Static tensile tests for 99.999%Al with two grain sizes were conducted with strain rates of 10~(-6) to 10~(-4)S~(-1) and temperatures of-150 to+250℃. The slip traces, the topography near the grain boundary on the surface of tensile specimens and the structure of dislocations were observed hy means of optical microscope and TEM. The results show that the strain hardening reduces with increase of temperature and decrease of strain rate, and it depends upon the interaction between grain boundaries and dislocations which are controlled by both temperature and strain rate. The hardening coefficient A as a function of deformation temperature T, strain rate e and grain size d was derived. (A/G)-T, (A/G)-ε and (A/G)-d curves were computed and compared with experimental data, where G is shear stress.

A Bordoni-type apparatus was used to measure the change of apparent Young's modulus of α-Fe induced by hydrogen. The solution of flexural vibration equation for a beam under stress indicates E=C(σ)ω~2. If the resonant frequencies of the first and third tons are measured at about the same time, E and σ can be calculated. The change of apparent Young's modulus after charging with hydrogen is defined as ΔE=ΔE_1(H)+ΔE_2, where ΔE_1(H) relates to the change of the perfect crystal interatomic cohesive force and ΔE_2 is induced by the change of stress. To measure ΔE_2, an artificially partial stress relaxation test was carried out. The result shows that during aging, after both charging and artificial stress releasing, the change of apparent modulus is the same, i.e., ΔE=ΔE_2. Thus, ΔE_1(H) associated with the interatomic cohesive force does not evidently change during aging with escaped hydrogen of 7 to 8 ppm at room temperature, i. e., this amount of hydrogen does not decrease the interatomic cohesive force of α-Fe. Forster's horizontal free-ends bar apparatus was also used in present work, the same result as above was obtained.

The martensitic transformation in Cu-29%Zn-3%Al alloy occurs thermoelastically. High voltage TEM observation shows that the parent phase belongs to DO_3 and martensite belongs to 18R in structure. Fine structures of tiny packages with a traverse size of～10nm in martensite plates have been seen at the thicker part of the sample. The boundary between β' and M at the thinner part was flat or sawtooth-like composed parallel dislocation lines: Although the reversibility of the transformation in TEM samples has been observed under an optical microscope, only the β'→M transformation observed on TEM. Probably, the thickness of thiner part of the foil is too small to store enough elastic energy which is the driving force of the reverse transformation.

The deformation behaviour of parent phase and the pseudo-elasticity were studied, and the variation of microstructure with aging and deforming was analyzed using optical microscopy and X-ray diffraction. The experimental results showed that the pseudoelasticity in parent phase state is closely related to the original martensite microstructures. The pscudoelasticity of the alloy can be considerably improved with the perfection of martensitic self-accommodation and proper ageing treatment.

The total driving force for the decomposition of retained austensite and that of martensite, the driving force for nucleation of cementite, the growth rate as well as the incubation period of the formation of cementite that precipitates from martensite and austenite are evaluated. The results reveal that in spite of the fact that the driving force for the decomposition of martensite is one order of magnitude less than that of austenite, the driving force for the nucleation of cementite that precipitates from martensite is far greater than that from austenite and the incubation period of the formation of cementite as it precipitates from martensite is one order of magnitude less than that from austenite. It is obvious that during the short time tempering, cementite firstly precipitates from martensite, while upon tempering with long duration, since the total driving force for the decomposition of the retained austenite is greater and the contraction of martensite resulted from its decomposition would enhance the decomposition of interlath retained austenite, the precipitation of cementite from austenite leads the temper martensite embrittlement-Therefore, as the segregation of the impurities(and cementite) on the grain boundary is not taken into consideration, the mechanism of the TME may be assumed to be the combination of the two related decomposition processes.

Sufficient Mg addition in Ni-base superalloy results in strengthening of γ' phase, consequently decreases the steady state creep rate. Segregation of Mg to grain boundaries(GB) causes raising of GB fracture energy, that retards the crack initiation and propagation, extends the 2nd and 3rd creep stage. Accommodation between deformations at GB and in grains may also be improved by addition of Mg, thus increases the creep ductility. The fracture mechanism transfers from dominantly wedge cracking to cavity cracking.

The spin ribbons and splat foils of various Mo-base alloys were made by the arc melt-spinning and hammer-anvil techniques. The mechenical properties, surface topography and microstructure have been studied. A strong grain refinement and an age hardening response have been observed in the as-quenched and annealed specimens, respectively. The precipitates which are responsible for age hardening were identified to be Mo_2B(C16, BCT) in Mo-B alloys and Mo_2B and more stable ZrB_2(A_3) in Mo-Zr-B alloys. The alloys in which the borides are as strengthening phases possess very high strength and hardness, indicating the prospect of developing high strength Mo-base alloys by rapidly solidified techniques.

The influence of Sr and Sb on the solidification process of Al-Si alloys. was investigated by differential thermal analysis(DTA). The contact angles between the melt and silicon substrates were measured, and the interfacial energies were calculated. It was obtained that Sr and Sb in the melt raised the Al-Si eutectic nucleation temperature and retarded the eutectic crystallization. Sr and Sb in the melt had no thermodynamic tendeney to absorb on silieon crystals, which was contrary to the traditional point of view. But Sr and Sb might accumulate on silicon crystals and affect the growth of Al-Si eutectics because the partition coefficients were less than 1.

Solid solubilities of Ce and Nd in α-Fe were determined with the aid of X-ray diffraction lattice parameter measurements and electron-microprobe quantitative analysis. The alloys were prepared by vacuum levitation melting using 99.987wt-%Fe, 99.9wt-%Ce and 99.95wt-%Nd, respectively. They were subsequently homogenized at 1200℃, then cooled down to room temperature to achieve quasi-equilibrium conditions. Solubilities of 0.048 wt-％Ce and 0.055 wt-％ Nd in α-Fe were obtained.

In the past, coarse grains were often formed in the central part of LD2 alloy forging after quenching, that made many products waste. In this paper, a simulated test was planned to study the formation of coarse grains by means of X-ray diffraction and metallographic observation. Some technological factors which have influences to the formation of coarse grains, such as strain, deformation and quenching temperature, soaking time, etc. have been studied. The causes of coarse grains and their formation mechanismas well as the elimination of coarse grains have been discussed.

The effect of fatigue crack initial life, N., on the shape of initial notch and stress ratio under the tensile loading for LY12R sheet specimens has been studied. A relation predicting fatigue life, in N_i=a+b△K_c has been obtained. The crack growth behavior for LY12R, three steels and a titanium alloy have also been analysed. The results show that the crack growth behavior is not sensitive for materials, dimension of specimens and loading condition so that the surface crack depth may be predicted by the empirical expresion, △a=f(△c). It was also found that the surface crack extension is controlled by. stress strength. factor when σ_(Nmax)/σ_y=0.9.

The initiation of microcracks and its connection with microstructure of WC-Co hardmetals have been studied by STEM. The microcracks in specimens are induced by high-frequency compressive fatigue. The causes of microcrack initiation are explained by traverse of slipping dislocations across sub-grain and WC/WC grain boundaries and the pile-up of dislocations near the boundaries. The reduction of substructure dimension is required to improve the alloy quality.

The dynamic process of stabilization of thermoelastic martensite in a Cu-Zn-Al alloy has been studied by means of electro-resistance and X-ray diffraction. It was found that the structure of the sample quenched into cold water ( References | Related Articles | Metrics

The existence form of V in normalized medium carbon HSLA steels has been investigated by means of extractive analysis and TEM. The results show that the amount of carbides diminishes and the relative amount of ferrite increases after normalizing at 950℃. Most of V precipitates in the form of VC and a little dissolves in the cementite. Addition of rare earth suppresses the precipitation of VC markedly. The dissolved rare earth causes CCT curves shift to the right and increases stability of the undercooling austenite, thus changes the form of decomposition products.

The effect of alloy constituent, annealing heat treatment and reaction temperature on the hydrogen absorption and desorption properties for TiMn_x alloys has been investigated. The results show that the alloys containing 39—44 at. -%Ti exhibite excellent hydrogen desorption properties. They have MgZn_2 type Laves phase structure with a unit cell dimension of a=0.483—0.485nm and c=0.792—0.796nm. The hydrogen absorption capacity is 165 ml/g and the hydrogen desorption amount is 140ml/g for TiMn_(1.49)H system at 30℃.

Only (V, Mo)C carbide remains in specimens queched from 820—870℃, the solution of it begins at 870℃ and stops at 920℃. While tempering at 400 to 700℃, the precipitates of Mo, V, Cr and Mn increase with increasing temperature and the maxinm amount of Mo, V precipitates was found at about 600℃, corresponding change of mechanical properties occurs above this temperature. However, the precipitation of Fe decreases at the temperature range of 500 to 700℃. Cr-rich M_3C was observed at 700℃.

On the basis of steady state principle of kinetics and experimental results, a rate equation was derived: V=kS[(C_N—C_A)/K_E], where V=digestion rate; k=rate constant; S=surface area of diaspore in bauxite; C_N, C_A=concentrations of hydroxide and aluminate ions, mol/L; K_E=equilibrium constant of digestion reaction. An equal-digestion-efficiency method was developed and used to process the digestion kinetics data of Pingguo bauxite. The results show that the chemical reactions on the diaspore surface are of first order to the hydroxide and aluminate ions. At 224—242℃ the apparent activation energy was calculated as 89.5 kJ/mol. It is obvious that in this temperature range the digestion process of Pingguo bauxite is controled by chemical reaction on diaspore surface. At 242—268℃ the Arrhenius plot slope changes rapidly and the apparent activation energy was found to be 44.4 kJ/mol. It is believed that the effect of mass-transfer step on digestion rate should be taken into consideration at 242—268℃.

The solubility of niobium carbide in γ-Fe of a microalloy steel, in which the Nb/C ratio is approximately equal to the stoichimetrie ratio of the carbide, has been determined by means of electrolytic extraction: lg([Nb]·[C]~(0.875))_v=2.97—7500/T±0.06(850—1200℃) The solubilities of it in γ-Fe and α-Fe have also been derived using the latest thermodynamic data, following results were obtained: lg([Nb]·[C]~(0.875))_v=3.24—7150/T(1100—1600K) lg([Nb]·[C]~(0.875))_0=4.87—10060/T(300—1000K)

Reaction constants of the formation of Ce_2O_3, CeS and Ce_2O_2S in liquid Ni at 1500 to 1600℃ have been determined, then the standard Gibbs energies (J·mol) were obtained: △G°_(Ce_2O_3)=-116240+315.8 T △G°_(Ces)=-570280+220.1 T △G°_(Ce_2O_2S)=-984850+238.5 T The reaction coefficients e_O~(Ce) and e_S~(Ce) have also be determined: e_O~(Ce)=-333451/T+149.7 e_S~(Ce)=-276228/T+146.0 The equilibrium phase diagram of a_o-a_s for Ni-Ce-S-O system at 1600℃ was also given.

The reaction equilibrium between slag-hot metal containing Nb at temperature of hot metal pretreatment was investigated. Hot metal and slag containing Nb_2O_5 from Baotou was used. Meanwhile, a_([O] in molten iron was measured by means of the elctrolyte oxygen cell technique for calculating a_(Nb_2O_5) in slag. It was shown that when [Si]>0.02％ and SiO_2/MnO<2,at the equilibrium state between slag-hot metal the selective removal of [Si] over [Nb] from Baotou hot metal is quite possible. The range of γ_(Nb_2O_5) values is 10°—10~(-2) at 1350℃. SiO_2/MnO of slag effects considerably on distribution ratio of Nb between slag-hot metal and on γ_(Nb_2O_5).

The particles of M_(23)C_6 precipitate in Ni-base superalloy M17G were selectively dissolved in an aqueous solution of 12％(NH_4)_2SO_4 (pH-value was adjusted to 9) in the potential range of +200 to +800 mV (S. C. E.). The anodie dissolution process has been investigated in terms of potential-sweep and potential-step polarization techniques. For the finely dispersive phase in the alloy, a new model has been developed to describe the selective anodic dissolution process, which is eontrolled by electrochemical polarization.

Abrasive wear resistance and fracturetoughness of white cast irons containing 2, 9, 15, 20 and 27 wt-%Cr have been investigated. Different contents of Cr and C have been added to the irons to keep the eutectic carbide constant (20—25%). Martensitic and austenitic matrices have been obtained by means of heat treatment. The results show that M_3C will transform to M_7C_3 and the microhardness of M_7C_3 itself will increase while the Cr/C ratio in iron increases. Meanwhile, the morph01ogy of carbides changes from Continuous network to rod or plate-like. All these make the carbides protect the matrices effectively, and improve the abrasive wear resistance of materials in pin-disc and wet rubber wheel wear tests. Wear resistance and fracture toughness have been discussed combinedly, that gives a general guide for designing and choosing wear resistant materials.

To determine M_6C and MC in high-speed steels separately, an etching quantitative phase analysis method without standard sample has been developed. Coexistent phases M_(23)C_6 and M_7C_3 do not interfere with the determination. Fast phase identification of M_6C, MC and M_(23)C_6 in high-speed steels can also been carried out by this method.

The possibility of CD carburizing and effect of C potential on the microstructure in surface layer of commercial medium-C alloy steel have been studied by thermodynamic analysis and experiments. A method used to calculated the C potential resulting in expected carburized microstructure has been proposed, which was supported by the experimental data. The structure of CD carburized layer for steel 4Cr5MoVSi provides a new possibility to improve the surface hardness and wear resistance of the steel.

The direct measurement of quenching rate during the amorphous ribbon formation of alloys Fe-Si-B and Ni-P by using an infrared thermal photography technique is described. Experimental results show that the critical quenching rate of amorphous alloy Fe-Si-B or Ni-P formation is 5.0×10~5 or 1.0×10~5℃/s related to the linear wheel speed 17.0 or 12.0 m/s respectively.

The thin foil samples of rare earth treated cast iron. were analysed by means of TEM. The results confirmed that the <0001> direction of graphite crystal is perpendicular to the "annual ring" lines revealed by ion bombardment. Each cone in a nodular graphite is composed of many microcrystallites with a small angle each other in their orientations. The morie patterns in the TEM picture of the graphite were also analysed. It is considered that they result from some structure defects such as twins existing in the graphite.