A. A. Mamonova

Effect of carbon and aluminum contents on the structurization of Al–Ti–C powder master alloy during reaction synthesis

The paper presents results of electron microprobe, X-ray diffraction, and differential thermal analyses of master alloys produced by reaction synthesis of Al–Ti–C powder mixtures of various compositions. It is shown that heating of all stating mixtures leads to in situ precipitation of titanium carbide particles and complex titanium–aluminum carbides. Spherical titanium carbide particles are the predominant strengthening phase in samples with high carbon content (10–13%) and disordered elongated acicular grains of complex titanium–aluminum carbides in samples with minimum carbon content (6%) and relatively high aluminum content (40%). It is established that 45 wt.% Al–11 wt.% C–44 wt.% Ti master alloy with practically equal aluminum and titanium contents is characterized by the finest strengthening phase particles after thermal synthesis.

The structure and phase composition of boride coatings on sintered powder steels

Results of metallographic and X-ray diffraction analyses of boride coatings produced by saturation of porous blanks from iron–carbon powder alloys are provided. It is established that the structure and phase composition of boride coatings made of iron–carbon powder alloys depend on the composition of borating mixtures: the amount of diffusion activator AlF3 in the borating mixture essentially influences the structure, phase composition, and hardness of the coating and a higher amount of the activator intensifies the borating process, leading to the formation of a very hard coating and borocarbides in the transition zone.

Structure formation processes in sintering of stainless-steel-base heterophase materials 1. Sintering of austenitic stainless-steel-base materials with additions of Cr3C2

Earlier [1-3], a series of basic and applied investigations of the processes of pressing, sintering, and hot compacting of chromium and chromium-nickel stainless steel powders were presented. These works are devoted primarily to powdermetallurgy steels with a single-phase homogeneous structure basically not differing from the structure of the stainless steels produced by traditional methods. Of interest is development of stainless-steel-base materials with a heterophase structure. Together with good corrosion resistance such materials may possess such specific properties as increased wear resistance. This is obtained by addition to the metallic matrix of various additions such as carbides, intermetallides, nitrides, borides, sulfides, etc. However, certain additions reduce the corrosion and certain mechanical properties of stainless steels, particularly plasticity. In order to provide the optimum combination of properties of such materials it is necessary to optimize their composition and structure. In this work the structure and properties of austenitic chromium-nickel stainless-steel-base materials with additions of chromium carbide Cr3C 2 in a quantity of up to 10% were studied. The powders of types Khl8N12, Khl8N15, Khl8N12, Khl8N12M2, and K.h23N18 stainless steels were prepared by atomization, calcium hydride reduction, and diffusion impregnation [4]. The specimens for tensile, bend, and impact mechanical tests were prepared by a single pressing and sintering in hydrogen and vacuum at 1200~ After sintering the microstructure was investigated and the density and hardness of the specimens and the microhardness of the structural constituents were determined. In addition, selective micro-x-ray spectral and x-ray structural analyses were made for the purpose of studying the composition of the matrix and the carbide inclusions and also of establishing the crystalline lattice parameters of the base. In order to study the influence of the degree of dispersion of the chromium carbide additions on the character of their interaction with the matrix a preliminary investigation including use of types Khl8N15, Kh18N12, and Khl8N12M5 stainless steel powders obtained by the above methods was made. Monodispersed chromium carbide powder with average particle sizes of 30, 80 130, and 200 #m (sifted through -0056, -0100 + 0063, -0160 + 0100, and -0250 + 0160 screens) was used. In all cases the quantity of Cr3C 2 was 10 wt. %. The specimens were sintered in vacuum at 1200~ It was established that the hardness and microhardness of the base of the specimens containing carbides are higher and their density somewhat lower than of the standard specimens. At the same time the microhardness of the carbides themselves also drops significantly as the result of sintering (Fig. 1). With a decrease in carbide inclusion size, all of these rules are strengthened, which is an indication of the more active interaction of the more dispersed carbides with the base. The nature of the powders of the base has significantly less influence on the character of its interaction with the carbides than their degree of dispersion. The more active interaction with the metallic matrix of specimens of atomized type Khl8N12M2 powder is confirmed by the higher absolute and relative increase in microhardness of the base of the these specimens in compared with those prepared from Khl8N12 and Kh18N15 powders prepared by methods of diffusion impregnation and calcium hydride reduction (Figs. 1, 2). The increase by several percent in the chromium content in the metallic matrix and the increase in its crystallin lattice parameters in comparison with the standard specimens simultaneously established by methods of micro-x-ray spectral and xray structural analyses (Table I) are apparently caused by diffusion of chromium and carbon from the carbides into the base. The greatest change in the crystalline lattice parameters of the base is observed with use of dispersed additions with an average

Features of Structurization During Sintering of Compacts from a Multicomponent Ti–Cr–Fe–Ni–Cu Charge

A heterophase alloy with hardness 103 HRB and a porosity of ~5% is produced by sintering compacts from a Ti–Cr–Fe–Ni–Cu multicomponent charge. It is demonstrated that after sintering a mixture of elemental powders, four phases with different types of lattice are formed: (i) two multicomponent phases with FCC-lattice, (ii) one Cr–Fe phase with BCC-lattice, and (iii) one phase with HCP-lattice with crystallographic constants based on titanium lattice. Well-defined peaks of Cr2Ti, Fe2Ti, and Ni3Ti intermetallides are seen in the X-ray photograph of the alloy.

Investigating the dependence of the properties of sintered boron-containing steels on conditions of synthesis and the content of employed foundry alloys

Results from investigating the effect of technological conditions for the synthesis of powdered boron-containing foundry alloys on their chemical and phase compositions and the content of foundry alloys in the charge on the structure and properties of sintered steels fabricated using them are presented. It is shown that using denser briquettes obtained at a pressure of ≥700 MPa allows us to reduce substantially boron evaporation through the gas phase during the synthesis of foundry alloys, relative to briquettes compacted at lower pressures. Using an elevated foundry alloy synthesis temperature (1200°C) leads to higher density of the post-sintered material, and thus to enhanced strength characteristics. Increasing the boron content in the initial charge increases the hardness and lowers the strength of sintered steels, while the curve of the strength’s dependence on the boron content after thermal treatment peaks at ∼0.8% B.

Interaction of the Components in Tih2–Mn–Si–Fe–C Powder Mixture During Thermal Synthesis of Multicomponent Master Alloy

The interaction of powder components in the titanium hydride–ferromanganese silicon system is investigated. It is demonstrated that titanium actively reacts with ferromanganese silicon during heating, which is accompanied by the dissociation of the latter and the formation of a complex multiphase system where the main phases are titanium silicide Ti5Si3 and titanium carbide TiC. It is noted, that additional carbon in the charge results in a fine alloy structure.

Effect of Alloying on the Structure and Mechanical Properties of Hot-Forged Aluminum-Matrix Powder Composites Al–Ti–C

The data of structural and phase analysis of the master alloys produced by thermal synthesis from three compositions of Al–Ti–C powder mixtures are presented. It is shown that depending on the content ratio of titanium and carbon, the heating of the mixture leads to in situ formation of dispersed particles of titanium carbide TiC or complex titanium-aluminum carbides. Aluminum matrix composites with titanium carbide phase as reinforcement are produced by hot forging using synthesized master alloys. It is established that an increase in the carbide content entails an increase in the strength and hardness of composites, while ductility decreases. Therefore, the hardness and strength properties of the composites produced from a charge prepared in a drum tumbler mixer are significantly lower than those of samples produced from a charge prepared in a planetary mill, whereas the ductility of the latter is slightly lower.

Effect of chromium and manganese nitride alloying on the evolution of the fine structure in powder hot-forged steels

The effect of alloying with chromium and manganese nitrides is studied on a fine crystal structure of powder iron produced by hot forging. The features of the fine structure and the phase composition are found to strongly depend on the kind of alloying nitrides. It has been shown that the introduction of both nitrides in the initial composition of powder mixture causes an increase in the lattice parameter of a matrix, its defectiveness, and the dislocation density, which results in an increase in the hardness of steel alloyed with nitrides. The defectiveness of the matrix crystal lattice, the dislocation density, and the hardness of hot-forged steels are slightly higher when manganese nitride is used as a nitrogen-bearing additive.

Interaction of Chromium Carbide with a Kh13M2 Steel Matrix

The paper examines the influence of sintering temperature in the range 1150–1300°C on interaction of chromium carbide Cr3C2 and a Kh13M2 steel matrix. It is shown that molybdenum actively participates in the interaction process, which leads to the formation of M7C3, M23C6, and M3C carbides even at 1150°C.

The Structure and Properties of Boride Coatings Depending on the Porosity of Powder Steel Preforms

Metallographic and X-ray diffraction analyses are used to examine the structure of boride coatings produced by saturation of iron and iron–carbon blanks with different porosities at 1000 and 1100°C and microhardness distribution along their depth is analyzed. It is shown that the thickness of the oxide layer increases with the original porosity of the blanks, but its density and surface microstructure is higher for samples with lower porosity produced at higher saturating temperatures. The morphology of boride layers depends on the porosity of the blanks.