X.K. Sun

Hydrogen permeation behavior in metastable austenitic stainless steels 321 and 304

Abstract The hydrogen permeation behavior in metastable austenitic stainless steels 321 and 304 were investigated by an ultrahigh vacuum gaseous permeation technique at the temperature range 100–400°C. The hydrogen permeation parameters of these steels in annealed condition are consistent with stable austenitic stainless steels, but after cold deformation, the permeation and diffusion activation energies decrease exponentially with increasing α′ content, the permeability and diffusivity increase exponentially with α′ content. Some quantitative expressions among hydrogen permeation parameters, α′ content and temperature were obtained. The hydrogen permeation models in metastable austenitic stainless steels were discussed.

HYDROGEN PERMEATION BEHAVIOR IN IN718 AND GH761 SUPERALLOYS

In the present work, two nickel-iron-chromium-base superalloys, INCONEL718 and GH761, were heat-treated to obtain different microstructures in the alloys. The hydrogen permeability and diffusivity for the two alloys in various conditions were determined using a gaseous-hydrogen permeation technique to examine the influence of microstructures on hydrogen permeation behavior. Measurements were made over the temperature range of 210 °C to 430 °C. It was shown that the dependencies on temperature for hydrogen permeability and diffusivity for the two alloys obeyed the Arrhenius relationship over the test temperature range and that the precipitated strengthening phases hardly affected the hydrogen permeation and diffusion behavior for the INCONEL718 alloy, but the hydrogen permeability and diffusivity in the aged condition were all slightly lower than those in the solution-treated (ST) condition for the GH761 alloy.

Hydrogen permeation and diffusion in iron-base superalloys

Abstract In this work, the hydrogen permeation and diffusion in three iron-base superalloys, JBK-75, Incoloy903 and GH35A, were investigated. A gaseous permeation technique was employed to measure the hydrogen permeabilities and diffusivities of specimens with different, heat treatments for a given alloy over the temperature range of 210–430°C. The effects of strengthening phase γ′ on the hydrogen permeation and diffusion in the alloys were examined. The results showed that the dependences of the hydrogen permeabilities and diffusivities in various alloys on the temperature obeyed Arrhenius relationship over the test temperature range and that the hydrogen permeation behavior in these alloys was essentially independent of their heat-treated conditions, i.e. which was not significantly affected by γt precipitates in the alloys. The hydrogen permeation parameters of the iron-base superalloys were approximately consistent with those of the austenitic stainless steels. The hydrogen transport in these alloys with f.c.c. structure was generally controlled only by the lattice diffusion of hydrogen.

Hydrogen permeation and diffusion in a 0.2C-13Cr martensitic stainless steel

The phenomenon of hydrogen embrittlement for engineering alloys, especially for alloy steels, has long attracted the attention of material researchers. Presently, it is thought that the occurrence of the phenomenon correlates with the processes of hydrogen entry and transport in metals. Therefore, a great effort has been made to understand the hydrogen permeation and diffusion in metals and alloys. Even so, the knowledge of the hydrogen permeation and diffusion in steels with a martensitic structure is still limited. In most of the investigations performed on martensite, the electrochemical permeation technique was employed for measurement; hence, only limited data near ambient temperature have been determined. A few results obtained at higher temperature are very scattered also. For instance, the hydrogen diffusivity of AISI 4130 steel in the quenched and tempered (martensite) condition is 2 orders of magnitude higher than of cryoformed 301 stainless steel (containing 90% of [alpha][prime] martensite). In the present work, the hydrogen permeability and diffusivity of a 0.2C-13Cr martensitic stainless steel (2Cr13), roughly corresponding to AISI 420, was determined by means of the gaseous permeation technique. Measurements were made above ambient temperature.

Preparation of Al nanoparticles in a controlled environment

Abstract In the present work we have studied the preparation of Al nanoparticles by the inert gas evaporation method, with the emphasis on control of the environment. We conclude that vacuum, gas purity, and leak and outgassing rates all exert an important influence on the preparation of clean nanoparticles, and that these three factors must be controlled within a definite range in order to make nanomaterials with clear crystal habits and clean interfaces. Two criteria for matching the three factors are given in the present work.

The formation of TiFe nanoparticles by gas condensation method

Ti-Fe nanoparticles were synthesized from TixFe100-x (x=50 similar to 85) alloys in an atmosphere of helium or hydrogen by gas condensation method. XRD and TEM were employed to analyze the particle size and structure. A FCC phase was observed which is a special martensite formed only in small sized particles(<20nm). It is found that the particles are all with FCC single phase when the helium gas pressure is 0.2 kPa or below, and with increasing the gas pressure multiple-phase particles are formed. Nanoparticles formed in hydrogen are similar to those formed in helium, but the difference between the evaporation rate of Fe and Ti is more remarkable due to hydrogen reaction

HYDROGEN PERMEATION CHARACTERISTICS OF INCOLOY907 ALLOY

The problem of brittle fracture induced by hydrogen ingress from environment must be considered for some high-strength alloys, particularly for the superalloys strengthened by [gamma][prime] precipitation, used in fields such as aerospace and nuclear power. Therefore, a number of studies on hydrogen performance of superalloys have been recently carried out. The understanding of hydrogen transport characteristics in these alloys is important to clarify the hydrogen embrittlement mechanism. Although hydrogen permeabilities and diffusivities of some superalloys have been reported, the study of the hydrogen permeation and diffusion in Incoloy 907 alloy, a type of Fe-Ni-Co based superalloy, is still absent to date. In the present work, a gaseous permeation technique was employed to measure hydrogen permeability and diffusivity in this alloy, in order to understand the relationship between hydrogen permeation and microstructure.

A nanocomposite of Al95In5 synthesized by ball milling

The microstructural evolution of Al95In5 powder mixture during ball milling is investigated using XRD, TEM, SEM EDX etc. It is shown that a nanocomposite of Al95In5 is formed after milling for 300 h. In the final milled product, the refined fn particles are embedded dispersively in the Al matrix and the grain sizes of Al and In reach 20 nm and 18 nm, respectively. Due to the partial fusion of the In component during milling, the conventional layered microstructure is not formed in the milled powders. The addition of In has a hindering effect on the grain refinement of the Al component. As tin impurity, Fe is dissolved in the Al matrix during milling, with a content of 0.87 at.% Fe after milling for 300 h, which results in a reduction of the lattice parameter of Al.

Stability in air of ultrafine particles of chromium

Abstract In this work, the structure, morphology and oxidation behavior in air of ultrafine Cr particles prepared by the gas evaporation method are investigated, using TEM, HREM, XRD and TG. The ultrafine Cr particles are easily oxidized when directly exposed to air or even when combustion occurs. After a protective treatment, a thin oxide film is formed on the surfaces of the particles, which makes them stable in the air. The growth morphologies of the Cr particles depend on the size and intrinsic structure. The starting temperature of pronounced oxidation for ultrafine particles is much lower than that for coarse particles.

SURFACE-STATE ANALYSIS OF FE50PD50 ALLOY ULTRAFINE PARTICLES

The surface state of Fe50Pd50 alloy ultrafine particles (UFP) has been investigated by AES and XPS. The results show that the surface of Fe50Pd50 alloy UFP was oxidized. There are two kinds of oxidized Fe existing on the surface of Fe50Pd50 alloy UFP. But the element Pd in the alloy UFP was not oxidized and stabilized the UFP. The surface of the alloy UFP is a bilayered structure.