李仲
,
英哲
,
刘敏
,
成会明
新型炭材料
doi:10.3969/j.issn.1007-8827.2005.02.003
采用传统的熔融纺丝技术大量制备了定向性良好的纳米碳管/聚丙烯复合纤维.扫描电镜观察证实了纳米碳管在纤维里的定向性以及分散性都得到了较大的改善.通过拉伸实验测试了纳米碳管/聚丙烯复合纤维的力学性能,采用Weibull统计分析发现纳米碳管的添加显著提高了复合纤维的拉伸强度,当添加纳米碳管的质量分数达到3 %时,纤维强度最高,达到61MPa,超过聚丙烯纤维强度120%.复合纤维拉伸断口的形貌特征也证实了纳米碳管添加对复合纤维拉伸性能影响存在临界现象.
关键词:
多壁纳米碳管
,
聚丙烯
,
复合纤维
,
熔融纺丝
,
拉伸强度
鄢东洋
,
吴会强
,
常志龙
,
郭彦明
,
黄诚
宇航材料工艺
通过对比2219铝合金单道氩弧焊和氦弧打底+氩弧盖面双道焊接头的常温及液氮温度拉伸性能、显微硬度分布、单向拉伸过程的数字散斑测量(DIC)结果,发现在常、低温条件下双道焊接头的拉伸强度和延伸率均比单道焊接头高10％～20％,单道焊接头焊缝及热影响区内材料的显微硬度值相比母材的降低程度比双道焊接头更为显著,其主要原因是单道焊接头的一次性热输入大于双道焊,材料受热影响更严重,焊漏高度及形状的可控性更差.
关键词:
2219铝合金
,
氩弧焊
,
拉伸强度
,
延伸率
,
显微硬度
,
数字散斑测量
张续
,
齐乐华
,
舒扬
,
付前刚
,
李贺军
新型炭材料
提出了碳碳键的断裂准则,建立了含空位缺陷碳纳米管的有限元模型,基于此断裂准则采用有限元方法对单壁碳纳米管的断裂行为进行了模拟研究,计算得到了碳纳米管的抗拉强度和极限应变,并研究了单原子空位缺陷对碳纳米管抗拉强度和极限应变的影响。结果表明理想单壁碳纳米管的抗拉强度约为100 GPa,极限应变约为20%。单原子空位缺陷显著降低了碳纳米管的抗拉强度和极限应变,使抗拉强度降低了20%~30%,极限应变降低了12%~18%,这也正是碳纳米管极限强度的实验结果远低于理论预测结果的原因。
关键词:
单壁碳纳米管
,
空位缺陷
,
有限元法
,
抗拉强度
,
极限应变
Nanlin SHI
,
Jiwei FENG
,
Yanfen GUO
,
Yuyin LIU
,
Z.X.Guo
材料科学技术（英）
Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.
关键词:
SiC fiber
,
null
,
null
,
null
,
null
Seok-Hwan Ahn
,
Insup Lee
材料科学技术（英）
Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established plasma nitriding method. No compound layer was formed during this process except the experiment carried out at 500℃ for 10 h. The main phase produced in the diffusion zone was identified to be γ′-Fe4(N, C). A diffusion depth increased with increasing treatment temperature and time (up to about 250 μm). The surface hardness of radical nitrided layer was about two times higher than that of the untreated surface. The tensile test was carried out to estimate the mechanical properties of surface-hardened SCM440 steel prepared at various plasma radical nitriding treatment time and temperature. The influence of radical nitriding treatment on the tensile strength of the specimen was found to be insignificant. The highest value of the ultimate tensile strength was obtained in the experiment carried out at 500℃ for 1 h. However, the elongation was greatly affected by the radical nitriding processing parameters. The maximum value of elongation, which is equal to about 18.1%, was also obtained under the condition of 500℃ for 1 h.
关键词:
Plasma radical nitriding
,
null
,
null
,
null
Jieshan HOU
,
Jianting GUO
,
Lanzhang ZHOU
材料科学技术（英）
Derived from Russian alloy CHS88U, six experimental Ni-base alloys named as A to F in the Ni-Cr-Co-W-Ti-Al-Hf system are designed, evaluated and processed. One of these alloys, F, shows excellent high temperature tensile strength and ductility with superior creep rupture properties. As predicted by using modeling tools such as PHACOM and NEW PHACOMP, there is hardly the tendency for formation of topologically close-packed phase (TCP) phase in alloy F. Furthermore, through microstructural observation, it is also found that no TCP phase is formed in alloy F after long-time exposure at high temperature. So alloy F has well balance of phase stability and mechanical properties in view of application for gas turbines. It is proved that d-electron approach can be applied for design and development of nickel-base superalloys for gas turbine application.
关键词:
Conventional Ni-base superalloy
,
null
,
null
,
null
Yujin WANG
,
Yu ZHOU
,
Guiming SONG
,
Tingquan LEI
材料科学技术（英）
In order to improve the high temperature strength of tungsten, 30~vol. pct ZrC particles were added to the tungsten matrix to form a 30ZrCp/W composite. The tensile properties from 20℃ to 1880℃ of the composite were examined. It was shown that with increasing testing temperature, the nonlinearity of the stress strain curve of 30ZrCp/W composite becames obvious over 1200℃ and the Young’s modulus decreases and the elongation increases. The ultimate tensile strength increases at first and then decreases with increasing testing temperature. The maximum strength of 431 MPa was obtained at 1000℃. The strengthening mechanism at high temperatures is the load transfer to ZrC particles and dislocation strengthening of the tungsten matrix with an effect of grain boundary strengthening.
关键词:
ZrCp/W composite
,
null
,
null
,
null
A.A.El-Daly
材料科学技术（英）
It is important, for electronic application, to decrease the melting point of Sn-5Sb solder alloy because it is relatively high as compared with the most popular eutectic Pb-Sn solder alloy. Adding Au or Ag can decrease the onset melting temperature (233℃) of this alloy to 203.5℃ and 216℃, respectively. The results indicate that the Sn-5Sb-1.5Au alloy has very good ultimate tensile strength (UTS), ductility, and fusion heat, which are better than both those of the Sn-5Sb-3.5Ag and Sn-5Sb alloys. The formation of intermetallic compounds (IMCs) AuSn4 and Ag3Sn enhanced the microstructure stability, while retained the formation of SbSn precipitates in the solidification microstructure, thus significantly improved the strength and ductility. For all alloys, both UTS and yield stress (σy) increase with increasing strain rate and decrease with increasing temperature in tensile tests, but changes of ductility are generally small with inconsistent trends.
关键词:
Sn-Sb solder
,
null
,
null
,
null
Xudong ZHANG
,
Wuzhu CHEN
,
Gang BAO
,
Lin ZHAO
材料科学技术（英）
This paper describes a way to improve the weld quality through suppressing the porosity formation and restraining the growth of columnar grains by using a weaving beam in laser welding. The experimental results show that the N2 porosity of beam-weaving laser welding low carbon steel can be remarkably reduced with increasing weaving frequency, and porosity can be eliminated when the weaving amplitude is only 0.5 mm; and the Ar porosity in the weld metal is decreased with increasing weaving frequency and amplitude when the welding speed is higher than 0.5 m/min. The beam-weaving laser welding of ultra-fine grained steel has been investigated. The experimental results show that beam-weaving laser welding with appropriate amplitude and frequency can partly restrain the growth of the columnar grain and improve the tensile strength of the weld metal.
关键词:
Welding
,
null
,
null
,
null
