Pulse Current Pressure Sintering Research Articles

Fabrication of dense ZrB2/B4C composites using pulsed electric current pressure sintering and evaluation of their high-temperature bending strength

ZrB2/x·vol%B4C (x = 30–90) composites were fabricated from ZrB2 and amorphous B/C powders using pulsed electric current pressure sintering (PECPS) from 1600 °C to 1900 °C for 6.0 × 102 s (10 min) under 50 MPa in a vacuum, accompanied by self-propagating high-temperature synthesis (SHS). Since the B4C phase was formed at 1600 °C, the relative density (Dr) was evaluated; the composites sintered at 1900 °C attained the highest Dr. Their Dr values increased gradually from 99.35% to 99.99% with increasing B4C contents up to 60 vol% and showed a constant value above 60 vol%. At room temperature, the mechanical properties of Vickers hardness (Hv), fracture toughness (KIC) and three-point bending strength (σb) were measured. Hv exhibited a monotonous increase from 20.3 to 32.7 GPa. On the other hand, KIC and σb revealed the same behavior for each of the compositions; both exhibited the highest values, i.e., 10.2 MPa m1/2 for KIC and 870 MPa for σb, in the 60 vol%B4C sample, and then the KIC decreased gradually to 9.73 MPa m1/2, and σb dropped suddenly from 850 MPa (70 vol%) to 340 MPa (80 vol%) and stayed as low σb in the 90 vol% B4C sample. Next, the high-temperature σb values of the composites (40–70 vol%) were measured in Ar. The composites (40–60 vol%) revealed high σb (≥640 MPa) from R.T.~1600 °C; the maximum value of 803.5 MPa was observed for the 60 vol%B4C composites at 1600 °C, and then the σb of all composites dropped to around 340 MPa at 1800 °C. From their stress-strain curves, elastic and plastic deformations were observed at 1600 °C and 1800 °C, respectively.

TiC/TiCN-based hard material with high oxidation resistance at high temperature

TiC/TiCN-based cermet is a candidate material for alternatives to WC-Co used in tools and dies. Typically, Ni and Co are used as metal binders of TiC/TiCN-based cermets. Being types of rare metals, it is therefore desired that these metal binders be replaced with the ubiquitous materials. Iron aluminide (FeAl) intermetallic compound is a candidate material for an alternative rare metal binder made from ubiquitous materials. FeAl is well known as an extremely corrosion-resistant material under oxidizing atmospheres, sulphidizing atmospheres, and in molten salts. Although TIC/TiCN-FeAl is a combination of intermetallic compound and carbide with very high hardness, it is brittle. TiC/TiCN-FeAl was processed through wet milling and pulsed electric current pressure sintering to improve mechanical properties, thus improving transverse rupture strength while keeping hardness intact. In this work, we attempted to improve the oxidation resistance performance of TiC/TiCN-FeAl at high temperature by changing raw materials.

Fabrication of novel ZrO2(Y2O3)–Al2O3 ceramics having high strength and toughness utilising pulsed electric current pressure sintering (PECPS)

Pulsed electric current pressure sintering (PECPS) makes it possible to produce novel monolithic and composite materials with well controlled microstructure or nanostructure, which has not been realised before. ZrO2 based ceramics containing 25 mol.-%Al2O3 and 0·90–1·125 mol.-%Y2O3, i.e. ZrO2(1·2–1·5 mol.-%Y2O3)–25 mol.-%Al2O3, revealing high bending strength σb≧1 GPa and high fracture toughness KIC ≧15·5 MPa m1/2 simultaneously, have been fabricated by PECPS of cubic ZrO2 solid solution (ss) powders containing both Al2O3 and Y2O3 prepared via a sol–gel process. Tetragonal ZrO2 (t-ZrO2) phase composite ceramics sintered at 1573 to 1623 K (1300–1350°C) for 10 min under 60 MPa in Ar were composed of ∼φ200 nm grains with high relative density ≧97·5%. Transmission electron microscopy observation cleared that these mechanical properties might originate from homogeneous distribution of α-Al2O3 particles in the dense t-ZrO2 matrix; the precipitation of α-Al2O3 could be achieved by adopting the ss powders and PECPS.

Fabrication of Full‐Density Mg‐Ferrite/Fe–Ni Permalloy Nanocomposites with a High‐Saturation Magnetization Density of 1 T

Dense nanocomposites consisting of spinel Mn‐doped Mg‐ferrite and permalloy, (Mg[Fe1 − xMnx]2O4(0 ≤ x ≤ 0.4)/53Fe–47Ni), have been fabricated from powder mixtures of MgO/α‐Fe2O3/MnO and N2‐atomized metal particles utilizing high‐pressure cold isostatic press (CIP), pulsed electric current pressure sintering (PECPS), and capsule‐free hot isostatic pressing (HIP). Metal particles were coated with the mixed oxide powders homogeneously under high shear compression in Ar. The coated powders were densified into relative densities of 83–85% by high pressure CIPing (1 GPa). They were then presintered at 823 K for 3 min under uniaxial pressure of 100 MPa in Ar using a PECPS. The pre‐sintered bodies had relative densities of 93–95% composed of spinel ferrite and permalloy; the mixed metal oxides were changed into magnesium ferrites by heating briefly at low temperature. Then, HIP (1123 K/6 h/196 MPa‐Ar) was adopted to densify the pre‐sintered bodies into a nearly full density; furthermore, a sintering atmosphere control was performed using ferrite muffles to maintain both phases. Sintered materials consisting of granular metal particles (φ 8.5 μm) isolated and surrounded by a thin ferrite discontinuous layer (0.2–1.3 μm) with a relative density ≥99.5% revealed both a saturation magnetization density ≥1 T and moderate permeability values of 30–35 at 1 MHz.

Fabrication of Full-Density Mg-Ferrite/Fe-Ni Permalloy Nanocomposites with a High-Saturation Magnetization Density of 1 T

Dense nanocomposites consisting of spinel Mn-doped Mg-ferrite and permalloy, (Mg[Fe1 − xMnx]2O4(0 ≤ x ≤ 0.4)/53Fe–47Ni), have been fabricated from powder mixtures of MgO/α-Fe2O3/MnO and N2-atomized metal particles utilizing high-pressure cold isostatic press (CIP), pulsed electric current pressure sintering (PECPS), and capsule-free hot isostatic pressing (HIP). Metal particles were coated with the mixed oxide powders homogeneously under high shear compression in Ar. The coated powders were densified into relative densities of 83–85% by high pressure CIPing (1 GPa). They were then presintered at 823 K for 3 min under uniaxial pressure of 100 MPa in Ar using a PECPS. The pre-sintered bodies had relative densities of 93–95% composed of spinel ferrite and permalloy; the mixed metal oxides were changed into magnesium ferrites by heating briefly at low temperature. Then, HIP (1123 K/6 h/196 MPa-Ar) was adopted to densify the pre-sintered bodies into a nearly full density; furthermore, a sintering atmosphere control was performed using ferrite muffles to maintain both phases. Sintered materials consisting of granular metal particles (φ 8.5 μm) isolated and surrounded by a thin ferrite discontinuous layer (0.2–1.3 μm) with a relative density ≥99.5% revealed both a saturation magnetization density ≥1 T and moderate permeability values of 30–35 at 1 MHz.

Superplastic deformation of hydroxyapatite ceramics with B 2O 3 or Na 2O addition fabricated by pulse current pressure sintering

High-density and fine-grained transparent hydroxyapatite (Ca 10(PO 4) 6(OH) 2: HAp) ceramics with B 2O 3 and Na 2O addition were fabricated using pressureless sintering and pulse-current pressure sintering between 1000 and 1100 °C; the superplastic deformation of these HAp specimens was evaluated. The relative density of pure HAp compacts pulse-current pressure sintered at 1000 °C for 10 min under a pressure of 50 MPa attained 99.9% and exhibited translucency. The tensile elongation of the pure HAp specimen, which was measured at 1000 °C under a strain rate of 1.48 × 10 −4 s −1, was as high as 364%. The relative density of HAp compacts with 3.0 mol.% B 2O 3 addition pulse-current pressure sintered under the same conditions as those of pure HAp compacts was 98.9%, whereas the grain size was as low as 0.24 μm. The elongation of HAp specimens, measured at a test temperature of 1000 °C under a strain rate of 1.48 × 10 −4 s −1, was as high as 578%.

パルス通電加圧焼結によるイットリア安定化ジルコニア粉末の緻密化メカニズム

The influence of an applied stress (σ) on densification behaviors of a mechanically milled 3Y-TZP ceramic powder by pulse current pressure sintering (PCPS) has been investigated. The densification rate vs temperature (ρ−T) and densification rate vs relative density (ρ−ρ) curves at the constant heating rates (HR=0.1, 0.3, 1.0 and 2.0 K/s) could be described using data points (T, ρ and ρ) selected from all the results of PCPS conducted at the various electric currents in the range of 700 to 1000 A. Although the ρ values increase with increasing HR, the T and ρ values corresponding to the peaks of ρ (ρmax) show almost the constant values of 1300 K and 0.8 (at σ=90.5 MPa) respectively, irrespective of HR. By the increase of σ, moreover, the T value corresponding to ρmax shifts to the lower T side, however the ρ value corresponding to ρmax remains unchanged. Although the stress exponent (n) values, which are the gradient of the ln ρ vs ln σeff lines (σeff: effective stress), increase continuously with increasing T, but the re-estimated n values from the ln ρ vs ln (σeff−σ0) lines (σ0: threshold stress) show almost the constant value of 1.85 to 1.97. Also, the apparent activation energy (Q) estimated from the Arrhenius plot of ln (σeff−σ0) vs 1/T is 521.14±18.43 kJ/mol. The obtained n and Q values suggest that densification of the 3Y-TZP powder compacts by PCPS proceeds by grain boundary sliding affected by the threshold stress as well as the creep deformation in the middle stress region, and rate-determined by lattice diffusion of the solute Zr4+ ions.

Fabrication of Mg Ferrite/permalloy Magnetic Nano-composites

Dense {Mg(Fe1-xMnx)2O4/53Fe-47Ni permalloy (0≤x≤0.4)} magnetic nano-composites consisting of spinel and alloy phases have been fabricated from N2-atomized metal particles and fine-powder mixtures of MgO/α-Fe2O3/MnO using a combination of pulsed electric current pressure sintering (PECPS) and hot isostatic pressing (HIP). Fe-Ni permalloy particles were coated with the mixed metal oxide powders homogeneously by passing these mixtures through a narrow gap (1 mm) under high shear compression in Ar. Mixed powder compacts of permalloy with the fine metal oxides were densified into the green bodies having relative densities of 83-85 % under isostatic high pressure of 1 GPa at room temperature. Then green powder compacts were pre-sintered at 823 K for 3 min under a uniaxial pressure of 100 MPa in Ar using a PECPS. The pre-sintered bodies composed of spinel ferrite and permalloy revealed the relative densities of 94-96 %; the mixed metal oxides changed into magnesium spinel ferrites Mg(Fe1-xMnx)2O4 during a short heating time. Then hot isostatic pressing (HIP: (1123 K/6 h/200 MPa-Ar)) was adopted to sinter the pre-sintered bodies into a near full density without an encapsulation, however, a sintering atmosphere control was performed using a ferrite muffle in order to maintain the both phase. Sintered nano-composites with the relative density more than 99.5 % have a saturation magnetization density ≥1 T and moderate permeability values of 30-35 at 10 MHz, which values have been expected from a material design.

The Study on Carbon Nanofiber (CNF)‐Dispersed B4C Composites

Carbon nanofiber (CNF)‐dispersed B4C composites have been synthesized and consolidated directly from mixtures of elemental raw powders by pulsed electric current pressure sintering (1800°C/10 min/30 MPa). A 15 vol% CNF/B4C composite with ∼99% of dense homogeneous microstructures (∼0.40 μm grains) revealed excellent mechanical properties at room temperature and high temperatures: a high bending strength (σb) of ∼710 MPa, a Vickers hardness (Hv) of ∼36 GPa, a fracture toughness (KIC) of ∼7.9 MPa m1/2, and high‐temperature σb of 590 MPa at 1600°C in N2. Interfaces between the CNF and the B4C matrix were investigated using high‐resolution transmission electron microscopy, EDS, and electron energy‐loss spectroscopy.

Fabrication of Ti-Ni-Zr Shape Memory Alloy by P/M Process

This work focuses on the fabrication of Ti-Ni-Zr high-temperature shape memory alloy by powder metallurgy (P/M) process. The effects of fabrication conditions on the microstructure and shape memory characteristics of Ti-50.2 mol%Ni-5 mol%Zr alloy were investigated. In this research, elemental Ti, Ni and Zr powders were used. These powders were mixed by a planetary ball mill at a rotational speed of 500 rpm for milling times of 0.6 ks (mixed powder) and 720 ks (MAed powder). The mixtures were sintered by a pulse-current pressure sintering equipment at 1153 K for sintering times of 1.8 ks and 1.2 ks. The solution treatment was carried out at various temperatures between 1073 K and 1273 K to homogenize the microstructure of the as-sintered alloy. The microstructure of the alloy became more homogeneous with an increase in solution-treatment temperature. In the case of the mixed powder, however, Zr-rich phases were observed in the microstructure of the solution-treated alloy. The alloy solution-treated at 1173 K showed a yielding behavior in the stress-strain curve, and the tensile strength and elongation of the alloy were more than 350 MPa and 2.5%, respectively. On the other hand, in the case of the MAed powder, the microstructure of the as-sintered alloy was homogeneous. The P/M alloy showed higher transformation temperatures than those of the wrought alloy. But, the alloy showed no shape memory effect and poor tensile property due to contamination of the MAed powder.

メカニカルミリング粉末のパルス通電加圧焼結による Ti50Al50-20 vol%(PSZ-45 mol%Al2O3)複合材料の創製

A nanocrystalline Ti50Al50-20 vol%(PSZ-45 mol%Al2O3) composite is fabricated by pulse current pressure sintering of the mixed powder of mechanically milled Ti-50 mol%Al powder and amorphous PSZ-45 mol%Al2O3 powder. The mechanically milled Ti-50 mol%Al powder and amorphous PSZ-45 mol%Al2O3 powder were prepared by the rotating-arm reaction ball milling system. For the powder of the Ti50Al50 -20 vol%(PSZ-45 mol%Al2O3), we have controlled the process variables of pulse current pressure sintering system such as stress, temperature and current. Then, the lowest consolidation temperature necessary to obtain a full densification of compact under the applied stress of 150 MPa is 1405 K at the surface temperature of compact. The X-ray diffraction method confirmed that the nanocrystallization occurs in an overall cross-section of Ti50Al50-20 vol%(PSZ-45 mol%Al2O3) composite with the crystalline size of 28 nm, 16 nm and 16 nm for γ-TiAl, α-Ti and cubic zirconia solid solution respectively. The composite material shows a high 0.2% proof stress value of 2.5 GPa obtained by compression test at room temperature.

Fabrication of a Functionally Graded TiNi Shape Memory Alloy Wire by Powder Metallurgy and Plastic Working (1st Report, Fabrication of a TiNi Shape Memory Alloy Billet and Its Phase Transformation Properties)

The martensitic and the reverse transformation temperatures are directly related to the bending rigidity of the TiNi shape memory alloy (SMA) wire. In this paper, aiming at obtaining a functionally graded TiNi shape memory alloy wire that varies in bending rigidity from high to low along the wire axis, a new fabrication process of combined powder metallurgy and plastic working is proposed. First, a multi-layered TiNi green compact, where Ti-Ni compositions varied layer by layer, was sintered by means of pulse current pressure sintering technique, and then it was hot-extruded and cold drawn into a wire. In this paper, as a first step of fabrication of a wire, we investigated transformation properties and texture morphologies of sintered and solution treated compacts. From differential scanning calorimetry and X-ray diffraction measurements, it was found that in this process the solution treatment of the billet plays an important role to induce the transformation temperature gradient in the sintered compact, since it greatly activates the interdiffusion between Ti and Ni particles.

Simultaneous Synthesis and Consolidation of W-Added ZrB<sub>2</sub> by Pulsed Electric Current Pressure Sintering and their Mechanical Properties

Dense zirconium boride (ZrB2)-based materials with and without tungsten (W) have been fabricated directly from mixtures of constituent elemental powders by pulsed electric current pressure sintering (PECPS) at 1800°C for 10 min under 30 MPa in a vacuum. Formation processes of monolithic, W-doped ZrB2 solid solutions (Zr1-xWx)B2 (0<x≤0.12), and composites consisting of ZrB2(ss) and WB2 were investigated. Their mechanical properties of Vickers hardness (Hv), fracture toughness (KIC), and bending strength (σb) at room temperature were evaluated. Solid solution and composite materials gave higher Hv (~20.7 GPa), KIC (∼4.4 MPam1/2), and σb (~600 and 690 MPa for the former and the latter, respectively) than those (14.1 GPa, 3.21 MPam1/2, and ~500 MPa) of the monolithic ZrB2 fabricated under the same conditions. Furthermore, the latter two materials exhibited excellent high-temperature σb values (~550-600 MPa) up to 1600°C in N2, in comparison with that (~320 MPa) of monolithic ZrB2 materials.

パルス通電加圧焼結法によるTi-Al-Siスパッタリングターゲットの作製

We investigated the relationships between sintering conditions of TiAlSi mixed powder and microstructures of the sintered compacts for the purpose of fabricating large sputtering targets (such as 160 mm ×100 mm). The pulse current pressure sintering (PCPS) method was employed in order to consolidate the mixed powders consisting of Ti50:Al40:Si10 (atomic %). Ti50Al40Si10 compacts were made under conditions of various pressures (49∼98 MPa) and temperatures (773 K∼873 K). When the sintering temperature was 833 K or higher, Al-Si liquid oozed out during the process. When the sintering temperature was lower than 833 K, many micro pores have been formed in the sintered compact. When the sintering pressure was high, the relative density of the compact was higher and metallic compounds have formed at the interface between Ti and Al/Si. Relative density of 97% was obtained from the compact sintered at 823 K under the pressure of 60 MPa. Water quenching test revealed that this sintered compact had high resistance to thermal shock due to the formation of metallic compounds. Applying this sintering condition, disk compacts of Φ190 mm×8 mm were successfully obtained and 160 mm×100 mm rectangular sputtering targets were fabricated from these disks.Then we investigated the microstructure and mechanical properties of Ti-Al-Si-N films deposited from the rectangular targets to confirm whether the targets are useful for sputtering. The targets were sputtered in a mixture of argon and nitrogen using an r.f. sputtering apparatus of facing target-type sputtering. The Ti-Al-Si-N films obtained the highest hardness of 43 GPa when they were deposited at 573 K without substrate bias. The hardness of the films was ∼20% higher than that of Ti-Al-N films. These results indicate that the Ti50Al40Si10 compacts sintered by PCPS are useful for sputtering targets.

203 粉末冶金プロセスにより作製したTi-Ni-Cu形状記憶合金の相変態特性(粉末成形とその評価1)

Ti-Ni-Cu Shape Memory Alloys were fabricated by mechanically alloyed powder using a pulse-current pressure sintering equipment. The effect of Cu content on the phase transformation behavior of the sintered alloys was investigated. An increase in Cu content changed the crystal structure of the alloy. The alloys in Cu content of 15at%Cu and 20at%Cu consists of B2, B19' and B19 phases. In the case of the Cu content of 20at%Cu, the alloy clearly shows the two-step transformation. The transformation hysteresis of the alloy was approximately 10K as narrow as that of the wrought alloy. The phase transformation behavior of the P/M alloy differs from that of the wrought alloy. This may be caused by a reduction of Cu content of the alloys due to composition segregation.

2915 パルス通電加圧焼結によるTi-Ni合金の熱・力学特性に及ぼす組成の影響(S34-2 粉末成形とその評価(2),S34 粉末成形とその評価)

2915 パルス通電加圧焼結によるTi-Ni合金の熱・力学特性に及ぼす組成の影響(S34-2 粉末成形とその評価(2),S34 粉末成形とその評価)

Study on the Pulse Current Pressure Sintering of Large Parts and its Application

Study on the Pulse Current Pressure Sintering of Large Parts and its Application

Fabrication of TiNi Powder by Mechanical Alloying and Shape Memory Characteristics of the Sintered Alloy

This paper presents the fabrication condition of TiNi alloy powder by mechanical alloying and shape memory characteristics of the sintered alloy. The effect of mechanical alloying condition on the characteristics of mechanically alloyed powder (MA powder) was investigated. Also, the difference in sintering behavior between the MA powder and the elementally mixed powders by V-blender and the shape memory characteristics of the sintered alloys were also examined. The MA powder was fabricated by milling using a planetary ball mill in a rotational speed between 200 and 500 min -1 for various milling times in an atmosphere of Ar gas. These two types of powders prepared in different processes were sintered using a pulse-current pressure sintering equipment at various sintering temperatures. The powder agglomerated and its particle size became larger with an increase in milling time. The mixture of Ti and Ni powders changed into an amorphous state by processing for 3.6 ks over 300 min -1 . The sintered alloy of the MA powder showed more uniform phase of TiNi than that of the elementally mixed powders sintered in a same manner, however, the former showed a lower density than the latter due to a larger particle size of the MA powder of before-sintering. It was found from the measurement of the transformation temperature of the sintered alloy of the MA powder using DSC that the alloy has shape memory characteristics, and the transformation temperatures of the alloy are higher than those of the alloy of the elementally mixed powders due to waste, of Ni powder.

Influence of Cyclic Deformation on Shape Memory Characteristics of Ti-Ni-Cu Alloys Fabricated by Pulse-Current Pressure Sintering Method

Ti-Ni-Cu shape memory alloy by elemental powders was fabricated by using a pulse-current pressure sintering method, and it was subjected to solid-solution heat treatment after sintering to homogenize the microstructure of the alloy. The influence of the thermo-mechanical cyclic deformation on the shape memory and thermo-mechanical characteristics of Ti-Ni-Cu alloy was investigated. The thermo-mechanical cyclic deformation improved the deformation behavior of the sintered alloy and made the thermo-mechanical behavior of the alloy stable caused by the introduction of dislocations. As a result, the recovery stress of the alloy after the cyclic deformation fairly increased. The transformation temperatures of the alloy after the cyclic deformation became lower than those of the alloy before the cyclic deformation. Therefore, the superelastic-like behavior of the alloy after the cyclic deformation appeared in an isothermal tensile test at lower holding temperature.

P20: Influence of Composition on Shape Memory Characteristics of Ti-Ni Alloys Fabricated by Pulse-Current Pressure Sintering(SHORT ORAL PRESENTATION FOR POSTERS II)

P20: Influence of Composition on Shape Memory Characteristics of Ti-Ni Alloys Fabricated by Pulse-Current Pressure Sintering(SHORT ORAL PRESENTATION FOR POSTERS II)