Gradient Structure of the Layer Applied to Hardox 450 Steel by Fe–C–Cr–Nb–W Powder Wire after Electron-Beam Treatment

Surfacing with composite coatings strengthened by carbide, boride, and other particles is currently of great interest in materials physics. The performance of the applied layer is primarily determined by the phase composition of the coating. To permit the selection of coatings capable of withstanding extremal operating conditions, including high loads and abrasive wear, their properties and structure must be investigated in detail. In the present work, state-of-the-art techniques in materials physics are used to study the structure, phase composition, and tribological properties of coatings applied to Hardox 450 low-carbon martensitic steel by Fe–C–Cr–Nb–W powder wire and then subjected to electron-beam treatment. The electron-beam parameters are as follows: in the first stage, energy density per pulse E_S = 30 J/cm²; pulse length τ = 200 μs; and number of pulses N = 20; in the second stage, E_S = 30 J/cm²; τ = 50 μs; and N = 1. These conditions are selected on the basis of calculations of the temperature field formed in the surface layer of the material by a single pulse. It is found that electron-beam treatment of an applied layer of thickness about 5 mm leads to modification of a thin surface layer (about 20 μm), consisting largely of α iron and the carbide NbC; small quantities of the carbides Fe₃C and Me₆C (Fe₃W₃C) are also present. This modified surface layer differs from the unmodified coating mainly in terms of the morphology and dimensions of the secondary-phase inclusions. In the modified surface layer, the inclusions are smaller and take the form of thin layers along the grain boundaries. In the unmodified coating, the inclusions are mainly rounded particles, chaotically distributed within the grain. After electron-beam treatment, the wear resistance of the applied layer increases by a factor greater than 70 with respect to Hardox 450 steel, while the frictional coefficient is significantly less (about a third as much).     

Improvement in the Mechanical Properties of Silicon Nitride Ceramic in High-Temperature Deformation Processes

Studies have been made on the changes in structure and properties of sintered materials: Si₃N₄ - 5 mass% Y₂O₃ - 2 mass% Al₂O₃, Si₃N₄ - 5 mass% Y₂O₃ - 5 mass% Al₂O₃, and Si₃N₄ - 40 mass% TiN on deformation in a high-pressure chamber of toroid type (pressure 4–5 GPa, temperature 1000–1600 °C), and also by direct extrusion with degrees of reduction of 55 and 72% (temperature 1750–1850 °C, pressure on the plunger 20–30 MPa). After pressure-chamber treatment, the materials have elevated mechanical characteristics: HV₁₀ ≈ 16.7 GPa, K_Ic up to 8.4 MPa · m^1/2 for the system Si₃N₄ - Y₂O₃ - Al₂O₃; and HV₁₀ ≈ 16.9 GPa, K_Ic up to 9.4 MPa · m^1/2 for Si₃N₄ - TiN. A structure feature is the small size of the coherent-scattering regions: 51 nm for Si₃N₄ and 65 nm for TiN in the system Si₃N₄ - TiN, and 33 nm for specimens in the system Si₃N₄ - Y₂O₃ - Al₂O₃. High-temperature extrusion results in a structure with β-Si₃N₄ grains elongated along the deformation direction. The anisotropic structure has K_Ic values in directions perpendicular to and parallel to the direction of extrusion of 11.5–12.0 MPa · m^1/2 and 7.5–7.8 MPa · m^1/2, respectively. The hardness after extrusion becomes 16.0 GPa.     

Physicomechanical properties of a composite material based on ultrahigh-molecular-weight polyethylene filled with ceramic particles

The effect of the shape of filler particles on the mechanical properties of a composite material based on ultrahigh-molecular-weight polyethylene produced by thermal compacting after preliminary mechanical activation of the initial materials is studied. As a filler, Al₂O₃ in the form of an ultradispersed powder with a particle size of 200 nm or as 1-??m microspheres is used. The effects of the fillers of both types on the mechanical properties of the composite material is found to be positive and comparable in the concentration range under study (1?C10 wt %). The degree of matrix hardening depends on the shape of filler particles.     

Effect of high pressure on the structure and properties of materials based on boron carbide

The effect of high pressure on the structure and properties of B₄C-SiC and B₄C-Al ceramics is studied. The effect of high pressure on micromechanical properties and crack resistance factor K_Ic of composite materials is investigated. High isostatic pressure treatment at 1300–1400°C leads to improvement of material mechanical properties and structure.     

Electroerosion behavior of a ceramic based on boron carbide: Phase composition, structure, and properties of protective spark coatings

Measurements have been made on the erosion resistance of B₄C-15% TiB₂ materials made by reactive sintering on hot pressing of B₄C-TiO₂-C powder mixtures. The composite material is used as an electrode for treating steel and titanium surfaces in spark alloying. It is shown that the method of preparing the boron carbide influences the erosion resistance of the ceramic much less than it does for the mechanical properties. The surface layers of the electrode materials are affected by the electrical discharge and give rise to secondary structures because of chemical interaction between the electrode materials on the one hand and elements in the gas medium on the other. The properties of these structures are responsible for the erosion characteristics of the electrode material and for the compositions and qualitative properties of the coatings.     

Preparation of Aluminum Metal Matrix Composite with Novel In situ Ceramic Composite Particulates, Developed from Waste Colliery Shale Material

A novel method is adapted to prepare an in situ ceramic composite from waste colliery shale (CS) material. Heat treatment of the shale material, in a plasma reactor and/or in a high temperature furnace at 1673 K (1400 °C) under high vacuum (10^?6 Torr), has enabled in situ conversion of SiO₂ to SiC in the vicinity of carbon and Al₂O₃ present in the shale material. The composite has the chemical constituents, SiC-Al₂O₃-C, as established by XRD/EDX analysis. Particle sizes of the composite range between 50 nm and 200 μm. The shape of the particles vary, presumably rod to spherical shape, distributed preferably in the region of grain boundaries. The CS composite so produced is added to aluminum melt to produce Al-CS composite (12 vol. pct). For comparison of properties, the aluminum metal matrix composite (AMCs) is made with Al₂O₃ particulates (15 vol. pct) with size <200 μm. The heat-treated Al-CS composite has shown better mechanical properties compared to the Al-Al₂O₃ composite. The ductility and toughness of the Al-CS composite are greater than that of the Al-Al₂O₃ composite. Fractographs revealed fine sheared dimples in the Al-CS composite, whereas the same of the Al-Al₂O₃ composite showed an appearance of cleavage-type facets. Abrasion and frictional behavior of both the composites have been compared. The findings lead to the conclusion that the in situ composite developed from the colliery shale waste material has a good future for its use in AMCs.     

Development of a high-performance green Fe–Al2O3 composites using Bayan Obo minerals: Enhancement effects of CeO2

With the deepening understanding for the concept of sustainable development, the utilization of minerals is no longer limited to the traditional way. In this study, an environment friendly method for preparing Fe–Al₂O₃ composites by using natural minerals was investigated. Additionally, the effects of CeO₂ on the properties of composites were studied. The mechanical properties of Fe–Al₂O₃ composites prepared by natural minerals are affected by the brittleness of glass phase. The strength and toughness of the glass phase in the composite are improved successfully by using rare earth oxides, indicating that the natural rare earths in Bayan Obo minerals have an enhanced influence on the properties of composite materials. The results show that the properties of glass phase can be significantly improved by addition of CeO₂. At the optimal addition of 3 wt% CeO₂, the composite achieves the density of 4.21 g/cm³, flexural strength of 401 MPa, Vickers hardness of 13.07 GPa and fracture toughness of 6.58 MPa⋅m^1/2. The composite has excellent mechanical properties, which can be used in engineering as a cheap structural material. This study aims at reducing waste emissions, improving energy efficiencies and avoiding waste of rare earth resources during the preparation of composite materials.     

Structure and properties of thin ceramic coatings in the system AlN-TiCrB2

The structure, composition and properties of coatings on Si, Al₂O₃ and GaAs single crystals prepared by radio-frequency magnetron sputtering of a AlN-TiCrB₂ target prepared by powder metallurgy are studied. Coating phase composition is different from that of the target material due to oxidation of aluminum nitride and its dissociation under ion bombardment conditions. The coatings have a very fine structure and marked resistance to high-temperature oxidation due to formation of solid solutions in the systems Al₂O₃-TiO₂-Cr₂O₃ and Al₂O₃-B₂O₃. The increase in mass of the target material at 1300°C is 1.4 mg/cm². After high-temperature oxidation the reinforced fine structure of the coating forms as interwoven Al₂O₃ fibers. Coatings of (AlN-TiCrB₂)-Al₂O₃ and (AlN-TiCrB₂)-GaAs are thermally stable up to 900°C and have a high microhardness (H _μ) and crack resistance (K_Ic = 4.7–3.3 MN/m^3/2). With an increase in annealing temperature (T ≥ 1000°C) coating mechanical properties worsen, but their adhesive strength increases. The AlN-TiCrB₂ target material may be recommended for preparing wear-and corrosion-resistant coatings on tools, and also on critical components operating under extreme conditions. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 39–47, May–June, 2006.     

Structure and strength of Al,Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C · s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ’ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

Effects of dispersal and mechanical boron alloying on the thermal stability of hydride phases in the Ti-B-H system

Methods have been applied from scanning electron microscopy, hydrogen thermal desorption, XRD, and differential thermal analysis on the effects of grain size and alloying with boron as regards the thermal stability and decomposition temperatures of hydride phases in mechanical alloys in the Ti-B-H system. The alloys were prepared by high-energy processing for 50 h in a planetary ball mill with mixtures of TiH_1.9 + 9 mass% B + 13 mass% Ti and also with TiH_1.9 + 50 mass% TiB₂ at speeds of 1000 rpm, in addition to mixtures of TiH_1.9 + 40 mass% B and TiH_1.9 + 50 mass% TiB₂, which were treated for 20 min at speeds of 1680 rpm. The dispersal on mechanical treatment and the addition of boron to the titanium hydride powder have substantial effects on the thermal stability. The processing of the mixture TiH_1.9 + 9 mass% B + 13 mass% Ti lasting 50 h in argon gave temperatures for the dissociation of the Ti(B, H)_x hydride phase in the mechanical alloy lower by 300 deg than the decomposition temperature for the initial titanium hydride TiH_1.9. The mechanisms have been identified for the effects of the dispersal and boron alloying on the thermal stability of the titanium hydride.     

Structure and strength of Al, Cu-Al3Ni directionally solidified composites

A series of Al₃Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 10⁴ °C. s/mm² (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al₃Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m² were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ′ phase. Massive Al₃Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.     

Fabrication of Al2O3/(ZrB2 + TiB2) Composite Using MACS and Microwaves

Because of the excellent thermal and mechanical properties of engineering ceramics, they have been used as structural materials or composite matrixes and reinforcements in recent years. Alumina, titanium diboride, and zirconium diboride have found important uses in the past two decades. In this study, Al₂O₃/(ZrB₂ + TiB₂) ceramic composite powders were fabricated in situ and mechanical activation by milling was used to assist combustion synthesis (CS). A mixture of Al, ZrO₂, TiO₂, and B₂O₃ powders were used as raw materials. Mechanical activation was done using ball milling of different durations. Afterward, combustion was initiated using microwaves on the activated mixtures. X-ray diffraction (XRD) and scanning electron microscopy were used to investigate the purity and microstructure of the products. XRD analysis of the samples in the final stages of the process revealed that Al₂O₃/(ZrB₂ + TiB₂) composite powder was successfully fabricated using mechanical activation and CS, but that the CS reaction did not occur in unmilled samples. It was shown that increasing milling time from 3 to 10 hours increased purity and homogeneity of the products to the point that no noticeable impurity existed in the samples milled for 10 hours.     

Thermomechanical deformation modeling of Al2xxxT4/SiCp composites

A constitutive model for metal matrix composites is developed and its capabilities for predicting cyclic isothermal and cyclic thermomechanical behavior are demonstrated. The silicon carbide particulate reinforced Al2xxxT4 alloy was studied experimentally and theoretically with the model. Cyclic stress-strain behavior of 15 and 20% reinforced silicon carbide particulate reinforced Al2xxx-T4 were successfully predicted at temperatures of 20, 200 and 300°C at strain rates between 3 × 10⁻⁵s⁻¹ and 3 × 10⁻³s⁻¹. The themomechanical stress-strain behaviors (T_min = 100°C, T_max = 200, 300°C) were studied experimentally and the results were closely predicted when temperature-strain phasing was in-phase and out-of-phase. This study clarifies the influence of mechanical property mismatch in the elastic and in the inelastic ranges vs the thermal property mismatch on composite and the matrix behaviors. The transverse and hydrostatic stresses in the matrix, developed during cyclic loading, are reported for both isothermal and thermomechanical loading conditions.     

Magnetic and structural properties of hot pressed Cu–SmCo5 composites obtained by mechanical alloying

Abstract

Cu–8 wt-%SmCo₅ alloys were obtained through mechanical milling for novel industrial applications. Copper and SmCo₅ powder mixtures were mechanically alloyed in a planetary ball mill to disperse SmCo₅ fine particles in the copper matrix with the aim to modify the structural, mechanical, electrical and magnetic properties. The resulting alloyed powders were characterised as a function of milling time. Under the magnetic field, SmCo₅ particles achieved M_s to improve the soft magnetic properties of copper–8 wt-%SmCo₅ to be used in dielectromagnetic components. The magnetic properties of Cu–8 wt-%SmCo₅ powders reached their optimum values after milling time ranging from 10 to 15 h. The consolidation of milled alloy powders was performed by uniaxial hot pressing at 923 K for 2 h under argon atmosphere to obtain dense compacts. The consolidation process resulted in good dense metal matrix composite materials with adequate properties of compression strength >900 MPa, 95 HRB in hardness, electrical conductivity up to 43% of that of the International Annealed Copper Standard (IACS) and magnetic properties such as coercive field, saturation and remanent magnetisation obtained at 218 Oe, 70·23 emu g^?1 and 6·09 emu g^?1 respectively at 300 K. The existence of a coercive field and a little magnetic memory of the consolidated system is a typical behaviour of magnetically soft materials. The variation of electric and magnetic properties and its dependence on structure strength change with milling time were discussed.     

Composite SHS materials based on titanium carbide and nikelide doped with a refractory component

This study is devoted to the synthesis and investigation of composite ceramic materials based on titanium carbide and nickelide with the use of the effect of dispersion strengthening by force of the dedicated alloying of reactionary mixtures with a nanodispersed refractory component. The influence of nanodispersed particles on the main combustion parameters in conditions of quasi-isostatic compression is shown. The phase composition and the structure of compact synthesis products, in which the main phase components are TiC and the Ti _x Ni _y intermetallic compound, are investigated. It is established that doping with a nanocomponent does not vary the phase composition qualitatively but leads to a substantial modification of the structure of the materials, at which the average grain size of the main refractory component decreases by a factor of 1.5–3.5. In addition, a similar effect is observed with a decrease in the TiC concentration in the composition of the samples. Complex investigations into the physicomechanical properties and heat resistance of fabricated materials are performed. The effect of the positive influence of refractory nanoparticles on such characteristics of alloys as hardness, strength, Young modulus, and durability to high-temperature oxidation are shown.     

Influence of additives of Al2O3 on properties of aluminum nitride-based ceramic

The properties of AlN-based materials with additives of 5–50 mass% Al₂O₃ are investigated. It is established that addition of Al₂O₃ to AlN increases the oxidation resistance of the materials as well as their mechanical strength and thermal resistance while preserving their electroinsulating properties and corrosion resistance to molten metals. AlN-Al₂O₃ composites may be used in high-temperature technology as refractory materials, electrical insulators, as well as radio-transparent materials.     

Phase composition, structure, and properties of aluminum materials mechanically alloyed with boron

The paper focuses on the formation of phase composition, structure, and properties of high-strength aluminum materials that are mechanically alloyed with boron and have a large effective thermal-neutron capture cross-section. A technology based on reactive mechanical alloying is proposed. It is intended to produce dispersion-hardened nanostructured materials in the Al-B system. Structural high-temperature materials with a low density and a great effective thermal-neutron capture cross-section can be obtained by complex alloying of aluminum with elemental boron (up to 40%) and B₂O₃ (1.5%). When the boron content reaches its maximum (40%), the strength of the material is σ_t = 380 MPa and σ ₁₀₀ ⁵⁰⁰ = 101 MPa; when the boron content decreases to 10%, the strength increases to σ_t = 560 MPa and σ ₁₀₀ ⁵⁰⁰ = 150 MPa.     

Modification of the structure of powder coatings on nickel and chromium-nickel bases by introducing nanoparticles of titanium diboride during electron-beam welding

Composite materials and coatings that contain titanium diboride in a metal host are widely used with the purpose of fabricating high-strength heat-resistant materials. Due to high hardness as well as heat and corrosion resistance, titanium diboride is a promising compound for use as a wear-resistant component of the composition “metal host-TiB₂.” The structure and mechanical properties of compositions TiB₂-PG-10N-01 and TiB₂-PKh20N80, which were obtained by a three-stage method involving the preliminary mechanical treatment of mixtures of elemental powders, the self-propagating high-temperature synthesis (SHS) reaction initiated in the activated mixture, and the subsequent mechanical treatment of the product of the SHS reaction, are investigated. To form the coatings, the method of electron-beam welding is applied.     

Structure and Properties of B4C - SiC Composites

We have investigated how the composition, grain morphology, and method of preparing the starting mixture affect the processes that form the structure and phase composition of B₄C - SiC composites during hot pressing. We found that, depending on the composition of the initial powder mixtures, which is responsible for different mechanisms of consolidation of ceramic materials during hot pressing, the grain size of the main B₄C phase and its defect content as well as the nature of the SiC phase distribution within the material differ significantly. When B₄C - SiC composites with a low SiC content are made from initial B₄C - B₄Si - B - C powder mixtures those composites have a high cracking resistance because of their fine grain structure.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 112–119, March–April, 2005.     

Self-propagating high-temperature synthesis of promising ceramic materials for deposition technologies of functional nanostructured coatings

Taking into account the demand for composite targets or precursors for ion-plasma technologies for the deposition of functional nanostructured coatings, this work is a review of recently obtained and previously unpublished results of synthesis in the combustion mode of a series of chemical classes of systems differing in regards to the mechanisms of combustion and structure formation. The experimental results for self-propagating high-temperature synthesis are presented for the following systems: Ti-Al-C, Cr-Al-C, Ti-Cr-Al-C, Cr-B, Ti-Cr-B, Ti-Ta-C, and Ti-Si₃N₄-Al-C. The compositions of reaction mixtures and conditions of obtaining the most interesting and needed materials with high mechanical properties and resistance to high-temperature oxidation are found.