The Preparation and Properties of Alumina Ceramics through a Two-Step Pressureless Sintering Process

2018 ◽  
Vol 922 ◽  
pp. 47-54
Author(s):  
Chang Suo Yuan ◽  
Zi Jing Wang ◽  
Qiang Zhi ◽  
Ya Ming Zhang ◽  
Xu Dong Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Relative Density ◽  
High Purity ◽  
Dominant Factor ◽  
Second Phase ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Alumina Ceramics ◽  
Soaking Time

In this paper, a high-dense alumina ceramics were prepared through the two-step pressureless sintering process with high-purity alumina powder as raw materials and high-purity MgO as sintering aids. The effects of the sintering temperature in the first-step (T1) and the soaking time (t) in the second sintering step (T2) on the density, microstructure and mechanical properties of the alumina ceramics were studied. The results indicated that the relative density increased with the increase of T1 temperature whereas it increased and then decreased with the increase of MgO content. Higher T1 temperature and extended soaking time caused larger grain size, which accompanied with the Ostwald ripening of the grain and led to non-uniformity of grain size distribution. The addition of MgO was beneficial to the decrease in grain size due to pinning effect of the second phase. For samples with shorter soaking time, sintering with higher T1 temperature led to better mechanical properties because of its high density. However, for the long soaking time, all samples after sintering at different T1 temperature were fully-densified, so the grain size become to the dominant factor of strength, thus samples with lower T1 temperature exhibited better mechanical properties due to the refinement grain. Excessive addition of MgO resulted in defects, by which the strength increased firstly and then decreased slightly with the increased MgO content. For the samples with 2.5wt.% MgO, the optimum condition for the two-step pressureless sintering was T1=1450°C and T2=1400°C for 20h, and the obtained sample achieved the relative density of 96% and the strength of 507±32MPa.

scholarly journals Improvement of mechanical properties of HfB2-based composites by incorporating in situ SiC reinforcement through pressureless sintering

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Ghadami ◽  
E. Taheri-Nassaj ◽  
H. R. Baharvandi ◽  
F. Ghadami
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Relative Density ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Vacuum Atmosphere ◽  
Sic Reinforcement ◽  
Microstructural Studies ◽  
Composite Samples

AbstractHfB2, Si, and activated carbon powders were selected to fabricate 0–30 vol% SiC reinforced HfB2-based composite. Pressureless sintering process was performed at 2050 °C for 4 h under a vacuum atmosphere. Microstructural studies revealed that in situ SiC reinforcement was formed and distributed in the composite according to the following reaction: Si + C = SiC. A maximum relative density of 98% was measured for the 20 vol% SiC containing HfB2 composite. Mechanical investigations showed that the hardness and the fracture toughness of these composites were increased and reached up to 21.2 GPa for HfB2-30 vol% SiC and 4.9 MPa.m1/2 for HfB2-20 vol% SiC, respectively. Results showed that alpha-SiC reinforcements were created jagged, irregular, and elongated in shape which were in situ formed between HfB2 grains and filled the porosities. Formation of alpha-SiC contributed to improving the relative density and mechanical properties of the composite samples. By increasing SiC content, an enhanced trend of thermal conductivity was observed as well as a reduced trend for electrical conductivity.

Elongated Grain Growth Mechanism of Alumina Ceramics with Additives

2010 ◽  
Vol 105-106 ◽  
pp. 844-847
Author(s):  
Yong Chang Zhu ◽  
Shou Fan Rong ◽  
Ji Wei Guo ◽  
Jun Gang Li
Keyword(s):  
Grain Growth ◽  
Growth Mechanism ◽  
Second Phase ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Alumina Ceramics ◽  
Effect Of Additives ◽  
Sintering Properties ◽  
Columnar Grain

The elongated grain evolution of alumina ceramics doping with Al2O3-CaO-SiO2(CAS), Nb2O5, and 3Y-TZP was studied under pressureless sintering. From in-situ growth elongated grain cooperating with second phase to toughen the alumina ceramics, microstructure and sintering properties were firstly studied systematically. The effect of additives on the alumina ceramics with columnar grain were analyzed by means of TEM, SEM, XRD, etc. Basing on the analyzed sintering process by the principle of dynamics, the elongated grain growth mechanism was further studied.

Sintering and Mechanical Properties of Alumina Ceramics Prepared by Nanosize Alumina

2007 ◽  
Vol 544-545 ◽  
pp. 821-824
Author(s):  
Indra ◽  
S.W. Oh ◽  
Hee Joon Kim
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Relative Density ◽  
Mechanical Characteristics ◽  
Indentation Test ◽  
Test System ◽  
Alumina Ceramics ◽  
New Materials ◽  
Size Dependent

This work examined the mechanical properties of alumina that can directly be enhanced by ratio of nano sized alumina powders additives to micro size alumina powders (n/m ratio). These new materials have mechanical properties that are strongly grain size dependent and often significantly different from those of their coarser grained counter parts. The mechanical characteristics of samples were observed by using the indentation test system. This data shows that the relative density for the sample is increased with increasing Meyer hardness.

Preparation and Properties of Al2O3 Particle Dispersed 3Y-TZP Nanoceramics Doped with TiO2

2007 ◽  
Vol 336-338 ◽  
pp. 2254-2256 ◽  
Author(s):  
Bo Jun Chen ◽  
Zhao Qiang Zeng
Keyword(s):  
Grain Size ◽  
Relative Density ◽  
Reduction Method ◽  
Al2o3 Particle ◽  
Second Phase ◽  
Sintering Process ◽  
Tio2 Content ◽  
Powder Mixing ◽  
Powder Dispersion ◽  
Grain Sizes

Al2O3 particle dispersed 3Y-TZP nanoceramics doped with TiO2 was fabricated by the vacuum reduction of Ti(OH)4, Al(NO3)3 and 3Y-TZ powders at 873K for 2h and sintered in air at 1573K~1823K for 2-6h. The relation between Al2O3 and TiO2 content, sintering parameters, relative density and grain sizes were studied. Microstructural investigations revealed that, in comparison with direct powder mixing, the reduction method is more efficient in achieving a homogeneous dispersed fine alumina second phase, which results in the reduction of matrix grain size and the increase of the relative density of the 3Y-TZP ceramic. TiO2 addition facilitates the sintering process but may cause significant abnormal grain growth which can be offset by the homogeneity of the powder dispersion. A final 3Y-TZP-TiO2 ceramic matrix with grain size below 500nm dispersed with ultrafine second phase Al2O3 was obtained.

scholarly journals Densification and Mechanical Properties of Alumina Ceramics via Two-Step Sintering With Different Holding Times

2021 ◽  
Vol 6 (4) ◽  
pp. 299-304
Author(s):  
Anis Syufina Mohammad Saufi ◽  
Ramesh Singh ◽  
K. Y. Sara Lee ◽  
Tao Wu
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Grain Size ◽  
Relative Density ◽  
Grain Growth ◽  
Vickers Hardness ◽  
Holding Time ◽  
Alumina Ceramics ◽  
Conventional Sintering ◽  
Viable Approach

The densification and mechanical properties of alumina ceramics were investigated via two-step sintering (TSS) with different holding time. The alumina ceramics were sintered at 1450 °C for 1 min during the first stage, followed by sintering at 1350 °C with different holding times (2-24h). Conventional sintering (CS) was also performed on the alumina ceramics at 1450 °C for 2 h for comparison purpose. It was found that dense alumina with a relative density above 98% could be attained when TSS with a holding time of more than 12 h. The samples exhibited Vickers hardness between 5-8 GPa and fracture toughness of about 6 MPa.m1/2. In contrast, conventional sintered alumina yielded low relative density (85%), large grain size (2 μm), low Vickers hardness (4.23 GPa) and fracture toughness (4.73 MPa.m1/2). This study revealed that TSS is a viable approach in aiding densification, suppressing grain growth, and improving the mechanical properties of alumina ceramics.

Mechanical Properties of ZrB2-Based Ceramics Reinforced by Nano-SiC Whiskers

2007 ◽  
Vol 353-358 ◽  
pp. 1564-1567 ◽  
Author(s):  
Hai Long Wang ◽  
Chang An Wang ◽  
Rui Zhang ◽  
Xing Hu ◽  
Dai Ning Fang
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Grain Size ◽  
Relative Density ◽  
Hot Pressing ◽  
Bending Strength ◽  
Sintering Process ◽  
Homogeneous Microstructure ◽  
Sic Whiskers ◽  
Xrd Techniques

In this paper, ZrB2-based ceramics containing up to 15 vol% nano-SiC whiskers were prepared by hot pressing at 1950°C under 20MPa pressure in flow argon. SEM and XRD techniques were used to characterize the sintered compacts. A fine and homogeneous microstructure was observed. The relative density of ZrB2-based ceramic containing 10vol% SiC whiskers reached to 97.7%. The bending strength and fracture toughness of the composite were 550 MPa and 8.08 MPa·m1/2 respectively, while those of the monolithic ZrB2 ceramic (0 vol% SiC whiskers added) were 424 MPa and 4.52 MPa·m1/2 respectively. The grain size of the ZrB2-based ceramics was reduced greatly by the addition of nano-SiC whiskers during the sintering process.

Influence of Ca2P2O7 on Sintering Ability, Mechanical Strength and Degradability of β-Ca3(PO4)2 Bioceramics

2007 ◽  
Vol 361-363 ◽  
pp. 23-26 ◽  
Author(s):  
Kai Li Lin ◽  
Lei Chen ◽  
Jiang Chang ◽  
Jian Xi Lu
Keyword(s):  
Mechanical Properties ◽  
Mechanical Strength ◽  
Relative Density ◽  
Dissolution Rate ◽  
Pressureless Sintering ◽  
Sintering Process

In the present study, Ca2P2O7-doped β-Ca3(PO4)2 bioceramics were fabricated by pressureless sintering process. The effect of Ca2P2O7 on the sintering ability, mechanical strength and degradability of the ceramics were investigated. The results showed that the Ca2P2O7 could apparently decrease the sintering ability and mechanical properties of β-Ca3(PO4)2. Moreover, the relative density and mechanical strength of the sintered samples decreased gradually with the increase of the Ca2P2O7 additive amount. However, the dissolution rate of the samples increased with the increase of the Ca2P2O7 additive amount.

Effect of TiO2 and MgO on Microstructure of α-Alumina Ceramics and its Sintering Behavior

2015 ◽  
Vol 1112 ◽  
pp. 519-523 ◽  
Author(s):  
Jarot Raharjo ◽  
Sri Rahayu ◽  
Tika Mustika ◽  
Masmui ◽  
Dwi Budiyanto
Keyword(s):  
Mechanical Properties ◽  
Sintering Temperature ◽  
Physical And Mechanical Properties ◽  
Basic Material ◽  
Sintering Behavior ◽  
Pressureless Sintering ◽  
Alumina Ceramics ◽  
Density Measurements ◽  
Technical Alumina ◽  
Platelet Structure

Observation on the effect of adding titanium oxide (TiO2) and magnesium oxide (MgO) on the sintering of α-alumina (Al2O3) has been performed. In this study, technical alumina used as basic material in which the sample is formed by the pressureless sintering/cold press and sintered at 1500°C which is lower than alumina sintering temperature at 1700°C. Elemental analysis, observation of microstructure, hardness, fracture toughness and density measurements were carried out to determine the physical and mechanical properties of alumina. The results indicate a change in the microstructure where the content of the platelet structure are much more than the equilateral structure. At sintering temperature of 1500°C, neck growth occurs at ceramics grain, supported by the results of the density test which indicate perfect compaction has occurred in this process.

Controlling Grain Size in Oxide Ceramics for Optimization of Strength and Wear Resistance

2012 ◽  
Vol 715-716 ◽  
pp. 703-710
Author(s):  
W.M. Rainforth ◽  
P. Zeng ◽  
L. Ma
Keyword(s):  
Grain Size ◽  
Sliding Wear ◽  
Second Phase ◽  
Alumina Ceramics ◽  
Size Dependent ◽  
Mild Wear ◽  
Accumulation Mechanism ◽  
Wear Transition ◽  
Magnitude Increase ◽  
Zirconia Toughened Alumina

t is well known that alumina ceramics undergo a time dependent wear transition during sliding wear. The transition, which is associated with 1-2 orders of magnitude increase in specific wear rate, involves a change from mild wear to intergranular fracture. The transition is strongly grain size dependent, with the time to the transition decreasing with grain size. However, there is a minimum grain size that can be achieved in fully dense alumina using commercially viable processing. Alternative strategies for reducing grain size and increasing toughness are through the addition of a fine second phase, with SiC and ZrO2being the most promising. The resultant composite not only has finer grain size, but also exhibits additional toughening mechanisms. This paper reports on the microstructural control in alumina, zirconia toughened alumina and alumina-silicon carbide composites. The grain size and residual stress distribution are related to the damage accumulation mechanism that occur during frictional contact, in particular the surface specific dislocation activity.

Effect of Nd Content and Heat Treatment on Microstructure and Mechanical Properties of Mg-Zn-Nd Alloy

2017 ◽  
Vol 898 ◽  
pp. 124-130 ◽  
Author(s):  
Shu Min Xu ◽  
Xin Ying Teng ◽  
Xing Jing Ge ◽  
Jin Yang Zhang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Grain Size ◽  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Cast Alloy ◽  
Second Phase ◽  
Casting Method ◽  
Magnesium Matrix ◽  
Microstructure And Mechanical Properties

In this paper, the microstructure and mechanical properties of the as-cast and heat treatment of Mg-Zn-Nd alloy was investigated. The alloy was manufactured by a conventional casting method, and then subjected to a heat treatment. The results showed that the microstructure of as-cast alloy was comprised of α-Mg matrix and Mg12Nd phase. With increase of Nd content, the grain size gradually decreased from 25.38 μm to 9.82 μm. The ultimate tensile strength and elongation at room temperature of the Mg94Zn2Nd4 alloy can be reached to 219.63 MPa and 5.31%. After heat treatment, part of the second phase dissolved into the magnesium matrix and the grain size became a little larger than that of the as-cast. The ultimate tensile strength was declined by about 2.5%, and the elongation was increased to 5.47%.

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