Impure Helium Research Articles

Creep Rupture Strengths of Several Nickel-base Superalloys in Impure Helium

Creep Rupture Strengths of Several Nickel-base Superalloys in Impure Helium

Cracking of Zr-2.5 wt% Nb alloy tensile specimens by stray contamination

It is shown that stressed specimens of Zr-2.5 wt% Nb alloy can suffer brittle failure as a result of stress corrosion cracking (SCC) caused by contamination with human perspiration. The SCC is analogous to that previously observed for Zircaloy-2 contaminated with traces of a eutectic mixture of sodium and potassium nitrate and chloride. The chlorides are a primary component of perspiration and the nitrate probably comes from oxidation of organic nitrogenous compounds in perspiration. The contamination is more potent when tests are carried out in impure helium than when carried out in air, presumably through the effect of the atmosphere on the state of the organic component of the contamination.

数種のニッケル基超耐熱合金の不純ヘリウム中クリープ破断強度

数種のニッケル基超耐熱合金の不純ヘリウム中クリープ破断強度

Ni-Cr-W-C系合金の不純Heガス中における高温腐食挙動

Influence of the minor alloy constituents such as Al, Mn and Si on the hot corrosion behavior of Ni-20Cr-20W-0.07C alloy was studied in 99.995% helium gas at 1 000°C, comparing with that behavior of commercial Ni-base superalloys (Hastelloy X and Inconel 617).The low oxidizing potential in the impure helium gas usually causes selective oxidation of these elements and the growth of oxide whiskers on the surface of specimen at elevated temperature.The intergranular attack was caused by selective oxidation of Al, Si and Mn. The spalling of oxide film was restrained by addition of Mn and Si, providing tough spinel type oxide film on the surface and ‘Keyes’ on the oxide-matrix interface respectively.The amount and the morphology of the oxide whiskers depended on Si and Mn content. More than 0.29% of Si content without Mn always caused the growth of rather thinner whiskers with smooth surface, and the whiskers analyzed by electron diffraction patterns and EPMA to be Cr2O3 containing Si. Mn addition changed the whiskers to thicker ones of spinel type oxide (MnCr2O1) with rough surface.On the basis of these results, the optimum content of Al, Mn and Si to minimize the growth of whiskers, the intergranular attack and the spalling of oxide film was discussed.

超合金の不純物を含むヘリウム中での酸化について

超合金の不純物を含むヘリウム中での酸化について

Environment-Dependence of the Mechanical Properties of Metals at High Temperature

Premature failure of engineering components can result from the combined influences of corrosion and residual or applied stresses to produce the effects found in corrosion fatigue and stress corrosion cracking.l,2 In choosing alloys for operation in the creep range it has usually been assumed that their strength and corrosion resistance are separately acceptable. However, there is now a growing awareness that chemical and mechanical effects at elevated temperatures will interact; this review summarizes experimental studies under externally applied stresses at temperatures above about 0.4 of the absolute melting point. We shall not be concerned with details of stresses and strains at oxide/metal interfaces since these have been reviewed elsewhere.3, 4 Early work on environmentdependent deformation has been reviewed5 and a conference on environment-sensitive mechanical properties, mostly dealing with effects at ambient temperature, was held in. 1965.6 Board 7 has discussed surface chemistry, creep, and fatigue in impure helium environments.

Collisional Processes and Similarity in High-Frequency Discharges in Helium

The validity of the similarity theorem for high-frequency discharges in helium is examined experimentally in non-uniform fields over a range of frequencies f from 5 to 70 Mc/s and gas pressure p from 1 to 30 mm Hg. The theorem is satisfied for similar discharge systems in pure helium but not when traces of impurity are present. The theorem is shown to be sensitive not only to changes in the parameters pa and f/p, where a is a linear dimension of the discharge tube, but also to changes in the purity of the gas when the impurity can introduce collisional processes which are not dependent on X/p. The failure of the theorem for impure helium for similar discharge systems is accounted for by the occurrence of collisions of the second kind between metastable atoms of helium and molecules of impurity.

LXXXII. The production of radiation and ionization by electron bombardment in pure and in impure helium

LXXXII. <i>The production of radiation and ionization by electron bombardment in pure and in impure helium</i>