Effects of Rare Earth Oxides on Microstructures and Properties of Magnesia Refractories

2008 ◽  
Vol 368-372 ◽  
pp. 1158-1160 ◽  
Author(s):  
Bao Guo Zhang ◽  
Zhou Fu Wang ◽  
Shao Wei Zhang ◽  
Xi Tang Wang ◽  
Zi Wei Xu
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Rare Earth ◽  
High Temperature ◽  
Mechanical Strength ◽  
Grain Boundaries ◽  
Bulk Density ◽  
Rare Earth Oxide ◽  
Rare Earth Oxides ◽  
Microstructure And Mechanical Properties

The effects of Y2O3, La2O3 and Nd2O3 on the sintering, microstructure and mechanical properties of magnesia refractories were investigated. Addition of rare earth oxide (ReO) to magnesia refractories increases the bulk density, decreases the porosity and improves the mechanical strength of the refractories. The improved sinterability was attributable to the vacancies generation associated with the solid-solution reactions between MgO and ReO. In the samples with ReO, rare earth silicate phases form at magnesia grain boundaries, providing additional bonding between magnesia grains and between magnesia grains and matrix. Consequently, the samples with ReO showed much higher high temperature strengths than those without ReO.

Microstructure and Mechanical Properties of Rare-Earth Doped Si3N4 and Si3N4/SiC Ceramics

2010 ◽  
Vol 65 ◽  
pp. 78-85 ◽  
Author(s):  
Peter Tatarko ◽  
Štefánia Lojanová ◽  
Zdeněk Chlup ◽  
Ján Dusza ◽  
Pavol Šajgalík
Keyword(s):  
Mechanical Properties ◽  
Rare Earth ◽  
Aspect Ratio ◽  
Ionic Radius ◽  
Earth Element ◽  
Rare Earth Oxide ◽  
Sic Ceramics ◽  
Microstructure And Mechanical Properties ◽  
Significant Difference ◽  
Rare Earth Doped

Microstructure and mechanical properties of Si3N4 and Si3N4 + SiC nanocomposites sintered with rare-earth oxide additives (La2O3, Y2O3, Yb2O3 and Lu2O3) have been investigated. The composites exhibited smaller grain diameter compared to that of monolithic materials. The aspect ratio of β-Si3N4 grains increased with a decreasing ionic radius of rare-earth elements in the Si3N4 monoliths as well as in the Si3N4-SiC nanocomposites. The hardness of both systems increased with a decreasing ionic radius of rare-earth element. The fracture toughness of the materials with coarser microstructure and higher aspect ratio was higher due to the more frequent toughening mechanisms. No significant difference between strength values of monoliths and composites was observed and the strength in the composites was determined mainly by the present processing flaws. Significantly improved creep resistance was observed in the case of composites and for materials with smaller ionic radius of RE3+.

Creep Behavior of Multi-Cation α-SiAlON Partially Stabilized Produced with an Yttrium-Rare Earth Oxide Mixture(CRE2O3)

2005 ◽  
Vol 498-499 ◽  
pp. 575-580
Author(s):  
Claudinei dos Santos ◽  
Kurt Strecker ◽  
M.J.R. Barboza ◽  
Sandro Aparecido Baldacim ◽  
Francisco Piorino Neto ◽  
...  
Keyword(s):  
Solid Solution ◽  
Rare Earth ◽  
High Temperature ◽  
Liquid Phase ◽  
Creep Behavior ◽  
Rare Earth Oxide ◽  
Si3n4 Ceramic ◽  
Creep Tests ◽  
Oxide Mixture ◽  
Metallic Cations

a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.

Microstructures and Mechanical Properties of AJ62 Magnesium Alloy with Y and Nd Elements

2011 ◽  
Vol 686 ◽  
pp. 253-259
Author(s):  
Xu Ning ◽  
Wei Dong Xie ◽  
Chun Mei Dang ◽  
Xiao Dong Peng ◽  
Yan Yang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Tensile Strength ◽  
Rare Earth ◽  
Magnesium Alloy ◽  
Room Temperature ◽  
Solution Treatment ◽  
Solid Solution Treatment ◽  
Microstructure And Mechanical Properties ◽  
Microstructures And Mechanical Properties

A series of Mg-6Al-2Sr-1.5Y-xNd (x=0, 0.3, 0.6, 0.9, 1.2) alloy samples were prepared and their microstructures were observed and mechanical properties were measured. The existing forms of Y and Nd were studied. The effects of Y and Nd on microstructure and mechanical properties of AJ62 alloy were investigated. The results show that the main existing forms of Y and Nd in AJ62 alloy are Al2Y and Al2Nd. The combined addition of rare earth Y and Nd can refine α-Mg matrix obviously and reduce the amount of the β-Mg17Al12phases; after solid solution treatment, the tensile strength of the alloys rise first and fall later with increasing content of Nd. When the content of Nd is about 0.6%wt, the values of tensile strengthes are up to the maximum both at room temperature and at 448 K.

Influence of Rare Earth Additions on the Microstructure and Mechanical Properties of Al7Si0.3Mg Alloys Processed by Semi-Solid Die Casting and Gravity Die Casting

2019 ◽  
Vol 285 ◽  
pp. 69-74 ◽  
Author(s):  
Long Fei Li ◽  
Da Quan Li ◽  
Min Luo ◽  
Yong Zhong Zhang ◽  
Yong Lin Kang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Rare Earth ◽  
Grain Boundaries ◽  
Die Casting ◽  
Eutectic Phase ◽  
Microstructure And Mechanical Properties ◽  
Die Cast ◽  
Rare Earth Additions ◽  
Semi Solid

Microstructures with fine globular grains and refined eutectic structures are important to enhance the mechanical properties of A356 alloys processed by semi-solid and gravity die casting. Rare earth (RE) additions have been shown to be capable of refining both the α-Al particles as well as modify the eutectic phase of alloys. In semi-solid die casting, Al7Si0.3Mg alloys with RE concentrations (0, 0.1 and 0.4 wt.%) were used to prepare semi-solid slurries using the SEED (Swirling Enthalpy Equilibrium Device) method, and subsequently semi-solid die cast. The same compositions of alloys were also applied to gravity die casting. The microstructure and mechanical properties of castings in two processes have been characterized. Compared to the grains produced in gravity die casting, globular grains with small size (260 μm) in the semi-solid die casting significantly enhance the UTS and elongation of alloys. Although the size of grains had no change with increasing RE concentrations in alloys. The Al-Si eutectics were changed to refined morphology with the 0.1 wt.% RE addition, which enhanced the ductility of alloys in two processes. When increasing the RE addition to 0.4 wt.%, the RE-rich phases precipitated at grain boundaries, which decreased the UTS and elongation of alloys.

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