A simple way to make pre-stressed ceramics with high strength

A pre-stressing design and a simple fabrication technology to substantially improve the strength of ceramic components are presented.Residual surface compressive stress is generated in ceramic components by pressureless sintering of a green bulk coated with a thin layer of low coefficient of thermal expansion(CTE).The stress level can be controlled by changing the cross-section area ratio,Young's modulus ratio and CTE ratio of the coating.Pre-stressed ZrO_(2) ceramics coated with Al_(2)O_(3) can achieve a flexural strength of 1330±52MPa,45% higher than their uncoated counterpart.Similarly,the flexural strength of building porcelain tiles is increased by 70%,from 67±3 MPa to 114±5MPa.The damage tolerance of pre-stressed ZrO_(2) ceramics is excellent with a high residual strength of ~1200 MPa in a thermal shock test at 325℃.This simple technique can improve the mechanical performance of ceramic components with no limitation of size and shape.

Evolution of microstructure and texture in copper during repetitive extrusion-upsetting and subsequent annealing

The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 ＋ 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200？C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350？C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.

High Ductility and Toughness of a Micro-duplex Medium-Mn Steel in a Large Temperature Range from—196 ℃ to 200 ℃

A medium-Mn steel （0.2C5Mn） was processed by intercritical annealing at different temperatures （625 ℃ and 650 ℃ ）. An ultrafine-grained micro-duplex structure consisting of alternating austenite and ferrite laths was de- veloped by austenite reverse transformation （ART） during intercritical annealing after forging and hot rolling. Ultra- high ductility with a total elongation higher than 30% was achieved in the temperature range from -196 ℃ to 200 ℃, and high impact toughness no less than 200 J at -40 ℃ was obtained. Based on the analysis of microstructure and mechanical properties, it was found that the enhanced ductility was determined by the phase transformation effect of austenite （TRIP effect）, while the delayed ductile to brittle transition was controlled by austenite stability.