Efficacy of HfN as sintering aid in the manufacture of ultrahigh-temperature metal diborides-matrix ceramics

2004 ◽  
Vol 19 (12) ◽  
pp. 3576-3585 ◽  
Author(s):  
Frédéric Monteverde ◽  
Alida Bellosi
Keyword(s):  
Hot Pressing ◽  
Applied Pressure ◽  
Thermomechanical Properties ◽  
Full Density ◽  
Secondary Phases ◽  
Homogeneous Microstructure ◽  
Sintering Aid ◽  
Metal Diborides ◽  
Ultrahigh Temperature ◽  
Average Size

HfB2 and (ZrB2 + HfB2)-based ceramics containing 19.5 vol% SiC particulate were developed from commercially available powders by hot-pressing. With the assistance of 3 vol% HfN as sintering aid, after hot-pressing at 1900 °C and 50 MPa of applied pressure, full density in both the composites was successfully achieved. The materials revealed a homogeneous microstructure, characterized by faceted diboride grains(2 μm average size) and SiC particles regularly dispersed. Limited levels of secondary phases were found. The thermomechanical properties of the composites were promising: about 22 GPa microhardness and 500 GPa Young’s modulus for both. The HfB2–SiC composite showed values of strength of 650 ± 50 and 465 ± 40 MPa at 25 and 1500 °C, respectively. Likewise, the (ZrB2–HfB2)–SiC composite exhibited values of strength of 765 ± 20 and 250 ± 45 MPa at 25 and 1500 °C, respectively. The excellent response at high temperature in air was attributed to the refractoriness of the phases constituting the composites and to the resistance to oxidation enhanced by the presence of the SiC particulate.

scholarly journals Densification of ultra-refractory transition metal diboride ceramics

2020 ◽  
Vol 52 (1) ◽  
pp. 1-14
Author(s):  
W.G. Fahrenholtz ◽  
G.E. Hilmas ◽  
Ruixing Li
Keyword(s):  
Transition Metal ◽  
Hot Pressing ◽  
Full Density ◽  
Oxygen Impurity ◽  
Self Diffusion ◽  
Melting Temperatures ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Metal Diborides ◽  
Transition Metal Diborides

The densification behavior of transition metal diboride compounds was reviewed with emphasis on ZrB2 and HfB2. These compounds are considered ultra-high temperature ceramics because they have melting temperatures above 3000?C. Densification of transition metal diborides is difficult due to their strong covalent bonding, which results in extremely high melting temperatures and low self-diffusion coefficients. In addition, oxide impurities present on the surface of powder particles promotes coarsening, which further inhibits densification. Studies prior to the 1990s predominantly used hot pressing for densification. Those reports revealed densification mechanisms and identified that oxygen impurity contents below about 0.5 wt% were required for effective densification. Subsequent studies have employed advanced sintering methods such as spark plasma sintering and reactive hot pressing to produce materials with nearly full density and higher metallic purity. Further studies are needed to identify fundamental densification mechanisms and further improve the elevated temperature properties of transition metal diborides.

Solid State Sintering of SiC-Ceramics

2009 ◽  
Vol 624 ◽  
pp. 71-89 ◽  
Author(s):  
Koushik Biswas
Keyword(s):  
Mechanical Properties ◽  
Silicon Carbide ◽  
High Temperature ◽  
Solid State ◽  
Grain Boundary ◽  
Hot Pressing ◽  
Amorphous Film ◽  
Structure Property ◽  
Secondary Phases ◽  
Sintering Aid

The most interesting feature in silicon carbide is the structure-property relation where the formation of different types of microstructure due to different structural modifications (polytypism) and grain-boundary/interfacial phase chemistry dictate the final properties of the monoliths. Since synthesis of SiC in last century, several methods such as hot pressing with a sintering aid (B, C), pressureless sintering with a sintering aid (B, C, Al) and reaction bonded (Si-SiC) were used to fabricate dense SiC. A newer method of fast sintering (spark plasma sintering) using pulsed current is also employed to consolidate nano/submicron size SiC with or without additives. The solid state sintered SiC materials have fine-grained equiaxed microstructure (grain size 1 to 4 µm) with thin layer of intergranular phases (amorphous film), exhibit moderate high-temperature creep and oxidation resistance, fracture toughness (3 to 4 MPam1/2) and have highly flaw-sensitive strength at room temperature. The high temperature mechanical properties are highly influenced by the presence of free C, Al and B + C containing grain-boundary phases. Moreover, during prolong processing, abnormal grain growth occurs resulting in anisotropic -SiC phase formation. The Si-SiC materials are poor candidates for high-temperature applications due to the limit set by the melting point of silicon, and the limitations of hot pressing (HPSiC) as a densification technique are well known. SPSed SiC without sintering additive revealed inferior mechanical properties attributed to poor bonding between adjacent grains. In the present survey, an overview of the new developments in silicon carbide processing and properties will be presented together with the information on structure-properties correlationship. Information on the structure of the grain-boundary/secondary phases and interfaces until now was not comprehensively analyzed.

scholarly journals Effect of Long-Term Creep on Microstructure of a 9% Cr Heat Resistant Steel

2014 ◽  
Vol 783-786 ◽  
pp. 1839-1844
Author(s):  
Valeriy Dudko ◽  
Alexandra Fedoseeva ◽  
Pavel Kozlov ◽  
Vladimir Skorobogatykh ◽  
Izabella Schenkova ◽  
...  
Keyword(s):  
Prior Austenite ◽  
Average Thickness ◽  
Resistant Steel ◽  
Secondary Phases ◽  
Heat Resistant Steel ◽  
Gauge Section ◽  
The Mean ◽  
Average Size ◽  
Term Creep

The effect of long-term creep at 600°C under 137 MPa on the microstructure of a P92-type steel was investigated. The microstructure after tempering consisted of laths with an average thickness of 400 nm. Dispersion of secondary phases consists of M23C6carbides with an average size of 85 nm located mainly on lath, block and prior austenite boundaries and MX carbonitrides with average size of 31 nm homogeniously distributed throughout. Creep with duration of 40738 hours led to coarsening of M23C6carbides up to 182 nm. Precipitation of Laves phase with an average size of 290 nm took place in both grip and gauge portions of ruptured specimen. Vanadium-rich MX particles were replaced by particles of Z-phase with sizes of 97 and 48 nm after long-term creep and aging, respectively. The average misorientation of the lath boundaries was approximately 2° and scarcely varied during creep, while the mean lath thickness increased to 890 nm in gauge section of ruptured specimen and remained essentially unchanged in the grip section. Dislocation density decreased slightly under long-range aging and creep.

Pressure assisted sintering of Al2O3–Y2O3 glass microspheres: sintering conditions, grain size, and mechanical properties of sintered ceramics

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Anna Prnová ◽  
Jana Valúchová ◽  
Monika Michálková ◽  
Beáta Pecušová ◽  
Milan Parchovianský ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Hot Pressing ◽  
Pechini Method ◽  
Sol Gel ◽  
Applied Pressure ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Glass Microspheres ◽  
Amorphous Powders

Abstract Glass microspheres with yttria-alumina eutectic composition (76.8 mol % Al2O3 and 23.2 mol % Y2O3) were prepared by sol-gel Pechini method and flame synthesis with or without subsequent milling. Prepared amorphous powders were studied by X-ray powder diffraction (XRD), particle size analysis (PSA), scanning electron microscopy (SEM) and differential thermal analysis (DTA). Hot pressing (HP), rapid hot pressing (RHP) and spark plasma sintering (SPS) were used to sinter amorphous precursor powders at 1600 °C without holding time (0 min). The preparation process including milling step resulted in amorphous powders with narrower particle size distribution and smaller particle size. All applied pressure assisted sintering techniques resulted in dense bulk samples with fine grained microstructure consisting of irregular α-Al2O3 and Y3Al5O12 (YAG) grains. Milling was beneficial in terms of final microstructure refinement and mechanical properties of sintered materials. A material with the Vickers hardness of HV = (17.1 ± 0.3) GPa and indentation fracture resistance of (4.2 ± 0.2) MPa.m1/2 was prepared from the powder milled for 12 h.

Large-area Nanosilver Die-attach by Hot-pressing Below 200°C and 5 MPa

2012 ◽  
Vol 2012 (HITEC) ◽  
pp. 000129-000134 ◽  
Author(s):  
Kewei Xiao ◽  
Jesus N. Calata ◽  
Hanguang Zheng ◽  
Khai D.T. Ngo ◽  
Guo-Quan Lu
Keyword(s):  
Atmospheric Pressure ◽  
Hot Pressing ◽  
Applied Pressure ◽  
Fractional Factorial ◽  
Maintenance Cost ◽  
Pressing Pressure ◽  
Hot Press ◽  
Large Area ◽  
Die Attach ◽  
Temperature Time

Sintered nanoscale silver joint is an emerging lead-free die-attach solution for high-temperature packaging because of silver's high melting temperature. For bonding small chips, the nanosilver solution can be achieved with a simple heating profile under atmospheric pressure. However, for bonding large-area chips, e.g. > 1 cm2 IGBT chips, uniaxial pressure of a few MPa has been found necessary during the sintering stage of the bonding process, which is carried out at temperatures below 275°C. Hot-pressing at high temperatures can cause significant wear and tear on the processing equipment, resulting in high maintenance cost. In this study, we ran a series of experiments aimed at lowering the hot-pressing temperature. Specifically, we examined a process involving hot-press drying, followed by sintering without any applied pressure. A fractional factorial design of experiments was used to identify the importance and interaction of various processing parameters, such as hot-pressing pressure/temperature/time and sintering temperature/time, on the final bond quality of sintered nanosilver joints. Based on the results, a simpler process, consisting of hot-press drying at 180°C under 3 MPa, followed by sintering at 275°C under atmospheric pressure was found to produce attachments with die-shear strength in excess of 30 MPa.

Formation of Fe3AlC Base Alloy by Mechanical Alloying and Vacuum Hot Pressing

2007 ◽  
Vol 534-536 ◽  
pp. 189-192 ◽  
Author(s):  
Kazuo Isonishi
Keyword(s):  
Mechanical Alloying ◽  
Hot Pressing ◽  
Base Alloy ◽  
Average Particle Size ◽  
Processing Route ◽  
Full Density ◽  
Second Phase ◽  
Average Particle ◽  
Vacuum Hot Pressing ◽  
Metallurgical Processing

Fabrication of Fe3AlC matrix in-situ composite, reinforced by a FeAl phase, was studied by using the powder metallurgical processing route. Especially, in order to disperse the second phase more finely, we chose the mechanical alloying process. We investigated the microstructural and mechanical properties of the consolidated material. After consolidation by vacuum hot pressing, the compact showed almost full density and consisted of a Fe3AlC matrix and FeAl second phase (average particle size was less than 1μm). The compact showed HV746, which was higher than that of the arc melted Fe3AlC monolithic material, HV650.

Processing of Porous Zirconium Tungstate and Their Thermomechanical Properties

2014 ◽  
Author(s):  
Mingang Wang ◽  
Truong Do ◽  
Patrick Kwon
Keyword(s):  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Processing Technique ◽  
Thermomechanical Properties ◽  
Processing Route ◽  
Full Density ◽  
Ceramic Powders ◽  
Zirconium Tungstate ◽  
Spherical Graphite ◽  
New Processing

This paper explores a new processing method to fabricate porous zirconium tungstate (ZrW2O8 or ZT) with the porosity content up to 40% in volume. The method uses spherical graphite powders that are mechanically stable, allowing us to compact with ceramic powders in dry condition. Thus, the ceramic powders mixed with spherical graphite powders can be compacted and sintered to a near full density. During sintering, the graphite powders burn out without damaging the powder compact due to their inherent near-zero thermal expansion. The processing route discussed in this paper is applicable to all oxide ceramics where the sintering can take place in air and above 700°C to dissociate the graphite. In this paper, we have applied this processing technique to fabricate porous ZrW2O8. Many porous ZrW2O8 with a range of porosity levels were fabricated and tested for their theromomechanical properties including elastic modulus (E) and coefficient of thermal expansion (CTE). The experimentally determined properties were compared with the predictions based on the micromechanical Mori-Tanaka scheme.

scholarly journals Nano-(Ta, Zr)C Precipitates at Multigrain Conjunctions in TaC Ceramic with 10 mol% ZrC and 5 mol% Cu as Sintering Aid

2018 ◽  
Vol 2018 ◽  
pp. 1-5
Author(s):  
Lianbing Zhong ◽  
Guihong Geng ◽  
Yujin Wang ◽  
Feng Ye ◽  
Limeng Liu
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Flexural Strength ◽  
Hot Pressing ◽  
Glassy Matrix ◽  
Sintering Aid ◽  
Uniform Dispersion ◽  
New Type

A fully dense TaC ceramic was prepared by hot pressing using 10 mol% ZrC plus 5 mol% Cu as a sintering aid. Formation of (Ta, Zr)C solid solution (ss) by reaction between TaC and ZrC facilitated densification. Addition of Cu refined the microstructure and consequently improved flexural strength of the TaC ceramics. TEM investigation found ubiquitous precipitation of nanocrystallites at multigrain conjunctions. The nanocrystallites were (Ta, Zr)C solid solution with uniform dispersion in an oxygen-rich glassy matrix. Although formation of nanoprecipitates may not much affect the mechanical properties of the TaC ceramic, the structure suggested a new type of nanoceramic worth further research.

Microstructure and Mechanical Properties of Spark-Plasma-Sintered SiC-TiC Composites

2005 ◽  
Vol 287 ◽  
pp. 335-339 ◽  
Author(s):  
Kyeong Sik Cho ◽  
Kwang Soon Lee
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Heating Rate ◽  
Spark Plasma Sintering ◽  
Sintering Temperature ◽  
Applied Pressure ◽  
Argon Atmosphere ◽  
Full Density ◽  
Plasma Sintering ◽  
Spark Plasma

Rapid densification of the SiC-10, 20, 30, 40wt% TiC powder with Al, B and C additives was carried out by spark plasma sintering (SPS). In the present SPS process, the heating rate and applied pressure were kept at 100°C/min and at 40 MPa, while the sintering temperature varied from 1600-1800°C in an argon atmosphere. The full density of SiC-TiC composites was achieved at a temperature above 1800°C by spark plasma sintering. The 3C phase of SiC in the composites was transformed to 6H and 4H by increasing the process temperature and the TiC content. By tailoring the microstructure of the spark-plasma-sintered SiC-TiC composites, their toughness could be maintained without a notable reduction in strength. The strength of 720 MPa and the fracture toughness of 6.3 MPa·m1/2 were obtained in the SiC-40wt% TiC composite prepared at 1800°C for 20 min.

scholarly journals Influence of the Uniaxial Hot-Pressing Sintering Condition on Bi4Ge3O12 Ceramic Scintillators

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Ivus L. O. Matos ◽  
Adriano B. Andrade ◽  
Zélia S. Macedo ◽  
Mário E. G. Valerio
Keyword(s):  
Hot Pressing ◽  
Applied Pressure ◽  
Emission Spectra ◽  
Secondary Phase ◽  
Sintering Process ◽  
X Ray Diffraction ◽  
X Ray ◽  
Characteristic Emission ◽  
Hot Pressing Sintering ◽  
Sintering Condition

The production of high-density bismuth germanate (Bi3Ge4O12) ceramic scintillators by uniaxial hot pressing was investigated as a function of different applied pressure conditions. The X-ray diffraction showed that the sintering process was able to eliminate the undesirable secondary phase present in the nonsintered samples. The height changes from samples with higher applied pressure rate and applied pressure duration lead to a better relative density value, >95% for samples sintered under a pressure of 0.14 and 0.18 MPa. The radioluminescence results showed that all samples have the characteristic emission spectra of Bi3Ge4O12 and that the hot-pressed samples have higher radioluminescence emission efficiency.

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