Effect of TiO2 and TiB2 on Pressureless Sintering of B4C

2012 ◽  
Vol 727-728 ◽  
pp. 1022-1027
Author(s):  
Rosa Maria da Rocha ◽  
Francisco Cristóvão Lourenço de Melo
Keyword(s):  
Powder Mixture ◽  
Vickers Hardness ◽  
Argon Atmosphere ◽  
Second Phase ◽  
Pressureless Sintering ◽  
Reactive Sintering ◽  
Concentration Increase ◽  
In Situ Formation ◽  
Equiaxed Grains

This paper presents results of experiments on pressureless sintering of boron carbide (B4C) with addition of titânia (TiO2) and titanium diboride (TiB2). The TiB2powder was added as a second phase and the TiO2powder for reactive sintering and in-situ formation of TiB2. The final concentrations of TiB2in the composites were 0 to 10 vol%. Sintering was performed at 2050 °C/30min in argon atmosphere. TiO2was completely transformed into TiB2with fine equiaxed grains distributed homogeneously. Composites obtained by in-situ reaction showed a densification increase with the concentration increase, while the composites with TiB2powder mixture showed low densification in all compositions. Relative Density of the composite with 10 vol% of TiB2obtained in-situ was 91% (TD) compared to 86 % for B4C only. Vickers hardness was about 29 GPa.

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.

scholarly journals The Effects of Transition Metal Oxides (Me = Ti, Zr, Nb, and Ta) on the Mechanical Properties and Interfaces of B4C Ceramics Fabricated via Pressureless Sintering

Coatings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1253
Author(s):  
Guanqi Liu ◽  
Shixing Chen ◽  
Yanwei Zhao ◽  
Yudong Fu ◽  
Yujin Wang
Keyword(s):  
Mechanical Properties ◽  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Milling Process ◽  
Second Phase ◽  
Pressureless Sintering ◽  
And Performance ◽  
Better Than

There is little available research on how different transition metal oxides influence the behavior of B4C-based ceramics, especially for Ta2O5 and Nb2O5. B4C-MeB2 (Me = Ti, Zr, Nb, and Ta) multiphase ceramic samples were prepared via in situ pressureless sintering at 2250 °C, involving the mixing of B4C and MeOx powders, namely TiO2, ZrO2, Nb2O5, and Ta2O5. The phase constituents, microstructures, and mechanical properties of the samples were tested. The results indicated that different transition metal elements had different effects on the ceramic matrix, as verified through a comparative analysis. Additionally, the doped WC impurity during the ball milling process led to the production of (Me, W)B2 and W2B5, which brought about changes in morphology and performance. In this study, the Ta2O5-added sample exhibited the best performance, with elastic modulus, flexural strength, Vickers hardness, and fracture toughness values of 312.0 GPa, 16.3 GPa, 313.0 MPa, and 6.08 MPa·m1/2, respectively. The comprehensive mechanical properties were better than the reported values when the mass fraction of the second phase was around five percent.

scholarly journals Effect of in situ VSi2 and SiC phases on the sintering behavior and the mechanical properties of HfB2-based composites

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Soheil Ghadami ◽  
Ehsan Taheri-Nassaj ◽  
Hamid Reza Baharvandi ◽  
Farzin Ghadami
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Vickers Hardness ◽  
Thermodynamic Calculations ◽  
Sintering Behavior ◽  
Pressureless Sintering ◽  
Vacuum Atmosphere ◽  
Second Phases ◽  
Microstructural Studies

Abstract In situ HfB2–SiC–VSi2 composite was fabricated by reactive pressureless sintering at the temperature of 2150 °C for 4 h under a vacuum atmosphere. In situ SiC and VSi2 reinforcements were formed using VC and Si powders as starting materials according to the following reaction: VC + 3Si = SiC + VSi2. Microstructural studies and thermodynamic calculations revealed that in situ VSi2 and SiC phases were mostly formed and homogeneously distributed in HfB2 skeleton. The results showed that the density of in situ HfB2–SiC–VSi2 composite was 98%. Besides, the mechanical properties of the composite were effectively enhanced by the formation of in situ second phases. The Vickers hardness and the fracture toughness of the composite reached 20.1 GPa and 5.8 MPa m−1/2, respectively.

Investigation on Formation Mechanism of Cu/Cr-Al2O3 Nanocomposite

2011 ◽  
Vol 364 ◽  
pp. 7-11
Author(s):  
Saeed Sheibani ◽  
Abolghasem Ataie ◽  
Saeed Heshmati-Manesh ◽  
Alfonso Caballero Martínez
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
High Temperature ◽  
Formation Mechanism ◽  
Copper Matrix ◽  
Milling Process ◽  
Argon Atmosphere ◽  
In Situ Formation ◽  
Two Stages

In this research, formation mechanism of a Cu/10 wt.% Cr-10 wt.% Al2O3 nanocomposite via mechanical alloying and subsequent heat treatment has been investigated. It was found that during milling process, Cu (Al) solid solution and Cu9Al4 phase were formed as intermediate products. Further heat treatment carried out under argon atmosphere at 900°C for 8 hours resulted in completion of Cr2O3 reduction by Al. The mechanism of in-situ formation of Al2O3 reinforcement in the copper matrix was also discussed as a two stages process. The SEM and TEM results confirmed the proposed mechanism and showed that the Cr dispersoids surrounded by Al2O3, in the nanometric scale. Also, the Cu matrix with mean crystallite size of 30 nm was stable at high temperature.

scholarly journals Microstructure and mechanical properties of Ti3(Al,Ga)C2/Al2O3 composites prepared by in situ reactive hot pressing

2020 ◽  
Vol 9 (6) ◽  
pp. 782-790
Author(s):  
Yuan Fang ◽  
Xiaohua Liu ◽  
Yuxia Feng ◽  
Jianfeng Zhu ◽  
Wei Jiang
Keyword(s):  
Mechanical Properties ◽  
Flexural Strength ◽  
Vickers Hardness ◽  
Hot Pressing ◽  
Raw Materials ◽  
Second Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Reactive Hot Pressing

AbstractIn this study, Ti3(Al,Ga)C2/Al2O3 composites were successfully synthesized by in situ hot pressing at 1350 °C for 2 h using Ti, Al, TiC, and Ga2O3 as raw materials. X-ray diffraction and scanning electron microscopy were used for characterizing the phase identities and microstructures of the sintered composites. The dependence of the Vickers hardness and flexural strength on the Al2O3 content was found to be in single-peak type. Ti3(Al0.6,Ga0.4)C2/10.3vol%Al2O3 composite exhibited significantly improved mechanical properties. Vickers hardness and flexural strength of the composite reached 6.58 GPa and 527.11 MPa, which were 40% and 74% higher than those of Ti3AlC2, respectively. Formation of solid solution and incorporation of second phase of Al2O3 resulted in the opposite influence on the fracture toughness. Finally, the hardening and strengthening mechanisms were discussed in detail.

scholarly journals Effect of Mechanical Activation on the In Situ Formation of TiB2 Particulates in the Powder Mixture of TiH2 and FeB

2017 ◽  
Vol 62 (2) ◽  
pp. 1393-1398 ◽  
Author(s):  
X.-K. Huynh ◽  
B.-W. Kim ◽  
J.S. Kim
Keyword(s):  
Mechanical Activation ◽  
Ball Milling ◽  
Powder Mixture ◽  
Electrical Power ◽  
Interface Reaction ◽  
High Energy ◽  
Decomposition Temperature ◽  
Homogeneous Microstructure ◽  
In Situ Formation

AbstractThe in situ formation of TiB2particulates via an interface reaction between Ti and FeB powders was studied. The effects of mechanical activation by high-energy milling on the decomposition of TiH2and the interface reactions between Ti and FeB powders to form TiB2were investigated. Powder mixtures were fabricated using planetary ball-milling under various milling conditions. The specific ball-milling energy was calculated from the measured electrical power consumption during milling process. High specific milling energy (152.6 kJ/g) resulted in a size reduction and homogeneous dispersion of constituent powders. This resulted in a decrease in the decomposition temperature of TiH2and an increase in the formation reaction of TiB2particulates in the Fe matrix, resulting in a homogeneous microstructure of nanoscale TiB2evenly distributed within the Fe matrix. In contrast, the powder mixture milled with low specific milling energy (36.5 kJ/g) showed an inhomogeneous microstructure composed of relatively large Fe-Fe2B particles surrounded by a thin layer of Fe-TiB2within a finely dispersed Fe-TiB2matrix region.

scholarly journals Formation of compact systems of super-Earths via dynamical instabilities and giant impacts

2019 ◽  
Vol 491 (4) ◽  
pp. 5595-5620 ◽  
Author(s):  
Sanson T S Poon ◽  
Richard P Nelson ◽  
Seth A Jacobson ◽  
Alessandro Morbidelli
Keyword(s):  
Initial Conditions ◽  
Post Processing ◽  
Significant Modification ◽  
Kepler Mission ◽  
Giant Impacts ◽  
Low Mass ◽  
In Situ Formation ◽  
Dynamical Instabilities ◽  
Gaseous Envelopes

ABSTRACT The NASA’s Kepler mission discovered ∼700 planets in multiplanet systems containing three or more transiting bodies, many of which are super-Earths and mini-Neptunes in compact configurations. Using N-body simulations, we examine the in situ, final stage assembly of multiplanet systems via the collisional accretion of protoplanets. Our initial conditions are constructed using a subset of the Kepler five-planet systems as templates. Two different prescriptions for treating planetary collisions are adopted. The simulations address numerous questions: Do the results depend on the accretion prescription?; do the resulting systems resemble the Kepler systems, and do they reproduce the observed distribution of planetary multiplicities when synthetically observed?; do collisions lead to significant modification of protoplanet compositions, or to stripping of gaseous envelopes?; do the eccentricity distributions agree with those inferred for the Kepler planets? We find that the accretion prescription is unimportant in determining the outcomes. The final planetary systems look broadly similar to the Kepler templates adopted, but the observed distributions of planetary multiplicities or eccentricities are not reproduced, because scattering does not excite the systems sufficiently. In addition, we find that ∼1 per cent of our final systems contain a co-orbital planet pair in horseshoe or tadpole orbits. Post-processing the collision outcomes suggests that they would not significantly change the ice fractions of initially ice-rich protoplanets, but significant stripping of gaseous envelopes appears likely. Hence, it may be difficult to reconcile the observation that many low-mass Kepler planets have H/He envelopes with an in situ formation scenario that involves giant impacts after dispersal of the gas disc.

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