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In this paper, the mechanical properties of bulk single‐phase γ‐Y2Si2O7 ceramic are reported. γ‐Y2Si2O7 exhibits low shear modulus, excellent damage tolerance, and thus has a good machinability ready for metal working tools. To understand the underlying mechanism of machinability, drilling test, Hertzian contact test, and density functional theory (DFT) calculation are employed. Hertzian contact test demonstrates that γ‐Y2Si2O7 is a “quasi‐plastic” ceramic and the intrinsically weak interfaces contribute to its machinability. Crystal structure characteristics and DFT calculations of γ‐Y2Si2O7 suggest that some weakly bonded planes, which involve Y–O bonds that can be easily broken, are the sources of the low shear deformation resistance and good machinability.

Direct atomic resolution observations of the layered stacking characteristics of TaCx slabs and Al atomic planes in ternary Ta–Al–C carbides were achieved. Layered ternary Ta–Al–C compounds have diverse structures. A previously unknown Ta6AlC5 carbide, as well as intergrown Ta2AlC–Ta4AlC3 and Ta4AlC3–Ta6AlC5 structures were identified. Theoretical lattice parameters and bulk modulus of Ta2AlC, Ta3AlC2, Ta4AlC3, and Ta6AlC5 are presented. Furthermore, the Ta–C bonds are much stronger than the Ta–Al bonds in ternary Ta–Al–C carbides, which accounts for the enhancement of bulk modulus with increasing Ta–C layers.

Thermal properties, namely, Debye temperature, thermal expansion coefficient, heat capacity, and thermal conductivity of γ‐Y2Si2O7, a high‐temperature polymorph of yttrium disilicate, were investigated. The anisotropic thermal expansions of γ‐Y2Si2O7 powders were examined using high‐temperature X‐ray diffractometer from 300 to 1373 K and the volumetric thermal expansion coefficient is (6.68±0.35) × 10−6 K−1. The linear thermal expansion coefficient of polycrystalline γ‐Y2Si2O7 determined by push‐rod dilatometer is (3.90±0.4) × 10−6 K−1, being very close to that of silicon nitride and silicon carbide. Besides, γ‐Y2Si2O7 displays a low‐thermal conductivity, with a κ value measured below 3.0 W·(m·K)−1 at the temperatures above 600 K. The calculated minimum thermal conductivity, κmin, was 1.35 W·(m·K)−1. The unique combination of low thermal expansion coefficient and low‐thermal conductivity of γ‐Y2Si2O7 renders it a very competitive candidate material for high temperature structural components and environmental/thermal‐barrier coatings. The thermal shock resistance of γ‐Y2Si2O7 was estimated by quenching dense materials in water from various temperatures and the critical temperature difference, ΔTc, was determined to be 300 K.

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Bulk Ta4AlC3 ceramic was prepared by an in situ reaction synthesis/hot‐pressing method using Ta, Al, and C powders as the starting materials. The lattice parameter and a new set of X‐ray diffraction data were obtained. The physical and mechanical properties of Ta4AlC3 ceramic were investigated. Ta4AlC3 is a good electrical and thermal conductor. The flexural strength and fracture toughness are 372 MPa and 7.7 MPa·m1/2, respectively. Typically, plate‐like layered grains contribute to the damage tolerance of Ta4AlC3. After indentation up to a 200 N load, no obvious degradation of the residual flexural strength of Ta4AlC3 was observed, demonstrating the damage tolerance of this ceramic. Even at above 1200°C in air, Ta4AlC3 still retains a high strength and shows excellent thermal shock resistance, which renders it a promising high‐temperature structural material.

In this article, a novel pressureless solid-liquid reaction method is presented for preparation of yttrium disilicate (␥-Y 2 Si 2 O 7 ). Single-phase ␥-Y 2 Si 2 O 7 powder was synthesized by calcination of SiO 2 and Y 2 O 3 powders with the addition of LiYO 2 at 1400°C for 4 h. The addition of LiYO 2 significantly decreased the synthesis temperature, shortened the calcination time, and enhanced the stability of ␥-Y 2 Si 2 O 7 . The sintering of these powders in air and O 2 was studied by means of thermal mechanical analyzer. It is shown that the ␥-Y 2 Si 2 O 7 sintered in oxygen had a faster densification rate and a higher density than that sintered in air. Furthermore, single-phase ␥-Y 2 Si 2 O 7 with a density of 4.0 g/cm 3 (99% of the theoretical density) was obtained by pressureless sintering at 1400°C for 2 h in oxygen. Microstructures of the sintered samples are studied by scanning electron microscope.