Content Of Intergranular Phase Research Articles

Effects of Sn addition on the microstructure and magnetic properties of MnBi bulk magnets

The Sn addition MnBi bulk magnets with high density and superior coercivity (Hc) were prepared by hot compaction. It was found that the added Sn was dispersed between the MnBi particles as an intergranular phase. The appropriate intergranular phase content could be beneficial in improving the Hc due to the strong magnetic isolation effects. The Hc of the MnBi/Sn bulk magnet was increased from 8.6 kOe to 11.5 kOe as the Sn addition contents were increased in the range of 0 wt.% to 5 wt.%. A relatively high squareness (Mr/Ms) of 0.91 was obtained for the 1 wt.% Sn addition Mn56Bi44 bulk magnet exhibiting the maximum energy product (BH)max of 7.8 MGOe with high Hc of 10 kOe at room temperature.

Microstructure evolution and high-temperature mechanical properties of porous Si3N4 ceramics prepared by SHS with a small amount of Y2O3 addition

Porous Si3N4 ceramics with well-developed microstructure and high flexural strength were successfully prepared by self-propagating high temperature synthesis (SHS) using a small amount of Y2O3 as sintering additive. Influences of Y2O3 content on the phase composition, microstructure evolution, flexural strength at both room temperature and elevated temperature of ~1400 °C and their fracture behavior of the obtained porous Si3N4 ceramics were investigated. Porous Si3N4 ceramic with high average aspect ratio of 4.03 and excellent flexural strength of 101 MPa was obtained by 0.4 wt% Y2O3 addition. It also shows good strength retention of 76.6% and evidently elastic fracture behavior at 1400 °C because of its rather low amorphous intergranular phase content. With the increase of Y2O3 content, the creep resistance of sample degraded owning to the softening of amorphous intergranular thus resulting in the degradation of high-temperature strength retention.

Effects of intergranular phase on the coercivity for MnBi magnets prepared by spark plasma sintering

MnBi magnets with a high content of low temperature phase (LTP) and excellent magnetic properties were prepared by spark plasma sintering (SPS) using ball milling powders as precursors without magnetic purification. A complicated intergranular phase, which contains Mn phase, Bi phase, MnO phase, and even amorphous phase in MnBi magnets, was characterized and reported systematically. It was found that the formation of intergranular phase which was contributed by ball milling precursors and sintering mechanism, jointly, had important influence on the magnetic properties. The appropriate content of intergranular phase was beneficial in improving the coercivity due to the strong magnetic isolation effects. The optimum magnetic properties with Mr=26.0 emu/g, Hci= 7.11 kOe and (BH)max=1.53 MGOe at room temperature, and a maximum value Hci= 25.37 kOe at 550 K can be obtained. Strongly favorable magnetic properties make SPSed MnBi magnets an attractive candidate material for small permanent magnets used in high-temperature applications.

The Fluorine Effect on the Grain-Growth of -SiAlON Ceramics

SiAlON ceramics are of major interest for industrial applications due to their excellent mechanical properties. The starting Si 3 N 4 powder (α or β), the type of sintering additive and sintering conditions govern the microstructural evolution of SiAlON ceramics. In this study, α ı :β ı SiAlON ceramics with an equal mole intergranular phase content, different type cation systems (Y:Sm:Ca and Ca:Ce) with different molar ratio (30:64:6 and 33:67) were produced by using coarse (d 50 =1 µm) β-Si 3 N 4 powder. CaF 2 and CaCO 3 were utilized as Ca sources. An increase in α ı -SiAlON amount in the case of employing CaF 2 as opposed to CaCO 3 in Y:Sm:Ca cation system was observed. Despite the fact that α ı -SiAlON phase cannot be stabilized in Ca:Ce (CaCO 3 as a Ca source) system, α ı -SiAlON phase stability and unpredictable α ı -SiAlON grain-growth in both a and c directions was easily achieved when use of CaF 2 . Furthermore, using CaF 2 instead of CaCO 3 gives rise to an increase in densities. Therefore, the impressive effect of CaF 2 on abnormal grain growth and α ı -SiAlON phase stabilization was discussed.

Relationship between microstructure and mechanical properties of undercooled K4169 superalloy

Various undercoolings 14-232 K of bulk K4169 superalloys were obtained by the method of molten glass fluxing combined with superheating cycling and the mechanical properties of undercooled K4169 with as-solidified state were tested. Microstructures and phases composition in undercooled bulk K4169 superalloy were identified by transmission electron microscope (TEM), scanning electron microscope (SEM) and optical microscopy (OM). The morphology of dendrites, grain size and intergranular phase all change with the increased undercooling. Meanwhile, the relationship between microstructure of undercooled K4169 superalloy and tensile properties was investigated. The experimental results show that the uniform distribution of Laves phase and the decrease of grain size and intergranular phase content are favorable for the improvement of mechanical properties. The maximum tensile strength and elongation obtained at undercooling of 232 K are 932.2 MPa and 6.5 %, respectively.

The effect of homogenization temperature on the corrosion resistance of extruded 7050 Al-alloy bars

The homogenization time is decreased from 28h to 6h by using high-temperature homogenization heat treatment. With increasing of the holding time, the content of intergranular phase decreases quickly at first. When the holding time is more than 6h, the content of intergranular phase keeps unchanged, and the area fraction of residual intergranular phase is 0.5%, lower than that (0.64%) of the two-step homogenization process. The mechanical properties of the extruded bars heat-treated by the high-temperature homogenization and the two-step homogenization heat treatment are almost the same. In the accelerated corrosion experiments, the maximum intergranular corrosion depth in the direction of perpendicular and parallel to the bar axis heat-treated by the high-temperature homogenization heat treatment are decreased by 43% and 60%, respectively, compared with that heat-treated by the two-step homogenization heat treatment.

Sliding-wear resistance of ultrafine-grained SiC densified by spark plasma sintering with 3Y2O3 + 5Al2O3 or Y3Al5O12 additives

The sliding-wear behavior of ultrafine-grained SiC densified by spark plasma sintering (SPS) with 3Y2O3 + 5Al2O3 or Y3Al5O12 additives was compared to elucidate the effect of the intergranular-phase source. Significantly greater sliding-wear resistance (i.e. lower mild- and severe-wear rates, and delayed mild-to-severe wear transition) is observed with the Y3Al5O12 additive, due to its carbothermal reduction during SPS resulting in a harder YAlO3 phase while reducing the intergranular phase content. Implications for the processing of superior SiC triboceramics are discussed.

Microstructural effects on the sliding-wear resistance of pressureless liquid-phase-sintered SiC under diesel fuel

Abstract The sliding wear of pressureless liquid-phase-sintered (PLPS) SiC ceramics under diesel fuel lubrication was investigated. It was found that the sliding-wear behaviour under diesel fuel is similar to what is observed under lubrication with the chemically similar paraffin oil: initial mild, plasticity-controlled wear followed by severe, fracture-controlled wear, with a well-defined wear transition. Compared to paraffin oil, however, diesel fuel lubrication decreases the extent of the mild-wear regime and results in damage that is more severe due to its lower viscosity. Also, it was found that the wear resistance under diesel fuel decreases with increasing contact load and sliding speed. Subsequent investigation of the effects of the intergranular phase content, grain size, and grain shape demonstrates nevertheless that the wear performance of PLPS SiC under diesel lubrication can be improved via microstructural control by (i) decreasing the intergranular phase content, and (ii) decreasing the SiC grain size or increasing its aspect ratio. The results of this work are likely to have relevant implications for the design of wear resistant PLPS SiC ceramic components for diesel engines.

Microstructural design of sliding-wear-resistant liquid-phase-sintered SiC: An overview

We have reviewed the effect of microstructure – content of intergranular phase, grain size, and grain shape – on the lubricated, sliding-wear of pressureless liquid-phase-sintered (LPS) SiC ceramics. The sliding-wear resistance in LPS SiC decreases with an increase in the content of the intergranular phase or an increase in the equiaxed-grain coarsening. However, the sliding-wear resistance is dramatically improved with anisotropic-grain coarsening. Based on these results we suggest two strategies for the microstructural design of low-cost, sliding-wear resistant SiC-based ceramics: (1) grain refinement, and (2) grain elongation. The latter strategy allows the materials to be simultaneously in situ toughened, and we describe its optimization by judicious selection of the SiC starting powder.

Compressive Creep of Hot-Pressed Si3N4 Ceramics Using CRE2O3-Al2O3 or CRE2O3-AlN Additive Mixtures

The creep behavior of hot-pressed Si3N4 ceramics was investigated. The proposal of this work is to investigate the use of yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, as sintering additive, since the cost of production of this material is 80% inferior to Y2O3. These ceramics were obtained by uniaxial hotpressing using different additive contents and mixtures (CRE2O3-Al2O3 or CRE2O3- AlN). Compressive creep tests were carried out at 13000C and 300 MPa, in air. The Si3N4-CRE2O3-Al2O3 ceramics demonstrated that the creep resistance is inversely proportional to the additive content. Mixtures with high intergranular phase content presented low creep resistance due to high oxidation and more pronounced softening of the intergranular phase. Si3N4-CRE2O3-AlN ceramics demonstrated better creep resistance with a steady-state creep rate of 7 x 10-8 s-1. This behavior is related to the a-SiAlON content, a solid solution of Si3N4 that incorporates a great fraction of intergranular phase, decreasing the amount of intergranular phase.

Effect of Microstructure on Sliding‐Wear Properties of Liquid‐Phase‐Sintered α‐SiC

We have studied, for the first time, the effect of the content of intergranular phase and grain size on the sliding‐wear resistance of pressureless, liquid‐phase‐sintered (LPS) α‐SiC (silicon carbide) ceramics. It was found that the sliding‐wear behavior of these ceramics is similar to what is observed in other polycrystalline ceramics: initial mild, plasticity‐controlled wear followed by severe, fracture‐controlled wear, with well‐defined wear transition. We have found that the increase in the content of intergranular phase and the grain coarsening leads to the degradation of the sliding‐wear resistance in LPS α‐SiC ceramics. A mechanistic model is used to rationalize these wear results, and to provide guidelines for the design and fabrication of low cost, highly wear‐resistant SiC‐based ceramics. This is likely to have important implications because SiC‐based materials are being used increasingly in contact‐mechanical and tribological applications.

The role of nitrogen in the intergranular glass phase of Si 3N 4 on high temperature applications and wear

The hot hardness of Si 3N 4 tool materials of the CeO 2 and CeO 2AIN doping systems, oxidation in air from 900 to 1450 °C, and turning of tool steel with ceramic inserts of the same compositions were investigated to determine the effect of the N content of intergranular phase. Si/N grain boundary diffusion was found to be the main controlling mechanism at high temperature for densification, mechanical behavior and chemical degradation of these materials in air, the passivation oxidation rate of the CeO 2AINSi 3N 4 system being dependent on the atomic fraction of N of the intergranular phase, with lower values for the N-rich compositions.