Proper addition of 0.002wt-% Mg to cast Fe_3Al alloy may obviously improvethe room and high temperature tensile properties. Auger spectra show that Mg segregatesnear grain boundaries as very thin layer. Observation under TEM reveals that a suitableamount of Mg enhances the ability of cooperative internal deformation so that the disloca-tions will ease the continuous slip deformation through grain boundaries. The fracture featureof Fe_3Al alloy is of transgranular cleavage at room temperature and cracks initiate at grainboundaries.

The positron annihilation technique was adopted to study the precipitationprocess in the Fe-V-N alloy. The characteristics of the clustering process of V-N, thebehaviour of V-N-vacancy complex and its influence on the precipitation process are dis-cussed. Over 200℃, quenched V-N-vacancy complex begins to migrate and accelerates theprecipitation. Two stages of precipitation process may be: clustering below 840℃ and growthof flakes over 840℃.

Observation under high resolution electron microscope shows that the contin-uous bombing of high speed ions produces a great amount of vacant site defects. The assem-bly of vacancies forms vacant dish, and the collapase of vacant dish forms stacking faulttetrahedrons and other crystal defects. The interfaces between phase ε(Fe_(2-3)N) and phaseγ′(Fe_4N) are smooth, straight and coherent, and they have the orientation relationships of(111)//(0001) and [110]/[1120].

The hydrogen content in the molten heavy rail steel is always very low duringmelting by LD process and a slightly increases in tapping and pouring at Panzhihua Iron andSteel Co. The average H_2 content varies from 2.0 (dry season) to 2.4 ppm (rainy season) atsmelting end, 2.8 ppm in ladle and 2.1 (dry season) to 2.3 ppm (rainy season) in ingot mould,which is corresponding to that of the molten steel with RH vacuum process. The low H_2 con-tent in molten steel is the main reason for no flake in heavy rail steel owing to melting by LDprocess and dry climate at Panzhihua region.

The fine second phase particles, average size about 86 nm, precipitating inferrite matrix of low carbon low vanadium steel will hinder the movement of dislocations infront of crack-tip, retard the thinning process in local area, and then proceed to impede theinitiation and propagation of micro-cracks. The propagating path of micro-cracks is control-led partly by the distribution of precipitates, a single particle has the action aforementionedweakly.

Effect of nitrogen on matrix structure of 3 different varieties of gray cast iron.i.e., sub-eutectic Fe-C-Si, and near-eutectic Fe-C-Si and Fe-C-Si-Mn, has been investi-gated. The eutectic colony structure of gray cast iron may be refined, the pearlite content in-creased and the microhardness of pearlite and ferrite raised with an addition of nitrogen. Theinfluence of nitrogen on the transformation temperature of the equilibrium and non-equilib-rium phases, as well as, the solution of nitrogen in ferrite and cementite seem to be the majorreasons to strengthening the matrix structure of gray cast iron.

Based on theoretical analysis about local strain, strain rate and dissolving rateat crack tip, the corrosion fatigue crack growth rate of steels ZG20SiMn and SM50B-Zc infresh water and 3.5%NaCl respectively were measured experimentally, and the pH and elec-trode potential within crack were also measured continously along with crack propagating.The hydrogen concentration of materials in the crack tip region were measured. It showedthat the increase of corrosion fatigue crack growth rate, caused by both the decreasing fre-quency and the raising stress ratio, was mainly accelerated by hydrogen embrittlement.

A decomposed triphase mixture NdH_2, α-Fe and Fe_2B, sized about 0.1μm,occurred in the matrix Nd_2Fe_(14)B of ingot after hydriding and the Nd_2Fe_(14)B phase of about 0.3.μm re-associated as dehydriding. The Nd-rich boundary phase, distributed around the ma-trix, in the ingot may diffuse into Nd_2Fe_(14)B matrix during hydriding. It shall remain asdehydriding and distributes homogeneously around some colonies composed of fine grains ofNd_2Fe_(14)B.

The Bi_2(Sr, Ca)_3Cu_2O_x system superconductor was prepared by different melt-ing procedures and after treatment. The effects of cooling rate, annealing temperature andtime, as well as melting procedures on phase transformation were investigated. The structureand properties were examined by X-ray diffraction, optical microscopy, EPMA, DTA, TGAand measurements of electric and magnetic properties. When the melt of nominal composition Bi_2(Sr, Ca)_3Cu_2O_x solidified in air, the Bi_2(Sr, Ca)_3Cu_2O_(8+δ)(2212) superconductive phaseis stable, the easily solidified product including Bi_2(Sr, Ca)_2CuO_(6+δ)(2201) phase is metas-table, and another may by amorphous if rapidly quenched. The last two may be transformedinto 2212 phase by after treatment with an optimal annealing temperature ranging 780-870℃. While 2201 phase, prepared by the laser floating zone melting method, may easily betransformed into 2212 phase with layer or filament in shape which is favourable to improvethe links among superconductive grains and critic current density.

For slag system of CaO-SiO_2-Al_2O_3-MgO-V_2O_5, time of V reduction toapproach the dynamical equilibrium is about 6 h. The equilibrium time is not evidently influ-enced by the ratio CaO/SiO_2, and shortens with the increase of temperature. If the ratio be-tween slag and iron-bath is 1/2, CaO/SiO_2 0.8 and temperature 1773 K, the maximum dis-tribution coefficient of V reduction is 32.4 and maximum recoverv of V is 96.1%.

The interfacial chemistry, synergistic effects and interfacial kinetics of thesynergistic extraction system D_2EHPA-MPA-Fe~(3+) have been studied, where MPA is amono-alkyl phosphate extraction with long carbon chain. D_2EHPA in the mixed extractionsystem strongly exhibits the effect on the thermodynamics of micella formation and interfaceproperties of MPA. Some thermodynamic parameters of micella formation were obtained.The interfacial adsorption behaviour of D_2EHPA is opposite to that of MPA. Theemulsification for single MPA and the mixed system was discussed. The synergistic effectswere found in this mixed extraction system. It is proved that the process of Fe~(3+) extractionfor non-mixed extraction system is controlled by chemical reaction, the controlling reactionoccurs at the interface, and the reaction rate equation is obtained.

Melted cast iron was inoculated by FeSi and then quenched to interrupt thedissolution. The non-metallic inclusions. in which the graphite coating was already occurred.formed in the dissolution region. They dissolved into the melt soon. but the inclusions coatedby graphite could exist for a longer time. The function of inoculant is to create an undercool-ing solution for carbon. thereby the non-metallic inclusions in the solution may be activatedas a nuclei for graphite.

Stainless steel AISI 321 in 0.5 mol / L HCl+0.5mol / L NaCl solution at 55℃is confirmed under the active anodic dissolution state. SCC of the steel in the solution can notbe reasonably explatined by the passive film rupture-repassivation theory and by thehydrogen embrittlement theory. It is believed that the fracture stress at the tip of cracks is re-duced by anodic dissolution due to its role in relieving strain hardening layer at crack tip.

Plots of corrosive wear loss vs load and anodic polarization curves duringwearing were examined for duplex stainless steel in 69% H_3PO_4 solution with or withoutCl~- by a pin-on-disc apparatus. Morphologies of tracks and debris as well as variation ofVicker hardness of worn surface were also tested. The Cl~- may impel the embrittlement andtearing of the worn surface, so as to accelerate the corrosive wear loss of the steel.

Effect of pre-creep on stress corrosion cracking (SCC) of austenitic stainlesssteel in the film-forming solution (42% MgCl_2 ) and non-film-forming solution (0.5mol/LHCl+0.5mol / L NaCl), and brass in NH_4OH solution was investigated by using constantload and constant deflection specimens. No matter whether austenitic stainless steel or brass.pre-creep had no effect on failure time and threshold stress intensity of SCC if the constantload specimen was used. But by using constantly deflected specimen, pre-creep could greatlyincrease the threshold stress intensity of SCC for both austenitic stainless steel and brass.

Dose of 1×10~(16) Mg~+ ion / cm~2 with 120 keV was implanted into theintermetallic compound Ni_3Al(0.1B). Studies were made of the corrosion behaviour bymulti-sweep cyclic voltammetry and optical microscopy. The corrosion resistance of the spec-imen after implanting by Mg~+ ions may be much improved to 0.5mol/L H_2SO_4 solution.Experimental measurements and computer simulation were carried out on the segregation ofMg atoms at the grain boundaries. Mechanism of beneficial effect of Mg~+ ion implantationon corrosion resistance was approaching.

Synthesis process of a TiAl+TiB_2 composite from Ti, Al and B powders wasstudied by means of differential scanning calorimetry and X-ray diffractometry. TiB_2 parti-cles may form in TiAl matrix at temperatures even below 700℃ owing to the exothermic reac-tion between Ti and Al powders. TiB_2 particles are very thermally stable, and almost no morechanged in their relative amount, morphology and size after the synthesized composite beingremelted. In addition, the existence of TiB_2 particles may be obviously affected on refinementof as-cast TiAl-base alloy microstructure.