Melting of high- and low-density polyethylene in mixtures with aluminum after plastic deformation under high pressure

Mixtures of low- and high-density polyethylene with aluminum were subjected to plastic deformation at a pressure of 0.5–4.0 GPa. DSC analysis showed that heating of samples at 110 and 140°C results in addition to the melting of polymers in the melting of ultrafine polymer crystallites at 40°C and also in chemical interaction at 80°C at the polymer–metal phase interface; crystallization of the polymer phase in deformed mixtures occurs at 14–18° higher than that of the initial polymers. Enthalpies of thermal processes in baric dependences reached extremum values at the pressures at which restructuring of the electron subsystem occurs in the deformed mixtures.     

Heat processes in mixtures of polymers with cyanuric acid after plastic deformation under high pressure according to calorimetric data

Mixtures of cyanuric acid with different polymers are subjected to plastic deformation under pressure of 1 GPa, and the DSC method is used to establish that endothermal processes with enthalpies that can reach 50 J g^-1 occur in deformed mixtures under heating in the range of 50–250°C. The occurrence of endothermal processes is related to the destruction of intermolecular bonds formed at the acid–polymer interface and due to formation of double electric layers and appearance of interphase electrostatic attraction.     

Thermal effects in mixtures of aluminum with polyvinyl chloride after plastic deformation under high pressure

PVC and mixtures of PVC with aluminum of different compositions were subjected to plastic deformation under a pressure of 0.5–3.0 GPa using setups of Bridgman anvil type. DSC data showed that ΔC _p in the polymer was doubled and T _c increased by 20°C. Chemical reactions occurred on the interfaces of freshly opened metal surface/polymer phase under pressure treatment in the mixtures. They were accompanied by formation of volatile and soluble products. When metal-polymer mixtures were heated under pressure after deformation, chemical reactions occurred in them starting at 40°C and reaching the maximum intensity in the temperature range of polymer transition from the vitreous to highly elastic state. Thermogravimetric studies of mixture samples of different compositions were carried out.     

A study of the mixtures of polystyrene and polyvinyl fluoride with aluminum after plastic deformation under high pressure using DSC and thermogravimetry

Mixtures of powdered polystyrene and polyvinyl fluoride with aluminum exposed to plastic deformation under pressure of 1 and 4 GPa, have been studied by DSC and thermogravimetry. It has been established that, in the deformed mixtures at temperatures up to 200°C, exothermal processes take place. Interaction between polymer decomposition products and aluminum has been studied, as have its oxidation and nitrogenation.     

Activation of thermal processes in mixtures of some vanadium compounds with LiOH as a result of plastic deformation under high pressure

V₂O₅, V₂O₃, HVO₃, and mixtures of these compounds with 15% LiOH were subjected to plastic deformation at a pressure of 2 GPa and room temperature on high-pressure testing machines of the type of Bridgman anvils. The investigation of the samples was performed using differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis. The presence of LiOH in the mixtures decreased the thermal stability of vanadium compounds. During plastic deformation the LiV₃O₈ phase was formed in mixtures, the amount of which increased with heating the samples to 200°C. It is assumed that the ions that form by treatment under pressure can affect the structure formation processes in mix samples.     

高温塑性变形中孔隙性缺陷自修复机理

通过物理模拟研究20MnMo材料内部孔隙性缺陷的修复过程,建立了孔隙性缺陷高温修复的修复再结晶机理。将孔隙性缺陷修复分为3个阶段:修复再结晶晶粒形核准备、修复再结晶晶粒形核、修复再结晶晶粒长大和改建,其中修复再结晶形核主要存在3种方式。孔隙性缺陷修复再结晶机理的提出对深入研究塑性变形中缺陷修复以及塑性变形对性能的影响作用具有重要理论意义,对缺陷修复规律在生产实际中应用具有重要的实用价值。     

Dislocation structure of cementite in granular pearlite after cold plastic deformation

Cementite microstructure of the U8 steel with a granular pearlite structure has been investigated by the method of electron microscopy. It has been established that, at the early stages of deformation, carbide particles are deformed through the movement of stacking faults, which are characterized by an α[010] partial shift in the (001) planes of cementite. The Burgers vector, the slip plane [010](001) of the split dislocations forming pileups, and deformation bands have been determined using gb analysis. The stacking fault energy has been estimated in a (001) cementite plane: γ_sf ～ 12.8 mJ/m². With increasing degree of deformation, an additional slip has been shown to occur in cementite by the system [100](011).     

Effect of rolling-assisted deformation on the formation of an ultrafine-grained structure in a two-phase titanium alloy subjected to severe plastic deformation

The effect of rolling in the temperature range 450–650°C on the fragmentation of the primary phase in a hot-rolled VT6 alloy rod preliminarily subjected to severe plastic deformation by equal-channel angular pressing at 700°C (scheme B _c, the angle between the channels is 135°, 12 passes) is studied. Rolling at 450°C without preliminary ECAP is shown not to cause α-phase fragmentation and to favor intense cold working of the alloy due to multiple slip. ECAP provides partial fragmentation of the initial structure of the α phase and changes the morphology of the retained β phase: it transforms from a continuous matrix phase into separated precipitates located between α particles. This transformation activates the fragmentation of the α phase during rolling at 550°C owing to the development of twinning and polygonization processes apart from multiple slip. Both a decrease (to 450°C) and an increase (to 625–650°C) in the rolling temperature as compared to 550°C lead to the formation of a less homogeneous and fragmented structure because of weakly developed recovery and intense cold working in the former case and because of the beginning of recrystallization and the suppression of twinning in the latter case. A relation between the structure that forms upon SPD followed by rolling and the set of its properties is found. A general scheme is proposed for the structural transformations that occur during ECAP followed by rolling at various temperatures.     

Dislocation pattern formation in the course of plastic deformation

The self-consistent evolution of a two-dimensional screw dislocation ensemble is investigated in plastically deformed crystal. A generalized isotropical multicomponent model for dislocation dynamics is proposed. It is found that the intense relaxation process of the excess Burgers vector of the two-dimensional screw dislocat ensemble results in the establishment of an effective diffusion regime for average density ρ,(r,t) evolution. In a two-component system this gives rise to mutual component interdiffusion, playing an important role in the nonlinear evolution stage. Two types of spatial structures are found to emerge in the course of plastic deformation: i) a one-dimensional structure, which is established due to rivalry between unstable modes and results in the emergence of reorientation bands in the crystal; ii) a two-dimensional structure, which is established due tocooperation of the modes and is responsible for the hexagonal cell formation in the crystal. It is shown that for a sufficiently low strain level a hexagonal cellular structure is preferable.     

Increase in the plasticity of molybdenum after high-rate deformation under pressure

The dependence of the plasticity of polycrystalline molybdenum on the strain rate has been studied after deformation performed under pressure and at an ambient temperature of 293 K. The samples were deformed in tensile tests. The strain rate of tensile deformation and the pressure in each experiment are constant. The range of the strain rate is 8.3 × 10^?7 to 8.3 m/s and the pressure is 0.1–500 MPa. At a pressure of ambient atmosphere, molybdenum at a strain rate less than 200 s^–1 in value (10^2.3 s^–1) fractures in a brittle manner with zero residual strain. The brittle fracture of the working part of a cylindrical sample occurs simultaneously in several places. The molybdenum plasticity decreases in the range of low strain rates regardless of the pressure and, on the contrary, plasticity under pressure increases in the range of high strain rates. The strain rate of tensile deformation at which the dependence of the plasticity on the strain rate under pressure changes is 8.3 × 10^–4 m/s (a strain rate of 0.25 s^–1). The high plasticity of molybdenum after deformation under pressure is observed at high strain rates.     

强交变磁场对冷塑性变形铝合金性能影响的研究

为揭示强交变磁场对金属塑性成形后力学性能的影响规律,采用对比实验的方法,研究了冷塑性变形后LY12铝合金试件在强交变磁场作用前后的残余应力和微观组织变化情况,残余应力测试采用超声波无损检测方法。研究结果表明,在足够强度的交变磁场作用下,可以使经过冷塑性变形后的LY12铝合金发生有利于提高其力学性能的变化,均匀化了由于塑性变形引起的组织缠结,细化了晶粒,并降低了残余应力。强交变磁场可以作为改善冷塑性变形后金属材料力学性能的有效方法。     

Effect of hot plastic deformation in the austenite interval on structure formation in low-alloyed low-carbon steel

The specifics of phase transformations under continuous cooling and problems of structure formation after hot plastic deformation and accelerated cooling of low-alloyed low-carbon steels are considered. The effect of hot plastic deformation in the austenite interval on the kinetics of γ → α transformation and the formation of a ferrite-bainite structure is demonstrated.     

The mechanism of nanocrystalline structure formation in Ni3Al during severe plastic deformation

The microstructure evolution of the intermetallic compound Ni₃Al during severe deformation by torsion under high quasi-hydrostatic pressure, which eventually results in the formation of a disordered nanocrystalline structure with a high level of internal stresses, was investigated as a function of the amount of shear strain. At the microstructural level, the crystals were first fragmented by the propagation of twins, then nanosized equiaxed crystallites with high misorientations were formed. At the macroscopic level, there is evidence that the cold-worked structure first formed at the sample surface and then propagated into the whole volume.     

高压条件下Pd-Ni合金熔体非晶形成过程及微观结构演化的分子动力学研究

利用分子动力学模拟方法,模拟了高压对Pd55Ni45合金非晶形成能力及快冷过程中局部结构的影响.在压力作用下,形成非晶的临界冷却速率明显下降.随着压力的增大,在相同的冷却速率下,体系中形成的团簇更多的是理想二十面体结构,不是缺陷二十面体结构.     

A study of the surface of niobium-base alloy after plastic deformation, nitriding, and double annealing

As a rule, niobium alloys subjected to mechanical or chemical heat treatment are poorly deformable in the process of manufacturing parts from them and have an unsatisfactory thermal stability. A combination of plastic deformation with chemical heat treatment (MCHT) of niobium alloys provides a high thermal stability and increases the strength by a factor of 3–4 while preserving a high ductility. It is interesting to determine the changes in the composition of the surface layers of alloys in different stages of MCHT. The present work describes the properties of specimens of industrial alloy 5VMTs after MCHT with the use of a local three-dimensional method of x-ray photoelectron spectroscopy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 20–21, June, 1997.     

Anomalous plastic flow of cerium near the isomorphic phase transformations under high hydrostatic pressure

Compression tests have been carried out on cerium specimens at room temperature (0.27T_m) under high hydrostatic pressures up to 1.2 GPa. A strong increase of the yield strength was observed for both isomorphic γ and α phases at pressures approaching the γ↔α isomorphic phase transformations. That increase was in good agreement with the theory of dislocations when the dependence of elastic properties and a lattice parameter of cerium on pressure was applied to calculate the effect of pressure on the yield stress controlled by the edge dislocations. An anomalous strong decrease of the yield stress was observed in both γ and α phases in the vicinity of both γ↔α phase transformations. That phenomenon was explained as an effect of pressure induced new phase atoms through spreading the cores of edge dislocations. A complete disappearance of work hardening in both γ and α phases was also observed in the wide range of pressures. The influence of hydrostatic pressure on the energy of grain boundaries of both phases was considered to be responsible for that property. The ratio of the grain boundary energy to the Peierls energy is suggested to be a criterion of the work hardening ability of f.c.c. polycrystals.