K.G. Prashanth

Production of Porous β-Type Ti-40Nb Alloy for Biomedical Applications: Comparison of Selective Laser Melting and Hot Pressing

We used selective laser melting (SLM) and hot pressing of mechanically-alloyed β-type Ti–40Nb powder to fabricate macroporous bulk specimens (solid cylinders). The total porosity, compressive strength, and compressive elastic modulus of the SLM-fabricated material were determined as 17% ± 1%, 968 ± 8 MPa, and 33 ± 2 GPa, respectively. The alloy’s elastic modulus is comparable to that of healthy cancellous bone. The comparable results for the hot-pressed material were 3% ± 2%, 1400 ± 19 MPa, and 77 ± 3 GPa. This difference in mechanical properties results from different porosity and phase composition of the two alloys. Both SLM-fabricated and hot-pressed cylinders demonstrated good in vitro biocompatibility. The presented results suggest that the SLM-fabricated alloy may be preferable to the hot-pressed alloy for biomedical applications, such as the manufacture of load-bearing metallic components for total joint replacements.

Is the energy density a reliable parameter for materials synthesis by selective laser melting

ABSTRACT The effective fabrication of materials using selective laser melting depends on the process parameters. Here, we analyse the suitability of the energy density to represent the energy transferred to the powder bed, which is effectively used to melt the particles and to produce the bulk specimens. By properly varying laser power and speed in order to process the powder at constant energy density, we show that the equation currently used to calculate the energy density gives only an approximate estimation and that hatch parameters and material properties should be considered to correctly evaluate the energy density. GRAPHICAL ABSTRACT IMPACT STATEMENT Al-12Si SLM samples were fabricated at constant energy density. The laser power and laser scan speed combination variation was used to demonstrate the significant changes needed with energy density equation.

Fabrication and Response of Al70Y16Ni10Co4 Glass Reinforced Metal Matrix Composites

Al70Y16Ni10Co4 glass was developed through powder metallurgy route. Al-based glass-reinforced metal matrix composites were produced by hot pressing and simultaneous extrusion of these powders.The consolidation parameters were selected from systematic calorimetric studies. The response of these composites is superior mechanical properties, and these properties increases with glassy reinforcement. Remarkable improvement in the wear properties were observed when subjected to abrasion test. The abrasive wear rate has been decreased from 2.46 × 10−4 m3/m for commercial Al-Mg-Si (6061) extruded alloy to 0.373 × 10−4 m3/m for 50 vol% glass reinforced 6061 composite. Similar improvements were observed with glass-reinforced aluminum matrix composites. Plowing as well as pullout of particles during abrasion tests corresponds to the wear of these composites.

Production, Kinetic Study and Properties of Fe-Based Glass and Its Composites

Fe-based glassy powders with four different compositions of varying copper content were produced by mechanical alloying of elemental powder mixtures. The thermal stability as well as the crystallization kinetics was investigated using differential scanning calorimetry in both isochronal and isothermal modes. The isochronal and isothermal activation energies have a similar value (∼560–570 kJ/mol). In addition, the Johnson–Mehl–Avrami (JMA) analysis shows that the transformation is diffusion controlled three-dimensional process, and the crystallization proceeds with increasing nucleation rate. Metal matrix composites were synthesized through powder metallurgy methods by uniaxial hot pressing and subsequent extrusion of commercially pure Fe powders, blended with Fe-glass reinforcement. The resultant properties of the composites strongly depend on the composition of the glassy reinforcement.

Influence of Mechanical Activation on Decomposition of Titanium Hydride

TiH2 particles were mechanically activated up to 10 h. Differential scanning calorimetry (DSC) was used for the kinetic studies. It shows the activation energy required for TiH x to α-Ti transformation is 140 kJ/mol. The mechanism of decomposition and the influence of particle size on transformation temperature as well as the sequence have been studied, based on detailed isothermal heat treatments at various temperatures followed by X-ray diffraction (XRD) studies. Results suggest that mechanical activation has a strong influence in decreasing the transformation temperatures as well as the temperature difference between the first step and second step transformation process.

Kinetic analysis of the non-isothermal crystallization process, magnetic and mechanical properties of FeCoBSiNb and FeCoBSiNbCu bulk metallic glasses

The crystallization kinetics of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 and {[(Fe0.5Co0.5)0.75B0.2Si0.05]0.96Nb0.04}99.5Cu0.5 bulk metallic glasses were evaluated using differential scanning calorimetry under non-isothermal condition. The fully glassy rods with diameters up to 2 mm were obtained by copper mold injection casting. Both glasses show good thermal stability, but the addition of only 0.5% Cu completely changes the crystallization behavior. The average activation energy required for crystallization decreases from 645 kJ/mol to 425 kJ/mol after Cu addition. Upon heating, the Cu-free alloy forms only the metastable Fe23B6 phase. In contrast, two well-separated exothermic events are observed for the Cu-added bulk glassy samples. First, the (Fe,Co) phase nucleates and then (Fe,Co)2B and/or (Fe,Co)3B crystallize from the remaining glassy matrix. The Cu-added alloy exhibits a lower coercivity and a higher magnetic saturation than the base alloy, both in as-cast as well as in annealed condition. Besides, the...

Al-based metal matrix composites reinforced with nanocrystalline Al-Ti-Ni particles

Al-based metal matrix composites containing different volume fractions of nanocrystalline Al70Ti20Ni10 reinforcing particles have been produced by powder metallurgy and the effect of the volume fraction of reinforcement on the mechanical properties of the composites has been studied. Room temperature compression tests reveal a considerable improvement of the mechanical properties as compared to pure Aluminum. The compressive strength increases from 155 MPa for pure Al to about 200 and 240 MPa for the samples with 20 and 40 vol.% of reinforcement, respectively, while retaining appreciable plastic deformation with a fracture strain ranging between 43 and 28 %.

Structural and Mechanical Characterization of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 Bulk Metallic Glass

Thermal stability, structure and mechanical properties of the multi-component Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass have been studied in detail. The glassy material displays good thermal stability against crystallization and a fairly large supercooled liquid region of 52 K. During heating, the alloy transforms into a metastable icosahedral quasicrystalline phase in the first stage of crystallization. At high temperatures, the quasicrystalline phase undergoes a transformation to form tetragonal and cubic NiZr2-type phases. Room-temperature compression tests of the as-cast sample show good mechanical properties, namely, high compressive strength of about 1,630 MPa and fracture strain of 3.3%. This is combined with a density of 6.32 g/cm3 and values of Poisson’s ratio and Young’s modulus of 0.377 and 77 GPa, respectively. The mechanical properties of the glass can be further improved by cold rolling. The compressive strength rises to 1,780 MPa and the fracture strain increases to 8.3% for the material cold-rolled to a diameter reduction of 10%.

High strength nanostructured Al-based alloys through optimized processing of rapidly quenched amorphous precursors

We report the methods increasing both strength and ductility of aluminum alloys transformed from amorphous precursor. The mechanical properties of bulk samples produced by spark-plasma sintering (SPS) of amorphous Al-Ni-Co-Dy powders at temperatures above 673 K are significantly enhanced by in-situ crystallization of nano-scale intermetallic compounds during the SPS process. The spark plasma sintered Al84Ni7Co3Dy6 bulk specimens exhibit 1433 MPa compressive yield strength and 1773 MPa maximum strength together with 5.6% plastic strain, respectively. The addition of Dy enhances the thermal stability of primary fcc Al in the amorphous Al-TM -RE alloy. The precipitation of intermetallic phases by crystallization of the remaining amorphous matrix plays important role to restrict the growth of the fcc Al phase and contributes to the improvement of the mechanical properties. Such fully crystalline nano- or ultrafine-scale Al-Ni-Co-Dy systems are considered promising for industrial application because their superior mechanical properties in terms of a combination of very high room temperature strength combined with good ductility.

Influence of Powder Characteristics on Processability of AlSi12 Alloy Fabricated by Selective Laser Melting

Selective laser melting (SLM) is one of the additive manufacturing technologies that allows for the production of parts with complex shapes from either powder feedstock or from wires. Aluminum alloys have a great potential for use in SLM especially in automotive and aerospace fields. This paper studies the influence of starting powder characteristics on the processability of SLM fabricated AlSi12 alloy. Three different batches of gas atomized powders from different manufacturers were processed by SLM. The powders differ in particle size and its distribution, morphology and chemical composition. Cubic specimens (10 mm × 10 mm × 10 mm) were fabricated by SLM from the three different powder batches using optimized process parameters. The fabrication conditions were kept similar for the three powder batches. The influence of powder characteristics on porosity and microstructure of the obtained specimens were studied in detail. The SLM samples produced from the three different powder batches do not show any significant variations in their structural aspects. However, the microstructural aspects differ and the amount of porosity in these three specimens vary significantly. It shows that both the flowability of the powder and the apparent density have an influential role on the processability of AlSi12 SLM samples.