A technique for determining ac impedance by Laplace transformation was proposed.In this technique,a linear function was suggested as an approxi- mation of transient curve in each sampling interval.Formulas for numerical integration in time domain were derived,and the accuracy of approximate expression of linear function was verified using various equivalent circuits.A computing programme with BASIC language was worked out.

The effect of quenching from intercritical temperature in(α+γ)region on hydrogen-induced cracking of a high strength steel 30CrMnSiA was studied. The results showed that an additional intereritical quenching from 860℃,per- formed between the oil quenching from 900℃ and tempering at 250℃,markedly improved the hydrogen embrittlement resistance of this steel.The minimum stress to hydrogen-induced cracking was increased by several times in steels with tempered martensltebut there was no effect on steel with sorbitic struc- ture having hardness below HRc36.The crack propagation rate of the steels with tempered martensite also decreased due to the intercritical quenching. The microanalyses of fractures with IMA and XPS showed that the segregation of impurities and the elements producing brittle failure at austenite grain boundaries was attenuated to a certain extent by this quenching.It would be bene- ficial for the superior hydrogen embrittlement resistance of the steel.In addition,the presence of minor ferrite and austenite grains refined could could also be helpful.

A new method for the determination of potential and pH value within the SCC cracks has been proposed.The simple device can be conveniently used to measure and follow the electrochemical behavior within the SCC cracks or any corrosion crevices with high accuracy. In this paper,both the results of the measurements within SCC cracks as well as crack tips of LC-4 aluminum alloy and a discussion with these data in relation to the potential-pH diagram of aluminum alloy were presented. The authors proposed an equivalent circuit model constructed by the couple of numerous corrosion microcells in accordance with the results of measure- ment to explain the data from our experiments.For aluminum alloy LC-4,the relationship between the pH and the crack tip potential will be: =-0.750-0.043 pH(SCE) In the Pourbaix diagram,the position of the corrosion system will extend through the region of passivity in response to the sensitivity of SCC of the alloy.

The micro-morphology of the initiation zone of SCC of Ti-5A1-2.5Sn alloy in 3.5% NaCl solution has been inspected by OM and SEM.A study of the SCC crack's details by OM,TEM,X-ray diffractometer and ion microanaly- zer has also been made.Based upon the results of these experiments,it is pro- ved that the hydrogen generated during SCC has really penetrated into the metal matrix,then concentrated at the maximum of triaxial stress in front of the crack tip,and precipitated as hydride particles of fct and bee lattice, resulting in rapid development of SCC.The source,transportation and acting position of hydrogen,as well as the role of internal hydrogen in SCC of tita- nium alloy have been discussed.

The Equation of Nucleation first worked out by Erdey-Gruz and Volmer, which has been widely accepted as a fundamental equation to describe the ki- netics of eleetroplated crystal grain formation,is N=a·exp[-b·η_k~(-2)] where N is the number of nuclei formed per unit time and η_k the total overpoten- tial. As a result of more general consideration,it is shown in this paper that the electrode overpotential can also be related to the free energy of the elec- trode/solution interface by the electrocapillary equation of Lippman.Then a more generalized equation of electro-crystallization can be proposed. When the exchange current density is large and surface diffusion is the rate determining step,i.e.,when η_k=η_(crystal),this generalized equation can be simplified to the E-G-V equation;and when the cathode has a very large activation overpotential,i.e.,η_kη_(crystal),this equation will be N=a·exp{-b'{σ_0-[(_(eq)-η_k)~3-_0~2]}~3} where _0 is the zero potential and σ_0 the free energy of the interface at zero potential;_(eq) is the equilibrium potential and b' is a constant. The authors tend to feel that generalized equation in this paper can des- ceibe the kinetics of nucleation in electrocrystallization more exactly,and can provide means of detecting any effects caused by addition agents etc.of the plating solution and so it can be used to develop means for laboratory research and plating shop controlling and monitoring.

The formation of passive film on 1Cr18Ni9Ti steel surface was studied with an ellipsometer.Some features of ellipsometer parameters(△,Ψ)of this very thin passive film(absorbing film)were studied in detail. Analytical results showed that the thickness of the passive film was about 50 and that film growth conformed to logarithmic relation.It was also found that the structure of the passive film changed with increased thickness. In fact,this film assumes a multi-film structure whose optical properties ch- ange gradually along the direction of stratification,

The corrosion fatigue of some low alloy steels in NaCl aqueous solution was experimentally investigated.The corrosion fatigue properties of the steels at room temperature were studied.Then the influence of temperature on CF crack growth rate for 18Nb steel was studied with the activation energy of CF crack propagation calculated to be 7.4-7.9 kcal/mol.It is thought that the depolarizing reaction of oxygen is probably the principal controlling fac- tor for the propagation of CF crack.

The effect of additions of 0.1%Y and 0.5%Y to M38' alloy on the oxidation behavior and mechanism was studied on samples exposed in air at 1000℃ for 100hrs.The results obtained indicated that the oxidation rate of the alloy with 0.1%Y was lower than that of the alloy without Y,while further increase of Y content to 0.5% increased the oxidation rate only slightly. However,the oxidation rates of all these three alloys obeyed a parabolic rate law.The oxidation rate of alloy without Y increased rapidly after exposure of 70hrs. The observed results from optical micrographs showed there was internal oxidation zone in the alloy without addition of yttrium,oxidized at 1000℃ for 100hrs,but internal oxidation did not appear in alloys with addition of yttrium.