In Jin Shon

Rapid sintering of nanocrystalline 8 mol.%Y2O3-stabilized ZrO2 by high-frequency induction heating method

Using a high-frequency induction-heating sintering (HFIHS) method, nanocrystalline 8 mol.%Y2O3-stabilized ZrO2 was obtained from ultra fine powders. The observed advantages of this process include very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. Nearly fully dense nanocrystalline 8 mol.%Y2O3-stabilized ZrO2, with a relative density of up to 99.8%, could be obtained with simultaneous application of 100 MPa pressure and an induced current within 10 min of sintering time without significant change in grain size. The influences of the sintering temperature and the mechanical pressure on the final density and grain size of the products were investigated. The hardness and fracture toughness of the dense ZrO2 ceramics produced by HFIHS were investigated.

Mechanochemical Synthesis and Rapid Consolidation of Binderless Nanostructured (Ti,V)C by Pulsed Current Activated Heating and Its Mechanical Properties

Solid-solution nanocrystalline powder, (Ti,V)C, was prepared via high-energy milling of Ti-V alloys with graphite. The synthesis process was investigated in terms of the phase evolution by analyzing XRD data. The rapid sintering of nanostuctured (Ti,V)C hard materials was performed by a pulsed current activated sintering process. This process allows quick densification to near theoretical density and inhibits grain growth. A dense, nanostructured (Ti,V)C hard material with a relative density of up to 100% was produced by simultaneous application of 80 MPa and a pulsed current for 2 min. The microstructure and mechanical properties of the resulting binderless (Ti,V)C were investigated.

Synthesis of dense MoSi2 by high-frequency induction heated combustion and its mechanical properties

Dense MoSi2 compound was synthesized with the high-frequency induction heated combustion synthesis method in one step from elemental powders of Mo and Si within 2 min. Simultaneous combustion synthesis and densification were carried out under the combined effects of induced current and mechanical pressure. A highly dense MoSi2 with a relative density of up to 98% was produced with simultaneous application of 60 MPa pressure and induced current. The percentages of the total shrinkage occurring before and during the synthesis reaction were 16% and 53%, respectively. The average grain size was about 15 μm and a slight amount of Mo5Si3 was observed at the boundaries of the MoSi2 grains. The fracture toughness and hardness values obtained were 3.5 MPa·m1/2 and 1050 kg/mm2, respectively. These values were similar to those of commercial ones.

Synthesis of dense WSi2 and WSi2-xvol.%SiC composites by high-frequency induction heated combustion and its mechanical properties

A method to synthesize the dense silicide WSi2 and WSi2-xvol.%SiC composites within two minutes in one step from W, Si and C elemental powders was investigated. Simultaneous combustion synthesis and densification were carried out under the combined effect of an induced current and mechanical pressure. Highly dense WSi2 and WSi2-xvol.%SiC (x=10, 20, 30) with relative density of up to 97% were produced under the simultaneous application of a 60 MPa pressure and the induced current on the reactant powders. The average grain size of WSi2 in WSi2-xvol.%SiC (x=0, 10, 20, 30) were in the region of 6.9, 6.1, 5.2, and 5.0 μm, respectively. The respective Vickers hardness values for these materials were 1375, 1540, 1710, and 1845 kg/mm2. From indentation crack measurements, the fracture toughness values were calculated to be 3.3, 3.8, 4.4, and 5.1 MPa·m1/2, respectively.

Mechanical Properties and Consolidation of WC-8wt.%Ni Hard Materials by HFIHS and PCAS

Two methods, High-Frequency Induction-Heated Sintering (HFIHS) and Pulsed Current Activated Sintering (PCAS), were utilized to consolidate WC-8wt.%Ni hard materials. The demonstrated advantages of these processes are rapid densification to near theoretical density in a relatively short time and with insignificant change in grain size. The hardness, fracture toughness, and the relative density of the dense WC–8Ni composites produced by HFIHS and PCAS were investigated. And the effect of variation in particle size of WC powder on the sintering behavior and mechanical properties were investigated.

Rapid Consolidation of Nanocrystalline Al2O3 Reinforced Cr Composite from Mechanically Alloyed Powders by Pulsed Current Activated Sintering

Nanopowders of Cr and Al2O3 was fabricated from CrO3 and 2Al by high energy ball milling. Dense nanocrystalline Cr-Al2O3 composite was consolidated by pulsed current activated sintering (PCAS) method within 1 min from mechanically alloyed powders. Highly dense Cr-Al2O3 with relative density of up to 99% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. The average grain size and mechanical properties of the composite were investigated.

Consolidation and Mechanical Properties of Nanostructured SiC from Mechanically Activated Powder by High-Frequency Induction-Heated Sintering

The rapid sintering of nanostuctured SiC hard materials was investigated with high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostuctured materials. A dense nanostructured SiC hard material was produced with simultaneous application of 500 MPa pressure and induced current within 2 minutes. The effect of the ball milling times on the sintering behavior, grain size and mechanical properties of binderless SiC was investigated.

The Effect of Holding Time on the Mechanical Properties and Microstructure of Sintered NbC Composite

High frequency induction heated sintering (HFIHS) method is one of the rapid sintering methods. The advantage of rapid sintering method is that grain growth can be prevented during sintering at high temperature. Refinement of grains was known to increase the yield and flow stresses of crystals. The relation between the yield stress and the grain size is known as Hall-Petch relation. NbC-10vol.%Co, Ni and Fe composites were fabricated by HFIHS at 1060°C for 0 and 3 min as holding times under a pressure of 80MPa.The relative density of NbC-10vol.%Co, Ni and Fe composites which were sintered at 1060°C for 0min as holding time under 80MPa were 91.90%, 91.26% and 91.26%, respectively. These composites are difficult to use industrial parts due to low relative density. The longer sintering time was conducted for increasing relative density in this study. Nano-sized specimens, which were calculated grain size by full-width at half maximum (FWHM), can be obtained by HFIHS. The value of hardness and fracture toughness was investigated using 20kgf load Vickers indenter.

Properties and Rapid Consolidation of Nanostructured Fe3Al Compound by High Frequency Induction Heating

A dense nanostuctured Fe3Al was consolidated by high frequency induction heated sintering method within 2 minutes from mechanically synthesized powders of Fe3Al and milled powders of 3Fe+Al. The consolidation was accomplished under the combined effects of a induced current and mechanical pressure. The grain size, sintering behavior and hardness of Fe3Al sintered from horizontally milled Fe+Al powders and high energy ball milled Fe3Al powder were compared. Keywords: Combustion synthesis; Nanomaterials; Mechanical properties; Rapid sintering

Simultaneous Synthesis and Densification of Nanostructured NbSi2-SiC-Si3N4 by Rapid Sintering

A dense nanostructured 5NbSi2-SiC-Si3N4 composite was synthesized by the high-frequency induction-heated combustion synthesis (HFIHCS) method within 1 minute in one step from mechanically activated powders of 4NbN, NbC and 14Si. A highly dense 5NbSi2-SiC-Si3N4 composite with relative density of up to 98% 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.