热工艺对激光选区熔化Hastelloy X合金组织及拉伸性能的影响

采用激光选区熔化技术制备Hastelloy X试样,研究热等静压和固溶处理对Hastelloy X试样显微组织及拉伸性能的影响。结果表明:沉积态组织中可观察到熔池形貌、柱状晶及晶内的胞晶结构,无析出物,其拉伸性能表现出高强度低塑性特点,高温拉伸断口沿激光扫描熔化道断裂。经热等静压后,组织演变为等轴晶,晶界及晶内存在较多的析出物,裂纹愈合,试样拉伸强度降低,塑性提升,尤其是高温屈服强度降低了约48%,高温伸长率提升了约59%。经热等静压+固溶处理后,晶粒尺寸及形貌与热等静压态相比近乎无差异,但晶内析出物明显减少,该状态下的综合拉伸性能最优。     

Effects of temperature and strain range on fatigue cracking behavior in Hastelloy X

The low cycle fatigue tests of Ni-base superalloy Hastelloy X have been carried out in the temperature range of 650 - 870 °C with various total strain ranges. A change of slope in the Coffin-Manson (C-M) plot was found at 870 °C: the fatigue life significantly decreased at the total strain range less than 0.6%. The fatigue cracks initiated at the surface of the specimens and propagated transgranularly, regardless of test condition. However, the fatigue crack initiation site on the surface shifted from grain interior to grain boundary (GB) predominantly when the discontinuity of slope in the C-M plot began to occur. The fatigue crack tended to initiate preferentially at the oxidized GB rather than grain interior at 870 °C with total strain range below 0.6%. Under this condition, cyclic stability was pronounced, while cyclic hardening occurred at the rest of test conditions. The dislocation structures responsible for the cyclic stress response may partly account for the determination of major fatigue crack initiation site.     

Sensitivities of measurement methods for the thermal radiative properties and optical constants of metals in the spectral range 0.4 to 10 μm

The sensitivities to measurement errors and potential effectiveness of six methods (involving reflection, emission, and ellipsometry) for determining the optical constants (index of refraction n and extinction coefficient k) of isotropic conductors are compared. The methods treated are generally regarded as most promising for use with high-temperature solid and liquid metals with smooth surfaces of high purity. For each method, contours of constant measured variable are plotted vs n and k. By analysis of the spacing and angle of intersection of these contours, we show that only methods based on measuring both amplitude attenuation and phase shift on reflection can yield n and k, and thus the spectral and directional emissivity, reflectivity, and absorptivity, with reasonable precision over the spectral range 0.4 to 10 μm. Methods based only on amplitude attenuation on reflection, or on the angular dependence of emission, are poorly suited to ranges of n and k that are typical of the infrared. The method of Beattie and Conn retains the ability to determine both optical constants to 10 μm.     

Study on the microstructure and dielectric properties of X9R ceramics based on BaTiO3

This paper investigated the microstructure and dielectric properties of BaTiO₃-Pb(Sn, Ti)O₃ system ceramics. The Curie point of BaTiO₃ is 130 °C. When the temperature is higher than 130 °C, the dielectric constant of BaTiO₃ drops severely according to Curie-Weiss law. Pb(Ti, Sn)O₃(PTS) was selected to compensate the dielectric constant doping of BaTiO₃ since it has high Curie temperature (Tc) point that is about 296 °C. The Curie temperature (Tc) point of BaTiO₃ was broadened and shifted to higher temperature because of the doping of PTS, so the temperature coefficient of capacitance (TCC) curves of the ceramics based on BaTiO₃ was flattened. When 2 wt% Pb(Ti_0.55Sn_0.45)O₃ was added, the sample showed super dielectric properties that the dielectric constant was >1750 at 25 °C, dielectric loss was lower than 2.0% and TCC was <±10% from −55 °C to 200 °C. Therefore the materials satisfied EIA X9R specifications.