铝合金的低温机械性能评估

基于多方面的数据资料,分析阐述了铝合金低温下机械性能的变化规律:随着温度的降低,铝合金屈服强度和抗拉强度有所增加,塑性和韧性有所提高,疲劳特性得到改善.评估了LD5铝合金低温下的机械性能,以及发生冷脆现象的可能性.研究表明:当LD5铝合金用于77 K以上低温环境时,若构件最大应力小于LD5室温下的屈服强度,则构件的低温机械性能可以得到保证.     

适用于低温环境的聚氨酯防水粘结材料研究进展

我国北方地区冬季的最低温度可达-40℃以下,传统防水材料存在低温性能较差,易开裂且无法低温施工,聚氨酯防水材料具有高耐候性、固化后可形成完整涂膜防水层,提高了工程抗渗防水能力.主要概述了聚氨酯材料化学反应机理的影响因素、分子结构与性能的关系,可低温使用的聚氨酯防水粘结材料微观和宏观试验方法及结论、施工及适用情况,通过对...     

Description of pressure cells suitable for low temperature specific heat and magnetization measurements

We describe two types of BeCu pressure clamps cells. The maximum pressure obtained is 12kbar for homogeneous clamps. It increases to 20kbar if maraging piston and plug are introduced. Frictional loss is evaluated and low temperature pressure measurements are presented. Specific heat and magnetization data of the clamps are also reported.     

Behaviour of Al-Mg alloys at high temperature

The behaviour of a few Al-Mg alloys (up to 7.1 wt% Mg) has been studied on heating in air at 500°C for 8 h or more. The precipitation of a spinel phase, MgAl₂O₄, is found to take place on the surface and along the transverse section (depth) of the specimen. The alloys seem to be resistant to internal oxidation below 4.5% Mg and thereafter prone to it. Beryllium modification does not suppress the progress of internal oxidation taking place in the Al-Mg alloys. The results have been interpreted on the basis of anodized photomicrographs and X-ray diffraction data.     

Back diode amplifiers for use at low temperature

The design of two amplifiers using negative resistance diodes is discussed. Measurements of the diode characteristics, voltage and power gain, and frequency response at $\text{? 1 K}$ are presented.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

Ultrasonic fatigue of nickel-chromium alloys at low temperatures

The influence of low temperature ultrasonic deformation on the electrical resistivity and magnetic properties of nickel-chromium dilute solid solutions is examined. It is shown that changes in the electrical resistivity and magnetic properties of prequenched samples after ultrasonic fatigue can be explained by order-disorder processes during fatigue. It is concluded that ordering at low temperatures during the ultrasonic deformation is associated with high strain rate and high vacancy concentration produced by deformation.     

Dental gold alloys with age-hardenability at intraoral temperature

Dental gold alloys with age-hardenability at intraoral temperature were developed. Either 3 or 6 at% Ga, Al, Zn, In, Ni or Pd were added to an equiatomic AuCu alloy and the effect of additives on the low-temperature age-hardenability was examined. Alloys containing Ga, Al or Zn exhibited excellent low-temperature age-hardenability. The hardness of an alloy containing 6 at% Ga or 6 at% Al was doubled in one to ten days by ageing at 37 °C. Pronounced hardening was not demonstrated in an as-cast alloy, but solution treatment for only a few minutes provided enough age-hardenability. The age-hardening rate at low temperature related closely with the melting temperature of the alloy. Experimental gold alloys exhibited electrochemical behaviour similar to that of a commercial Type IV gold alloy. It is therefore concluded that AuCu alloy with added Ga, Al or Zn is expected to have enough age-hardenability and corrosion resistance for clinical use in the oral environment.     

Endless recrystallization of high-entropy alloys at high temperature

In traditional physical metallurgy, once recrystallization occurs, it will proceed to 100% along with time even at relatively low temperatures, resulting in the limited thermal stability of partially recrystallized alloys. Here, we proposed the strategy of achieving the endless recrystallization state at high temperature(～0.6Tm) in high entropy alloys for the first time. The partially recrystallized microstructures remained stable after annealing at 700 °C for 1440 h toward endless recrystalliza...     

Fe-Cr合金钢高温性能研究

本文试验研制了四种Fe-Cr合金材料,其在900 ℃时的热膨胀率在10～11×10-3范围内,其中FeCr-4合金的热膨胀率为10.27×10-3,与钇稳定氧化锆(YSZ)相比,热膨胀率逐渐接近;与传统合金材料相比,热膨胀率之差均有了明显下降,因而降低了界面热应力,有效改善层间的热失配现象.随着温度的升高,各合金试样的电阻率呈平缓增大的趋势.在850℃时,四种合金试样的电阻率在0.95～1.17×10-3 Ω·cm范围内,其中Fe-Cr-4试样的电阻率较低,为1.17×10-3 Ω·cm,满足用作SOFC连接体材料导电性能的要求.Fe-Cr -1、4两种合金试样的抗氧化性能较好,随着氧化时间的延长,试样表面形成稳定的3Cr2 O3 Fe2 O3氧化层,氧化增重逐渐趋于稳定.累计氧化455 h后,Fe-Cr-1、4两种试样对应的氧化增重在0.0002 g/g左右;而Fe-Cr-2、3两种试样仍在0.0004 g/g以上.     

Physico-chemical characterisation of native air-formed oxide films on Al-Mg alloys at low temperature. Influence of water

Natural oxide films on two cold-rolled Al-Mg alloys were studied using several techniques (XPS, SIMS, ToF-SIMS, GDOS, SEM, TEM, Wetting measurements). The aim was to characterise and compare the oxide layers formed on the two materials in order to better understand the influence of the thermomechanical history. The experimental tools used allowed the determination of the influence of the annealing process on the nature and structure of the oxides. The hydration and Brönsted behaviour were also investigated. The thickness of the layer, the amount of magnesium oxide and its dissolving resistance in water are strongly modified by the annealing. The oxide film formed on the annealed material is twice as thick as the one on the non-reheated material. The layer on the annealed material contains more magnesium oxide and contains the crystalline forms:-Al₂O₃ and bayerite (Al(OH)₃). On the contrary, the oxide film formed on the as-rolled material seems to be amorphous. The magnesium oxide is less soluble in water in the annealed film than in the non-reheated one. Furthermore, aluminium and magnesium oxides were found to be hydroxylated on both alloys, and the layer surfaces to behave like a Brönsted meaning base.     

Elastic properties of two titanium alloys at low temperatures

Sound velocities and elastic constants were determined semi-continuously for two annealed polycrystalline titanium alloys between 4 and 300 K. Results are given for: longitudinal sound velocity, transverse sound velocity. Young's modulus, shear modulus, bulk modulus, Poisson's ratio, and elastic Debye temperature. A pulse-superposition technique was used.     

The lattice thermal conductivity of alloys at low temperatures

The scattering of phonons by solute atoms in concentrated, binary, substitutional alloys is re-examined, and the corresponding thermal resistivity at low temperatures is calculated for several alloys. Satisfactory agreement with experimentally determined values is obtained. It is shown that the solute atoms are relatively inefficient scattering centres in concentrated alloys compared with their behaviour in dilute alloys.     

Hypervelocity crater formation in aluminum alloys at low temperatures

The penetration and perforation of three kinds of aluminum alloys at room temperatures and low temperatures in the velocity range from about 0.5 to about 3.7 km/s were investigated experimentally. Main interests were focused on the depth and diameter of craters and their relations to the impact velocity. As a result, very distinctive features of the temperature effect on the shape and size of craters were found. Also, the effect of impact-induced phase transition of projectiles on the crater formation was examined about carbon steel, aluminum alloy and NaCl projectiles.     

Nqr experiments on Sc-Y alloys at very low temperatures

We have performed Nuclear Quadrupole Resonance (NQR) experiments on an alloy of scandium and yttrium. We find that the characteristic resonance frequencies in zero external field are 50 percent larger than in pure scandium. This increase in frequency makes the Sc-Y alloy a better candidate for absolute thermometry below 500 µK. However, the spin-lattice relaxation time of this alloy is more than an order of magnitude longer than in the pure scandium. In addition, we have observed an abrupt increase in the Korringa constant for temperatures below 5mK.