Increasing Sintering Pressure Research Articles

Effect of pressure on sintering behavior of polycrystalline diamond

Polycrystalline diamond composites (PDC) have been used as a cutting material in a multitude of fields, from mechanical processing to oil and gas drilling. In this study, PDC samples were prepared under high pressure and high temperature (HPHT) conditions within a pressure interval of 5.5 to 10.5 GPa by sintering diamond powder (average grain size ~3 μm) with WC-10 wt% Co substrate. Samples obtained with varying sintering pressures and temperatures were characterized using Vickers hardness tester, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that: (1) within a specified material system, each distinct sintering pressure condition corresponds to a unique optimal sintering temperature that yields the pinnacle of consolidation efficiency in samples. This optimal temperature exhibits a linearly increasing trend with rising sintering pressure; (2) at the intersection where the sintering pressure attains its optimal match with temperature, an increase in pressure fosters more intimate contact and stronger inter-grain bonding among diamond particles, thus amplifying the DD bond formation effect, which consequently leads to a linear enhancement in the Vickers hardness values of PDC with increasing sintering pressure; (3) simultaneously, under conditions of optimal temperature matching, elevating the sintering pressure notably decreases the cobalt content within the polycrystalline diamond layer of PDC samples. These findings furnish crucial experimental evidence for optimizing PDC material properties, significantly contributing to the advancement of both theoretical exploration and technological innovation within the field, carrying profound academic value and practical guidance implications.

Strengthening Hf0.95Ta0.05B2 ceramic with ultrafine grains and high-density dislocations

Full densification and fine microstructures are the two key optimization targets of ceramic materials. Although fine Hf0.95Ta0.05B2 powder (~ 0.36 μm) has been synthesized, it was still difficult to obtain densified Hf0.95Ta0.05B2 ceramics with ultrafine grains (< 1 μm) using conventional high temperature sintering. Increasing sintering pressure could provided higher densification driving force, but it usually negatively promoted grain growth for nanoceramics. Our strategy was to gain the fully dense Hf0.95Ta0.05B2 ceramic under a high pressure at a selected temperature with retarded grain growth. In this work, fully dense Hf0.95Ta0.05B2 ceramic was prepared at 1700 °C under a high pressure of 200 MPa. The limited grain growth was achieved with the average grain size of 0.6 μm. Therefore, the mechanical properties were significantly improved, including Vickers hardness (24.8 GPa) and fracture toughness (4.2 MPa.m1/2), which were ascribed to Hall-Petch and dislocation strengthening mechanism.

Light weight- low modulus biocompatible titanium alloys processed via spark plasma sintering

There is a wide range of biomedical applications for titanium and its alloys due to their biological inertness, excellent biocompatibility, superior corrosion resistance, and little to no adverse reactions. However, the commonly used titanium (Ti-6Al-4 V) alloys have been reported to have high elastic modulus (116 GPa) compared to human bone (10–40 GPa), resulting in bone atrophy caused by stress shielding, a phenomenon of bone degradation caused by an insufficient supply of stress from the implant. The presence of aluminum and vanadium in titanium alloys has also been linked to neurodegenerative diseases like Alzheimer's. A new class of titanium biomedical alloys (Ti-35 Nb-7Zr-5Ta (wt%) also referred to as TNZT alloys) with low toxic alloying elements (niobium, tantalum, and zirconium) and capable of combating the problems associated with Ti-6Al-4 V alloys are being developed. In the present study, various physical, structural, mechanical, and biological properties of such TNZT alloys have been explored, along with their relationship to sintering processing parameters such as sintering temperature (400, 600, 800, and 1000 °C) and sintering pressure (20, 40, and 60 MPa). The sample sintered at 1000 °C demonstrated a single β-phase (BCC) of titanium which clearly indicates that selected sintering temperatures preserve the BCC β-phase in titanium without the formation of the HCP α-phase. Both density and elastic modulus of spark plasma sintered (SPS) TNZT samples increased with increasing sintering pressure and temperature, and the underlying mechanisms were discussed. All the sintered TNZT alloys exhibited excellent biocompatibility and have the potential for use as long-lasting and high-performance biomedical materials.

The Influence of Sintering Pressure on the Preparation, Friction Properties, and Magnetic Properties of Ti2AlC-TiC and Ti3AlC2-TiC Composites Under High-Pressure and High-Temperature

Due to their high melting point, low density, and affordable price, TiC ceramics have emerged as one of the most promising ultrahigh temperature structural materials. However, its development and usage are severely constrained by its weak mechanical characteristics. The Ti2AlC-TiC and Ti3AlC2-TiC composites were synthesized by using the laminated metal-ceramic Ti2AlC/Ti3AlC2 as the binder, combined with high-temperature and high-pressure sintering technology (GPa order of magnitude confinement system). The thermal analysis shows that the exothermic heat of Ti/1.2Al/2TiC is less than that of 3Ti/1.2Al/2C, 2Ti/1.2Al/C, and 3Ti/1.5Al/C. The ratio of Ti/1.2Al/2TiC can suppress the thermal explosion phenomenon during the sintering process and improve the safety of the high-pressure sintering process. XRD results showed that the main composition of the sintered products was Ti2AlC-TiC at 2∼3.5 GPa and Ti3AlC2-TiC at 4∼5 GPa. As the sintering pressure increased from 2 GPa to 5 GPa, the bonding phase changed from Ti2AlC to Ti3AlC2. The thickness of the synthetic Ti3AlC2 layer is near 0.1 µm under 5 GPa. The average friction coefficient of Ti2AlC-TiC composites sintered 2 GPa with POM is as low as 0.1767, while the average friction coefficient of Ti3AlC2-TiC composites with POM increased to 0.3468∼0.3797. The wear width of Ti2AlC-TiC is lower than that of Ti3AlC2-TiC composites sintered under 4–4.5 GPa. The wear width of Ti3AlC2-TiC composites decreases following the rise of sintering pressure and is reduced to 0.3504 mm under 5 GPa. Ti2AlC-TiC and Ti3AlC2-TiC composites with PP ball counterparts have friction coefficients of 0.375 to 0.45 and worse wear resistance than that of POM balls. Ti3AlC2-TiC composites synthesized at 5 GPa with a Cu ball had the smallest friction coefficient (0.4558) and the smallest wear scar width (0.6289 mm). The friction coefficients and wear widths of synthetics with Al pairs ranged from 0.48–0.697 and 0.851–1.087 mm, respectively, and varied irregularly with increasing sintering pressure. Ti2AlC-TiC composites synthesized at 2 GPa with agate and glass pairs have coefficients of friction of 0.5 and 0.61, respectively. Abrasion widths of Ti2AlC-TiC composites synthesized at 2 GPa with agate and glass pairs were 1.3 mm and 0.72 mm, respectively. The friction coefficient of synthetics with agate and glass pairs increases with increasing sintering pressure. The magnetization and magnetization intensity of the Ti3AlC2-TiC composites are stronger than those of Ti3AlC2. Ti2AlC-TiC and Ti3AlC2-TiC composites held promise to serve in the field of ceramic grinding processing applications.

Preparation and Properties of Layered SiC-Graphene Composites for EDM.

Three and five-layered silicon carbide-based composites containing 0, 5, and 15 wt.% of graphene nanoplatelets (GNPs) were prepared with the aim to obtain a sufficiently high electrical conductivity in the surface layer suitable for electric discharge machining (EDM). The layer sequence in the asymmetric three-layered composites was SiC/SiC-5GNPs/SiC-15GNPs, while in the symmetric five-layered composite, the order of layers was SiC-15GNPs/SiC-5GNPs/SiC/SiC-5GNPs/SiC-15GNPs. The layered samples were prepared by rapid hot-pressing (RHP) applying various pressures, and it was shown that for the preparation of dense 3- or 5-layered SiC/GNPs composites, at least 30 MPa of the applied load was required during sintering. The electrical conductivity of 3-layered and 5-layered composites increased significantly with increasing sintering pressure when measured on the SiC surface layer containing 15 wt.% of GNPs. The increasing GNPs content had a positive influence on the electrical conductivity of individual layers, while their instrumented hardness and elastic modulus decreased. The scratch tests confirmed that the materials consisted of well-defined layers with straight interfaces without any delamination, which suggests good adhesion between the individual layers.

Effect of applied pressure on microstructure and properties of hot‐pressed Ca‐doped LaCrO3 ceramics

AbstractHigh‐density chromium deficient calcium‐doped lanthanum chromite‐based ceramics (La0.8Ca0.2Cr0.98O3) were prepared by hot pressing (HP) at different sintering pressures, and the highest density can reach 98.8%. The effects of sintering pressure on the microstructure, mechanical properties, and electrical conductivity of La0.8Ca0.2Cr0.98O3 materials were studied. The experimental results show that HP can increase the density of lanthanum chromite‐based ceramic materials and significantly inhibit the growth of grain size. As the sintering pressure increases, the strength and hardness gradually increase, but the fracture toughness decreases. When the sintering pressure is greater than 58 MPa, the presence of the second phase CaCr2O4 can be detected in the XRD results of the sintered ceramics. The SEM results showed that CaCr2O4 had two completely different morphologies in the sintered ceramics, and it was initially speculated that the possible causes were due to two different generation pathways. The electrical conductivity decreases with increasing sintering pressure, whereas the maximum electrical conductivity obtained is 18.61 S/cm in vacuum at 800°C for pressureless sintering ceramic.

Effect of sintering pressure on electrical transport and thermoelectric properties of polycrystalline SnSe

Tin selenide (SnSe), which has high thermoelectric (TE) performance due to its low thermal conductivity, is considered as a promising TE material. It is good that TE properties were reported in single crystal form because polycrystalline SnSe exhibits low electrical conductivity compared to that of single crystal SnSe. To improve the electrical conductivity of polycrystalline SnSe, the effects of the pressure applied during spark plasma sintering (SPS) on the electrical charge transport and the TE properties of the polycrystalline SnSe were investigated. Degree of texture was enhanced with increasing sintering pressure from 30 to 120 MPa during SPS, which lead to the increase in carrier mobility, which resulted in the increase in electrical conductivity. Increase in pressure led to a significant increase in thermal conductivity due to an increase in the lattice thermal conductivity, which can be attributed to the decrease in phonon scattering at the grain boundary. A ZT of $${\sim }0.7$$ was obtained at 823 K from the polycrystalline SnSe sintered with a pressure of 60 MPa, which can result from large increase in electrical conductivity with very small increase in the thermal conductivity. This study shows that the TE properties of the polycrystalline SnSe can be enhanced by controlling the degree of texture which can be accomplished by changing the pressure applied during SPS.

Effects of Sintering Pressure on the Densification and Mechanical Properties of Nanosilver Double-Side Sintered Power Module

Modern power electronics has the increased demands in current density and high-temperature reliability. However, these performance factors are limited due to the die attach materials used to affix power dies microchips to electric circuitry. Although several die attach materials and methods exist, nanosilver sintering technology has received much attention in attaching power dies due to its superior high-temperature reliability. This paper investigated the sintering properties of nanosilver film in double-side sintered power packages. X-ray diffraction results revealed that the size of nanosilver particles increased after pressure-free sintering. Compared with the pressure-free sintered nanosilver particles, the 5-MPa sintered particles showed a higher density. When increasing sintering pressure from 5 to 30 MPa, the shear strength of the sintered package increased from 8.71 to 86.26 MPa. When sintering at pressures below 20 MPa, the fracture areas are mainly located between the sintered Ag layer and the surface metallization layer on the fast recovery diode (FRD) die. The fracture occurs through the FRD die and the metallization layer on the bottom molybdenum substrate when sintering at 30 MPa.

Effect of Sintering Conditions on Microstructure and Mechanical Strength of Cu Micro-Particle Sintered Joints for High-Power Semiconductor Module Applications

In this study, the feasibility of low-cost micro-sized Cu-sintering technology for high-power semiconductor packaging has been evaluated. A Cu paste with micro-sized Cu powders and a metal content of approximately 76 % as a bonding material was fabricated. The sinter-bonding reactions and mechanical shear strengths of Cu-sintered joints were evaluated at different sinter bonding pressures and temperatures for 10 min during the sintering process. The thickness of the Cu sintered joints decreased with increasing sintering pressure and temperature. Good interfacial uniformity and stable metallurgical microstructures were observed in the Cu joints sintered at a sintering pressure of 10 MPa and a sintering temperature of 300 °C. It was confirmed that a pressure and temperature assisted sintering process could create relatively dense sintered layers and good interfacial uniformity in the Si chip/Cu-sintered layer/DBC joints. The die shear strength of the Cu-sintered joints increased with increasing sintering pressure and temperature. Despite a short sinter-bonding duration of 10 min, relatively good metallic bonding and dense sintered microstructures created by a sintering pressure of 10 MPa resulted in shear strength of approximately 20 MPa of the Cu- sintered joints. Key words: Cu paste, Cu sintering, Cu powder, Power electronics, Sinter-bonding, Shear strength

Micrometer-sized titanium carbide with properties comparable to those of nanocrystalline counterparts

The influence of sintering pressure on the mechanical properties of bulk titanium carbide (TiC) fabricated through work hardening at high pressure and high temperature is investigated systematically. A series of pure polycrystalline TiC samples are prepared by sintering micrometer-sized TiC powders at a pressure of 9.0–14.0 GPa and a temperature of 1500 °C. These samples are then characterized by various techniques for determining their residual stress, grain size, density, microstructural defects, hardness, and fracture toughness. The results demonstrate that the Vickers hardness HV and the fracture toughness KIC depend strongly on the sintering pressure. It is found that the mechanical properties of the sintered samples improve with increasing sintering pressure. The relative density increases with increasing sintering pressure, reaching near full density at 14.0 GPa. The hardness and fracture toughness of the sample sintered at 1500 °C at 14.0 GPa pressure are 31.2 GPa and 4.2 MPa m1/2, respectively. The high-pressure and high-temperature environment causes severe plastic deformation of the grains, as well as a high density of dislocations, resulting in a dislocation pileup. The latter, together with the production of defects such as sub-boundaries and stacking faults, provides strengthening and stabilizing effects and improves the material hardness.

Effect of Sintering Conditions on the Mechanical Strength of Cu-Sintered Joints for High-Power Applications.

In this study, the feasibility of low-cost Cu-sintering technology for power electronics packaging and the effect of sintering conditions on the bonding strength of the Cu-sintered joint have been evaluated. A Cu paste with nano-sized Cu powders and a metal content of ~78% as a high-temperature bonding material was fabricated. The sinter-bonding reactions and mechanical strengths of Cu-sintered joints were evaluated at different sinter bonding pressures, temperatures, and durations during the sintering process. The shear strength of the Cu-sintered joints increased with increasing sintering pressure. Good interfacial uniformity and stable metallurgical microstructures were observed in the Cu joints sintered at a high sintering pressure of 10 MPa, irrespective of the sintering time. It was confirmed that a high-pressure-assisted sintering process could create relatively dense sintered layers and good interfacial uniformity in the Cu-sintered joints, regardless of the sintering temperatures being in the range of 225–300 °C. The influence of the sinter bonding pressure on the shear strengths of the Cu-sintered joints was more significant compared to that of the sintering temperature. Durations of 10 min (at 300 °C) and 60 min (at 225 and 250 °C) are sufficient for complete sintering reactions between the Si chip and the direct bond copper (DBC) substrate. Relatively good metallic bonding and dense sintered microstructures created by a high sintering pressure of 10 MPa resulted in high shear strength in excess of 40 MPa of the Cu-sintered joints.

Increase of energy products of Zn-bonded Sm-Fe-N magnets with low oxygen content

To increase the maximum energy product, (BH)max, of Zn-bonded Sm-Fe-N magnets, a process for preparing a Sm-Fe-N powder with a low oxygen content was developed. The Sm-Fe-N powder containing 0.23 wt% oxygen was prepared by ball milling and nitriding, and the powder remanence and coercivity were 140 A·m2kg−1 and 0.72 MA·m−1, respectively.Arc plasma deposition (APD) was used for Zn addition. Fine Zn particles several tens of nanometers in size were deposited on the Sm-Fe-N powder under vacuum conditions, and APD prevented the oxygen content increasing in the Zn-deposited Sm-Fe-N powder. The low-oxygen Sm-Fe-N powder was pressed and sintered by spark plasma sintering (SPS), and 3.3 wt% Zn-bonded and Zn-free Sm-Fe-N magnets were prepared. For both Zn-bonded and Zn-free Sm-Fe-N magnets, the density increased with increasing sintering pressure, and the relative density of the Zn-bonded Sm-Fe-N magnet was 89% and that of the Zn-free Sm-Fe-N magnet was 85% after SPS. The coercivities of the Zn-bonded and Zn-free Sm-Fe-N magnets were both high at 1.1 and 0.8 MA·m−1, respectively. (BH)max of these magnets increased with increasing relative density, and the highest (BH)max value of the Zn-bonded Sm-Fe-N magnets was 153 kJ·m−3 and that of the Zn-free Sm-Fe-N magnet was 179 kJ·m−3.

Effect of Sintering Pressure on the Porosity and the Shear Strength of the Pressure-Assisted Silver Sintering Bonding

The microstructure, thickness, porosity, and shear performance of the silver (Ag) sintering layers under different sintering pressures were investigated. Experimental results demonstrated that the thickness and the porosity of the sintering layer decreased when the sintering pressure varied from 5 MPa to 30 MPa. This densification phenomenon facilitated the enhancement of the Ag sintering layers. The shear strength was improved significantly from 44.19 MPa to 69.41 MPa when the sintering pressure increased from 5 MPa to 10 MPa. When the sintering pressure ranged from 10 MPa to 30 MPa, the shear strength presented a slow increase from 69.41 MPa to 73.38 MPa. According to the results of the failure analysis, fracture mode transformation was considered as the basic reason for this phenomenon. The increasing sintering pressure promoted the bonding of the nano-Ag particles during the sintering process. Consequently, the fracture of the sintered-Ag layer transformed from brittle fracture to ductile fracture because of the increasing sintering pressure. The delamination area between Cu and Ni layers coated on the bottom Mo plate was clearly enlarged with the increasing sintering pressure. The delamination between Cu and Ni layers coated on the bottom Mo plate turned to be the main failure mode when the sintering pressure was higher than 10 MPa.

Synthesis and Thermoelectric Properties of SnSe by Mechanical Alloying and Spark Plasma Sintering Method

The bulks of polycrystalline SnSe materials were successfully prepared by the mechanical alloying (MA) and spark plasma sintering (SPS) method. X-ray powder diffraction analysis showed that pure Sn and Se powders were synthesized into the SnSe phase by MA, and after SPS under 30–120 MPa, the single phase bulks of SnSe materials were successfully prepared. Scanning electron microcopy images displayed that the grain size of SnSe shows refinement with higher pressure. The electrical properties of the sintered samples increased with increasing sintering pressure. The thermal conductivity results show that the thermal conductivity remained low, in the range of 0.50–0.85 W m−1 K−1, with the different sintering pressure. The samples sintered under 100 MPa have the best thermoelectric properties; the dimensionless figure of merit ZT reached 0.71 at 873 K.

Microstructure and Mechanical Properties of ZrB&lt;sub&gt;2&lt;/sub&gt;/h-BN Multiphase Ceramics by Low-Temperature Reactive Sintering

In the present paper, the ZrB2/h-BN multiphase ceramics were fabricated by SPS (spark plasma sintering) technology at lower sintering temperature using h-BN, ZrO2, AlN and Si as raw materials and B2O3 as a sintering aid. The phase constitution and microstructure of specimens were analyzed by XRD and SEM. Moreover, the effects of different sintering pressures on the densification, microstructure and mechanical properties of ZrB2/h-BN multiphase ceramics were also systematically investigated. The results show that the ZrB2 was obtained through solid phase reaction at different sintering pressures, and increasing sintering pressure could accelerate the formation of ZrB2 phase. As the sintering pressure increasing, the fracture strength and toughness of the sintered samples had a similar increasing tendency as the relative density. The better comprehensive properties were obtained at given sintering pressure of 50MPa, and the relative density, fracture strength and toughness reached about 93.4%, 321MPa and 3.3MPa·m1/2, respectively. The SEM analysis shows that the h-BN grains were fine and uniform, and the effect of sintering pressure on grain size was inconspicuous. The distribution of grain is random cross array, and the fracture texture was more obvious with the increase of sintering pressure. The fracture mode of sintered samples remained intergranular fracture mechanism as sintering pressure changed, and the grain refinement, grain pullout and crack deflection helped to increase the mechanical properties.

Effect of consolidation pressure on phase evolution during sintering of mechanically alloyed Al86Ni8Y6 amorphous powders via spark plasma sintering

Mechanically alloyed amorphous Al86Ni8Y6 powders were consolidated by spark plasma sintering (SPS) and the effect of varying sintering pressure (100–400MPa) on phase transformation and resulting mechanical property was studied. Fully amorphous Al86Ni8Y6 powder obtained via mechanical alloying exhibited good thermal stability with a wide glass transition range of 45°C. Higher sintering pressure (400MPa) during SPS resulted in (i) better densification (98%) with improved inter-particle bonding and moreover, (ii) retention of higher volume fraction (~92vol%) of amorphous phase with lower amount of intermetallic nano-precipitates, indicating improvement in thermal stability of the amorphous phase. Vickers microhardness test showed improvement in hardness with increasing sintering pressure attributed to a larger fraction of the retained amorphous phase and better inter-particle bonding. Nanoindentation test exhibited similar trends in hardness and elastic modulus with wide variation in hardness and elastic modulus values attributed to the distribution of comparatively soft nanocrystalline Al and very hard intermetallic precipitates in the amorphous matrix.

Correlation between sintering pressure and electrical properties of hot-press sintered gallium arsenide-polyaniline-polyethylene composite varistors

GaAs-polymer composite varistors are prepared using hot pressing method at a temperature of 130°C and different pressures and their current–voltage characteristics are investigated. The results show that these varistors can be used to protect circuits from 35V up to 52V over voltages. In addition, it is found that the varistor breakdown voltage and its nonlinearity as well as its impurity band gap increase by increasing sintering pressure while the corresponding barrier height decreases. Each sample has hysteresis which increases through the increase in sintering pressure. This causes the varistors to have lower lifetime due to their high degradation. These results are both investigated and analyzed using SEM micrographs.

Low-Pressure Joining of Large-Area Devices on Copper Using Nanosilver Paste

Low-temperature joining technology using nanosilver paste has been widely demonstrated for attaching power chips on silver or gold metallized substrates. In this paper, we investigate the processing conditions of nanosilver paste for bonding large-area chips on a plain copper surface. A double-print, low-pressure-assisted sintering process is developed for attaching the chips on copper. An evaluation criterion used in the process development is the bond strength of mechanical chips that are made of alumina and sintered on direct-bond-copper (DBC) substrates. The bond strength, measured by the die-shear test, is found to be in excess of 40 and 77 MPa at sintering pressures of 3 and 12 MPa, respectively, during sintering. Characterization of the bondline microstructure reveals a void-free sintered joint, the density of which increases, with increasing sintering pressure. Sintering in air causes partial oxidation of the copper surface, but the oxide can be easily removed by dipping in 1% hydrochloric acid solution. To evaluate the impact of the bonding and acid-cleaning process on device characteristics, a large-area insulated-gate-bipolar-transistor (IGBT) chip is bonded to DBC substrate and then wire-bonded for electrical testing. Test results shows that the die-attach process does not alter the IGBT performance.

Influence of porosity on the transport properties of Bi2Te3-based alloys by field-assisted sintering

Abstract

IR and Raman spectroscopy study of YAG nanoceramics

Y 3Al 5O 12 (YAG) nanoceramics fabricated by low-temperature high-pressure sintering were investigated using Raman and FT-IR techniques. It was found that the Raman scattering intensity decreased significantly with increasing sintering pressure. The spectra showed also broadening of the Raman and IR bands. The XRD and TEM studies showed that during fabrication of nanoceramics the average grain size decreased and a partial amorphization took place. It was concluded that these effects are responsible for the changes in the Raman and FT-IR spectra.