The behaviour of structure and mechanical properties of porous single-phase and two-phase (in-situ composites) titanium nanolaminates Ti3SiC2, Ti3AlC2 and T4AlN3 made by reactionary sintering method was investigated, using methods of micro- and macroindentations, uniaxial compression, and also TEM and REM investigations. Regularities, features and mechanisms of deformation and fracture processes of each material in the temperature range 293-1573 K are established. Temperature-strain and force boundaries of their existence in a plastic state are established.It is shown that, on increase of the strength characteristics and also increase of resistance to deformation and creep at average and high temperatures, titanium nanolaminates settle down in the following sequence: Ti3AlC2 - Ti4AlN3 - Ti3SiC2. An explanation for the received proportion of high-temperature properties for titanium nanolaminates is offered, according to which there are two factors responsible for lower meanings of strength characteristics of nanolaminates containing aluminium. First - lower bonding energy of aluminium atoms among themselves and with titanium atoms in their crystal lattices. Second - higher test temperature in relation to decomposing temperature of these compounds.It is shown that deformation epsilon=5 % of porous materials can considerably raise its specific high-temperature strength, down to excess of its values for a compact material.

The influence of elastic-plastic substrate characteristics on the 'nanocrystal chromium film with 400 nm thickness-substrate' system is investigated, and the results are presented. The silicon, polycrystalline corundum, glass, and freshly cleaved single crystal of NaCl are used as a substrate. Some interesting singularities of the influence of elastic-plastic substrate characteristics on the system mechanical behaviour are revealed.

The structural-texture growth with the increase of deformation power in iron and steel after cold axisymmetric plastic broach is investigated. The change of the grains' shape from equiaxial shape to the strongly elongated one as the result of shear deformation is revealed. Shear-deformation degree is estimated as e = 2.7. According to experimental data, the cell structure in a near-surface layer is formed.

The ternary compound of titanium-siliceous carbide Ti3SiC2, one of the representatives of Nan laminates, prepared by solid-phase sintering is investigated in compact and porous (q=0.03-0.41) states. Features of its short-term and long-term hardness (?=10 N) behavior in the temperature range from 20 to 1200?? at a holding time of 1-60 min were studied. It is shown that a temperature of about 700?? and holding time under load of about 10 min are critical values of the indentation procedure that correspond to an intensive decrease of hardness. The presence of porosity results in a decrease in hardness. a deformation scheme of compact and porous titanium-siliceous carbide Ti3SiC2 in the temperature range from 20 to 1200?? is proposed. .

Phase equilibria in the alpha/alpha(2) phase region of the Ti-Al-Si-Nb system at Nb content 2.5, 3.5 and 5 at.% were studied in alloys as-cast and heat-treated at 800 degreesC. Samples were prepared by arc-melting technique, homogenized at 1350 degreesC and then heat-treated at 800 degreesC, followed by ice water cooling. The structure of the alloys was characterized by means of X-Ray diffraction, differential thermal analysis, electron probe microanalysis, scanning electron microscopy and transmission electron microscopy.The continuous solid solutions with variable compositions (Ti1-x,Nb-x)(3)(Si1-yAly) (eta) (0.05less than or equal toxless than or equal to0.07, 10(-3)less than or equal toyless than or equal to0.02) was detected at 800 degreesC for the first time in the multi-component alloys based upon the Ti-Si system. It was stabilized by Nb additions in the alloys with low Al content. A peritectoid reaction beta + alpha-->eta was observed. Additions of Al neutralized the stabilizing effect of Nb resulting in an alpha + Ti5Si3 (z) equilibrium. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

The specific mechanical characteristics of sandwich type porous laminated alumina are analyzed. Internal layer material is obtained by using of powder former while external layers are compact and made from the same material by tape casting. Dependencies of relative stiffness and bending strength on porous to compact layer thickness ratio are considered. Energy adsorption mechanism for alumina-based porous laminated composites is considered.

The use of traditional methods of powder metallurgy including sintering and long -term homogenizing does not permit to obtain bars with sufficient plasticity because of the presence of molten fragile phase appearing on the particle boundaries in the process of long term sintering. The main idea of this work is to get the homogeneous Ni-Mo alloys owing to the effect of superhigh - speed diffusion which appears by the optimum modes of hot deformation of heterocomponent powder mixture. In this case the process of alloy formation runs in a short interval of time due to the nigh activity of dispersed powder components and mechanical activation of the mass transfer process. The investigations showed that in the Ni-Mo powder system this mechanism can be realized under deformation temperature 1450K. We have obtained almost homogeneous alloys with the solid solution structure from Ni-30% Mo powder mixture. Previous sintering during which the processes of diffusion homogenization start results in considerable deceleration of homogenization in the course of following deformation.

A novel refractory alloy produced in the Institute for Problems of Materials Science, Kiev, Ukraine, has been characterized. The composition of the alloy is Ti-6Si-SAl-7Zr (wt.%) with a specific density of 4.6 g/cm(3). The powder particles produced from this alloy by the plasma rotating electrode process (PREP) are spherical in shape with a very small variation in size (the average particle size was about 350 mu m). The particles have a dendritic microstructure and consist of three phases, disordered alpha-Ti, ordered Ti3Al and ordered Ti5Si3. The Ti5Si3 phase is stable on heating up to 1100 degrees C while disordering of the Ti3Al phase occurs near 1000 degrees C. Tensile properties of the cast alloy were studied at temperatures in the range of 20 degrees C to 800 degrees C. The yield strength and tensile strength of the cast alloy are higher than those of a gamma-TiAl-based alloy. The fracture toughness of the alloy is about 17-20 MPa root m within the temperature range of 20 degrees C to 600 degrees C. The oxidation resistance of the alloy was significantly superior to conventional titanium alloys, being similar to that of a silicon nitride ceramic at temperatures up to 950 degrees C. The results obtained suggest that the alloy could potentially be used in high-temperature engine applications up to 800 degrees C.

In the temperature dependence of the yield stress of deformed titanium in the range above 550-600 degrees C, a domain of the abrupt destrengthening is observed, that can be connected with the development of grain-boundary climb. The two processes going on simultaneously (i.e. the assimilation of crystal lattice dislocations by boundary and the sliding of grain-boundary dislocations) result in a two-fold increase of the activation energy of grain-boundary slipping, that initiates the abrupt drop in a stress above 0.7T(PT) for deformed titanium.

The temperature dependences of fracture toughness as well as sequences of fracture mechanisms changes of deformed and recrystallized chromium alloyed with 0,5% (w/w) La2O3 were studied in a wide temperature range. It was found, that the fracture toughness is nonmonotonously depended on temperature. As temperature is raised cleavage fracture toughness increases up to 500 degrees C for deformed state and up to 600 degrees C for recrystallized one. The dynamic deformation ageing is responsible for appearance of brittle intergranular fracture and decreasing the fracture toughness of recrystallized material at temperature above 600 degrees C. Sharp increasing of the dependence of deformed material above 500 degrees C is due to plane-strain to plane-stress transition. The decreasing fracture toughness of deformed material at higher temperature results from changing of fracture mechanisms from cleavage to pore coalescence.

The adaptation of true elastic limit, sigma(c), of molybdenum alloy MHBII (T=0.09-0.61T(melt)) as a function of temperature for the estimation of thermoactivation characteristics permits to identify, the mechanisms of the plastic deformation at its early stages when dislocations concentrate predominantly in the regions adjacent to the grain boundaries. The comparison of these mechanisms with those, which are at the level of yield stress value, discovers their distinctive features.

The fractographic features of polycrystalline chromium alloys fracture have been studied in a brittle state. The fractographic analysis shows that a brittle fracture of chromium occurs by cleavage, and the cleavage crack branching which is typical of chromium, caused the sample to fracture into three parts. It has been established that the crack shape at the moment of branching is almost square and does not depend upon the cross-section shape of specimens. The temperature dependences of a branching crack length and branching stress intensity factor are obtained for polished and notched specimens. It has been established that the temperature dependences of the notched specimen are controlled by fracture toughness and that of the polished specimens is controlled by the crack initiation stage. The least square method is used for approximation of the temperature dependences. Fracture toughness is estimated with a branching stress intensity factor.

The effect of structure and size on the yield stress and fracture toughness of layer composite Cr-V was studied. The relation between the strength and layer thickness was determined. It was shown that composite strength and fracture toughness increase simultaneously and can become in three time larger than these for the base chromium alloy, if the layer thickness is less than 8 mu m.

Temperature dependence of fracture toughness of molybdenum sheet was studied in the temperature range — 196–300 °C. It was found that nonmonotonous behaviour of this dependence is due to the change in cleavage crack nucleation mechanism.

The regularities of changes of the averaged size and misorientations of deformation cells during the high plastic deformation of b.c.c. polycrystals are analysed on the bose of original and literature experimental results. The analysis results in equations omega = alpha e(3/2) and d = K/(Delta sigma " + K'e), where omega is the averaged misorientation angle, d is the averaged cell size, e is the true strain, alpha, K' K, and Delta sigma " are constants of the material in a given structural state. The structural changes ore compared with the work hardening curve.

The features of smooth changes of limit state of molybdenum dislocation cellular structure in passage from high-temperature dynamic: recovery to dynamic recrystallization are studied by methods of building of diagram true deformation - temperature, optical and electron microscopy.

The fracture mechanisms of [100] and [110] chromium single crystals at uni-axial tension in a temperature interval between −75 °C and 50 °C have been studied with scanning electron microscopy. The significant findings are that [100] single crystals exhibit the sub-critical crack growth by cleavage at temperatures above the lower limit of the brittle-to-ductile transition while [110] crystals exhibit cleavage crack branching after a few per cent of plastic deformation. The preferable direction of cleavage crack propagation along the {100} planes is [110]. Planes of microcracking and delamination at the brittle fracture are {112} planes. Fracture energies of [100] and [110] single crystals were estimated by measuring sub-critical cracks and cleavage cracks before branching. The temperature dependence of [100] crystal surface energy was described as the Arrenius's function with activation energy Uo = 0.2 eV. The nucleation of cleavage crack is discussed as a thermoactivated process with the same nature as yield of the BCC metals.