Phase composition of the barrier layer rusts of two alloy steels with different corrosion resistance in sea water was determined by conversion electron Mossbauer spectroscopy for the first time. It seems that, the barrier layer rusts of the two kinds of steel after exposure to air have similar composition. They consist of about 80% β-FeOOH and 20% γ-FeOOH. The problems raised by the above results such as the effect of alloy elements on corrosion process and the formation of the deposited layer rust are discussed. It is suggested that samples taken out from sea water are different from samples in sea water. In the barrier layer rust formed on samples taken out from sea water there remained final state phases (β-,γ-FeOOH)only. The intermediate state phases observed on samples in sea water are lost by oxidation, dehydration and age effect etc. after the samples are taken out from the sea.

Potentiostatic anodic polarization of low alloy steels in 3.5%NaCl solution can be used to imitate the electrochemical process of local micropits formed on these steels while corroding in sea water. The relative amount of the intermediate phase occuring in micropits may be increased by this accelerated test method. This micro intermediate product has been detected by the use of Mossbauer effect, so that we can determine the true composition of the barrier layer rust formed on low alloy steels in sea water, which could not be determined directly in sea water previously. Experimental results show that different low alloy steels possess different phase composition of the barrier layer rust. In addition to the final state phases, β-,γ-FeOOH, which were found in all the samples after corroding in sea water, there are also microcrystalline or amorphous intermediate, state iron rusts of different composition—similar to green Rust I, Fe_2(OH)_3Cl etc. These intermediate state rusts tend very easily to oxidize, dehydrate and age in the atmosphere. They will transform step by step to the final state phases such as FeOOH or Fe_3O_4 or both depending on conditions. While these intermediate phases were growing locally in the barrier layer rust, corrosion resistance of the alloy may be decreased. In Ni-or Cr-containing low alloy steels, the formation of some intermediate, phases in the early stage is inhibited, but the formation of other intermediate phases in the later stage can be promoted. Therefore, Ni-,Cr-containing low alloy steels show good corrosion resistance in the early stage, but bad corrosion resistance in the later stage. According to Mossbauer spectroscopy and corrosion electrochemistry,suggestions for developing and evaluating corrosion resistant low alloy steels in sea water are made.

The authors have investigated the effect of the addition of 0.1% and 0.8% Ce on isothermal oxidation of Ni—Cr—Cu for 100 hours at 1200℃in air, and on cyclic oxidation for 500 hours at 1200℃ in air. It is thought that a small amount of addition of cerium to the Ni—Cr—Cu alloys reduces the oxidation rate considerably in the later stage. The spalling resistance of the scale is also increased with the addition of cerium. The decrease of oxidation rate results from a combination of various effects, They are: (1) Cr rich protective scale is more rapidly formed because of faster diffusion of chromium; (2) cerium-containing oxide concentrating near scale/alloy interface complexes with vacancies, so that voids at scale/alloy interface are reduced; (3) cerium-containing oxide dissolved in the scale blocks the short-circuit diffusion of Cr~(3+) along oxide grain boundries. The main causes for the increase of spalling resistance with cerium addition are: (1)the grains of scale are refined by addition of cerium, thereby improving the ability of such scales to plastic deformation and to accommodation to thermal stress; (2) the keying effect of rare-earth oxide in the 0.8% Ce-containing alloy improves oxide adherence with substrate, and changes the distribution state of thermal stress.

The structures of the scales formed on low alloy SiMoVNbAl and Cr_5Mo steels have been investigated. It has been found that the addition of aluminum and chromium can greatly improve the scaling resistance of low alloyed steels in high-temperature conditions, The enrichment of alloying elements in the scale is one of the important reasons for the better resistance against hightemperature corrosion of these steels.

The oxidation of Fe-Cr-Al and similar alloys containing 0.51% Y was studied in air at 1200℃ up to 500hrs. The oxide scales were analysed using X-ray diffraction, scanning electron microscope, electron and ion probe microanalysis. It can be seen from the kinetics data obtained that the alloy containing Y has slightly higher oxidation rates at initial stage, but after some 20hrs the weight gain of the alloy drops drastically. It is interesting to find out that the crystals of α-Al_2O_3 scales formed on Fe-Cr-Al-Y alloy are columnar grains perpendicular to the alloy-oxide surface. The oxide film of the yttrium containing alloy can with·stand higher compressive stress than that of the yttrium free alloy. The addition of yttrium to the heat-resistant Fe-Cr-Al alloy may remarkably enchance the adhesion of the oxide scale formed at elevated temperatures. Yttrium added to the alloy is concentrated at grain boundaries and will preferentially react with oxygen diffusing into the alloy matrix. The formation of Y_2O_3 at grain boundaries will prevent internal oxidation of the alloy.

A preliminary approach to the effect of H-induced crack, as an environment-induced defect, on the processes of material failure has been made. Experimental results show that, as a primary approximate, the H-induced crack may be considered as a set of face defects paralleling to the rolled plane, and it has only a little effect on the routine strength indices, but enhances the susceptibility to brittle fracture of materials. HIC and HSC are two kinds of cracking basically independent of each other. The decisive factor in the environmental fracture is the susceptibility to HSC of materials. The environmental fracture process for materials having both HSC and HIC susceptibility may be expressed by the schematic model diagram as suggested in this paper. This diagram can explain a series of experimental phenomena observed during the environmental fracture of structural steels with middle and low strength. In general, the equipment or structures made of HSC resistant materials may operate safely though they may have induced cracks.

Equations of ellipsometry were mathematically treated. A BASIC program for use with microcomputer for computing ellipsometric theoretical curves of adsorption film on solid state, with various angles of incidence of polarised light and various media, was worked out. The program is given together with some computing results.

A study has been made of the effects of twenty metal additions in small amount on the corrosion resistance in 3% NaCl solution of Al-Zn euteetic fillets on pure aluminum as well as on LY12 (2024) base metals as determined by weight loss and by metallographic technique. It is shown that corrosion resistance effectively increses with the addition of small amounts of alkaline earth and rare earth elements, such as Be, Mg, Sr and La. The addition of heavy metals, such as Bi, Sn, Pb, Cd, Tl, Cu, Ni and Ga causes serious intercrystalline corrosion in the fillets. Less effective are the additions of transition metals and alkali metals.