The Effect of Ball Milling on Properties and Sintering of Nanostructured TiB2.

TiB2 powder was milled in a high-energy ball mill (Pulverisette-5 planetary mill) at 250 rpm for various time periods (0, 1, 4, and 10 h) and consolidated by the high frequency induction heated sintering (HFIHS). The effect of milling on the sintering behavior and crystallite size of TiB2 powders were investigated. A nanostructured dense TiB2 specimen with a relative density of up to 98% was readily achieved within very short time (two min). The ball milling effectively refined the crystallite structure of TiB2 powders and facilitated the subsequent consolidation. The sinter-onset temperature was reduced remarkably by the prior milling for 10 h. Accordingly, the relative density and mechanical properties of TiB2 compact increased as the milling time increased.

Mechanical Properties and Rapid Sintering of Nanostructured WC-Al2O3-Al Hard Materials.

Nanostructured WC-Al2O3-Al composites was sintered using rapid high-frequency induction heated sintering (HFIHS) and the mechanical properties such as hardness and fracture toughness with consolidation were investigated. The HFIHS method induced a very fast densification nearly at the level of theoretical density and successfully prohibited grain growth, resulting in nano-sized grains. The fracture toughness was improved due to the consolidation facilitated by adding Al to WC-Al2O3 matrix. The WC-Al2O3 composites added with 5 and 10 vol.% Al showed higher hardness and fracture toughness compared with that of WC-Al2O3.

Simultaneous Synthesis and Consolidation of Nanostructured HfB2-SiC Composite.

A dense nanostructured 2HfB2-SiC composite was simultaneously synthesized and consolidated by the pulsed current activated sintering method in one step within very short time (two minutes) from mechanically activated 2Hf, B4C and Si powders. Simultaneous combustion synthesis and consolidation were achieved through the combination of the effects of the pulsed current and mechanical pressure. A highly dense 2HfB2-SiC composite with 97.5% relative density was achieved under the simultaneous application of a pressure of 80 MPa and the pulsed current. The fracture toughness of the 2HfB2-SiC composite was higher than that of monolithic HfB2.

Mechanical Properties and Synthesis of Nanocrystalline Ta - 1.67Al2O3 Composite by Pulsed Current Activated Heating.

Mixtures of Ta2O5 and Al nanopowders were prepared using high energy ball milling method. Nanocrystalline Ta - 1.67Al2O3 composite was simultaneously synthesized and densified by pulsed current activated combustion synthesis method in a short time from mechanically activated mixtures of Ta2O5 and Al powders. The relative density of the Ta - 1.67Al2O3 composites was 98%. The average grain sizes of Ta and Al2O3 in the Ta - 1.67Al2O3 composite heated up to 1520 °C were determined as 205 and 40 nm, respectively. A Vickers diamond indentation technique were used to evaluate the hardness and fracture toughness of the Ta - 1.67Al2O3 composite under applied load 20kgf. The average Vickers hardness and fracture toughness value were 1340 kg/mm² and 7.9 MPa·m1/2, respectively.

Mechanochemical Synthesis and Rapid Consolidation of Nanostructured Nb-ZrO2 Composite.

Nb2O5 and Zr powders at a molar ratio of 1:2.5 were milled using a high-energy ball mill. The mixture powders produced Nb and ZrO2 nanopowders through a solid replacement reaction (Nb2O5+ 2.5Zr 2Nb + 2.5ZrO2). The synthesized nanopowders were consolidated via high-frequency induction heated sintering (HFIHS) within two min. The mechanical properties (hardness and fracture toughness) of nanostructured 2Nb-2.5ZrO2 composite were then evaluated. Both the hardness and fracture toughness of the 2Nb-2.5ZrO2 composite were higher than those of monolithic ZrO2.

Simultaneous Synthesis and Consolidation of Nanostructured ZrB2-ZrO2 Composite.

A dense nanostructured 2ZrB2-ZrO2 composite was synthesized by the high-frequency inductionheated combustion synthesis (HFIHCS) method within 2 min in one step from mechanically activated powders of 2B2O3 and 3Zr. Simultaneous combustion synthesis and densification were accomplished under the combined effects of the induced current and mechanical pressure. A highly dense 2ZrB2-ZrO2 composite with relative density of up to 95.5% was produced under the simultaneous application of a pressure of 80 MPa and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.

The Effect of BN Reinforcement on the Mechanical Properties of Nanostructured Al2O3 Ceramics.

In spite of many attractive properties, the low fracture toughness of Al2O3 ceramic below ductilebrittle transition temperature limits its wide application in industry. One of the most obvious methods to improve the fracture toughness has been to add reinforcing compounds to fabricate nanostructured composite materials. In this respect, BN was evaluated as the reinforcing agent of Al2O3 ceramics using pulsed current activated sintering (PCAS). Highly dense alumina-BN composites with a relative density of up to 100% were achieved within short periods (2 min) by PCAS under a 80 MPa pressure. The rapid sintering method allowed the retention of the nanostructure by inhibiting the grain growth. The grain size of alumina was reduced remarkably by the addition of BN. The addition of BN to Al2O3 ceramic simultaneously improved the hardness and fracture toughness of alumina-BN composite.

Rapid Sintering of Nanostructured WC-Graphene Composites and Their Mechanical Properties.

The current concern about WC focuses on its low fracture toughness below the ductile-brittle transition temperature despite its many attractive properties. To improve its mechanical properties, the approach generally utilized has been the addition of a second phase to form composites and to make nanostructured materials. In this paper, graphene was evaluated as the reinforcing agent in WC ceramics using a novel sintering method (high-frequency induction heated sintering method). Highly dense nanostructured WC and WC-graphene composites were obtained within two min at 1550 °C. The effect of graphene on the grain size and the mechanical properties (hardness and fracture toughness) of WC-graphene composites was evaluated.

The Effect of Ball Milling on Properties and Consolidation of Nanostructured ZrB2.

ZrB2 powders were milled using high-energy ball for various durations and consolidated using the pulsed current activated sintering (PCAS). The effects of milling on the sintering behavior and crystallite size ZrO2 powders were investigated. A nanostructured dense ZrB2 specimen with a relative density of up to 97% was readily achieved within 3 min. The ball milling effectively refined the crystallite structure of ZrB2 powders and facilitated the subsequent consolidation. The sinter-onset temperature was reduced appreciably by the prior milling for 10 h. Accordingly, the relative density of ZrB2 compact increases as the milling time increases. The hardness and fracture toughness of sintered ZrB2 increased as the density increases.

Synthesis and Consolidation of Nanostructured Nb2C-Al2O3 Composite.

Although an extremely hard ceramic material, niobium carbide has low fracture toughness to use wide applications. To fabricate nanostructured composite is common method to improve fracture toughness. Nanopowder mixture of Nb2C and Al2O3 were synthesized according to the reaction (Al4C3+6Nb+3O2 → 3Nb2C+2Al2O3) from Al4C3 and Nb powders by high-energy ball milling. The synthesized mixture of Nb2C and Al2O3 powders was consolidated by pulsed current activated sintering method within two min under the 80 MPa pressure. Nb2C and Al2O3 in the composite were nano-sized phases. The fracture toughness of a nanostructured Nb2C-Al2O3 composite of this study is better than that of previous study.

High-Frequency Induction Heated Synthesis and Consolidation of Nanostructured Al-TaC Composite and Its Mechanical Properties.

The significance of Al matrix composites reinforced with metal carbide having low density and very high hardness increases in order to reduce CO2 emissions and improve the efficiency of energy in automobile and transportation industries. Nanopowder mixture of Ta and Al4C3 were fabricated by high energy ball milling. Highly dense nanostructured 4Al-3TaC composite was consolidated by high-frequency induction heated sintering within one min from the mechanically activated nanopowder mixture of Ta and Al4C3 under the 80 MPa pressure. The microstructure, sintering behavior and mechanical properties (hardness and fracture toughness) were evaluated using FE-SEM and Vickers hardness tester.

Pulsed Current Activated Sintering of Nanostructured ZrO2 and 3YSZ and Their Mechanical Properties.

As nanostructured materials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. When conventional sintering processes are used to sinter nano-sized zirconia powders, concomitant grain growth leads to the destruction of the nanostructure. This focuses attention on consolidation methods in which grain growth can be eliminated or significantly reduced. To accomplish this, rapid sintering methods have been widely used to sinter nano-sized powders. Nanopowders of ZrO2 and 3YSZ were fabricated and rapidly consolidated using high-energy ball milling and the pulsed current activated sintering (PCAS). The sintering behavior and crystallite size ZrO2 and 3YSZ powders were evaluated. A nanostructured dense 3YSZ compact with a relative density of up to 99% was readily obtained within one min. The hardness and fracture toughness of ZrO2 and 3YSZ sintered from powders milled for 10 h were 450 and 1160 kg/mm², 3 and 4.4 MPa·m1/2. Not only hardness but also fracture toughness of 3YSZ are higher than those of ZrO2.

Pulsed Current Activated Synthesis and Consolidation of Nanostructured Ti-TiC Composite and Its Mechanical Properties.

Ti and CNT powders were milled by high energy ball milling. The milled powders were then simultaneously synthesized and consolidated using pulsed current activated sintering (PCAS) within one minute under the applied pressure of 80 MPa. The advantage of this process is not only rapid densification to near theoretical density but also to prevent grain growth in nano-structured materials The milling did not induce any reaction between the constituent powders. Meanwhile, PCAS of the Ti-CNT mixture produced a Ti-TiC composite according to the reaction (Ti + 0.06CNT --> 0.94Ti+0.06TiC, Ti+0.12CNT --> 0.88Ti+0.12TiC). Highly dense nanocrystalline Ti-TiC compos- ites with a relative density of up to 99.5% were obtained within one minute. The hardness and fracture toughness of the dense Ti-6mole% TiC and Ti-12 mole% TiC produced by PCAS were also investigated.

Mechanochemical Synthesis and Rapid Consolidation of Nanostructured CoTi-Al2O3 Composite by Pulsed Current Activated Sintering and Its Mechanical Properties.

Nano-powders of CoTi and Al2O3 were synthesized from CoTiO3 and 2Al powders by high energy ball milling. Nanocrystalline Al2O3 reinforced composite was consolidated by pulsed current activated sintering within one minute from mechanochemically synthesized powders of CoTi and Al2O3. The relative density of the composite was 97%. The average hardness and fracture toughness values obtained were 1180 kg/mm2 and 8.5 MPa · m1/2, respectively.

High Frequency Induction Heated Synthesis and Consolidation of Nanostructured TaSi2-WSi2 Composite.

A dense nanostructured TaSi2-WSi2 composite was simultaneously synthesized and sintered by the high frequency induction heating method within 2 minutes from mechanically activated powder of Ta, W and Si. A highly-dense TaSi2-WSi2 composite was produced under simultaneous application of a 80 MPa pressure and the induced current. The mechanical properties and microstructure were investigated.

Properties and fabrication of nanostructured 2Cr-Al2O3 composite for prosthetic bearing replacements.

Cr2O3 and Al powder were used as raw powders, and were milled by the high energy ball milling method. The nanostructured 2Cr-Al2O3 composite from the milled powder was both synthesized and densificated within a short time, by the pulsed current activated sintering (PCAS) apparatus. The relative density of the sintered 2Cr-Al2O3 composite was 99%. The hardness and the fracture toughness of the specimen were 1630 kg/mm(2), and 9.3 MPa·m(1/2), respectively. The weight loss of the composite was measured by a pin-on-disk type apparatus, without a lubricant. Lastly, the 2Cr-Al2O3 composite has a very good cell viability.

Influence of oxygen concentration on mechanical properties of molybdenum powder during sintering.

In this study, the influence of oxygen concentration on the mechanical properties of sintered bodies produced from commercial and low-oxygen molybdenum powder via pulsed-current-activated sintering was determined. The hardness of the sintered bodies increased with the sintering temperature up to 1,500 degrees C and then decreased with further temperature increase. The hardness of the sintered low-oxygen-molybdenum body was slightly higher than the rest of the sintered bodies. This was because the relative density of the sintered low-oxygen-molybdenum body increased more than that of others as the sintering temperature increased. Furthermore, the grain size of the sintered commercial-molybdenum body was larger than that of the sintered low-oxygen-molybdenum body. This was attributed to the positive effect of molybdenum oxide on grain growth during sintering. Thus, it was established that low-oxygen molybdenum powder can suppress grain growth during sintering, resulting in improved mechanical properties of the sintered bodies.

Rapid synthesis and consolidation of nanostructured 4Fe-Al2O3 composite by pulsed current activated sintering.

Nanocrystalline 4Fe-Al2O3 composite was simultaneously synthesized and consolidated by pulsed current activated sintering (PCAS) method within 5 min from mechanically activated powders of Fe2O3 and 2FeAl. The average grain size and mechanical properties of the composite were investigated. The average grain sizes of Fe and Al2O3 prepared by PCAS were about 75 nm and 54 nm, respectively. The average hardness and fracture toughness values obtained were 770 kg/mm2 and 9.3 MPa x m1/2, respectively.

A new method for the identification and quantification of magnetite-maghemite mixture using conventional X-ray diffraction technique.

The electrical explosion of Fe wire in air produced nanoparticles containing the binary mixture of magnetite (Fe(3)O(4)) and maghemite (γ-Fe(2)O(3)). The phase identification of magnetite and maghemite by the conventional X-ray diffraction method is not a simple matter because both have the same cubic structure and their lattice parameters are almost identical. Here, we propose a convenient method to assess the presence of magnetite-maghemite mixture and to further quantify its phase composition using the conventional peak deconvolution technique. A careful step scan around the high-angle peaks as (511) and (440) revealed the clear doublets indicative of the mixture phases. The quantitative analysis of the mixture phase was carried out by constructing a calibration curve using the pure magnetite and maghemite powders commercially available. The correlation coefficients, R(2), for magnetite-maghemite mixture was 0.9941. According to the method, the iron oxide nanoparticles prepared by the wire explosion in this study was calculated to contain 55.8 wt.% maghemite and 44.2 wt.% magnetite. We believe that the proposed method would be a convenient tool for the study of the magnetite-maghemite mixture which otherwise requires highly sophisticated equipments and techniques.

Rapid consolidation of nanostuctured TiCu compounds.

TiCu nanopowder was produced using an electrical wire explosion method and subsequently consolidated into dense nanostuctured TiCu by a high frequency induction heated sintering method. The consolidation was accomplished by the combination of an induced current and a high mechanical pressure within two minutes. This process results in very quick densification to near the theoretical density and prohibits grain growth in nano-structured materials. The grain sizes and mechanical properties of the sintered TiCu were investigated.