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Ceramic coatings with a thickness range of 1.5–5.5 μm were successfully prepared with polysilazane (PSN1) as a precursor and aluminum (Al) powder as an active filler. The effect of Al content on chemical composition, microstructure, and mechanical properties of the coatings was investigated. Chemical composition analysis revealed that Al powder was completely converted into Al 2 OC and AlN phases during the ceramization process, accompanied by volume expansion. Ceramic coatings derived from less Al powder containing PSN1/Al showed more compacted surface morphology and continuous microstructure. The surface hardness and elastic modulus of ceramic coatings decreased with the increase of the volume fraction of Al from 10% to 40% (Al/PSN1, v/v). The maximum surface hardness and elastic modulus of coatings were 6.38 GPa and 107.66 GPa, respectively.

Al2O3 toughened with Ti3SiC2 has been investigated for improved toughness. Hot-pressed Al2O3–Ti3SiC2 composites were manufactured and characterized. Addition of Ti3SiC2 inhibited the growth of alumina grains though pinning mechanism. The experimental results showed that the Vickers hardness decreased with an increase in Ti3SiC2 content, and the fracture toughness and strength increased with Ti3SiC2 content. Maximum toughness (8.78±0.12 MPa m1/2) and maximum strength (500±10.2 MPa) were achieved through the addition of 50 wt.% Ti3SiC2 content, which is compared to alumina toughened by other materials.

SiC whisker reinforced Si 3 N 4 /BN fibrous monolithic ceramics were fabricated by in situ synthesizing. The specimens were heated up to the test temperature and then quenched in a water bath of 25 °C. The thermal shock resistance parameters were calculated according to the elastic modulus, Poisson ratio, thermal expansion coefficient, strength and work of fracture. The thermal shock resistance critical temperature, Δ T , was 700 °C, which was improved more than SiC whisker reinforced Si 3 N 4 ceramic. BN soft cell boundaries had an effect on the thermal shock behavior of the Si 3 N 4 /BN fibrous monolithic ceramics. The microstructures of the composites were observed by SEM.

Layer structured LaPO4 was added to Al2O3 ceramic matrix to improve the machinability of the composites. Densification, hardness and microstructures of the Al2O3/LaPO4 ceramic composites have been studied at various sintering temperatures (1300, 1400, 1500, 1600 °C) and different LaPO4 contents (pure Al2O3, 10 wt.% LaPO4, 20 wt.% LaPO4, 30 wt.% LaPO4, 40 wt.% LaPO4, pure LaPO4). X-ray diffraction analysis showed that only Al2O3 and LaPO4 phases exist in the Al2O3/LaPO4 composites with different LaPO4 content even sintered up to 1600 °C. Bulk density, hardness and microstructures of the Al2O3/LaPO4 composites are largely dependent on the LaPO4 content and sintering temperature. Due to the layered structure of LaPO4 and the weak interface between the Al2O3 and LaPO4 phase, the 40 wt.% Al2O3/LaPO4 composite can be easily machined using cemented carbide drills instead of conventionally diamond tools.

This paper provides a new material design method for machinable ceramics within an overall methodology. Examples are provided to illustrate the use of the methodology in specific ceramic materials, and machinability of the materials is characterized with cemented carbide drills instead of diamond tools. This method enables the use of composition compound and structure design combination for the purposes of improving machinability of ceramics while allowing for retaining mechanical properties of the materials. At the same time, this method also provides the basic design principle for the other comparable, but intrinsically different, ceramic systems based on chemical compatibility and thermodynamic properties. Graded machinable Si3N4/h-BN and Al2O3/LaPO4 composites were designed, fabricated and characterized.

Si–C–Ti powder was synthesized by reactive pyrolysis of poly(methylsilaacetylene)(PSCC) precursor mixed with metal Ti powder. Pyrolysis of PSCC/Ti mixture with certain atomic ratio was carried out in argon atmosphere between 1300 °C and 1500 °C. The metal-precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy equipped with EDX. Ti3SiC2 phase was obtained from reaction of PSCC and Ti for the first time. Ti3SiC2 formation started at 1300 °C and its amount increased significantly at 1400 °C. In addition, liquid formed by additive CaF2 could promote the formation of Ti3SiC2 phase.

In the present study, the room-temperature properties of Al2O3-Ti3SiC2 composites with different Ti3SiC2 contents are determined. The composites are prepared by attrition milling Al2O3 and Ti3SiC2 mixture powders followed by spark plasma sintering (SPS) under vacuum. From a closer examination of the dependencies of the electrical conductivity on compositions in this system, we determined the percolation threshold at which an interconnected network of electrically conductive phase arises. Since the hardness of Ti3SiC2 is lower than that of Al2O3, the Vickers hardness decreased with the increasing of Ti3SiC2 content while the fracture toughness and the strength increased. The maximum strength (673 MPa) and the maximum toughness (9.3 MPa·m1/2) were reached in the pure Ti3SiC2 material.

Spin-flip probabilities from bulk defects and phonons are determined for the mesoscopic Cu channels of nonlocal spin valves (NLSVs). The NLSV spin signals are analyzed by a new approach to consistently extract the in situ values of the Cu spin diffusion length, effective spin injection (detection) polarization, and Cu resistivity. The size variations of the spin injectors (detectors) between NLSVs are treated by normalizing the spin signals to be commensurate with a standard injector (detector) size. The microstructure variations are statistically accounted for by measuring many NLSVs on the same substrate. From the Cu resistivity and spin diffusion lengths at 10 K and 295 K, the spin-flip probabilities from bulk defects and phonons are determined to be (3.9 ± 0.8) × 10−4 and (2.8 ± 1.2) × 10−4, respectively.