Dynamic Hot Pressing Research Articles

HIGH-PERFORMANCE METHOD OF PRODUCTION OF POWDER FRICTIONAL PRODUCTS ON FE-BASIS WITH HIGH TECHNOLOGICAL AND OPERATIONAL PROPERTIES

Physical and technological bases of DHP-PFM method for production of dry friction powder friction articles on Fe-base with high technological and operational indices for a wide range of practical use have been developed. The DHP-PFM method is that the dynamic hot pressing (DHP) provides production of the new powder frictional materials (PFM) through an underlayer from carbonyl iron between frictional material and a basis (framework) with electroplated nickel coating. Friction lining compaction is made of charge of ФМК-79 type and has high hardness and low porosity. Processes of the choice of composition of furnace charge, formation of structure and properties of new powder frictional materials on Fe-to a basis are investigated. The method is characterized by high productivity, energy saving, simplified technology and provides the possibility to use existing technological equipment for making structural powder products. Method of DHP-PFM manufacturing of dry friction powder friction linings can be used for manufacturing of friction units of transmissions of light track machines with high specific power. The friction material received by this method from furnace charge of FMK-79 type can be used as unified for such frictional units as the main friction clutch, an onboard friction clutch, tape and disk brakes.

New Iron-Based Dry-Friction Components for the Transmissions of Light Tracked Vehicles

The manufacture, analysis, and testing of new iron-based frictional components (brake-pad blanks) operating with dry friction are considered. The components are produced by dynamic hot pressing and are intended for the transmissions of light, high-power tracked vehicles.

TO THE COMPARISON OF TWO METHODS OF MANUFACTURING NEW DRY FRICTION PRODUCTS

The technological indicators of manufacturing methods and the physicotechnical and tribotechnical properties of new dry friction friction products made of friction powder materials based on Fe , two different methods, are used: separate pressing and sintering under pressure and dynamic hot pressing. Approximate dependencies of effect of porosity of friction materials on their tribotechnical properties are obtained.

On some prospects for further development of Academician V.N. Antsiferov ideas in the field of structural powder materials

The paper discusses the further development of some ideas of V.N. Antsiferov and the scholar school created by him in obtaining structural powder materials and products. The prospects for obtaining concentration-inhomogeneous steels and trip-steels are noted. The great potential lies in the control of the thickness and volume of the zone of deformation martensitic transformation occurring during fracture. It is advisable to continue the preparation of fullerene- and nitrogen-containing powder compositions and to study the structural heredity of powder steels. The possibility of the synthesis of fullerene-containing phases during the liquidphase sintering of the iron–cast iron and iron–graphite compositions and their subsequent redistribution in the bulk of the material during dynamic hot pressing is worth noticing. Producing nitrogen-containing steels by mechanical activation of powders followed by sintering in dissociated ammonia is advisable to use for obtaining not only wear-and corrosion-resistant materials, but also heat-resistant ones. The studies on the decomposition of supercooled austenite in powder steels of various doping systems with different technological backgroung (sintered, hot-deformed, infiltrated, etc.) are promising. The potential for development is the research of hot-deformed concentration-inhomogeneous materials, obtained, in particular, on the basis of powders of the Distaloy type. The techniques developed by the Antsiferov’s school are significant. The most important one is the method for determining the concentration variation coefficient, as well as a magnetometric complex and a mathematical model, which makes it possible to predict the decomposition of supercooled austenite. Antsiferov’s works can be used for obtaining lean powder steels with the lower bainite structure, which provides the optimal combination of strength and toughness.

Powder forging in PSRSPU

The technology of powder forging (PF) gained significant development after the Second World War. In 1990, almost simultaneously, two monographs were published, which examined the scientific and practical aspects of PF [1 , 2] . Kuhn and Ferguson gave a review of the studies on obtaining parts for structural purposes by PF, which were performed in North America and Europe by that time. The monograph by Kuhn and Ferguson published in English is available to a wide circle of specialists in the field of powder metallurgy (PM). Monograph by Dorofeyev Yu. G. et al. was published in Russian, which had limited readership. In this monograph experience in developing PF technology on the territory of the former Soviet Union was extended. For a variety of historical circumstances, the most significant volume of scientific and practical developments of PF was held at the Department of Materials Science and Problematic research laboratory of dynamic hot pressing of the Platov South-Russian State Polytechnic University (PSRSPU). Previously, the University was named the Novocherkassk Polytechnic Institute. Part of the works was performed in collaboration with the Institute for Problems of Materials Science (Kiev, Ukraine) [3] .

APPLICABILITY OF 110G13P TYPE POWDER STEEL FOR PRODUCTION OF CONSOLIDATION DETAILS OF HIGH PARAMETERS POWER FITTINGS

The special power fittings are one of the basic elements defining reliability of operation of thermal and nuclear power plants which main function consists in ensuring operation of automatic control systems of the power unit parameters by regulation of working environment streams. Wear-resistant welding made by CN-6L electrodes is mainly used now for ensuring operability of sealing surfaces of fittings. Using of Hadfield steel having high resistance to shock abrasive wear as a special material of sealing surfaces of pipeline fittings is of interest. Despite its obvious advantages, Hadfield foundry steel isn't applied in pipeline fittings because of having cracks, foundry defects and big structural heterogeneity. Therefore the possibility of using of powder metallurgy methods for receiving details of sealing of special pipeline fittings on the basis of the 110G13 compositions received by electro-contact sealing and dynamic hot pressing methods is considered in the work. Powder compositions materials based on Hadfield steel with glass component are determined to be perspective for armature engineering using for small details of heavy loaded sealings as their introduction into furnace charge increases leakproofness and provides grindability of products. Technological process of valve saddles of shutoff fittings production by a method of dynamic hot pressing is presented.

Effect of Heat Treatment on the Structure and Mechanical Properties of Höganäs Hot-Worked Powder Steels

Mechanical properties are analyzed for powder steels in relation to heat treatment after dynamic hot pressing. Dependences are obtained specifying the effect of annealing temperature and tempering on powder steel’s microstructure and mechanical properties.

Structure and properties of powder hot-stamped materials based on the Fe–Mn–C composition

Technology is developed for preparing low-manganese steels by dynamic hot pressing. Operating and strength properties are established for these steels. Possible areas are demonstrated for their application in manufacturing components for structural purposes.

Structure and Properties of Heat-Resistant Steels Obtained from Powders after Mechanical Activation

The effect of mechanical activation of heat-resistant steel 55Kh20N4AG9 powders on the structure and properties of high-density material obtained by dynamic hot pressing with extrusion elements was investigated. Mechanical activation improves the chemical homogeneity of the highly alloyed material, decreases the particle size of the strengthening carbonitride phase, promotes its interaction with dislocation tangles and increases their thermal stability. Mechanical activation of powders with intermediate anneals promotes the accumulation of thermally stable defects in the crystal structure and leads to the accelerated formation of a cellular fragmented structure in the austenite, characterized by a high dislocation density in block walls. The developed cellular fragmented substructure is retained after dynamic hot pressing and subsequent heat treatment, and elevates the mechanical properties of the high-density heat-resistant powder metallurgy steels.

Effect of the parameters of dynamic hot pressing on the structure and properties of the powder material ZhGr0.8D2N3G3CaF214. II. Heating temperature and time before dynamic hot pressing, protective atmosphere in sintering and dispersity of solid lubricant

With heating temperature before DHP equal to 1000°C and heating time of 1200 sec, the specimens have the best antifriction characteristics. On the other hand, an increase of τDHP impairs the physicomechanical properties (except impact toughness), and a change of the temperature has an ambiguous effect on them.

Antifriction characteristics of materials produced by dynamic hot pressing (DHP)

An investigation was carried out into the wear behavior of a collar-ring frictional pair and into the effects of lubrication, operating conditions, and structure and chemical composition of the ring on the antifriction characteristics of the pair. As iron-graphite and iron-copper-graphite materials produced by the DHP process developed by the authors possess excellent antifriction characteristics, they can be used for collar rings in rubber-metal frictional pairs. With the optimum material composition proposed (5% C + 5% Cu + Fe), the wear resistance of a pair is one and a half to two times higher than that obtained with type 45 steel (without lubrication) and the running-in time is 15–30 min as against 60–90 min with type 45 steel.

A laboratory unit for the dynamic hot pressing of powder materials

A laboratory unit for the dynamic hot pressing of powder materials

Comparison of results of theoretical and experimental determinations of pressure in dynamic hot pressing

1. An analysis has been made, within the framework of rheological theory, of the densification of porous iron compacts during dynamic hot pressing. Using the results of the analysis, curves of pressure variation with relative density and time were constructed. It is shown that pressure oscillograms and maximum (peak) values of pressure obtained by calculation and experiment are in good agreement. 2. It is shown that, at densities close to theoretical, calculated values of pressure are higher than experimental values, because in the calculation no allowance is made for the compressibility of the solid phase of a porous body.

Chemical and structural heterogeneity of wear-resistant materials produced by electric-pulse sintering

1. It has been established that electric-pulse sintering under pressure is characterized by more rapid diffusion compared with conventional sintering and dynamic hot pressing. This is probably due to the high temperatures generated in this process at the contact boundaries and to the specific character of the process. 2. It is shown that electric-pulse sintering under pressure can be employed for the production of materials with either markedly nonequilibrium or nearly equilibrium structures.

Densification of a porous body during hot extrusion

1. A theoretical analysis is made of the densification of porous, viscous Newtonian and non-Newtonian bodies during hot extrusion. Equations are derived expressing the variation of the pressure and discharge energy as functions of relative density, fluidity of the solid phase forming the porous body, the coefficient of elongation, and ram velocity. The equations are applicable also in the limiting case of hot extrusion of a nonporous body. 2. It is demonstrated that, with a porous body whose solid phase is incompressible, the nonporous state cannot be attained by hot extrusion, and the relative density of specimens grows with increase in the value of coefficient of elongation. 3. Published experimental data indicate that the equations derived correctly describe the process of hot extrusion of porous materials. Using data obtained for porous iron, it is shown that the hot extrusion ofγ-iron is accompanied by plastic flow with an energy of activation close to that for flow in dynamic hot pressing; the two processes also have the same index of nonlinearity of flow, n=4. 4. Equations are derived for the energy of extrusion of a porous body processed under dynamic conditions with shock loading.

Densification of uniaxially reinforced powder materials by dynamic hot pressing in a rigid sheath

A model is proposed describing the densification of a uniaxially reinforced material with a porous matrix during dynamic hot pressing in a rigid sheath. An equation is derived relating the specific work of densification of a composite of a given geometry to its linear shrinkage. A description is given of the densification kinetics of a composite material during dynamic hot pressing.

Dynamic hot pressing of a porous non-Newtonian solid

1. An analysis is made of the densification of porous G13 steel to demonstrate that the rheological theory of the dynamic densification of a porous non-Newtonian solid can be employed for describing the behavior of real porous solids during dynamic hot pressing. The limits of applicability of the theory are examined. 2. A method is proposed for the processing of experimental data upon the densification of materials during dynamic hot pressing. Using this method, it is possible to extract from such data useful information concerning the densification process and the mechanism of the deformation of the solid phase in a porous solid and also to distinguish between a static and a dynamic hot pressing process. 3. From the results of the analysis it follows that, during dynamic hot pressing, high pressures — exceeding by more than an order those employed in static hot pressing — are generated within a short densification time (of the order of 10−3 sec). Under the action of these pressures, the material experiences intense plastic flow. This process, whose rate is a nonlinear function of stress, is less sensitive to temperature than creep, which is linked with diffusional mass transport.

Diffusion of manganese in iron obtained by dynamic hot pressing

The study indicates that in substitutional solid solutions with vacancy diffusion the diffusion mobility should be higher in materials produced by dynamic hot pressing.

Densification of a porous solid during hot forging

1. For a porous, viscous, compressible solid whose solid phase is incompressible and obeys a non linear law of flow, an analysis is made of the extent of densification during hot forging under uniaxial and biaxial impact compression conditions. Expressions are derived for the variation of density and densification time as functions of impact parameters and flowability of the solid phase of the porous solid. 2. It is shown that densification conditions in the hot forging of a porous solid are less favorable than in dynamic hot pressing. 3. It is demonstrated that, in both forging and dynamic hot pressing, increasing the mass of the striking tool improves densification conditions to a greater extent than does increasing the impact velocity.

Calculation of the specific work of densification in the dynamic hot pressing of laminated reinforced materials

1. On the basis of an analysis of a model, an equation has been derived for calculating the work of densification in the DHP of reinforced materials as a function of the plasticity properties of their matrices and the geometric parameters of the composites, with allowance for the distribution of normal stresses over the contact surfaces between the fibers and matrices and also for the friction between these elements. 2. A comparison of experimental and calculated values of specific work of densification in the DHP of copper and nickel base composites reinforced with molybdenum wire has shown that taking into account the above factors increases the accuracy of calculations of work of densification for reinforced materials.