Hot-press Sintering Method Research Articles

The High-temperature Oxidation Resistance and Thermal Shock Resistance of Al2O3-Ti(C,N)-(Ni,Mo) Cermet Die Material

The experiment prepared Al2O3-Ti(C,N)-(Ni,Mo) cermet die material by vacuum hot-pressing sintering method, and researched the high-temperature oxidation resistance and thermal shock resistance by the method of SEM, XRD and metallographic microscope to analyze the material’s surface feature and phase ingredient. The results show that the Al2O3-Ti(C,N)-(Ni,Mo) cermet die material has better high-temperature oxidation resistance and thermal shock resistance. The material have slight oxidation reaction in 800℃ and the reaction become sharply in 1000℃. After oxidation reaction, the staple resultant is TiO2. After 20h oxidation reaction in 1000℃, the material surface form platelike successive pyknotic oxidation film. The material’s critical temperature difference is 290℃~320℃, improving 26.1% and 45% respectively compared with Al2O3-Ti(C,N) and Al2O3 ceramics. Thermal shock damage mainly for criss-crossed and throughout the matrix crack.

Promising cermets of TiN-Ni for intermediate temperature solid oxide fuel cell interconnects application

Abstract Novel TiN-Ni cermets as potential interconnects for intermediate temperature solid oxide fuel cells (IT-SOFCs) are proposed in this study. The cermets with 30, 50 and 70 vol% Ni are fabricated by optimizing the process parameters of the hot-pressed sintering method. With the increase of Ni content in the cermets, the relative density, electrical conductivity, and thermal conductivity are pronounced improved, and the maximum values reach 99.6%, 1.7 × 10 4 S cm −1 and 45 W m −1 K −1 , respectively. In addition, the coefficient of thermal expansion (CTE) of the TiN-Ni cermets in the range of (9.7–13.2) × 10 −6 K −1 shows a superior match with other components of IT-SOFCs. Furthermore, the cermets with 70 vol% Ni exhibit excellent oxidation resistance and electrical conductivity retention with a weight gain of only 0.7% and a high conductivity of 1.6 × 10 4 S cm −1 after oxidizing at 800 °C for 100 h. Our work demonstrates that the TiN-Ni cermets can be used as promising interconnects for the practical application of IT-SOFCs.

Influence of graphite content on the dry sliding behavior of nickel alloy matrix solid lubricant composites

Solid lubricant materials are promising for high performance machines and mechanical systems. In this paper, the nickel alloy matrix solid lubricant composites containing Ag, BaF2/CaF2 and three different amounts of graphite were prepared by hot pressed sintering method. The tribotests were performed sliding against Si3N4 ball in air from room temperature to 800°C. The effect of graphite content on the tribological behavior of the composites under high temperatures was studied. Micro-Raman, XRD and SEM analysis were used to analyze the morphologies and chemical composition of the worn surface and the wear mechanisms were also discussed.

Fabrication, interfacial characterization and mechanical properties of continuous Al2O3 ceramic fiber reinforced Ti/Al3Ti metal-intermetallic laminated (CCFR-MIL) composite

Continuous Al2O3 ceramic fiber reinforced Ti/Al3Ti metal-intermetallic laminated (CCFR-MIL) composite was fabricated using a vacuum hot pressing (VHP) sintering method and followed by hot isostatic pressing (HIP). The microstructure characteristics of the interfaces between Ti and Al3Ti, as well as Al2O3 fiber and Al3Ti intermetallic were analyzed by scanning electron microscopy (SEM). Elemental distribution in the interfacial reaction zones were quantitatively examined by energy-dispersive spectroscopy (EDS). The phases in the composite were identified by X-ray diffractometer (XRD). The mechanical properties of the CCFR-MIL composite were measured using compression and tensile tests under quasi-static strain rate. The experimental results indicated that the residual Al was found in Al3Ti intermetallic layer of CCFR-MIL composite. The interfacial reactions occurred during HIP and the reaction products were determined to be Al2Ti, TiSi2, TiO2 and Al2SiO5 phases. Compared to Ti/Al3Ti MIL composite without fiber reinforcement, both the strength and failure strain of CCFR-MIL composite under both compressive and tensile stress states increased due to the contribution of the continuous ceramic Al2O3 fiber.

Effect of Grinding Treatment of Fly Ash on Compressive Strength of Hardened Geopolymers using Warm Press Method

In this study, starting mixed wet powders were uniaxially compressed at 200 MPa for 40 min and simultaneously heated at 200°C to form hardened bodies. Three different starting slurries composed of 100 g of fly ash powders with particles of different sizes after grinding treatment, 15 g of reagent-grade sodium, and 33.3 g of fresh water were considered. In this time, the uniaxial pressure was fixed at 200 MPa. This method is called the warm press method because the heating temperature is not as high as that in the conventional hot press sintering method used for ceramics. When ground fly ash with a diameter of 6.8 μm was used, the average compressive strength of the hardened bodies reached approximately 120 MPa. As the heating temperature and duration were increased at the fixed uniaxial pressure of 200 MPa, the compressive strength of the geopolymers increased. When ground fly ash with a diameter of 6.8 μm was used and the heating temperature and duration were 280°C and 60 min, respectively, the compressive strength of the geopolymers reached approximately 150 MPa.

Hot-Press Sintering of the W-40wt.%Cu Composite Tape-Casting Film

In this research, the W-40wt.%Cu composite tape-casting films were prepared through the vacuum hot-press sintering method, and the effect of sintering temperature on the microstructures and properties of the W-40wt.%Cu composite samples was studied. Microstructures of the W-40wt.%Cu tape-casting film and the prepared samples were analyzed by field emission scanning electron microscopy (FE-SEM). The phase of the samples was investigated by X-ray diffraction (XRD). The relative density, Vickers hardness, bending strength and electrical conductivity of the samples were investigated. The results show that the relative density of the W-40wt.%Cu composite materials enhances with the increasing of the sintering temperature, at the same time the mechanical and electrical properties are better with the increasing of the sintering temperature. The W-40wt.%Cu composites prepared at the condition of 900°C-200MPa-2h have the relative density of 97%, the bending strength of 507.3MPa, the Vickers hardness of 376.2HV and the electrical conductivity of 32.5% IACS, respectively.

Effects of Multi-Phase Reinforcements on Microstructures, Mechanical and Tribological Properties of Cu/Ti3SiC2/C/BN/GNPs Nanocomposites Sintered by Vacuum Hot-Pressing and Hot Isostatic Pressing

Cu/Ti3SiC2/C/BN/GNPs nanocomposites were prepared by vacuum hot-pressing (HP) sintering and hot isostatic pressing (HIP) sintering methods. Microstructures, mechanical and tribological properties of Cu/Ti3SiC2/C/BN/GNPs nanocomposites were investigated. Microstructures were examined by optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscope (SEM). Mechanical properties were determined by the relative density, micro-Vickers hardness, as well as tensile strength, compressive strength and shear strength. Tribological behavior of the Cu/Ti3SiC2/C/BN/GNPs composite against the GCr15 steel ring was evaluated using an M-2000 wear tester with high tangential sliding velocity. Results demonstrated that BN and graphene nano-platelets (GNPs) have an impact on the microstructures and mechanical properties of Cu/Ti3SiC2/C/BN/GNPs nanocomposites. Based on microstructures, and mechanical and tribological properties of Cu/Ti3SiC2/C/BN/GNP nanocomposites, strengthening, fracture and wear mechanisms for synergistic enhancement by multi-phase reinforcements were analyzed.

Comparative study on microstructure and electrical properties of (K0.5Na0.5)NbO3 lead-free ceramics prepared via two different sintering methods

Two different sintering methods, i.e., a hot-press sintering method and a conventional sintering method, were utilized to prepare (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics. Microstructure, dielectric, ferroelectric, and piezoelectric properties of the ceramics obtained via the two methods were comparatively studied. Both the ceramics exhibit a single orthorhombic phase. The ceramic via the conventional sintering method shows micron-sized grains and poor densification with many pores. By means of the hot-press sintering, the mean size of grains decreases to 0.1 μm and relative density increases to 96%. The evolution of domains with electrical field was detected via a scanning probe microscope, indicating field-induced domain switching on the microscale. Compared to the conventional sintering, the hot-press sintering causes an increase in the dielectric constant from 183 to 830, remnant polarization from 8.5 to 17.3 μC cm−2, piezoelectric constant from 60 to 120 pC N−1, and helps a decrease in the dielectric loss from 0.46 to 0.02, coercive field from 20 to 16 kV cm−1. The hot-press sintering facilitates improving the electrical properties of the (K0.5Na0.5)NbO3 ceramic.

Relationship between the ferromagnetic phase and the magnetoelectric coupling in hot pressed Pb(Mg1/3Nb2/3)O3-PbTiO3 based particulate composites

ABSTRACTThe influence of ferromagnetic phase properties on the magnetoelectric response of hot pressed particulate composites formed by 80 mol% of 0.675[Pb(Mg1/3Nb2/3)O3]–0.325[PbTiO3] as piezoelectric matrix and 20 mol% of NiFe2O4, CoFe2O4 or BaFe12O19 phases was analyzed. The hot pressing sintering method was suitable for obtaining composites with apparent density higher than 94% and electric resistivity close to 109 Ω.m, independently of the ferromagnetic phases used. The magnitude of the magnetoelectric coupling seems to be governed by the piezoelectric properties of ferroelectric PMN-PT matrix, and the zero bias magnetoelectric coefficient values are determined by the ferromagnetic hardness of the magnetic phase.

The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)

In order to meet the requirements of an increased efficiency applying to modern devices and in more general terms science and technology, it is necessary to develop new materials. Combining various types of materials (such as metals and ceramics) and developing composite materials seem to be suitable solutions. One of the most interesting materials includes Cu-Al2O3 composite and gradient materials (FGMs). Due to their potential properties, copper-alumina composites could be used in aerospace industry as rocket thrusters and components in aircraft engines. The main challenge posed by copper matrix composites reinforced by aluminum oxide particles is obtaining the uniform structure with no residual porosity (existing within the area of the ceramic phase). In the present paper, Cu-Al2O3 composites (also in a gradient form) with 1, 3, and 5 vol.% of aluminum oxide were fabricated by the hot pressing and spark plasma sintering methods. Two forms of aluminum oxide (αAl2O3 powder and electrocorundum) were used as a reinforcement. Microstructural investigations revealed that near fully dense materials with low porosity and a clear interface between the metal matrix and ceramics were obtained in the case of the SPS method. In this paper, the properties (mechanical, thermal, and tribological) of composite materials were also collected and compared. Technological tests were preceded by finite element method analyses of thermal stresses generated in the gradient structure, and additionally, the role of porosity in the formation process of composite properties was modeled. Based on the said modeling, technological conditions for obtaining FGMs were proposed.

Evidence of Normal to Anti Ferroelectric Phase Transition of PLZT Transparent Ceramics of Different Zr/Ti Ratio

The lanthanum-modified lead zirconate titanate transparent ceramics with different Zr/Ti ratio were prepared by the hot pressing sintering method. A single perovskive structure with a dense microsctructure was obtained and the transgranular fracture of PLZT ceramics tended to be more serious As the Zr/Ti ratio increases, the transmittance of PLZT ceramics tended to be higher and the transgranular fracture became more serious. The P-E loops changed froe a square hysteresis loop to a double tending slim hysteresis loop. Besides,the S-E loops changed from a approximate parabolic shape to a butterfly shape. These two loops confirm the transition from normal ferroelectric to anti ferroelectric phase occured with the Zr/Ti ratio increasing.

Characterizations of a hot-pressed Er and Y codoped CaF2 transparent ceramic

In this work, Er:CaF2 transparent ceramic codoped with non-active ions (Y3+ ions) was fabricated by hot-pressed (HP) sintering method. Er and Er/Y codoped CaF2 nanoparticles were synthesized by a simple coprecipitation method, the phase composition and the shape of obtained nanoparticles were analysed by X-ray diffraction patterns and transmission electron microscopy, respectively. Fluorite transparent ceramics were fabricated by HP sintering method at a temperature of 800°C. For 2mm thickness ceramic samples, the optical transmission of Er, Y:CaF2 transparent ceramic in the near-infrared range reached about 90%, and the optical transmission of Er, Y:CaF2 transparent ceramic was much higher than Er:CaF2 ceramic sample. Microstructures were characterized using SEM analysis, the two ceramic samples exhibited nearly pore-free microstructure and the average grain sizes were less than 1.0μm. The absorption, upconversion and infrared emission spectras of ceramic samples were also measured and discussed.

A study on the damping capacity of BaTiO3-reinforced Al-matrix composites

To study the damping capacity of BaTiO3/Al composites, Al composites reinforced with BaTiO3 powder (average grain sizes: 100 and 1000 nm) were fabricated by the hot-pressing sintering method. The damping properties of pure Al and BaTiO3/Al composites were investigated and compared based on the dynamic mechanical analysis over a wide range of temperatures (50–285∘C). Compared with pure Al matrix, 1000 nm BaTiO3/Al composites with 5 and 10% mass fractions of BaTiO3 exhibited better damping capacity. For 100 nm BaTiO3/Al composite, its damping capacity is slightly higher than that of pure Al below 145∘C, while it becomes lower above this degree. The damping capacity enhancement of BaTiO3/Al composites can be explained by the ferroelastic domain damping. Furthermore, 5 and 10% BaTiO3/Al composites have higher bending strength and hardness than pure Al sample.

Effect of Ti Element on the Mechanical Properties of Cu-Matrix Bonding Diamond Tool Bits

Using the hot-pressing sintering method, Cu-matrix bonding diamond tool bits including 0, 4 and 8 % Ti content (wt.%) were prepared. The effect of Ti content on the mechanical properties of Cu-matrix bonding diamond tool bits was studied. The experimental results showed that the influence of Ti content on the flexural strengths of Cu-matrix bonding bits and diamond tool bits are significant. Furthermore, the morphologies and compositions of fracture surfaces of diamond tool bits were characterized by scanning electron microscope and energy dispersive spectroscopy. The results illustrated that when the Ti content was 4%, the interface bonding between the diamond and the Cu-matrix bonding was the strongest, the flexural strength had the maximum values of the Cu-matrix bonding bits and the diamond tool bits, the values were 644 MPa and 515.8 MPa respectively.

Effects of Sintering Atmosphere on the PLMNT Transparent Ceramics Prepared by Hot-Press Sintering Method

La modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PLMNT) transparent electro-optic (EO) ceramics with pure perovskite phase were fabricated by the uniaxial hot-press sintering method. An improved hot-press sintering technique with varied atmosphere was proposed to eliminate the pore defects. It consists of four stages: 1) sintering at a relatively low temperature (800°C) in the vacuum atmosphere first, and then in the pure O2 atmosphere; 2) sintering in a pure O2 atmosphere at high temperature by uniaxial hot-press method; 3) replacing the O2 atmosphere with CO2 gas to eliminate the residual closed pores; 4) finally exchanging CO2 atmosphere with pure O2 gas to eliminate the oxygen vacancies. The research results certified that the thermal treatment in the vacuum atmosphere and CO2 atmosphere could eliminate the residual closed pores and improve the transmittance of the PLMNT transparent ceramics effectively. By the improved hot-press sintering technique, the optical transmittance of the polished PLMNT transparent ceramics with a thickness of 0.35mm increases from 61% to 64% at 632.8nm. The reasonable explanation was given about the mechanism of the improvements of this sintering technique.

Synthesis and characteristics of La3+–Co2+ substituted Sr-hexaferrites for microwave LTCC circulators

The La3+–Co2+ substituted Sr0.7La0.3Fe11.7Co0.3O19 ferrites with 2–5wt% Bi2O3·B2O3·SiO2·ZnO (BBSZ) glass were synthesized by conventional sintering (CS) method, microwave sintering (MS) method, and hot press sintering (HPS) method at a low sintering temperature of 850°C compatible with the low temperature co-fired ceramics (LTCC) systems, respectively. These ferrites were chiefly characterized by X-ray diffraction, precision density balance, and vibrating sample magnetometer. It is observed that the addition of BBSZ can promote the low temperature sintering of the ferrites, as well as the formation of M-type phase. But the excessive addition of non-magnetic BBSZ is inclined to reduce the magnetic properties for the ferrites. Detailed effects of the BBSZ amount on their low temperature sintering characteristics are revealed and explained. The proper addition of BBSZ is suggested to be 4, 4, and 5wt% for the CS ferrites, MS ferrites, and HPS ferrites, respectively. Notably, the obtained MS ferrites can provide relatively high saturation magnetization of 65.3emu/g, magnetic anisotropy field of 1528.8kA/m, and intrinsic coercivity of 336.1kA/m as low temperature sintered M-type hexaferrites for use in microwave LTCC circulators.

Effect of Process on the Microstructure and Strain Performance of the (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectric Ceramics

The microstructure, electrical property and strain performances of the Pb0.97La0.02(Zr0.775-xSn0.145+xTi0.08)O3 (PLZT) antiferroelectric ceramics which were prepared by conventional solid state synthesis (CSS), hot-pressing sintering (HP), aqueous gelcasting assisted solid state sintering method (GASS) and aqueous gelcasting assisted hot-pressing sintering (GAHP) method were compared and investigated systematically. Compared with the ceramic obtained by CSS, Pb0.97La0.02(Zr0.66Sn0.26Ti0.08)O3 ceramic prepared by timesaving HP showed higher density and more homogeneous microstructure, whose saturated polarization (Ps) and maximum longitude strain (Smax) were 42 μC/cm2 and 0.45% respectively. Finally, aqueous gel-casting assisted method was used to develop the microstructure, electrical property and strain properties of materials. Pb0.97La0.02(Zr0.70Sn0.22Ti0.08)O3 ceramic obtained by more cost-effective GASS (Ps = 40 μC /cm2, Smax = 0.47%) exhibited 37.5% larger in saturated polarization and 36.2% higher in maximum longitude strain than by CSS.

Infiltrated W–Cu composites with combined architecture of hierarchical particulate tungsten and tungsten fibers

In this article, novel W–Cu composites reinforced with topologically-inserted tungsten fibers (Wf) have been fabricated by hot-press sintering and infiltration method. By pre-sputtering of ~100nm thick chromium layer onto the surface of Wf, the contiguity or connectivity between Wf and neighboring tungsten particles (Wp) or Cu after sintering and infiltration was enhanced. Combined SEM, TEM and STEM techniques confirmed that the intact interfaces of Wf/Wp and Wf/Cu free from precipitates, impurities and porosities would provide desirable strength and ductility. Further mechanical tests also validated its superior compressive strength and plasticity at various temperatures, together with significantly improved tensile strength (by 23.6%) and hardness (by 9.3%) for the W–Cu composite after reinforcement with Cr-coated Wf, which promotes the engineering application of the composite greatly.

Preparation and properties of negative thermal expansion Zr2P2WO12 powders and Zr2P2WO12/TiNi composites

Abstract Zirconium tungsten phosphate (Zr2P2WO12, denoted as ZWP) powders were synthesized via hydrothermal method for the first time. Nickel titanium (TiNi), as a shape memory alloy, is a very important industry material with large positive coefficient of thermal expansion (CTE), while ZWP is a kind of negative thermal expansion materials. TiNi alloys with and without addition of ZWP powders were compacted by hot-pressing sintering method at 1100 C for 3 h. The obtained ZWP ceramics showed a CTE of about −2.012 × 10−6/K. The ZWP/TiNi composites with reduced CTEs were successfully synthesized without decomposition of ZWP or reactions between ZWP and TiNi alloy. From the results of X-ray powder diffraction, no phase transitions occurred during sintering. SEM images show that the ZWP powders consist of relatively homogeneous particles with sizes around 360 nm. With increasing the ZWP content in the composites, the relative density of the obtained ZWP/TiNi composite materials reduced and the hardness increased.

3D Printing Fabrication of Amorphous Thermoelectric Materials with Ultralow Thermal Conductivity.

Thermoelectric materials are prepared by developing 3D printing technology. The 3D fabricated Bi0.5 Sb1.5 Te3 samples exhibit amorphous characteristics and thus show an ultralow thermal conductivity of 0.2 W m(-1) K(-1) . 3D printing fabrication readily generates bulk thermoelectric samples of any shape, which is not the case with traditional hot-pressing and spark plasma sintering methods.