Al0.1CoCrFeNi high-entropy alloy (HEA) was synthesized successfully from elemental powders by mechanical alloying (MA) and subsequent consolidation by spark plasma sintering (SPS). The alloying behavior, microstructure, and mechanical properties of the HEA were assessed using X-ray diffraction, electron microscope, hardness, and compression tests. MA of the elemental powders for 8 h has resulted in a two-phased microstructure: α-fcc and β-bcc phases. On the other hand, the consolidated bulk Al0.1CoCrFeNi-HEA sample reveals the presence of α-fcc and Cr23C6 phases. The metastable β-bcc transforms into a stable α-fcc during the SPS process due to the supply of thermal energy. The hardness of the consolidated bulk HEA samples is found to be 370 ± 50 HV0.5, and the yield and ultimate compressive strengths are found to be 1420 and 1600 MPa, respectively. Such high strength in the Al0.1CoCrFeNi HEA is attributed to the grain refinement strengthening.

Composites of 0–20 vol% Ti-coated cBN (cBN@Ti) particles dispersed in WC–Ni were densified by spark plasma sintering under 50 MPa at 1300 °C. The cBN particles were distributed homogeneously with a Ti-rich interfacial layer between the cBN particles and WC–Ni matrix. Increasing cBN@Ti to 20 vol% decreased the sample densification, but all the composites were still >97.5% dense. The Vickers hardness and flexural strength initially increased and then decreased, reaching the maximum values of 1820 HV10 with 15 vol% cBN@Ti and 1500 MPa with 5 vol% cBN@Ti, respectively, whereas the fracture toughness KIC gradually increased from 8 to 13 MPa m1/2. For cutting rocks, the wear significantly decreased with 5–15 vol% cBN@Ti but increased with 20 vol% cBN@Ti because of cBN particles pull-out.

A bulk NbCr2 Laves phase matrix composite toughened with ductile Cr phase has been fabricated by spark plasma sintering (SPS) using pre-alloyed NbCr2 and Cr powders. The sintering behaviour and phase morphological evolution of the sintered alloy were investigated. The results show that a series of microstructure evolutions along the sintering temperature occurred: elongated Cr phase with uniform dispersion of fine NbCr2 and Cr phase → coarse Cr phase with matured fine NbCr2 and Cr → coarse Cr and Nb phases with lamellar eutectics. The microstructural evolution and phase transformation along the sintering temperature are analyzed by considering the inhomogenous temperature distribution and the accelerated atomic diffusion due to the pulsed electric current applied during SPS. The room temperature fracture toughness of the sintered samples is expected to be markedly improved due to the absence of lamellar or the occurrence of ductile Cr and Nb phases.

A superelastic Ti–40Nb alloy enhanced with Cu element (0, 2.5, 5, 7.5, and 10 wt%) was synthesized by a spark plasma sintering method to obtain biomaterials with an antimicrobial effect. The microstructure results showed that β phase was the main phase in (Ti–40Nb)–Cu alloys while Ti2Cu was synthesized with the Cu addition above 5 wt%. (Ti–40Nb)–Cu alloys exhibited high compressive strength over 1693.08 MPa, high yield strength of 1140.26–1619.14 MPa, low elastic modulus in the range of 43.91–58.01 GPa, low elastic energy (14.81–24.73 MJ/m3), and together with large plastic strain over 18.5%. High concentration of Cu ion released steadily from alloys in early 7 days, then the released concentration of Cu ion showed long-lasting and moderate. Comparing with the Ti–40Nb alloy, high antimicrobial activity was pronounced on (Ti–40Nb)–Cu alloys, and (Ti–40Nb)–Cu alloys showed more inhibitory activity against bacteria (E. coli and S. aureus) than fungi (C. albicans). Cu contents in alloys influenced the Cu ion release, which in turn affected the antimicrobial activity. As a good combination of low elastic modulus, high mechanical properties, good elastic energy, and excellent antimicrobial performance, (Ti–40Nb)–Cu alloys offer potential advantages to prevent stress shielding and exhibit an excellent antimicrobial property for hard tissue replacements.

We present a novel route to fabricate 3D nanoporous α-Ti foams by dealloying of TiCu master alloy in solid state using Mg powders. Pure open-cell nanoporous α-Ti foams are fabricated with BET surface area of 34.4 ± 0.8 m2/g and pore size in the range of 2–50 nm. The dealloying using powders is a solid state chemical reaction process to form Cu2Mg phase and Ti/Mg nanocomposites. The constituent of Cu in the TiCu alloy was dissolved into Mg powders thanks to the kinetics of interface reaction and volume diffusion. The pore-forming mechanism is a solid-state interdiffusion process. The ligament coarsening is from 492 to 650 nm with increasing of the dealloying temperature. The hardness and elastic modulus in nanoporous α-Ti foam follow linear decay fit with ligament size increasing. Our results demonstrate a facile strategy for the fabrication of nanoporous Ti foams with novel nanostructures and tailored properties.

Different volume fractions (0.5–4.5 vol%) of carbon nanotubes (CNTs) were used to reinforce a binary Fe50Co soft magnetic alloy. The first method for dispersion involved dry mixing and ball milling of the powder, while the second included wet mixing in dimethylformamide under ultrasonic agitation, drying and then dry ball milling. The powders were consolidated using spark plasma sintering. Tensile test and SEM analyses were performed to characterize the mechanical properties and the fracture surface of the sintered materials. The best magnetic and mechanical properties were achieved using the first method. A maximum enhancement in tensile strength of around 20% was observed in the 0.5 vol% CNT composite with improved elongation compared to the monolithic Fe50Co alloy. In addition, the magnetic properties were enhanced by adding CNTs up to 1 vol%, and an improvement in densification was observed in composites up to 1.5 vol% CNT with respect to monolithic Fe50Co alloy.

Laves phase NbCr2-based composites toughened with different volume fractions of Cr phase were fabricated by spark plasma sintering (SPS). The microstructural evolution and mechanical properties of these spark plasma sintered NbCr2/Cr composites were investigated. The mechanical properties evaluations indicate that the introducing of Cr phase consolidated by SPS has a beneficial effect on the mechanical properties of the NbCr2 Laves phase. When the content of Cr phase in the NbCr2 Laves phase increases to 30 wt%, the hardness measured by a Berkovich nanoindenter operated with the continuous stiffness measurements mode attains the maximum value of 13.44 GPa, which is increased by about 56% over the as-cast NbCr2 Laves phase. More importantly, the room-temperature fracture toughness of the NbCr2-30wt%Cr alloy is increased to 18.9 MPa·m1/2, which is 16 times higher than that of the as-cast NbCr2 Laves phase (1.2 MPa·m1/2). The microstructural analysis indicates that the residual of Cr phase and formation of Nb solid solution can provide remarkable toughening of the NbCr2 Laves phase by fine grain toughening, dual ductile phase toughening, and interface toughening mechanisms. A possible formation mechanism of Nb solid solution during SPS has been proposed by considering the composition distribution.

The microstructural evolution during spark plasma sintering of ultrafine WC–1 wt% Si (n-WC–Si) is presented. At 1323 K (T < TmSi), extensive stacking faults on the $\left\{ {10\bar 10} \right\}$ prismatic planes are observed. The defect microstructure can be described as a combined shear of $1/6\left\langle {\bar 12\bar 13} \right\rangle$ on the prism planes and simultaneous out-diffusion of carbon through the faults to the interparticle boundaries. At temperatures near TmSi (1673 K), a large fraction of abnormally grown platelets is observed. These platelets contain a single planar defect on their basal planes, described by a ${1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}\left\langle {10\bar 10} \right\rangle$ translation of the carbon atoms across a Σ1 grain boundary (GB). Three factors contribute to the abnormally high density of platelets: (i) the low-temperature prismatic dislocations interact to form facet-roughening steps/kinks that act as nucleation sites, (ii) a liquid phase triggers an increased growth rate in the vicinity of the Si inclusions, and (c) the basal twin produces a re-entrant edge for 2D nucleation.

The NbCr2 Laves phase was fabricated by spark plasma sintering (SPS) using spherical Nb and Cr powders. The experimental results revealed that increasing the sintering temperature to 1773 K can result in the formation of NbCr2 Laves phase as major phase, but it always appeared with trace amounts of Nb and Cr solid solutions. Based on the theoretical calculations, the residual of Nb and Cr solid solutions was attributed to the inhomogeneous distribution of temperature increase from the particle-contacting surface to the center of particle when pulsed current passed through. Moreover, the hardness and fracture toughness of the SPS-processed NbCr2 attained 14.05 ± 0.67 GPa and 8.9 MPa·m1/2, which were 1.6 and 7.4 times of the as-cast NbCr2 Laves phase (1.2 MPa·m1/2). The formation of ductile Nb and Cr solid solutions and fine grains were considered to be the reason for the remarkable enhancements in mechanical properties.

The mechanisms of densification and creep were examined during spark plasma sintering (SPS) of alumina doped with a low and high level of zirconia or yttria, over a temperature range of 1173–1573 K and stresses between 25 and 100 MPa. Large additions of yttria led clearly to in situ reactions during SPS and the formation of a yttrium-aluminum garnet phase. Dopants generally lead to a reduction in the densification rate, with substantial reductions noted in samples with ∼5.5 vol% second phase. In contrast to a stress exponent of n ∼ 1 for pure alumina, the doped aluminas displayed n ∼ 2 corresponding to an interface-controlled diffusion process. The higher activation energies in the composites are consistent with previous data on creep and changes in the interfacial energies. The results reveal a compensation effect, such that an increase in the activation energy is accompanied by a corresponding increase in the pre-exponential term for diffusion.

We report on the occurrence of sinter-hardening with concurrent improved plasticity in fine-grained Fe79.3Mo4.5P8.1C6.75B1.35 bulk alloys fabricated by spark plasma sintering (SPS) of metallic glass composite powder. When the sintering temperature is higher than the austenite transformation temperature, the as-fabricated bulk alloys are composed of expected wattle martensite plus Fe3P, Fe7C3, and Fe3Mo3C. Meanwhile, the martensite-containing bulk alloys exhibit increased hardness, fracture strength as well as concurrent improved plasticity. The fracture stress and strain of the martensite-containing bulk alloys are as high as 2573 MPa and 8.6%, respectively. The formation of the martensite microstructure is attributed to that high sintering temperature leads to the austenitization transformation and consequently formed austenite partially transforms into martensite under rapid cooling rate provided by SPS system. The results obtained provide insight into fabrication of iron alloys with good mechanical property by powder metallurgy.

This study aims at presenting a way to obtain nanostructured materials. Austeniticstainless steel (316L) nanopowders and ferritic/martensitic alloy steels (Fe14Cr) aresintered with the Spark Plasma Sintering (SPS) technique. This technique leads to a fullydense/nano-sized microstructure material after a short treatment. The optimal sinteringtemperature was found to be 850°C for both materials. The relationship between the Vickers Hardnessand scale of the microstructure is in good agreement with the Hall-Petch Law.

The present work demonstrates the synthesis of Cu–10 wt% TiB2 composites with a theoretical density of more than 90% by tailoring the spark plasma sintering (SPS) conditions in the temperature range of 400–700 °C. Interestingly, 10 wt% Pb addition to Cu–10 wt% TiB2 lowers the sinter density and the difference in the densification behavior of the investigated compositions was discussed in reference to the current profile recorded during a SPS cycle. The sintering kinetics and phase assemblage were also discussed in reference to surface melting of the constituents prior to bulk melting temperature, temperature dependent wettability of Pb on Cu, diffusion kinetics of Cu as well as the formation of various oxides. An important result is that a high hardness of around 2 GPa and relative density close to 92% ρtheoretical was achieved for the Cu–10 wt% TiB2–10 wt% Pb composite, and such a combination has never been achieved before using any conventional processing route.

Development of metallic glasses is hindered by the difficulties in manufacturing bulk parts. We report on the preparation of glassy alloys using the spark plasma sintering of gas atomized powders. The Zr57Cu20Al10Ni8Ti5 alloy processed has a high glass forming ability. Densification is obtained at the glass transition temperature (390 °C) under high pressure (≈500 MPa). Systematic study of the effect of powder particles size and sintering time is performed through structural and thermal analyses. Local and partial devitrification of the amorphous alloy is detected, resulting from local temperature overshoots. From these analyses, an approach of the spark plasma sintering mechanism of metallic glasses is proposed.