Martin Balog

Compaction of ultra-fine Al powders

The possibility of preparing bulk sub-micron grained profiles with superior mechanical properties was investigated. A bottom-up route was used, wherein commercial ultra-fine powders were consolidated with the aim of preserving the initial fine-grained structure and thus obtain unique mechanical properties. A relatively simple and cheap technique for preparation of Al bulk profiles through conventional direct extrusion compaction was established. During extrusion initial powder particles were deformed and fragmentised into ultra-fine elongated grains mostly aligned along the extrusion direction. Moreover, extensive energy induced into the input powder during compaction yielded fine distorted oxide dispersoids homogenously distributed within the final compacts. These do in fact represent MMC where Al matrix is reinforced with nanoscale alumina particles. The influence of powder size and other processing parameters on consolidation behaviour and mechanical properties of compacted profiles, their structure and thermal stability are reported and discussed. Overall comparison with conventionally prepared SAP materials is made.

The effect of a particle–matrix interface on the Young’s modulus of Al–SiC composites

In order to improve the Young’s modulus of Al–SiC composites, the matrix-reinforcement interface was modified via chemical reactions between the Al matrix and SiC particles. To prepare diverse interfaces, various types of composites were fabricated using the direct hot extrusion of Al-based powder mixtures containing 30 vol% untreated or oxidized SiC particles. The extruded composites were subjected to different annealing treatments. A detailed microstructural characterization of the Al–SiC interfacial regions was performed. The effect of the interface on the Young’s modulus and on the other mechanical properties of the composites was systematically investigated. Depending on the interface quality, the Young’s modulus of the composites can be varied over the range of 88–121 GPa. The results proved the importance of a stiff phase—comparable to SiC stiffness at the interface, which leads to the SiC particles contributing more effectively to the increase in the composite Young’s modulus. Conversely, the segregation of liberated Si at SiC interface led to decrease of composites Young’s modulus.

CP Ti Fabricated by Low Temperature Extrusion of HDH Powder: Application in Dentistry

Powder metallurgy (PM) commercial purity titanium (CP Ti) was fabricated and studied, with an aim of utilization for dental application. PM CP Ti was manufactured using a cost effective approach, where affordable hydrogenation–dehydrogenation (HDH) process Ti 99.4 wt.% powder was consolidated via the following sequence of PM techniques: cold isostatic pressing, warm vacuum pressing at 420 °C and warm direct extrusion at 500 °C. The paper presents the first studies on processing, microstructure, testing of mechanical properties, fatigue performance and bonding strength with different veneer coatings. By employed consolidation process sound material with low porosity (1.5%) and sustained oxygen content (0.21 wt.%) was attained. The tensile properties obtained for PM CP Ti (UTS = 701 MPa, YS0.2 = 512 MPa, ε = 13 %) were improved over to those for cast / milled CP Ti Grade 4 reference, the material commonly used in dentistry. Tested using the ISO 14801 standard for dental implants, the samples machined from PM CP Ti showed fatigue performance similar to CP Ti Grade 4. PM CP Ti used as a metal base material in restoration metal – ceramic systems showed very good bond strength with three commercially available veneering ceramics and complied with the ISO 9693 standard. Within the limitations of this paper, the preliminary results demonstrated that performance of economic PM CP Ti is equal or superior to CP Ti Grade 4 reference material and it can be used in prosthodontics.

Novel Ultrafine-Grained Aluminium Metal Matrix Composites Prepared from Fine Atomized Al Powders

The paper reviews the developments to date of novel ultrafine-grained (UFG) Al metal matrix composites (MMCs) reinforced and stabilized with nanometric Al2O3 phase produced in situ by compaction of fine gas-atomized Al powders. This is followed by a discussion of the recent developments of the novel UFG Al-AlN MMCs produced by partial nitridation of fine gasatomised Al powders. The paper summarizes previously published data with an addition of the new unpublished results.

High strength potential of aluminium nanocomposites reinforced with nonperiodical phases

Extrusion of rapidly solidified Al94V4Fe2 ribbons and Al94V4Fe2/Al powder mixtures was studied. TEM studies revealed microstructural heterogeneity in as-received ribbons containing α-Al, quasicrystalline, nanoscale amorphous and Al10V intermetallic phases. Bulk profiles containing different amounts of cryo-milled Al94V4Fe2 particles and Al powders were prepared via hot extrusion. Temperature was found to play the decisive role in the extrusion process. The lack of plasticity led to insufficient material flow during extrusion and was found responsible for the formation of macroscopic voids. Al94V4Fe2 extruded bars exhibited quite satisfactory properties in compression tests, however preliminary failed in tensile tests due to insufficient consolidation. The addition of 1 mm Al powder into the Al94V4Fe2 particles yielded extrusions at lower loads or at lower temperatures, resulting in composite samples with Al matrix reinforced with nanoscale nonperiodic phases. This approach appeared quite promising for the overall design of applicable technological routes inducing the non-periodic structures into bulk profiles.

Bioactive Ti + Mg composites fabricated by powder metallurgy: The relation between the microstructure and mechanical properties

Metallic implant materials are biomaterials that have experienced major development over the last fifty years, yet some demands posed to them have not been addressed. For the osseointegration process and the outcome of endosseous implantation, it is crucial to reduce the stress shielding effect and achieve sufficient biocompatibility. Powder metallurgy (PM) was utilized in this study to fabricate a new type of titanium (Ti) + magnesium (Mg) bioactive composite to enable stress-shielding reduction and obtain better biocompatibility compared with that of the traditional Ti and Ti alloys used for dental implants. Such composites are produced by well-known cost-effective and widely used PM methods, which eliminate the need for complex and costly Ti casting used in traditional implant production. The relation between the microstructure and mechanical properties of as-extruded Ti + (0-24) vol% Mg composites was investigated with respect to the Mg content. The microstructure of the composites consisted of a biodegradable Mg component in the form of filaments, elongated along the direction of extrusion, which were embedded within a permanent, bioinert Ti matrix. As the Mg content was increased, the discrete filaments became interconnected with each other and formed a continuous Mg network. Youngs modulus (E) of the composites was reduced to 81 GPa, while other tensile mechanical properties were maintained at the values required for a dental implant material. The corrosion behavior of the Ti + Mg composites was studied during immersion in a Hanks balanced salt solution (HBSS) for up to 21 days. The elution of Mg pores formed at former Mg sites led to a further decrease of E to 74 GPa. The studied compositions showed that a new Ti + Mg metallic composite should be promising for load-bearing applications in endosseous dental implants in the future.

Ultra-lightweight superconducting wire based on Mg, B, Ti and Al

Actually, MgB2 is the lightest superconducting compound. Its connection with lightweight metals like Ti (as barrier) and Al (as outer sheath) would result in a superconducting wire with the minimal mass. However, pure Al is mechanically soft metal to be used in drawn or rolled composite wires, especially if applied for the outer sheath, where it cannot provide the required densification of the boron powder inside. This study reports on a lightweight MgB2 wire sheathed with aluminum stabilized by nano-sized γ-Al2O3 particles (named HITEMAL) and protected against the reaction with magnesium by Ti diffusion barrier. Electrical and mechanical properties of single-core MgB2/Ti/HITEMAL wire made by internal magnesium diffusion (IMD) into boron were studied at low temperatures. It was found that the ultra-lightweight MgB2 wire exhibited high critical current densities and also tolerances to mechanical stress. This predetermines the potential use of such lightweight superconducting wires for aviation and space applications, and for powerful offshore wind generators, where reducing the mass of the system is required.

Reinforcement Size Dependence of Load Bearing Capacity in Ultrafine-Grained Metal Matrix Composites

The length-scale effects on the load bearing capacity of reinforcement particles in an ultrafine-grained metal matrix composite (MMC) were studied, paying particular attention to the nanoscale effects. We observed that the nanoparticles provide the MMCs with a higher strength but a lower stiffness compared to equivalent materials reinforced with submicron particles. The reduction in stiffness is attributed to ineffective load transfer of the local stresses to the small and equiaxed nanoparticles.

Warm Pressing of Al Powders: An Alternative Consolidation Approach

This paper presents the warm pressing as an alternative powder metallurgy approach to conventional press-and-sinter or hot working (e.g., extrusion, forging) consolidations of Al powders into complex near-net-shape parts with required mechanical properties. In this study gas-atomized Al powders (A1050 and A6061) with various particle sizes were consolidated by uniaxial pressing, with minimum plastic deformation induced, at temperatures of 22 and 430 °C, respectively. The materials pressed at 22 °C showed poor strengths, ductility and electrical conductivity. The properties were improved markedly when pressing temperature increased to 430 °C and reached values comparable to A1050 and A6061 materials fabricated by conventional powder and ingot metallurgy approach. Similarly, the properties of the materials pressed at 22 °C were improved after annealing at 300 °C for 2 h. This indicated the formation of sufficiently strong interfacial bonding between native oxide layers on adjacent Al powder particles (i.e., grains) when processing temperature increased to 300 °C. With interfacial bonding established, the fracture mechanism changed from brittle to ductile character.

Titanium-Magnesium Composite for Dental Implants (BIACOM)

We report on the study on the titanium-magnesium (Ti–Mg) bioactive metal-metal composite utilized for a fabrication of dental implants. The biomedical Ti-12vol.%Mg composite, named BIACOM, is manufactured using a cost effective approach, where a mixture of elemental Ti and Mg powders is extruded at low temperature to sound profiles. Microstructure of composite comprises filaments of biodegradable Mg component, which are arrayed along extrusion direction and are homogenously distributed within permanent, bioinert Ti matrix. Compared to Ti Grade 4, the reference material used for dental implants, the properties of as-extruded composite include significantly reduced Young’s elastic modulus (92.1 GPa) and low density (4.12 g.cm−3), while the mechanical strength of Ti Grade 4 is maintained. Dynamic testing of dental implants fabricated from as-extruded composite, realized to follow the ISO 14801 standard for endosseous dental implants, confirms fatigue performance of BIACOM implants equal to the one of the reference material. Exposure of as-extruded composite samples to Hank’s solution, realized in order to simulate behavior in human body over the time after implantation, yields gradual dilution of Mg from composites surface and volume. Corroded Mg leaves at prior Mg filament sites pores within Ti matrix, which remains intact. This provides further decrease of Young’s modulus and enhances macro and micro roughness at implants surface. As a result, BIACOM shows improved mechanical compatibility (i.e., reduction of stress-shielding) and better osseointegration potential.