Y. H. Li
,
M. Krzyzanowski
,
J. H. Beynon and C. M. Sellars IMMPETUS( Institute for Microstructural and Mechanical Process Engineering: The University of Sheffield
,
Sheffield SI 3JD
,
UK)
金属学报(英文版)
In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot" sandwich" rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.
关键词:
interfacial heat transfer
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null
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null
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null
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null
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null
Scripta Materialia
Three-dimensional atom probe has been applied to investigate the solubility of Si in Al(3)SC in an Al-0.16Sc-0.05Si alloy. It was found that L1(2)-structured Si-containing Al(3)Sc precipitates formed after the alloy was aged at 300 degrees C. Results of first-principles calculation indicated that Si atoms tend to substitute Al sites in Al(3)Sc, and thus the precipitates can be represented as (Al,Si)(3)Sc. The (Al,Si)(3)SC was found to have a dramatic precipitation-strengthening effect in the cast alloy. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
Aluminium alloys;Ageing;3DAP;Precipitation;Hardness test;aluminum-alloys;coherency loss;evolution;zr
Weiping SHEN
,
Fei WANG
,
Zhuohui WU
,
Changchun GE
材料科学技术（英）
This paper presents results of combustion synthesis (Self-Propagating High Temperature Synthesis, SHS) of Si3N4 under nitrogen with argon, hydrogen or ammonia. Higher percentages of α-Si3N4 content were obtained in large size cakes in SHS with hydrogen and ammonia than those with argon. Effect of the auxiliary gases for combustion synthesis of Si3N4 on α phase content, on phase transformation of α-Si3N4 to β-Si3N4 in SHS Si3N4 and on oxygen content in SHS Si3N4 were investigated.
关键词:
Combustion synthesis
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null
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null
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null
张宝林
,
庄汉锐
,
罗新宇
,
李文兰
硅酸盐通报
doi:10.3969/j.issn.1001-1625.1999.02.008
介绍了β-Si3N4及添加β-Si3N4的α-Si3N4的气氛加压烧结,β-Si3N4在GPS中具有不低于α-Si3N4的烧结活性,而且陶瓷显微结构更容易调节.由GPS β-Si3N4制备的陶瓷材料晶粒比较均匀,具有较高的力学性能,尤其是高的韦泊模数.添加于α-Si3N4中的β-Si3N4对陶瓷材料显微结构具有明显的调控作用.
关键词:
气压烧结
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β-Si3N4
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显微结构
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力学性能
Journal of Materials Research
The oxidation behavior of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) in air has been investigated. The oxidation kinetics of bulk Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) at 900-1300 degrees C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO(2), Al(2)O(3), and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) has been improved compared with Zr(2)Al(3)C(4), and is much better than Zr(3)[Al(Si)](4)C(6) to larger fraction of protective oxidation products, Al(2)O(3) and aluminosilicate/mullite.
关键词:
single-crystals;thermoelectric properties;zrc/zro2 interface;zirconium carbide;high-temperatures;bulk zr2al3c4;carbon;mullite;microstructure;ceramics
姚怀
,
徐巧玉
,
唐敬友
,
苌清华
机械工程材料
以Y2O3-Al2O3-La2O3体系作烧结助剂,在5.4～5.7 GPa、1 620～1 770 K的高温高压条件下进行了α-Si3N4与γ-Si3N4粉体的烧结,研究了烧结体的相对密度、韦氏硬度和物相组成.结果表明:α-Si3N4、γ-Si3N4在烧结后完全转变为β-Si3N4;在相同烧结条件下,γ-Si3N4烧结体的相对密度、维氏硬度比α-Si3N4的高γ-Si3N4与α-Si3N4烧结体的最高相对密度与维氏硬度分别为99.20%,23.42 GPa和98.78%,21.87 GPa;烧结体由相互交错的长柱状β-Si3N4晶粒组成,显微结构均匀.
关键词:
氮化硅
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超高压烧结
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维氏硬度
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显微结构
刘谊
,
刘永胜
,
张立同
,
成来飞
,
徐永东
无机材料学报
doi:10.3724/SP.J.1077.2006.00979
以SiCl4-NH3-H2为反应体系, 采用化学气相渗透(CVI)法制备Si3N4p/Si3N4透波材料. XRF测试表明试样主要含Si、N、O三种元素. XRD测试表明复合材料主要成分为α-Si3N4和非晶沉积物和非晶SiO2, 并有微量的β-Si3N4和晶体Si, 高温热处理可使非晶沉积物转变为α-Si3N4和β-Si3N4. SEM照片显示颗粒团间结合不够致密, 残留气孔偏大. 试样的弯曲强度最高为94MPa, 介电常数为4.1～4.8.
关键词:
Si3N 4p/Si3N4透波材料
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null
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null
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null
刘谊
,
刘永胜
,
张立同
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成来飞
,
徐永东
无机材料学报
doi:10.3321/j.issn:1000-324X.2006.04.035
以SiCl4-NH3-H2为反应体系,采用化学气相渗透(CVI)法制备Si3N4P/Si3N4透波材料.XRF测试表明试样主要含Si、N、O三种元素.XRD测试表明复合材料主要成分为α-Si3N4和非晶沉积物和非晶SiO2,并有微量的β-Si3N4和晶体Si,高温热处理可使非晶沉积物转变为α-Si3N4和β-Si3N4.SEM照片显示颗粒团间结合不够致密,残留气孔偏大.试样的弯曲强度最高为94MPa,介电常数为4.1～4.8.
关键词:
Si3N4P/Si3N4透波材料
,
化学气相渗透(CVI)
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弯曲强度
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介电常数
