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ZrB_2+SiC陶瓷高温氧化过程中SiC耗尽层的形成机制研究 王超1,王宝来1,栾旭1,梁军1 (1.哈尔滨工业大学,黑龙江,哈尔滨,150001) 摘要:ZrB_2+SiC陶瓷在高温氧化过程中会形成一层多孔的SiC耗尽层.本文首先计算了在高温氧化过程中的主要氧化产物.通过对氧化过程中相变机制的分析,利用质量守恒,固体区域体积守恒并结合反应速率方程,研究了SiC耗尽层的形成与演化过程,给出了孔隙率随温度的变化规律.结果表明:氧化过程中生成相的体积膨胀及SiC的初始体积含量是影响SiC耗尽层孔隙率的主要因素.对计算结果的分析解释了试验中发现的在低SiC含量下不出现耗尽层,以及氧化层破坏的现象. 关键词:ZrB_2+SiC陶瓷; SiC耗尽层; 氧化; 孔隙率; 高温; ZrB_2+SiC; SiC depletion layer; oxidation; porosity......
镁合金激光焊接气孔问题的实验研究 陈武柱1,郑世卿1,单际国1,任家烈1,张婧1 (1.清华大学,北京,100084;2.先进成形制造教育部重点实验室,北京,100084) 摘要:对变形镁合金AZ31B,AZ80A,砂铸镁合金AM60B,AZ91D及压铸镁合金AM50A激光焊接气孔倾向进行研究.研究表明:变形镁合金激光焊气孔倾向很小,在较宽的焊接工艺参数范围内均能得到无气孔的焊缝. 砂铸镁合金AM60B及AZ91D激光焊时气孔对气体保护条件非常敏感,在侧吹气体保护角度及流量选择不合适时气孔率非常高,在优化的气保护条件下可得到气孔率较低的焊缝.而压铸镁合金AM50激光焊缝中气孔问题非常突出,调整工艺参数无法解决气孔问题,焊接过程中的加热及添加填充材料可以在一定程度上减少气孔. 关键词:气孔; 激光焊接; 变形镁合金; 砂铸镁合金; 压铸镁合金; porosity; laser......
sintering; porous Pd bulk; porosity; deuterium gas loading; [全文内容正在添加中] ......
metal can only give limited porosity and uncontrollable pore morphologies. In the present study, a newly developed method of powder metallurgy using the space-holder technique was used to fabricate porous titanium with controllable porosity. The morphological features and mechanical properties of the products were fully investigated. The results show that the porosity is in the range of 55%-75......
:Three-dimensional porous poly-lactic acid(PLA) scaffold was fabricated using fused deposition modeling(FDM) method including 30%, 50% and 70% nominal porosity... significantly with increasing the porosity of scaffold. The microstructure of scaffolds were studied by scanning electron microscope(SEM), showing that the pores had a regular arrangement and their morphology......
was fabricated by freeze casting with tert-butyl alcohol as solvent. The porous Y2SiO5 ceramic possessed long straight pore structure. With decreasing solid loading from 20 to 10 vol.%, the porosity... to 0.05 W/mK for the porous body with a porosity of 57%.关键词:......
. The porosity of the porous material increased with increasing the addition of pore forming agent, and the hollow spherical porous material with a porosity of 81.62% were obtained when the addition of pore forming agent was 40%. The compression test indicated that this kind of materials possesses excellent energy absorption capability, and the compression resistance decreased with the increasing of porosity......
electron microscope fractography analyses were conducted to evaluate the variation of the volumetric porosity and fractographic porosity with the GBF process,respectively.The fractographic porosity of the specimens can be minimised under specific GBF conditions in terms of the buoyant velocity and the absorbing capacity of gas bubbles,the inclusion of oxide films,whereas the volumetric porosity can......
uenced by the microstructure of the anodic fi lm such as the fi lm porosity, and the order and continuity of the hexagon columnar cells. The fi lm microhardness increases as the porosity... the fi lm porosity decreases and the order and continuity of the cells are also improved. Under the condition of the same anodizing time, as the current density increases, the fi lm microhardness......
ceramic is a promising high-temperature thermal insulator in harsh environment.However,all the published relevant works faced serious problems,such as severe linear shrinkage,low porosity and low strength.In this study,porous Y2SiO5 ceramic with low sintering shrinkage and high porosity was successfully prepared by foam-gelcasting method using gelatin as the gelling agent.The effects of sintering......
