Influence of strain rate effect on material removal and deformation mechanism based on ductile nanoscratch tests of Lu2O3 single crystal

Relationships between crystal structure and microwave dielectric properties of Li2(Mg1−xCox)3TiO6 (0 ≤ x ≤ 0.4) ceramics

The unique material nature (e.g. hard, brittle, heterogeneous and orthotropic) of SiC-based Ceramic Matrix Composites (CMCs) highly affects the outcomes of machining process by inducing high thermo-mechanical loads during material removal. This can result in severe material damage which in turn causes a reduction of the in-service life of critical structural ceramic components (such as in aero-engines or nuclear reactors). In this study, the phenomenon by which the material removal mechanism during drilling influences the CMC surface integrity are discussed by characterising the fracture and deformation phenomena on the CMC's constituents - i.e. SiC and Si materials. Moreover, the strain induced to the surface, together with the changes in chemical composition are characterised via micro Raman spectroscopy and related to the principles of residual stresses upon cutting. This results in a novel understanding of the material removal process that governs cutting of SiC-based CMCs while emphasising how the different microstructure, morphology and nature of ceramics behave under the same cutting conditions. This study has therefore led to a comprehension of how the microstructure of complex hierarchical ceramic materials such as SiC/SiC CMCs is affected by a mechanical cutting process and opens avenues to understand the structure damage under other machining operations (e.g. milling, grinding).

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On understanding the microstructure of SiC/SiC Ceramic Matrix Composites (CMCs) after a material removal process

Smoothed particle hydrodynamics simulation and experimental analysis of SiC ceramic grinding mechanism

The LiNiPO4 ceramic for the LTCC technology was prepared via the traditional solid-state reaction route and its dielectric properties were investigated for the first time. The best dielectric properties of LiNiPO4 ceramics with a er of 7.18, Q×f value of 27,754 GHz and τf of −67.7 ppm/°C were obtained in samples sintered at 825 °C for 2 h. Rietveld refinement was firstly employed to study the crystal structure and dielectric properties of LiNiPO4 ceramics. Unfortunately, the relatively large negative τf was unfavorable to practical applications. Therefore, we introduced TiO2, which possessed a considerable positive τf, to obtain a desired τf value. The prepared LiNiPO4 ceramics with 15 wt% TiO2 sintered at 900 °C for 2 h exhibited excellent dielectric properties of er∼11.49, Q×f∼10,792 GHz, τf∼−2.8 ppm/°C. The Ag co-fired experiments confirmed the excellent chemical compatibility with LiNiPO4-TiO2 ceramics which might be potential dielectric LTCCs for high frequency applications.

The microwave dielectric properties and crystal structure of low temperature sintering LiNiPO4 ceramics

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

A single grain grinding experiment with fixed speed ratio v s / v w was designed to decouple the effect of grinding speed and undeformed chip thickness (UCT) on the SiC material removal mechanism during elevating the grinding wheel speed. Ground surface and subsurface topography, grinding forces, and specific energy were measured with grinding speed ranging from 20 to 160 m/s and maximum UCT a gmax from 0.02 to 3 μm. The results demonstrated the grinding force and specific grinding energy show an evident decreased tendency with the increasing of grinding speed, despite the a gmax value was kept at 0.03, 1 μm. However, at a gmax  = 0.3 μm, the grinding force has a peak value with the increment of grinding wheel speed. The subsurface has the same trend. Based on the subsurface morphologies, grinding forces, grinding energy, the critical grinding wheel speeds v s  = 100, 80, 80 m/s were determined at the a gmax  = 0.03, 0.3, 1 μm, respectively. Besides, grinding forces show different growth rates with the gradually increasing a gmax at three stages under typical grinding speeds due to the transition of material removal mechanism. The critical a gmax values for ductile-brittle transition and beginning of brittle regime grinding are determined as 0.3 and 1 μm by surface and subsurface morphologies, grinding forces, grinding energy, respectively.

Wenbo Zhou

Papers

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

Experimental investigation on materials removal mechanism during grinding silicon carbide ceramics with single diamond grain

Numerical investigation on the influence of cutting-edge radius and grinding wheel speed on chip formation in SiC grinding

Microwave dielectric properties of Li(Mg1−xNix)PO4 ceramics for LTCC applications

Preparation and microwave dielectric properties of Li(Mg1–xCox)PO4 ceramics for low-temperature cofired ceramic applications