Alumina microhardness

Testing. Chemical analyses are done on all manufactured abrasives, as well as physical tests such as sieve analyses, specific gravity, impact strength, and loose poured density (a rough measure of particle shape). Special abrasives such as sintered sol—gel aluminas require more sophisticated tests such as electron microscope measurement of a-alumina crystal si2e, and indentation microhardness. 

Abrasive particles are a key component in CMP slurry. The most commonly used abrasive particles include silica, alumina, ceria, zirconia, titania, and diamond. Table 21.1 listed a set of information on each type of abrasive particles such as density, microhardness, and isoelectric points (lEP). It is important to point out that the specific values for these properties depend highly on the preparation techniques and the specific states of the samples. The values listed in the table represent an average of the most commonly reported data. For example, the isoelectric point for silica is a function of the number of hydroxyl groups, type and level of adsorbed species, metal impurity in the solid matrix, and the treatment history of the materials [1]. There are three major types of silica according to their preparation methods fumed, colloidal, and precipitated. The common sources for obtaining these abrasive particles are listed in Table 21.2. As examples, some of the more specific information on... 

Microhardness of both particulate and platelet composites was evaluated at ambient temperature with a Vickers microhardness indenter with an indent load of 9.8 N using five indents for each composite in accordance with ASTM C 1327 [28]. Figure 16 shows the results of Vickers microhardness measurements for both composites. Microhardness increased linearly with increasing alumina content for the particulate composites up to 20 mol% alumina and then leveled off above 20 mol%. Microhardness of the platelet composites remained almost unchanged up to 10 mol% and then decreased appreciably at 30 mol%, resulting in a significant difference in hardness at 30 mol% between the two composites. Individual microhardness data for both composites are also summarized in Tables 1 and 2. 

The microhardness of all ceramic samples was in 17-21 GPa range. The best hardness of 21 GPa had AMI (MgO doped alumina) ceramics. This value is comparable to the hardness of monocrystall alumina - leucosapphire 20.9 GPa. High ceramics properties (table 4) prove the assumption that particle aggregates of the powders obtained by MPC and LE methods are weak and don t influence the compaction process with the following sintering. 

It was found that the microhardness of the nanosized alumina / tetragonal zirconia (T-YSZ) composite ceramics depends from the T-YSZ amount and increases from 17 to 20 GPa with the decrease of its amount from 60 down to 7 wt.%. The fracture toughness of the samples is around 5-6 MPa m° . At that the best elimination of the crystallites growth of alumina (140 nm) was observed for the composite ceramics with the equal amount of a-AbCh and T-YSZ phases and sintered at 1410°C up to the relative density of 0.997. 

The microhardness along the depth of the specimens does not change, and it is very similar for all materials. On the surface, the influence of the alumina layer on the... 

Fig 1. Porosity and microhardness (HV0,1(X)) of plasma sprayed Al203-SiC nano-composite coatings deposited with trial parameters (open bars) and optimised parameters (shaded bars) using a proprietary plasma torch. For comparison, properties for a plasma sprayed pure alumina coating are included. 

Following satisfactory powder characterisation, Al203-SiC nano-composite coatings were successfully deposited using the nano-composite feed powders. Optimisation of spray parameters gave microhardness behaviour equivalent to or superior to commercial plasma sprayed pure alumina coatings. 

---