particle size. The presence of dendrites of NiAl (β) phase was consistent with the diagram proposed by Schramm and not with the traditional diagram of Singleton et al. The microstructure of the material consolidated at 1100°C and 1200°C was studied. A monophasic structure was observed after HIP, and no relevant microstructural differences were seen between the two temperatures used.

Extrudability of PM 2124/SiCp aluminium matrix composite

Abstracts are not published in this journal

Aluminum/Ni3Al composites processed by powder metallurgy

Abstract The suitability of powder metallurgy for processing aluminium matrix composites reinforced with Ni 3 Al powder particles was evaluated. The composite exhibited a sound bond between the matrix and reinforcement, with no interfacial reaction during consolidation by extrusion or even after a heat treatment of 1000 h at 300 °C. These results show the advantages of powder metallurgy compared with ingot metallurgy.

Amorphous and nanostructured Al–Fe–Nd powders obtained by gas atomization

Abstract In this work, an Al90Fe5Nd5 alloy was atomized and its microstructure, thermal stability, transformation sequence and microhardness investigated as a function of powder particle size. The atomized powder contained on average a 25% volume fraction of amorphous materials, reaching 42% in the

Thermal oxidation of medical Ti6Al4V blasted with ceramic particles: Effects on the microstructure, residual stresses and mechanical properties

Roughening of Ti6Al4V by blasting with alumina or zirconia particles improves the mechanical fixation of implants by increasing the surface area available for bone/implant apposition. Additional thermal oxidation treatments of the blasted alloy have already shown to be a complementary low-cost solution to enhancing the in vitro biocompatibility and corrosion resistance of the alloy. In this work, the effects of oxidation treatment on a grit blasted Ti6Al4V biomedical alloy have been analysed in order to understand the net effect of the combined treatments on the alloy fatigue properties. Synchrotron radiation diffraction experiments have been performed to measure residual stresses before and after the treatments and microstructural and hardness changes have been determined. Although blasting of Ti6Al4V with small spherical zirconia particles increases the alloy fatigue resistance with respect to unblasted specimens, fatigue strength after oxidation decreases below the unblasted value, irrespective of the type of particle used for blasting. Moreover, at 700°C the as-blasted compressive residual stresses (700MPa) are not only fully relaxed but even moderate tensile residual stresses, of about 120MPa, are found beneath the blasted surfaces. Contrary to expectations, a moderate increase in hardness occurs towards the blasted surface after oxidation treatments. This can be attributed to the fact that grit blasting modifies the crystallographic texture of the Ti6Al4V shifting it to a random texture, which affects the hardness values as shown by additional experiments on cold rolled samples. The results indicate that the oxidation treatment performed to improve biocompatibility and corrosion resistance of grit blasted Ti6Al4V should be carried out with caution since the alloy fatigue strength can be critically diminished below the value required for high load-bearing components.

In vitro degradation of biodegradable polylactic acid/magnesium composites: Relevance of Mg particle shape

UNLABELLED Absorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone in the implantation site. In this work, biodegradable composites formed by a polylactic acid matrix reinforced with 10%wt. magnesium microparticles were processed and their in vitro degradation investigated during 28 days. A joint analysis of the amount of H2 released, the changes in pH in buffered (PBS) and non-buffered media (distilled water), the variations in mass, microstructure and the mechanical performance of the specimens was developed. The main aim was to elucidate the relevance of Mg particles shape on tailoring the degradation kinetics of these novel composites. The results show that the shape of the Mg reinforcing particles plays a crucial role in the degradation rate of PLA/Mg composites, with spherical particles promoting a lower degradation rate than irregular particles. This fact is only partially due to the smaller surface area to volume ratio of the spherical particles. Irregular particles promote a faster formation of cracks and, therefore, an increasingly faster degradation of the polymeric matrix. In every case, the amount of H2 released by the composites was well below that released by monolithic Mg. The pH of PBS during degradation remained always within 7.2 and 7.4. PLA/Mg reinforced with spherical particles retains more than 90% of its mechanical properties after 7 days of immersion and more than 60% after 28 days. STATEMENT OF SIGNIFICANCE The increasing demand for temporary orthopaedic implants is the driving force to seek new strategies to decrease costs and simultaneously improve patients comfort as well as simplify surgical procedures. Resorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone. We are presenting for the first time results of the degradation kinetics of a new material based on polylactic acid reinforced with 10%wt. Mg microparticles. This work analyzes the relevance of Mg particle shape (irregular and spherical) on tailoring the degradation behaviour of these composites. Conclusions withdrawn from this study help to customize bioabsorbable materials in order to meet the requirements for a specific application and patient.

Significance of the contacting and no contacting thermoelectric power measurements applied to grit blasted medical Ti6Al4V

Grit blasting is a surface plastic deformation technique aimed to increase the surface area available for bone/implant apposition, which contributes to improve fixation and mechanical stability of Ti-6Al-4V implants. Besides roughening, grit blasting also causes surface contamination with embedded grit particles and subtle subsurface microstructural changes that, although does not challenge their biocompatibility, might influence other surface dominated properties like corrosion and ion release. Additional benefits are expected due to the induced compressive residual stresses, hence enhancing fatigue strength. The net effect depends on the type of particles used for blasting, but also on the amount of the subsurface cold work associated to the severe surface plastic deformation. In this work we study the potential of the non-contacting and contacting thermoelectric power (TEP) measurements in the analysis of the global changes induced in the Ti6Al4V when blasting the alloy with Al2O3 or ZrO2 particles, which yields a coarse and a fine rough surface, respectively. To reveal the effect of residual stresses, a set of specimens were thermally treated. The study proves that the non-contacting technique is more sensitive to the presence of residual stresses, whereas the contact technique is strongly influenced by the grain size refinements, work hardening and changes in solute.