Tensile properties of Ti3SiC2 in the 25–1300°C temperature range

Although significant progress has been achieved in understanding the mechanical behavior of bulk, polycrystalline Ti₃SiC₂ in compression and flexure, as far as we are aware there are no reports in the literature dealing with its mechanical response under tension. In this paper, we report on the functional dependence of the tensile response of fine-grained (3–5 μm) Ti₃SiC₂ samples on strain rates in the 25–1300°C temperature range. The tensile response of Ti₃SiC₂ is a strong function of strain rate and temperature. Increases in testing temperatures, and decreases in testing strain rates lead to large (≈25%) tensile plastic deformations. Strain-rate jump/drop tests and stress-jump creep tests confirm the high values for the strain-rate sensitivity coefficients (0.42–0.56) obtained from the tensile tests. These values are equal to, or greater than, the strain-rate sensitivity of most superplastic ceramics. The large strains to failure result primarily from a high degree of damage, not from a microstructure that remains self-similar throughout deformation (as in superplasticity). Another important distinction between superplasticity in ceramics and the deformation of Ti₃SiC₂ is that in the former the grains are typically about an order of magnitude smaller than the ones tested here.     

Tensile behaviour of gas pressure sintered silicon nitride in the 1600–1700°C temperature range

The tensile behaviour of a silicon nitride ceramic has been studied between 1600 and 1680°C under strain rates from 6×10⁻⁶ to 1.2×10⁻⁵ s⁻¹. At low temperature and/or high strain rate, the behaviour was essentially brittle: failure occurred by cavitation along boundaries of acicular grains lying normal to the tensile axis and linking of these cavities by interfacial debonding. At 1650°C, the deformation started to be ductile: a stress peak was observed in the tensile curve and cavities formed at multigrain junctions while grain boundary sliding began to occur. As the temperature increased, the contribution of grain boundary sliding to deformation increased at the expense of the cavitational component. The stress peak is interpreted in terms of a relaxation effect that governs the competition between cavitation and grain boundary sliding.     

The electrochemical behaviour of iron in stagnant and stirred potassium carbonate-bicarbonate solutions in the 0–75°C temperature range

The corrosion and passivation of polycrystalline iron electrodes in carbonate-bicarbonate solutions are studied in the 0–75°C temperature range. The influence of the solution ionic strength, stirring velocity, and potential scan rate on the electrodissolution of the base metal and the formation of both the prepassivating and the passivity surface layers are considered. The chemical dissolution of the prepassive film and the electroformation of the different surface compounds are discussed in terms of a complex reaction pathway involving both simultaneous and consecutive stages including the corresponding ionic equilibria.     

Evolution of the structure and mechanical properties of a bulk-nitrided corrosion-resistant ferritic steel upon tempering in the temperature range of 400–700°C

Methods of the X-ray diffraction analysis and electron microscopy were used to study changes in the structural phase state and mechanical properties of bulk-nitrided 08Kh17T steel (0.08 wt % C, 17 wt % Cr, 0.8 wt % Ti, 0.5 wt % Si, 0.8 wt % Mn, 0.025 wt % S, and 0.035 wt % P) upon tempering in the temperature range of 400–700°C. The changes in the mechanical properties of the nitrided steel upon tempering are associated with the predominance of either the solid-solution or precipitation strengthening, i.e., with the presence of martensite in the steel structure at low temperatures of tempering and the precipitation of particles of Cr₂N nitrides of different dispersity upon increasing the tempering temperature. The greatest increase in the ultimate tensile strength and yield stress (1.8–2.5 times) at a satisfactory plasticity (no less than 10%) of the bulk-nitrided steel is achieved by tempering bulk-nitrided steel in a temperature range of 600–700°C.     

The oxidation of ta single crystals andpolycrystals in the temperature range 850°C–1100°C

Single crystal cylinders of Ta have been oxidized in dry oxygen at approximately 700torrin the temperature range 850–1100°C. At the lower temperatures the oxidation rate is more rapid over {110} planes, the scale showing shear failures associated with pores resulting from the oxidation of suboxide platelets, in agreement with earlier investigations. Above 950°C the anisotropy initially decreases and the porosity of the scale diminishes, although on metallographic grounds the suboxide plates are still regarded as isothermal features of the oxidation. This is attributed to increasing scale plasticity. In a narrow temperature range near 1025°C the shear failures are absent, and very rapid oxidation of {100} faces occurs, with the development of a porous oxide which again appears to have resulted from platelet induced porosity. It is suggested, again on metallographic grounds, that platelets are present isothermally below {100} surfaces, but not below {110} surfaces, although they are precipitated on cooling.Above 1050°C, all porosity disappears and the oxidation becomes isotropic. However, there is still some reason to believe that at least some of the suboxide platelets are isothermal.     

The inhibition of the corrosion of iron in the pH range 6–9

Abstract

Previously it was shown that upon immersion the air-formed film on iron broke down by a two-stage process, the first step being the cathodic reduction of ferric ions to ferrous. This breakdown was retarded by dissolved oxygen.

It has now been found that inhibitive ions in neutral solution stimulate the oxidation of ferrous ions by dissolved oxygen and thereby impede the first step in the breakdown process.     

Study of the tensile behaviour of tungsten wires from ambient temperature to 320 °C in relation to their microstructure

The tensile test results have been interpreted in terms of the microstructure typical of drawn tungsten wires; the influence of test temperature between 25 °C and 320 °C is significant and is linked to the dependence of the mechanical behaviour of tungsten versus temperature and to the development with increasing temperature of a necking zone in which damage and rupture take place in two stages, a localized damage controlled first by the hoop stress associated to the notch effect linked to necking and rupture under the axial stress and the notch effect just mentioned.     

Hot strip processing of low carbon enameling grades in the range of 600 to 700 °C

The processing of continuously cast low carbon steel grades for enameling usually requires a high coiling temperature. Low-temperature coiling, however, is required to ensure deep drawability. A steel composition characterized by low AIN leads to a material combining both good formability and enamelability ratio for hot strip coiling temperatures in the range of 600 to 700 °C. The influence of the coiling temperature on the mechanical properties, cementite morphology, H permeation, and enamel adhesion was studied in detail.     

Effect of short-circuiting on the oxidation kinetics of copper and its doped varieties in the temperature range of 523–1073 K

The influence of shorting circuitry attachment between metal-oxide and oxideoxygen interfaces on the oxidation kinetics of copper, lithium-doped copper (Li: 400 ppm), and chromium-doped copper (Cr: 12 ppm) have been studied in dry air in the temperature range of 523–1073 K. Oxide film or scale growth under short-circuiting as well as under normal oxidation conditions conforms to the parabolic rate law. The oxidation kinetics under short-circuiting resulted in decreased rates for Cu and Li-doped Cu up to a temperature of 773 K, while Cr-doped Cu exhibited an enhancement in rate compared to its normal oxidation in the same temperature range. However, above 873 K, all three systems under shorting circuitry attachment exhibited enhanced rates compared to their normal oxidation rates in conformity to the existing theoretical model. Use of additional resistances in series in the outer short-circuit Pt path have clearly established that below 773 K Mott's fieldinduced migration plays the most important role, while at elevated temperatures Wagner's electrochemical potential-gradient factor acts as the main driving force in the scale-growth process. The results have been interpreted on the basis of average defect concentration, the electrochemical potential gradient, electrical field gradient, and transport coefficient in the Cu₂O layer.     

A comparison of the plastic behaviour of Fe3Al and Fe3Si in the temperature range of 300–973 K

The plastic behaviour of Fe₃Al and Fe₃Si is compared in view of the different diffusivities of Fe atoms in these intermetallic phases. In case of Fe₃Al serrated yielding and vanishing strain rate sensitivity (S) in a range of intermediate temperatures (T=400–800 K) indicates some kind of dynamic strain aging effect. In spite of the higher diffusivity of Fe in Fe₃Si, serrations and S ⩽ 0 have been found only in a small temperature interval around 800 K. Possible reasons are discussed using experimental information on the temperature and strain rate dependences of the critical resolved shear stress and on the slip line development measured and observed during compression tests in vacuum (300–973 K) on near stoichiometric Fe₃Al single and polycrystals and Fe₃Si single crystals. In addition the coarsening of D0₃ domains (in case of Fe₃Al) during TEM in situ heating has been observed.     

Studies of the oxidation of titanium in carbon dioxide—I. Characteristics within the reaction temperature range 675–800°C

The oxidation of titanium in carbon dioxide has been examined in the temperature range 675–800°C, involving assessment of kinetics, and metallographic and microhardness studies on oxidized substrates and scales. Overall linear kinetics were exhibited—in the temperature range 675–750°C two consecutive linear stages were observed, whereas at 775 and 800°C this linear/linear pattern was less well defined, tending to be replaced by simple linear kinetics.Microhardness studies indicated the presence of oxygen gradients within the substrates. The microhardness contours merged after long exposure periods indicating oxygen saturation, the time for saturation coinciding with the linear/linear transition time.A linear/linear scaling pattern was also observed, the time for the scaling transition coinciding with both that for the total weight gain transition and for attainment of oxygen saturation. The macroscopic features of scales could be correlated with these transition phenomena.     

Equilibrium in the reaction of carbon dioxide with liquid copper from 1090° to 1300°C

A study has been made of the equilibrium in the reaction of carbon dioxide with liquid copper. The equation for the reaction may be written as follows: \(2\;\text{Cu}\;(\text{liq})\;+\;\text{CO}_2\;(\text{g})\;=\;\underline{\text{Cu}_2\;\text{O}}\;+\;\text{CO}\;(\text{g})\)The equilibrium constant for this reaction was determined from 1090° to 1300° C.     

Effect of cold work on the oxidation of iron from 400–650 °C

The oxidation of Fe cold-worked to various degrees has been investigated at 400–650 °C in oxygen. From 400 to 600 °C cold-worked Fe oxidizes faster than annealed Fe and the rate is higher the greater the degree of cold work; the oxide formed on annealed Fe is porous and separates from the metal. At 650 °C cold work has no effect and solid scale only is formed.On annealed Fe below 600 °C the cation vacancies diffusing inwards through the thickening Fe₃O₄ layer develop pores at the oxide-metal interface. This slows the oxidation rate by impeding metal transfer. On cold-worked Fe, the extra dislocations in the surface metal inhibit the nucleation of pores by acting as vacancy sinks.     

Effect of grain size and partial disordering on ductility of Ti3Al in the temperature range of 20–600°C

The effect of grain size and partial disordering on ductility and flow stress of an intermetallic Ti₃Al was studied in the temperature range of 20–600°C using tension and compression testing. The ductility of the fully ordered material increased considerably when the grain size decreased from 27 to 0.1 μm, and, at the smaller grain size, an elongation of 4.8% was achieved at room temperature. Partial disordering of the crystal lattice led to a decrease in ductility at temperatures below 500°C, but had no influence on the ductility at 500 or 600°C. The critical grain size at which a brittle-to-ductile transition occurred in the fully ordered material was determined for each temperature studied. This critical grain size increased as the temperature was increased. It was found that, when the mean grain size decreased and temperature increased, the fracture mode changed from a brittle transcrystalline mode to a brittle intercrystalline mode and, finally, to a ductile transgranular mode. The increased ductility was correlated with an enhanced grain boundary relaxation capability at increased temperatures and decreased grain sizes.     

Tensile properties of high strength cast Mg alloys at room temperature：A review

As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution＆peak-aged（T6）cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd（Y）-Ag〉Mg-Gd（Y）-Zn〉Mg-Gd-Y/Sm/Nd〉Mg-Y-Nd（WE series）〉ZK61〉Mg-Nd〉AZ91〉Mg-Sn.Mg-Gd（Y）-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd（Y）-Zn based alloys.The high yield strengths of Mg-Gd（Y）-Ag and Mg-Gd（Y）-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.     

The influence of ionic composition on the electrodissolution and passivation of iron electrodes in potassium carbonate-bicarbonate solutions in the 8.4–10.5 pH range at 25°C

The influence of ionic composition on the electrodissolution and passivation of iron electrodes in potassium carbonate/bicarbonate buffers is studied over the concentration range of anions compatible with the regulating capacity of the buffer, at 25°C, by using voltammetric and rotating disc electrode techniques. Data are discussed on the basis that the interaction between Fe²⁺ and HCO₃⁻ ions plays an important role at the outer part of the passivating layer where the local pH resulting from the thickening of the passivating layer is determined by the coupling of different ionic equilibria.