Reactive Liquid-phase Sintering Research Articles

Influence of sintering aids on properties of dense Si2N2O ceramic developed by spark plasma sintering

Through reactive liquid phase sintering, dense and homogenous pellets with a diameter of 40 mm were successfully achieved after 50 min. These samples contain at least 95 vol% of Si2N2O. The microstructure, fracture toughness, coefficient of thermal expansion (673–1673 K), dielectric properties and high-temperature oxidation resistance were investigated to determine the influence of sintering aids such as lanthanide oxides (Sm2O3 and Y2O3) and metal oxide (Al2O3). The nano-sized grains generated have a uniform distribution. The composition of the sintering aid has no influence on the coefficient of thermal expansion or the dielectric properties. The crack propagation mode shifts from transgranular to intergranular in Al2O3 samples, which increases the fracture toughness. The lanthanide oxide samples, on the other hand, outperform the Al2O3 samples in terms of oxidation resistance, as a protective SiO2 and Ln2Si2O7 layer forms on the surface of the oxidized samples.

Microstructure and Mechanical Properties of Ti-Cu-Based Materials Produced by Using Reactive Melt Infiltration and Liquid Phase Sintering Techniques

Microstructure and Mechanical Properties of Ti-Cu-Based Materials Produced by Using Reactive Melt Infiltration and Liquid Phase Sintering Techniques

Cu strengthened Al-Si-Cu semi-solid billet fabricated by liquid phase reaction sintering

A high-strength Al-6Si-6Cu semi-solid billet was prepared by liquid phase reaction sintering. Compared with the pure Al grains in the Al-6Si (wt%) semi-solid billet, Cu nanoparticles precipitated in Al grains of the Al-6Si-6Cu (wt%) semi-solid billet. The interface modified by geometrically necessary dislocations (GNDs) makes Cu nanoparticles show a strong pinning effect on dislocations. Under this pinning action, the Al-6Si-6Cu semi-solid billet possesses an outstanding strain-hardening rate, and its yield strength (YS) and ultimate strength (US) increased by 120% and 67.4%, reaching 220 MPa and 360 MPa respectively. The analysis of strengthening mechanism suggests that Orowan strengthening provided by Cu nanoparticles is the main strengthening mechanism of Al-6Si-6Cu semi-solid billet, which provides 83% of the total yield strength.

Microstructural properties, thermodynamics and kinetics of Al-Si semi-solid billet fabricated by liquid phase reaction sintering

This study proposes a method of preparing an Al-Si semi-solid billet by cold pressing and liquid phase reaction sintering with Al and Si elemental powders. The microstructural evolution and tensile properties of the billets were evaluated. Thermodynamic and kinetic analyses of the reaction were also conducted. The kinetic equation for the accurate prediction of the liquid phase content was derived. Al and Si elemental powders were reacted at 585 °C, 595 °C and 605 °C to form a liquid phase and were uniformly distributed in the billet. After reaction sintering, semi-solid billets with equiaxed Al particles that were uniformly distributed in the liquid phase were formed. Increases in Si content and reaction temperature contributed to the increase in liquid phase content after thermodynamic equilibrium. An increase in temperature and a decreased in porosity promoted the kinetic formation of the liquid phase. Meanwhile, the kinetic equations y6 wt% = 86.61·exp(−25487.4/RT)·t0.35 and y8 wt% = 95.5·exp(−36154.2/RT)·t0.4 described the relationship between the liquid phase formation ratio and the reaction temperature and time while accurately predicting the liquid phase content during the reaction. The increase in liquid phase content in the microstructure improved the strength of the billet but reduced its elongation. Moreover, the fracture mode of the billet changed from a ductile fracture to a brittle fracture. The billet fracture was mainly attributed to the generation and propagation of cracks in the liquid phase.

Microstructure evolution and mechanical properties of Al-8wt. % Si semi-solid billet fabricated by powder metallurgy liquid phase reaction sintering

Abstract The Al-8wt. % Si semi-solid billets were successfully prepared by a new liquid phase reaction sintering process with Al and Si elemental powders. The reaction mechanism of the Al and Si elemental powders was investigated, and the thermodynamics and dynamics of the reaction process were studied. The effect of the microstructure evolution on the mechanical properties was analyzed. In the reaction process, the reaction product Al(Si)(L) liquid phase wets the Al particles well, and the liquid phase content increased with increasing reaction temperature and time. It was found that the kinetic model given by ψ = 4.6 × 105exp(-1.05 × 105/RT)t1/3 can accurately predict the actual liquid phase formation fraction. With increasing reaction temperature, the viscosity of the liquid phase decreases and the Si atom diffusion coefficient increases. This will increase the formation rate of the liquid phase and decrease the length of lath Si. The increased liquid phase content increases the strength of the billet and decreases its elongation. The shear crack is the main reason for the instability of the billets during the deformation process. Acting as a crack source, Si particles accelerate the generation and propagation of cracks, and promote the instability fracture of the billet.

Synthesis and characterization of Ge doped Cu2ZnSn(S,Se)4 bulk in the presence of reactive liquid phase sintering aid

The quaternary chalcogenide Cu2Zn(Sn1-xGex)(S,Se)4 bulks, where x is Ge/[Ge+Sn] molar ratios of 0, 0.15, 0.30, and 0.45 were synthesized via reactive liquid phase sintering at 600 °C for 30 min in the tube furnace and characterized systematically. Together with Sb2S3 as a reactive liquid phase sintering aid, the effects of Ge incorporation on densification, grain boundary, crystal phase purity, crystalline size, and electrical properties were studied. The morphology of the resulted Cu2Zn(Sn1-xGex)(S,Se)4 bulk was found to be more densified and compacted at Ge/[Ge+Sn] molar ratio of 0.15 compared to the rests. The X-ray diffraction peaks were shifted towards a higher angle as Ge fraction was increased. The hole concentrations for the entirely p-type bulks were determined to be 3.67 × 1018, 1.40 × 1018, 1.28 × 1018, and 8.90 × 1017 cm−3 at Ge/[Ge+Sn] molar ratios of 0, 0.15, 0.30, and 0.45, respectively. The effects on conductivity and mobility were consistent with their interrelations. Hence, the synthesis and study of Ge incorporated Cu2ZnSn(S,Se)4 bulk using powder technique allows identifying the composition which is expectedly more important for the fabrication of thin film solar cells.

Rapid fabrication of pure p-type filled skutterudites with enhanced thermoelectric properties via a reactive liquid-phase sintering

Filled skutterudites have great potential for power generation. However, the conventional melting–quenching–annealing–sintering process requires a time-consuming annealing process to accomplish the phase transformation. A new strategy to realize the complete phase transformation in a short time is an urgent need for filled skutterudite. In this study, a modifying reactive liquid-phase sintering enabled by introducing the extra BaSb3 in the spark plasma sintering process was successfully applied to fabricate pure BaFe4Sb12 skutterudites in less than 30 h. It is found that increasing BaSb3 liquid content can effectively promote the phase transformation to BaFe4Sb12 skutterudite through accelerating the chemical reaction between the quenched mixtures during the sintering process. However, an abnormal grain growth would take place with further increasing the liquid content. An optimal ZT value of 0.62 at 800 K was achieved for the BaFe4Sb12 skutterudite due to the enhanced Seebeck coefficient and the increased electrical conductivity as well as the decreased lattice thermal conductivity induced by the single-phase composition. This work demonstrates that pure filled skutterudite with enhanced TE performance can be fabricated by the simple and efficient reactive liquid-phase sintering without longtime annealing process.

CALPHAD-guided alloy design and processing for improved strength and toughness in Titanium Boride (TiB) ceramic alloy containing a ductile phase

A CALPHAD-guided alloy design strategy is used here to design and process fully dense titanium boride (TiB) ceramic alloys containing a ductile phase for toughening. This involved the construction of high temperature phase fields of the Ti-B-Fe-Mo quaternary alloy system using the CALPAHD approach. To design the compositions, ternary phase diagrams of Ti-B-Fe, Ti-B-Mo, and Fe-Mo-B systems were first constructed using the thermodynamic databases that were verified to predict well the binary phase diagrams of components. Using this as a basis, the pseudo-ternary diagrams of the Ti-B-Fe-Mo system were constructed to map the high temperature phase fields over a wide range of composition. This made it possible to identify relatively lower reaction sintering temperatures for various alloy compositions. Two compositions of TiB ceramic alloys with the ductile beta-phase (both having ∼85% TiB and ∼15% β-Ti phase), were considered for the demonstration of the present approach. Based on the pseudo-ternary phase fields, these two compositions could be processed using electric-field-activated sintering (EFAS), in a relatively short time, at their respective liquid-phase-forming temperatures. The processing temperature was as low as 1423 K for a Fe/Mo-rich ceramic alloy composition, but the formation of brittle intermetallic phase FeTi here was found to be detrimental to mechanical properties. The second TiB ceramic alloy composition, which was Fe/Mo-lean, could be processed at 1623 K. This composition is shown here to possess a very good combination of high flexural strength (∼850 MPa) and high fracture toughness (∼7.7 MPa√m), making it attractive for potential applications. The identification of the liquid phase reaction sintering regions in the ternary phase diagrams, and the eventual finding of one composition giving a relatively high strength and toughness, demonstrate that this is an effective approach for alloy design. The microstructural factors that control the strength and toughness have been identified and the ways to increase these properties further, in this class of materials, are suggested.

Liquid-Phase Reaction Sintering Behavior at below 200 °C and Electrical Sheet Resistance of Sn-58Bi/Cu Composite Pastes

To fabricate a film with the highest electrical conductivity through liquid-phase reaction sintering below 200 °C using composite pastes containing both Sn-58Bi and Cu particles as a filler material, the effects of process parameters, such as the mixing ratio of the fillers, reaction temperature, and reaction time, were evaluated and the parameters were optimized. The lowest sheet resistance of 0.0278 Ω/□ was obtained when the composite paste of Sn-58Bi/40 wt% Cu was sintered at 190 °C for 180 s. The reduced resistance was attributed to the increase in the portion of acicular Cu6Sn5 phases. The phases were formed by the dissolution and precipitation of Cu, and the three-dimensional linkage of irregular polygonal Cu6Sn5 phases using the acicular Cu6Sn5 through a Bi phase of the highest electrical resistivity. The reaction time, which was prolonged up to 180 s during the reaction at 190 °C, maximized the number of acicular Cu6Sn5 and irregular polygonal Cu6Sn5 phases, through the formation of fine Cu6Sn5 phases by splitting behavior of coarse Cu6Sn5 phases. Key words: Sn-58Bi, composite paste, reaction sintering, sheet resistance, acicular Cu6Sn5

Effects of Li2O-B2O3-SiO2 glass on the low-temperature sintering of Zn0.15Nb0.3Ti0.55O2 ceramics

The influences of Li2O-B2O3-SiO2 glass (LBS) on the activation energy, phase composition, the stability of the structure and microwave dielectric properties of Zn0.15Nb0.3Ti0.55O2 ceramics have been systematically investigated. LBS glass acted as flux former and contributed to the reactive liquid-phase sintering mechanism, which remarkably lowed the sintering temperature from 1150 °C to 900 °C and enhanced the shrinkage and densification of ceramic at the low sintering temperatures. The ceramics with 1.5 wt% LBS glass sintered at 900 °C for 3 h show great properties: εr = 73.59, Q × f = 8024 GHz, τf = 270.54 ppm/°C.

Investigating on sintering mechanism and adjustable dielectric properties of BLMT glass/Li2Zn3Ti4O12 composites for LTCC applications

A series of novel low temperature co-fired ceramics were fabricated in x BLMT-(100-x) Li2Zn3Ti4O12 (2.5 ≤ x ≤ 80 wt%) composites sintered at 900 °C. The sintering mechanism, phase composition, microstructure and dielectric properties of the composites were investigated. The results showed that the sintering mechanism of composites with <20 wt% BLMT glass could be attributed to non-reactive liquid-phase sintering and LaBO3 phase was crystallized from glass beside Li2Zn3Ti4O12 phase, while composites with ≥20 wt% glass were controlled by the coexistence of viscous sintering and reactive liquid-phase sintering, BLMT glass crystallized forming LaBO3, MgLaB5O10 and a small amount of rutile phase, nevertheless, more rutile phase was formed by reacting between glass and ceramic. As BLMT glass was increased, LaBO3, MgLaB5O10 and rutile phase gradually dominated the material and Li2Zn3Ti4O12 phase decreased. Meanwhile, the dielectric constant (εr) and quality factor (Q × f) demonstrated gradually decrease, whereas the temperature coefficient of resonant frequency (τf) presented a trend of fall first then rise. Typically, the composite with 60 wt% glass displayed excellent dielectric properties with εr = 14, Q × f = 23,000 GHz, and τf = −3.56 ppm/°C. The corresponding fitting equations of εr, Q × f and τf on the BLMT glass content were obtained by the Origin software, which indicated that the dielectric properties of BLMT/Li2Zn3Ti4O12 composites could be precisely adjusted by adding the suitable content of glass. Therefore, the sintering process, phase composition and dielectric properties of BLMT/Li2Zn3Ti4O12 composites can be controlled by varying the content of Li2Zn3Ti4O12 ceramic and B2O3-La2O3-MgO-TiO2 glass.

Effect of initial Co content on the microstructure, mechanical properties and high-temperature oxidation resistance of WCoB-TiC ceramic composites

WCoB-TiC ceramic composites with various initial Co content (varying between 10wt% and 47wt%) were fabricated by liquid phase reaction sintering (LPRS) in a vacuum furnace. The microstructure, hardness, transverse rupture strength (TRS) and high-temperature oxidation resistance of WCoB-TiC ceramic composites were investigated. The results revealed that initial Co content had an important influence on phase composition of sintered specimens. When the initial Co content was low, the hard phases in WCoB-TiC ceramic composites were W2CoB2 and TiC. However, when initial Co content was at or higher than 19.6wt%, W2CoB2 hard phase changed to WCoB, and CoB changed to Co2B. With the increase of initial Co content, the hardness and TRS of WCoB-TiC ceramic composites increased firstly and then decreased. WCoB-TiC ceramic composites with an initial Co content of 18.2wt% showed the highest hardness of 91.6 HRA, and WCoB-TiC ceramic composites with an initial Co content of 19.6wt% showed the highest TRS of 1783MPa. Mass gain followed parabolic oxidation kinetics, and the mass gain increased dramatically when initial Co content exceeded 19.6wt%.

Microstructure and Mechanical Properties of Mo2FeB2 Based Cermets with/without Nb Addition

Four series of Mo2FeB2 based cermets with different Nb content between 0 and 6 wt.% had been successfully fabricated by liquid phase reaction sintering (LPRS). The densification behavior, microstructural characteristics and mechanical properties of Mo2FeB2 based cermets were investigated. The result shows that with the increase of Nb content, the grain size decreased, but more pores formed. Meanwhile, the hardness and transverse rupture strength both be increased first and then decreased. Mo2FeB2 based cermets doped with 4 wt.% Nb content have the highest hardness and TRS of HRA 90.6 and 1970 MPa.

Effects of Ge substitution on morphology and electrical properties of Cu2Sn(S,Se)3 bulk at a fixed Se/[Se+S] composition

Ge-substituted Cu2Sn(S,Se)3 bulks with Cu2(Sn1-xGex)(S,Se)3 formula at x = 0, 0.25, 0.50, 0.75, and 1.0 were synthesized by reactive liquid phase sintering, where the heating process was held at 200°C for 20min before reaching the sintering temperature of 600°C for 30min. In the presence of volatile Sb2S3 sintering aid, the effects on densification, grain boundary, crystalline size, and electrical properties of Ge-substitution were investigated. Cu2(Sn1-xGex)(S,Se)3 showed p-type behavior for all x values. It was found that the mobility was increased sharply and carrier concentration was decreased rapidly as the x-value was increased. The electrical conductivities were found to be 14.0, 22.7, 36.8, 126, and 153S/cm at x = 0, 0.25, 0.50, 0.75, and 1.0, respectively. X-ray diffraction (XRD) peaks were shifted to the higher angle and band gaps increased upon successive increasing of the Ge/[Ge+Sn] fraction being 1.19, 1.21, 1.22, 1.24, and 1.26eV at x = 0, 0.25, 0.50, 0.75, and 1.0, respectively. The studies of Ge-x-CTSSe bulks were based on GeSn defects and supported by the data of morphological, structural, electrical, and optical properties.

Low temperature sintering kinetics of BaZn2Ti4O11 dielectric ceramic in the presence of a liquid phase

The sintering temperature of BaZn2Ti4O11 ceramic (Ba-Zn-Ti) dropped from 1200 °C to 850 °C in the presence of a liquid phase containing Li2O and B2O3, and the ceramic remained excellent dielectric microwave properties. Experiments on the wetting behavior, activation energy, phase composition, microstructure and microwave dielectric properties of the ceramics were carried out to understand the mechanism of the sintering kinetic. The results reveal that the sintering process of the Ba-Zn-Ti significantly accelerated at a low temperature even with a higher activation energy, due to the existence of liquid phase causes decomposition of BaZn2Ti4O11, which provides extra energy at the early stage of sintering, called reactive liquid-phase sintering.

Microstructure and mechanical properties of Mo2FeB2 ceramic-steels with Nb/V addition

ABSTRACTSeven series of Mo2FeB2 ceramic-steels with Nb/V content between 0 and 6 wt-% had been successfully fabricated by liquid phase reaction sintering. The microstructure was studied by means of field emission scanning electron microscope, energy dispersive spectroscopy and X-ray diffractometry. The hardness (HRA), transverse rupture strength (TRS) and wear resistance were also measured. The results reveal that the grain size decreased with the increase of Nb content, but had little change with the increase of V content. With the increase of Nb/V content, the hardness and TRS both enhance first and then descends. Mo2FeB2 ceramic-steels with 4 wt-% Nb content show the highest hardness and TRS of HRA 90.6 and 1970 MPa and the best dry sliding wear resistance.

Low temperature sintering kinetics of BaO-0.15ZnO-4TiO2 dielectric ceramic in the presence of a liquid phase

The influence of Li2O-B2O3-SiO2 glass (LBS) on the activation energy, phase composition, reaction mechanisms, and microstructure of the BaO-0.15ZnO-4TiO2 ceramics (Ba-Zn-Ti) were investigated to understand the mechanism of the sintering kinetic. The results reveal that the sintering process of the Ba-Zn-Ti significantly accelerated at a low temperature even with a higher activation energy, due to the reaction of Ba-Zn-Ti and LBS caused by the existence of liquid phase, which provides extra energy at the early stage of sintering, called reactive liquid-phase sintering. The sintering temperature of Ba-Zn-Ti significantly dropped from 1150 °C to 875 °C attribute to the presence of liquid phase caused by LBS, and obtained excellent dielectric microwave properties.

CuO/V2O5-Codoped Bi3/2ZnNb3/2O7 (BZN) Ceramic for Embedded Capacitor Layer in Integrated LTCC Modules

Sintering additives for Bi3/2ZnNb3/2O7 (BZN) ceramic have been studied to facilitate use of BZN as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional printing modules. Among the additives studied, a CuO/V2O5 mixture was the most promising for cofiring BZN ceramic with a commercial low-permittivity (e r) LTCC sheet (MLS-22; NEG Co., Japan) and Ag electrode. BZN codoped with 0.5 wt.% CuO/V2O5 was successfully densified at 860°C by reactive liquid-phase sintering, and the resulting dielectric properties were acceptable for use of the CuO/V2O5-codoped BZN for embedded capacitors in LTCC modules. The room-temperature permittivity (e r) of the CuO/V2O5-codoped BZN was 148 at 1 MHz, and the capacitance thermal stability was ±1.3% within the temperature range of −55°C to 125°C. The physical and chemical compatibilities of the CuO/V2O5-codoped BZN with heterogeneous layers (low-e r LTCC layer and Ag electrode layer) in LTCC modules were also examined. A cofiring test of the doped BZN ceramic with MLS-22 LTCC sheet revealed that thickness control of the two heterogeneous layers was a key factor to avoid crack formation during cofiring. The optimum thickness ratio of doped BZN to MLS-22 layers was less than 0.25:1. A chemical compatibility test revealed no severe reaction between the doped BZN/MLS-22 and doped BZN/Ag layers.

Magnetic field effects on liquid-phase reactive sintering of MnBi

Magnetic fields effects on liquid-phase reaction sintering on MnBi were investigated. The liquid-phase reaction was so fast even in a zero field that the fraction of in-field sintered ferromagnetic MnBi phase was independent of the external magnetic field. However, the ferromagnetic MnBi crystals in the in-field sintered sample were oriented along the external magnetic field direction. The Lotgering factor of the in-field sintered sample was 0.99. This result indicated that almost completely anisotropic MnBi phase could be obtained by in-field liquid phase reactive sintering.

Influence and effectivity of Sm2O3 and Cr3C2 grain growth inhibitors on sintering of WCoB–TiC based cermets

With WC, TiB2 and Co powders as raw materials, WCoB–TiC based cermets were prepared by liquid phase reaction sintering (LPRS) in a vacuum furnace at 1400°C. In this work, the consolidation of WCoB–TiC based cermets with Sm2O3 or Cr3C2 as grain growth inhibitor was studied. The amounts of inhibitor are 0; 0.3; 0.6 and 0.9wt%. The effects of Sm2O3 and Cr3C2 on the grain growth of WCoB–TiC based cermets were studied. The microstructure and mechanical properties of WCoB–TiC based cermets were analyzed by field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It is found that that Sm2O3 and Cr3C2 not only retard the densification of the WCoB–TiC based cermets, but also significantly suppress the growth of WCoB-grains and TiC-particles. Specimens doped with 0.3wt% Sm2O3 exhibit the optimum mechanical properties (hardness and wear resistance). Whereas mechanical properties (hardness and wear resistance) of specimens linearly increase with the increase of Cr3C2.