The M_5 temperature and the yield strength of austenite at M_5 tem-perature have been measured for five Fe-Mn-C alloys. The experimental results showthat there is a linear relationship between them. The effect of the solution strength-ening of austenite on martensite morphology is also studied. It is pointed outthat there is a characteristic temperature of strengthening in austenite, T_c. Marten-site morphology is mainly dislocated laths when M_5>T_c, and is mainly twinnedplates when M_5 References | Related Articles | Metrics

Two lath structures and the kinked ε martensite were observed in thehigh manganese non-magnetic steel. Both the short non-continuous lath formed byquenching and the long thin straight lath induced by plastic defomation are com-posed of ε martensite and fcc twin. The transformation mechanism was discussed.The crystallographic analysis indicates that the ε martensite at both sides of thefcc twin boundary is of kinked morphology owing to the orientation of their ma-trixes differed from each other. The kinked region is hcp twin.

The snap-acting transition and snap-acting two way shape memory(TWSM) effect have been obtained in a TWSM spring made of Ni51Ti49 alloyusing the constrained effect of stress on the driving force of TWSM element. Whenthe snap-acting transition has been realized, M_s=M_f and A_s=A_f; hysteresis is rec-tangular, the height (TWSM effect) and width (hysteresis) of the rectangle can bereadjusted by means of constrained stress. The results of resistance measurementsshow that the snap acting TWSM effect mentioned above was supplied mainlyfrom the transformation of P-R. The gradients of the driving force with respectto temperature near critical point have been calculated. The thermodynamic modelhas been proposed to account for the snap-acting transformation.

The microstructure and the mechanical properties from room temper-ature up to 1050℃ of Ni_3Al base alloys containing 0--0.6 at.-%Zr, 0--7.7 at.-%Crand 0--2.22 at.-%B have been investigated. It was found that the temperature depen-dence of their yield strength variation reveals to be anomalous, i. e., the strengthincreases with the elevating of temperature, and thence decreases till it surpassedthe peak value. Both Zr and Zr + Cr may improve the yield strength of thealloys in the entire range or testing temperatures, as well as the tensile strengthand elongation under high temperature. B is favourable to raise the tensile andyield strength of the alloys, and also the plasticity. But the strength will reduce asB added over 1.37 at.-%. The Ni_(20)Al_3B_6 and Ni_3Al eutectic mixture like islandsand globes precipitated inside grain and along grain boundaries, which are harmfulto the strength and ductility, may be formed when the B content exceeds the limitof solubility.

The effects of chemical composition and cooling rate after solidifi-cation on the grain coarsening temperature, T_(GC), of the V-Ti-N microalloying steelshave been investigated. It is shown that the T_(GC) may be obviously raised byadding even a little Ti to the base steels so as to precipitate a great deal of fineTi-bearing grains of about 10 nm. The T_(GC) does not increase with the cooling rate,as it is over a certain critical value. The T_(GC) is insensitive to any variation ofN content at simulated cooling condition of 150mm continuouscast slab. TheT_(GC) may be dropped down about 100℃ by adding 0.33 wt-% Mo to the steels.The sensitivity of T_(GC) to cooling condition is related with Ti and N contents.

An investigation was conducted to examine the symmetric lowcycle push-pull fatigue behaviour of the Cr-Mn-N dual-phase stainless steel whichwas separated into two specimen groups A and B by solution treated at 1050 and1250℃ respectively. The fatigue life of A is almost twice as long as B under sametotal amplitude of strain. Within the tested amplitude range of strain, ±0.4-±1.2%, the cyclic softening is observed both of them after the cycle saturated, whilethe saturation stage is earlier reached under lower amplitude of strain. The aver-age energy loss of each cycle increases and the sum of energy loss of total life ofeach specimen decreases with the increase of strain amplitude. Observation on thefatigue fracture surface under SEM shows that the specimen A is mixed type and thetransgranular mode predominantly with clear fatigue striation, and the specimen Bis mainly the intergranular mode.

The influence of laser surface melting and induction hardening on thesurface structure, contact fatigue life and failure behaviour of the nodular graphitecast iron has been investigated. The contact fatigue life may be improved by bothlaser treatment and induction hardening, but the failure process and type aredifferent from each other. The former is due to lump and deep spalling caused bycrack propagation between the hardened layer and the substrate, and the later is dueto nubbly and surface flaking caused by the oil wedged action into surface cracks.The improvement on the contact fatigue life of the nodular cast iron was alsosuggested.

The resistance to crack propagation at earlier stage for a high strengthstructural steel of certain ductility with relation to its microstructures, stressstates, deformation history and strain characteristic has been investigated. The resist-ance to crack propagation is mainly determined by the plastic constrain ahead ofthe crack tip and the elastic energy and plastic work absorbed in the stress-strainfield. These are connected with the state function of triaxial stress. The deforma-tion history and strain characteristic during deformation of material are describedby the flow line in which the deformation history and strain characteristic re-strain the crack initiation at stage II and the crack propagation at stage III. Thestrain hardening rate may sensitively reflect the stress distribution and micro-frac-ture mechanism in the interior of material.

The feature and microstructure change of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlledlow-cycle fatiguing. The results show that the cyclic softening is featured in bothvariedly hardened steels under strain controlled in the amplitude range of Δε_t,/2=0.6 - 1.8×10~(-2). The softening effect is mainly gathered in the prior some cycles.And the stress amplitude varies slightly in the sequential cycles, i. e. the softeningeffect is minified. No obvious saturation phenomenon of stress is observed duringthe whole cyclic deformation. The cyclic softening was analyzed under TEM thatit is related to heterogeneity of plastic deformation. The softening of the steelstested is caused by the formation or the dislocation cell structure with low densityand low internal stress, and by the redissolution of fine carbides into matrix.

By the test of fatigue crack growth in distilled water at temperaturesvaried from 18 to 55℃, the confirmation of the intensive temperature effect on thecorrosion fatigue for super strength steel 30CrMnSiNi2A and the compound expres-sion concerning the effects of ΔK and temperature on crack growth rate (CGR)have been made. Because the apparent activation energy (36.7 kJ/mol) resulted byregressive analysis of CGR data is nearly equal to the activation energy of hydro-gen diffusion in γ-Fe, it is strong enough to support the theory of hydrogen assis-ted crack growth. The overload retardation effect, which is significant to the fa-tigue crack propagation in atmosphere, greatly decreases in corrosion fatigue crackgrowth, especially at lower frequency, e. g., 0.1Hz. This phenomenon may be ex-plained as the increase of the SCC component of CGR after an overload.

By adding small amount of Mg to the wrought superalloys, their steadystage of creep, and especially the tertiary stage of creep are prolonged, and thesteady creep rate is decreased in the cases of low strain rates. At higher strain ra-tes, however, the effect of Mg on creep rate has been found to be vanish. Thesemay be attributed to the Mg dissolution in the matrix. A mechanism of the effectof Mg addition on creep behavior is proposed.

The effect of quenching temperature on the stress corrosion crackingof 30Cr3SiNiMoV ultra-high strength steel in 3.5% NaCl aqueous solution has beenstudied. The threshold K_(Iscc) may continuously increase with the quenching tempera-ture raised from 870 to 1200℃. All of the fractures are intergranular. The ana-lyses of the segregation along prior austenitic grain boundaries, grain size and othermicrostructural factors revealed that the reason of the increase of K_(Iscc) is mainlydue to the coarseness of prior austenitic grains.

The distribution of residual austenite in the laser hardening layer ofthe gray cast iron and the change in amount of residual austenite during slidingwearing have been investigated by X-ray diffractometer. The thin foils of the hard-ening layer worn down have been observed by electron microscopy. It was reveal-ed that two types of martensite are strain-induced by sliding wearing under loadof 1.72 MPa on the hardening layer of residual austenite. The strain-induced mar-tensite is profitable to improve the sliding wearing resistance.

The hardness and electric conductivity of Cu-Zr, and Cu-Zr-Si alloys varied withdifferent aging regimes were measured and the factors influencing the electric conductivity wereanalyzed. It is believed that a little Si can fine the precipitates and better the resistance tosoften. The improvement of material properties by aging and the effect of cold work were alsodiscussed.

By means of ftactal analysis, the fractal dimension with relation to the impacttoughness, impact fracture characteristics and microstructures of steel under low temperatureimpact have been investigated. Experimental results show that the logarithms of impact tough-ness increase monotonically with the increase of fractal dimension. The microstructures havea great influence on the fractal dimension. There is a certain correlation between the fractaldimension and fracture mechanism.

The interaction between Cu and liquid Sn was studied by microstruc-ture observation. The curve of the dipping time with related to dissolving anddiffusion of Cu in liquid Sn was given. The Cu dissolves rapidly in liquid Sn atthe beginning, then an intermetallic compound, Cu_6Sn_5, forms, and the dissolvingfollows to slow down. At temperature up to 350℃, the feather-like Cu_6Sn_5 is sud-denly growing up and spreads through the dipped Sn layer. The way to inhibitthe growth of the intermetallic compound, Cu_6Sn_5, was also approached. Thus, onthe above mentioned basis, the phyical meaning of the wetting curve traced by themeniscograph wettability tester has been derived as film detaching, Cu dissolvingand Cu_6Sn_5 growing.

The corrosion behaviour and mechanism of superpure austenitic stain-less steel 00Cr25Ni22Mo2N in urea processing environment was studied. The resultsshow that the gas extraction tube made of non-sensitized 00Cr25Ni22Mo2N steelsuffered intergranular corrosion. Corrosive media penetrated not only into the tubewall through grain boundaries but also expanded from the boundary towards theinterior of the grain. Therefore, funnel shape penetration paths were formed, whichwere wider but less deep than common intergranular corrosion of sensitized stain-less steel. Neither depletion of Cr nor precipitates were found at the grain bound-ary. However, P (and Si) was segregated at grain boundaries to a great extent.Semiquantitative calculation indicates that P content at the grain boundary isabout 25 wt-%, three oders of magnitude higher than the content within the grain.Suggestion is made that the potential difference between the grain and its bound-ary due to the segregation resulted in the observed intergranular corrosion.

The phase composition of Co-30Cr-6Al-0.5Y coating deposited by plan-ar magnetron sputtering as well as the effect of sputtering parameters on it havebeen investigated. The sputtered coating is composed of hcp ε-phase or fcc α-phaseof Co solid solution with a minority β-CoAl intermetallic phase. The hcp ε-Cophase and the fcc α-Co phase assumed a <100> and <110> preferred orientationrespectively. Both phase type and orientation extent depend on the sputtering para-meters. If the substrate surface is paralleled to the target face during sputtering, thecoating will be of fine crystal with compact structure and smooth surface; if it isrotated, the coating will be to the contrary.

Nonstable growth of Al-Si eutectic in constrained condition has beeninvestigated by means of change of the pulling velocity in an unidirectional solidi-fication system. In constant acceleration growth, a retard effect of response of eu-tectic interflake spacing on the growth rate has been observed. However, in cons-tant deceleration growth, the interflake spacing is determined by the initial growthrate and does not response to the decreasing of growth rate.

The perpendicular anisotropy, coercivity and Kerr rotation angle ofthe amorphous Tb_(32)Fe_(54)Co_(14) films were studied. The X-ray, electron diffraction,XPS and AES profile confirmed that no obvious change in their amorphous struc-ture and oxygen concentration is observed after annealing at 100℃, while theirproperties alter evidently under bending stress. It is believed that the perpendicularanisotropy in the Tb_(32)Fe_(54)Co_(14) film mainly arises from the induced stress duringpreparation and the magnetostriction coupling stress, as well as, the thermalinstability of the film is related closely to the stress relaxation during annealing.

The amorphous CoZr soft magnetic films with superior properties wereprepared by radio-frequency sputtering under pressure of 0.5 Pa Ar. The saturationmagnetization of the amorphous CoZr film with relation to the Zr content andtemperature was investigated. The amorphous CoZr films composed of differentconstituents obey the Bloch T~(3/2)-law in a wide range of temperatures. The numberof electrons transferred from each Zr atom to 3d energy band of Co calculatedby the rigid band model is about 2.27.

The evaluation of the relative stability of initial permeability hasbeen made for the pre-annealed amorphous ferromagnetic alloys Fe_(76)Si_(10)B_(14), Fe_(40)Ni_(38)Mo_4B_(18) and (Fe_(0.1)Ni_(0.35)Co_(0.55))_(78)Si_8B_(14) by the experlmental values of average activa-tion energy and frequency factors on the basis of the empirical expression deducedby experimental data of the kinetics of their permeability decay. Calculated resultsshow that the relative stability of permeability is sufficient for practical uses inthe temperature range within 100℃, although the permeability instability can notbe substantially eliminated. In other words, the permeability decay is considerablysmall within a period of considerable length.

The formation of borides M_2B, M_3B_2 and M_(23)B_6 may be carried outfrom the melt-quenched Fe_(70)Cr_(18)Mo_2SiB_9 during 700-1150℃ annealing. As the tem-perature raising, the M_2B, the majority being Fe_2B, may be gradually replaced byCr_2B via the co-existence between Fe_2B and Cr_2B. The Cr_2B may be formed by transformation of Fe_2B through the atomic substitution and structural adjustment. Thethin slice of remaining Fe_2B is sandwiched between (100) faces of (Cr,Fe)_2B asstacking fault. The M_3B_2 is virtually composed of the Mo_(1+x)(Fe,Cr)_(2-x)B_2 where x(0≤x≤1) increases with the increase of temperature.

The regularity and mechanism of the microplastic deformation of1Cr18Ni9Ti stainless steel both solution-treated and prestrained were investigated.In the different steges of microplastic deformation, stage Ⅰ corresponds to the dis-location moving and exhausting in the regions near grain boundaries, Stage Ⅱ, be-ing the early stage of macroplastic deformation, corresponds to the extensive opera-tion and generation of dislocations in the interior of grains and also dislocationemission from grain boundary. The regularities of effect of prestrain on macro-and micro-yield strength are different.

An attempt was made on the quantitative prediction of the relation-ship batween yield stress and R-value along the directions parallel and perpendicul-ar to rolled Ti plate based on analysis of the previous experimental data. It is sh-own that the yield stress along one direction and another is synchronized withR-value. Based on the theory of plasticity a formula of σ_(1s)/σ_(7s)=[1+1/R_2)/(1+1/R_1)]~(1/2)was proposed. In statistic estimation, the calculated results after the formula are inbetter agreement with the experimental data. The availability of this formula wasbriefly discussed also.

A ZTA-SiC_W ceramic composite of room temperature strength 935-1110 MPa and fracture toughness 9.7MPa·m~(1/2) was prepared by the sol-gel process.Its microstructure and fracture feature have been examined by means of X-raydiffraction analysis and electron microscope observations. The results show that thewhiskers are well dispersed and the matrix has an obvious texture character. Betweenthe whisker and matrix, there is a great number of transcrystalline and trans-crystalline connective relation other than part of conventional polycrystalline connective ones. Certain secondary cracks closely related with local whisker groupare found on the fracture surface. It may be a new reinforcing and tougheningmechanism by whisker group, of which the whiskers in the local whisker grouparrest synergetically the crack propagation accompaning with the formation of se-condary cracks.

The chemical reaction as solid state between pressless sintered Si_3N_4 substrate andTi-deposited film has been studied by X-ray diffraction analysis. The reaction all depends up-on temperature. It seems no reaction below 973 K; Ti_2N and Ti_5Si_3 are the reaction productsfrom 1073 to 1123K, and finally, till 1173K, the Ti-deposited film over Si_3N_4 substrate willexhaust itself and the reaction products change into TiN and Ti_5Si_4. The lattice constant of Si_3N_4is unaltered thronghout postannealing. This implies that the Ti atoms will never dissolve intoSi_3N_4 lattice.

The lattice constants and chemical composition of Ti, Nb and V precipitateswith different particle sizes have been measured by means of CBED and EDAX. The precisionof CBED method is up to 0.02%. The error of these two methods is less than 1%. It wasobtained that the concentration ratio of Nb and V, C_(Nb)/C_V, and the lattice constants in theNb-V steel decrease with the decrease of the particle size of the precipitates, but, there is noregularity for lattice constant of Ti, Nb and V precipitate against their particle size in theTi-V-Nb steel.

Based on the crystallographic nature, two major characteristic textures of the deepdrawing automobile steel sheet are represented with inverse pole figures. The correlation betweenthe texture of deep drawing steel sheet and its deep drawing properties may be simply anddirectly analysed by the quantitative texture technique. An verification was made that theresult obtained by this technique is in agreement with that after ODF quantitative analysis.

A proposal for two types of press close to die, Including blanks coming in dieand covering die, and four criteria for mability is put forward in the study of the superplasticair bulge forming of the metallic thin wall components. A dimensionless weigh mathematicmodel for the criteria of superplastic air bulge forming was developed to be: Q_w=1.56WS/HF+2.37(θ-φ)π/180-r/r_0+0.19The superior formability of components is approaching if Q_W≥1, and the worse, if Q_W<1. Itwas confirmed by practice that the above mentioned model is with more accuracy.