Dispersion-hardened Materials Research Articles

Destruction of reinforced concrete structures of sewage systems

Composites materials are artificially created materials that consist of two or more components that differ in composition and are separated by a pronounced boundary. The development of modern composite materials is associated with the discovery of high-strength whiskers, with the study and use of aluminides and high-strength alloys. At present, various composite materials have been developed and used: fibrous; reinforced with whiskers and continuous crystals and fibres of refractory compounds and elements; dispersion-hardened materials; layered materials; alloys with directional crystallization of eutectic structures; alloys with intermetallic hardening. There are many technologies for producing composites: imbibition of reinforcing fibres with matrix (base) material; cold pressing of components followed by sintering; sediment of the matrix by plasma spraying on the hardener, followed by compression; batch diffusion welding of multilayer tapes of components; joint rolling of reinforcing elements with a matrix, and etc. The use of composites makes it possible to reduce the weight of aircraft, cars, ships, increase the efficiency of engines, and create new constructions with high performance and reliability. The development of composites with high impact resistance is an important direction in the industry. The strength characteristics of a layered composite material are decisive under shear loads, loading of the composite in directions other than the orientation of the layers, and cyclic loading. In this paper, we study the non-stationary interaction of an absolutely rigid body on a two-layer reinforced composite material. The action of the striker is replaced by a non-stationary vertical even distributed load, which changes according to a linear function, in the area of initial contact, which is assumed to be unchanged over time.
 In contrast to the previous articles (Parts I and II), in this papers there is an investigation of the strain-stress state, the fields of the Odquist parameter and normal stresses depending on the material of the first (upper) layer.

Investigation of the Microstructure of Sintered Ti-Al-C Composite Powder Materials under High-Voltage Electrical Discharge.

Dispersion-hardened materials based on TiC-AlnCn are alloys with high heat resistance, strength, and durability that can be used in aircraft and rocket technology as a hard lubricant. The titanium-rich composites of the Ti-Al-C system were synthesized via the spark plasma sintering process. Composite powder with 85% of Ti, 15% of Al, and MAX-phases was processed using high-voltage electrical discharge in kerosene at a specific energy of 25 MJ kg-1 to obtain nanosized particles. This method allows us to analyze the most efficient, energy saving, and less waste-generating technological processes producing materials with improved mechanical and physical properties. An Innova test indentation machine was used to determine the hardness of the synthesized composites. The microhardness of Ti-Al-C system samples was determined as approximately 500-600 HV. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were performed to identify the hard titanium matrix reinforced by intermetallic phases and the clusters of carbides. Three types of reinforcing phases were detected existing in the composites-TiC, Al4C3, and Al3Ti, as well as a matrix consisting of α- and β-titanium. The lattice parameters of all phases detected in the composites were calculated using Rietveld analysis. It was determined that by increasing the temperature of sintering, the amount of aluminum and carbon increases in the carbides and intermetallic phases, while the amount of titanium decreases.

Problem of plane strain state of two-layer body in dynamic elastic-plastic formulation (Part III)

Composites materials are artificially created materials that consist of two or more components that differ in composition and are separated by a pronounced boundary. The development of modern composite materials is associated with the discovery of high-strength whiskers, with the study and use of aluminides and high-strength alloys. At present, various composite materials have been developed and used: fibrous; reinforced with whiskers and continuous crystals and fibres of refractory compounds and elements; dispersion-hardened materials; layered materials; alloys with directional crystallization of eutectic structures; alloys with intermetallic hardening. There are many technologies for producing composites: imbibition of reinforcing fibres with matrix (base) material; cold pressing of components followed by sintering; sediment of the matrix by plasma spraying on the hardener, followed by compression; batch diffusion welding of multilayer tapes of components; joint rolling of reinforcing elements with a matrix, and etc. The use of composites makes it possible to reduce the weight of aircraft, cars, ships, increase the efficiency of engines, and create new constructions with high performance and reliability. The development of composites with high impact resistance is an important direction in the industry. The strength characteristics of a layered composite material are decisive under shear loads, loading of the composite in directions other than the orientation of the layers, and cyclic loading. In this paper, we study the non-stationary interaction of an absolutely rigid body on a two-layer reinforced composite material. The action of the striker is replaced by a non-stationary vertical even distributed load, which changes according to a linear function, in the area of initial contact, which is assumed to be unchanged over time. In contrast to the previous articles (Parts I and II), in this papers there is an investigation of the strain-stress state, the fields of the Odquist parameter and normal stresses depending on the material of the first (upper) layer.

Non-removable butt joints of an aluminum-matrix composite material dispersion-hardened by particles of SiC, made by friction stir welding

Friction stir welding of butt joints of aluminum-matrix dispersion-strengthened composite materials is considered. It is shown that with an increase in the content of strengthening SiC particles, the range of welding modes that ensure the formation of a joint without defects is significantly narrowed. It was found that under cyclic loads, welded joints begin to fail from the face of the weld. Keywords: friction stir welding, aluminum matrix dispersion-hardened composite material, mode, structure, roughness, strength. vikov1956@mail.ru

The Influence of Scale Parameters of Strengthening Phase on Plastic Shear Zone in Heterophase Alloys with Incoherent Nanoparticles

In this paper, the mathematical simulation is used to study and analyze the shear zone or plastic deformation at a meso-level in dispersion-hardened crystalline materials with an aluminum matrix and incoherent nanoparticles. This study also considers both the macro-level or the behavior of the flow stress curves and the micro-level or the formation of linear and point defects. It is found that the size of the shear zone lowers with the growth in the degree of deformation in all the dispersion-hardened materials at issue. The average size of this zone does not depend on scale parameters of the strengthening phase. The formation and accumulation of various dislocation types in the shear zone mostly depend on the particle size.

Fixed joints of dispersion-hardened composite materials based on aluminium, made by friction stir welding

ABSTRACT Structural features and mechanical properties of welded compounds of composite materials on an aluminium basis, with dispersal hardening of particles of aluminium oxide and silicon carbide, obtained by welding friction with mixing, were investigated. It has been shown that the use of friction welding with mixing provides a fairly high level of mechanical properties of compounds of studied composite materials. At the same time, there are no significant phase-structural changes in the seam metal and the accompanying areas of the compound compared to the main material. The mechanical properties and structure of the joints of granular aluminium alloy 01419 and the foundry composite based on the System Al–Zn–Mg have been studied. Welding it is shown that the STP does not initiate significant structural changes in these materials.

Study into the Effect of the Amount of the Strengthening Phase in an Aluminum-Based Dispersion-Hardened Composite on Fracture Regularities

The results of studying the static tensile strength of aluminum-based dispersion-hardened composite materials with various contents of the Al2O3 strengthening phase are given. The materials under study are fabricated according to a new in principle technology based on burning out the aluminum melt when interacting with oxygen or an oxygen–nitrogen mixture. The fractographic patterns of the static fracture surfaces were studied for the samples fractured at maximal stresses. It is established that samples with a low Al2O3 content have a poorly viscous fracture pattern mainly consisting of a single fibrous zone. A radial zone appears in the fractograph with a twofold increase in the amount of the solid phase, while the alternation of viscous fracture, according to the detachment and shear mechanism with the manifestation of a brittle cleavage fracture signs, is observed with a threefold increase in the Al2O3 content. An analysis of fracture profilograms of the samples containing 10 and 30% inclusions of the solid phase reveals no abrupt drop in the surface relief, but an absolutely different fracture character is herewith found. However, in both cases, the form of profilograms is not pronounced by any abrupt relief jumps or extreme profile values, which makes it possible to affirm the stability of fracture processes. This is not true for the fracture of the sample with 20% Al2O3, in which a rather significant one-time drop is observed. The features of varying the fracture surface profile and distinctions over the arrangement place and number of crack nucleation regions in the samples under study are revealed using optical microscopy.

The Influence of in situ Formed TiB2–VB2 Borides on the Structure and Properties of Hot-Pressed B4C–(TiH2–VC) Ceramic System

A method of the reaction hot pressing was used to produce composites from the B4C–(5–15%)(TiH2–VC) system, established the peculiarities of their structures and measured physico-mechanical parameters. The dense dispersion-hardened materials having a high bending strength (Rbm = 420–580 MPa) and increased fracture toughness (KIc = 4.1–4.8 MPa·m1/2) on retention of the HKN = 19–20 GPa are promising for the use in the conditions of the severe abrasive wear.

The Influence of Incoherent Nanoparticles on Thermal Stability of Aluminum Alloys

In this paper, the mathematical simulation is used to study the effect from the size of incoherent nanoparticles on thermal strength of heterophase aluminum alloy in materials with the similar volume fraction of the strengthening phase. It is shown that during the deformation process, the particle size affects the evolution of shear dislocations, prismatic dislocation loops and dislocation dipoles. It is found that if the volume fraction of incoherent particles is low, the behavior of the flow stress curves depends on the particle size. The paper identifies the variation range of scale parameters for thermal stability of dispersion-hardened materials.

Mathematical Modelling of the Calculation of the Stiffness Characteristics of Composite Materials

This article provides an overview of the analysis of the selection of the reduced (equivalent) characteristics of the material. The selection and definition of the elastic characteristics of composite materials depend on many factors: the geometry of the design element of the structure, the stress-strain state and the mathematical model of this state, the calculation methods, and the necessary accuracy of the solution. Technical methods for calculating elements such as rods, plates, and shells are analytically related to the formulation of resolving equations. One of the most common approaches to implementing practical tasks is the method of bringing an inhomogeneous material to a homogeneous isotropic or orthotropic material. In this paper, the most common options for choosing the mechanical characteristics of a composite material are considered. A restriction is introduced - work in the elastic region and the compatibility of deformations of the matrix with reinforcement. These limitations are in good agreement with the reliability of the construction. The article gives a qualitative analysis of formulas depending on the task. A choice of design for a dispersion-hardened material is proposed for a uniform reinforcement distribution for bent elements. The above analysis of formulas for determining the efficiency of physical and mathematical characteristics of composite rods, plates, and shells, allows for the calculation of more complex problems.

NANOSTRUCTURAL MECHANICALLY ALLOYED DISPERSION STRENGTHENED MATERIALS BASED ON METALS

Development of modern industries requires creation of new materials, which have, along with special properties, high strength and heat resistance. The most difficult is the provision of the latter. To increase it, it is necessary to reduce the amount of free movement of dislocations to a maximum permissible value, localize movement of defects of the crystal structure within the grain (subgrain), minimize the runoff of defects of the crystal structure at grain boundaries, exclude intergranular sliding, which can be successfully realized in dispersion-hardened materials. To obtain them, a promising technology is based on the reaction mechanical alloying. The article presents the results of the author’s work, which made it possible to establish the regularities in the formation of phase composition, structure and properties at all stages of obtaining mechanically alloyed dispersed-hardened materials based on metals, which are the basis for the production of basic structural alloys-aluminum, copper, iron and nickel. These alloys are used for products operating under severe temperature-strength conditions – at temperatures reaching 0.85T ml of the substrate. They have tensile strength 1.2–1.5 times higher than that of analogues, and on their basis a new area of materials science of structural materials was created – nanostructured mechanically alloyed dispersed-hardened materials based on metals. The most promising areas of application of technologies based on reaction mechanical alloying in the field of materials science are: 1) high-strength materials for machine parts, tooling and products of various functional purposes operating under severe temperature and force conditions; 2) powders for gas-thermal spraying and coating of them; 3) nanocrystalline modifying ligatures and modifiers. The results of industrial introduction are given – two small-scale enterprises for the production of import-substituting science-intensive products were created.

Evolution of Dislocation Subsystem Components During Plastic Deformation Depending on Parameters of Strengthening Phase with L12 Superstructure

The paper presents results of mathematical modelling of plastic deformation in dispersion-hardened materials with FCC crystal system and L12 superstructure particles. Research results show that the size and the distance between particles of the strengthening phase affect the strain hardening and the evolution of the dislocation subsystem of the FCC alloy hardened with coherent L12 superstructure particles. It is found that increased size of ordered particles or decreased distance between them enhances the abnormal growth in the flow stress and the density of the dislocation subsystem components. Investigations show that prismatic dislocation loops predominate in the dislocation subsystem of materials having a nano-dispersion strengthening phase.

Modeling of Plastic Deformation of Dispersion-Hardened Materials with L12 Superstructure Particles

The paper presents a mathematical model of plastic deformation in FCC materials strengthened with particles having L12 superstructure. The model is based on balance equations for various deformation defects with regard to their transformation during plastic deformation. Research results show that the size and distance between particles of the strengthening phase affect the thermal strengthening, strain hardening and the evolution of the dislocation subsystem of the FCC alloy strengthened with coherent particles with L12 superstructure. The temperature anomaly is detected for strength properties of materials having different volume fractions of the strengthening phase. It is shown that the incoherent strengthening phase increases the flow stress of the material and suppresses the temperature anomaly of its strength properties.

Study of structural features, strength properties, and heat resistance of a dispersion-hardened composite material based on nickel intermetallide

A method for production of a composite material (CM) hardened by hafnium oxide particles with columnar structure based on VKNA-1B grade alloy is described. The method involves making heat-resistant nickel alloy powders with a particle size ≤100 μm. The obtained powders of the matrix VKNA-1B alloy are dispersed and alloyed mechanically in an attritor with the hardening additive HfO2, and next the semifinished material is extruded with subsequent rolling. The production technique parameters of the CM based on the nickel aluminide–HfO2 system are determined. The developed material is intended for advanced aircraft engines, first of all, parts of a combustor, doors of a controlled nozzle, and nozzle blades of gas turbine engines (GTEs). The physical and mechanical properties and the heat resistance of the composite material obtained are studied.

Investigation of Thermal Hardening of the FCC Material Containing Strengthening Particles with an L12 Superstructure

UDC 539.37 A mathematical model of plastic deformation of dispersion-hardened materials with an fcc matrix containing strengthening particles with an L12 superstructure having a coherent relationship with the matrix is presented. The model is based on the balance equations of deformation defects of different types with taking into account their transformation during plastic deformation. The influence of scale characteristics of the hardening phase, temperature, and deformation rate on the evolution of the dislocation subsystem and strain hardening of an alloy with an fcc matrix hardened by particles with an L12 superstructure is studied. A temperature anomaly of mechanical properties is found for the materials with different fcc matrices (Al, Cu, Ni). It is shown that the temperature anomaly is more pronounced for the material with larger volume fraction of the hardening phase.

Plastic Behavior of Heterophase Alloys with a Fcc Matrix Hardened by Particles with an L12 Superstructure

Using a mathematical model of plastic deformation of dispersion-hardened materials, the effect of the scale characteristics of the hardening phase with an L12 superstructure on the temperature dependence of the flow stress and evolution of the dislocation subsystem of heterophase alloys with the fcc matrix is studied. It is found that in materials with a nanoscale hardening phase, more intensive strain hardening and more severe temperature anomaly of mechanical properties is observed, than in materials containing larger particles at the same volume fraction of the hardening phase.

STRUCTURE AND PROPERTIES OF THE TI–NB–C DISPERSION-HARDENED MATERIAL WITH A BINDER

The influence of a metallic nickel-based binder on the structure and properties of the (Ti, Nb)C ceramic material is investigated. The samples are fabricated by technology of SHS forced compaction with the subsequent thermal treatment in a vacuum furnace at 850 °C for 1 h. The composition and structure of fabricated samples are investigated by XPA, SEM, and EDS. Supersaturated solid solutions based on carbide (Ti, Nb)C decompose after annealing with the formation of nanodimensional phases NbCo NbAl in a binder. The β-(Ti, Nb) solid solution is a dispersed phase at a low binder content (5 %), and the (Cr, Al) solid solution—at 20 %. Properties of fabricated materials such as density, porosity, hardness, strength, and heat resistance are determined. A binder decreases the material porosity from 9 to 2 %, which increases the mechanical properties and heat resistance. The dispersion-hardened material of the Ti–Nb–C system with binder contents of 20 and 30 % is recommended for the application as a constructive and functional ceramics.

Mathematical modeling of the deformation behavior of heterophase alloys at various characteristics of the strengthening phase

Further development of techniques and technologies urgently requires the creation of new materials with unique properties. One of the most popular and promising areas in materials science is the creation of composite materials with desired properties. Currently, in practice peening by dispersed particles is widely used to improve the properties of metal materials. It is necessary to investigate in detail the influence of various factors on the behavior of dispersion-hardened materials in a variety of conditions to control the properties of materials. Physical experiment, in addition to large investments, often takes a long time. This paper presents a mathematical model of plastic deformation of dispersion-hardened materials with a face-centered cubic (fcc) matrix and with incoherent and coherent nanoscale particles. Application of this model can significantly reduce the time of research and necessary amount of physical experiment. The results allow optimizing of experiment, identifying ways to improve the properties of the materials.

Influence of Hardening Phase of Coherent and Incoherent Coupling with FCC Matrix on Evolution of Deformation Defect Subsystem and Strain Hardening of Heterophase Alloys

A mathematical model of plastic deformation of dispersion-hardened materials with FCC matrix and strengthening particles having various coupling with the matrix is presented. The model is based on the equations of balance of deformational defects of various types with allowance for their transformation in the process of plastic deformation. The influence of scale characteristics of the strengthening phase, temperature, and strain rate on the evolution of the dislocation subsystem and on strain hardening of an alloy with FCC matrix is investigated.

Influence of the Type of Phase Boundary on the Deformation Behavior and Evolution of a Defect Subsystem of Heterophase Alloys with FCC Matrix, Strengthened by Micro- and Nanoparticles

A mathematical model of plastic deformation of dispersion-hardened materials with FCC matrix and strengthening particles having various coupling with the matrix is presented. The model is based on the equations of balance of strain-induced defects of various types with allowance for their transformation in the process of plastic deformation. The influence of scale characteristics of the strengthening phase, temperature, and strain rate on the evolution of the dislocation subsystem and on strain hardening of an alloy with FCC matrix is investigated. Strain hardening is observed in materials with nanosized strengthening phase that is more intense than in materials with larger particles, independent of phase coupling with the matrix, for the same volume fraction of the strengthening phase.