RU2612106C2 - Method of titanium-based composite workpiece manufacturing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to titanium-based composite workpiece manufacturing. Method involves preparation of charge containing titanium alloy waste, and change compaction by pressing to form workpieces. Charge is prepared by adding titanium powder to titanium alloy waste treated in alkaline solution at the 70/30 weight ratio of waste and titanium powder, obtained charge is pickled in acid solution to ensure deoxidation and hydrogenisation up to 0.1-1 wt % of hydrogen in titanium, then the charge is ground along with mixing and heated to pressing temperature, after pressing, impurities are removed from workpiece surface, the workpiece is lubricated, rolled and dehydrogenised thermally.

EFFECT: improved mechanical properties, strength and plasticity of workpieces.

3 cl, 1 ex

Description

The claimed technical solution relates to powder metallurgy, in particular, to the molding of powdered raw materials of composite billets with an optimal ratio of strength and ductility for the subsequent manufacture of critical products operating in heavily loaded machine parts, and can be used in various industries, as well as for efficient utilization of titanium chips, fine trimmings and crushed scrap of titanium alloys.

A known method of manufacturing billets of titanium (patent RU 2529131, IPC B22F 3/02; C22C 14/00, publ. 09/27/2014; claimed. 03/19/2013), which includes placing particles of a titanium sponge in the press chamber, compacting particles to obtain the workpiece, pressing it, removing contaminants from the surface of the workpiece, coating it with grease and subsequent rolling; before placing the titanium sponge particles in the press chamber, they are heated in a vacuum heating furnace to a temperature of 700 ... 800 ° C, doped with hydrogen to a concentration of 0.1 ... 0.9 wt. %, after which they reduce the temperature in the furnace to a temperature not lower than 300 ° C, compacting is carried out at a temperature of 300 ... 700 ° C, compact billets are pressed by a semi-continuous method through a die at a temperature of no higher than 700 ° C with a draw ratio of no more than two, and then at a temperature not exceeding 700 ° C and a drawing ratio of at least three, while the rolling of the billets is carried out at a temperature not exceeding 700 ° C, after which annealing is carried out in vacuum at a temperature not lower than 700 ° C. The method provides the ability to process difficultly deformed titanium at relatively low temperatures, increasing mechanical properties, in particular the ductility of the resulting workpieces, reliability, service life and reduced tool consumption.

Common to the known and proposed methods are compacting a mixture of titanium particles into preforms, high-temperature processing and heating of preforms to a pressing temperature, pressing a semi-finished product; before pressing, hydrogen titanium is hydrogenated to a concentration of hydrogen in titanium above 0.1 wt. %, after pressing, contaminants are removed from the surface of the workpiece, coated with grease and subsequent rolling.

The disadvantages of this method include the low strength properties of the semi-finished product, not allowing it to produce critical products that work in heavily loaded machine parts and structures. The method does not include the use in the technological cycle of waste machining titanium and its alloys.

A known method of manufacturing products from titanium alloys, protected by Eurasian patent 018035 B1 B22F and C22C, which includes the operation of mixing the powder of the base containing titanium with powders of alloying elements forming alloys with titanium, molding into blanks, sintering in vacuum at temperatures at which liquid phases are formed; while mixing the powder of the base containing titanium with the powders of the alloying elements, the powder of the base is obtained by mixing the two components, the first component of the powder of the base uses hydrogenated titanium powder, the second component uses powder of unseparated titanium obtained from unseparated titanium sponge, and / or hydrogenated titanium powder, and / or standard titanium powder, with particle sizes less than 500 microns, with the following ratio of ingredients: the first component of the basic powder ova 50 ... 80 wt. %, the second component of the powder base 10 ... 40 wt. % alloying powder - the rest; the first component contains (2.0 ... 3.9) wt. % hydrogen, the second component from the powder of unseparated titanium obtained from unseparated titanium sponge contains up to 2.0 wt. % chlorine and / or up to 2.0 wt. % magnesium, or (0.2 ... 1.0) wt. % hydrogen, the ratio between the particle sizes of the powders of titanium, hydrogenated titanium and alloying powders is 1: (0.5 ... 2.0) :( 0.01 ... 0.7); molding the resulting mixture into blanks is carried out in molds or by direct rolling of powders, or by cold isostatic pressing or injection molding to a relative density of at least 60% under a pressure of 400 ... 960 MPa; then the molded preforms are heated to 300 ... 900 ° C and kept in this temperature range for at least 30 minutes in an atmosphere of hydrogen released from hydrogenated titanium, and the products are sintered in the β-region of titanium by heating in vacuum to a temperature of 1000 ... 1350 ° C at which they withstand at least 30 minutes; alloying powder contains 60 wt. % aluminum and 40 wt. % vanadium with a particle size of less than 70 microns; a mixture of hydrogenated titanium powders consists of a powder that contains less than 1.0 wt. % hydrogen and has a particle size of less than 100 microns, and a powder that contains approximately 3.9 wt. % hydrogen and has a particle size of less than 250 microns, and a standard titanium powder has a particle size of less than 500 microns.

Common to the known and claimed methods is the presence of operations for grinding titanium alloy waste with the simultaneous introduction of particles doped with titanium hydrogen into them by mixing, compacting the mixture into preforms, thermal hydrogenation, heating the preforms to a pressing temperature, pressing the semi-finished product and thermal dehydration.

The disadvantages of this method include the complexity and multi-stage technological operations that require high accuracy of the technology of preparation of the mixture, which complicates the preparation of a given chemical composition and microstructure of a titanium alloy having a chemical bond between the powder components and high homogeneity of the final titanium alloy. Obtained, according to this method, the titanium alloy will have strength and ductility, regulated by a given chemical composition, while composite materials can be ductile, due to the viscous component and durable, due to the solid filler. The method does not provide for the possibility of involving in the technological cycle the waste obtained during the machining of titanium alloys.

A known method of producing semi-finished products from waste titanium alloys (patent RU 2056975, IPC B22F 8/00; B22F 3/16, publ. 03/27/1996; claimed. 06.03.1994). The known method is characterized in that titanium alloy waste is crushed in it, compacts are compacted, thermal hydrogenation is carried out, heated to a pressing temperature, the semi-finished product is pressed and thermal dehydration is carried out; at the same time, titanium hydride powder is introduced into the ground waste by mixing, after compacting, the workpiece surface is hardened and a protective hermetic shell is formed; the formation of the shell is carried out with its subsequent drying; drying of the shell and thermal hydrogenation are carried out simultaneously, dehydration of the semi-finished products is carried out with the simultaneous hydrogenation of titanium at the stage of cooling the semi-finished product, surface hardening is carried out by ultrasonic treatment, the formation of the protective shell is carried out by spraying a coating of high-temperature enamel, thermal hydrogenation is carried out by heating the billet for pressing by decomposition of titanium hydride.

Common to the known and claimed method are: grinding waste titanium alloys with the introduction of particles doped with titanium hydrogen by mixing, compacting the mixture into preforms, thermal hydrogenation and heating the preforms to a pressing temperature, pressing the semi-finished product and thermal dehydration.

The disadvantage of this method is the presence of additional operations: operations of hardening the compact surface by ultrasonic treatment or local heating; application and drying of enamel coating. The semi-finished products obtained by the known method have high strength, but insufficient plasticity, which complicates their further processing, and products made from them have not sufficiently high performance characteristics. A significant disadvantage of this method is the inability to evacuate the products of hydrogen reduction of titanium oxides, as this is prevented by a protective enamel shell. As a result of this, impurities and inclusions remain in the semi-finished products, which impair the mechanical properties and limit the possibilities for subsequent processing.

The closest claimed technical essence and the achieved effect is a method for producing semi-finished products from waste titanium alloys (patent RU 2131791 C1, B22F 8/00; publ. 06/20/1999; declared. 03/13/1998). The known method is characterized in that it is used to grind the initial titanium alloys into granules and mix them with titanium hydride powder, compact the mixture into billets, form a protective hermetic shell on the surface of the billet, heat it by pressing and thermal hydrogen distillation, followed by pressing, in which the billets are compacted in the form of tablets with their subsequent connection, at least in pairs, with a layer between them of titanium hydride, for example in the form of a plate; as a protective containment, a hollow glass made of a refractory heat-resistant alloy with a pressing die built into its bottom is used; heating for pressing is carried out in two stages, while the first stage of heating is used to clean the surface and the surface layer of granules from oxides by dissolving them in the volume of granules, and in the second stage, the collected preform for surface thermal hydrogen distillation is carried out by layer-by-layer decomposition of titanium hydride in the collected harvesting; purification of the surface layer from oxides is carried out to a depth of 20% of the average thickness of the granules, while heating is carried out to a temperature not exceeding 400 ° C, and hydrogenation of the layer purified from oxides is carried out up to the concentration corresponding to titanium hydride. The method reduces the cost of obtaining semi-finished products by increasing the productivity of the process and leads to higher product quality.

Common to the known and claimed method are: grinding waste titanium alloys with the introduction of particles doped with titanium hydrogen by mixing, compacting the mixture into billets, hydrogenating and heating the billets to a pressing temperature, pressing the semi-finished product and thermal dehydration.

The disadvantages of the method include

- multi-stage technological cycle;

- the need to use an airtight shell, in the form of a glass of refractory heat-resistant alloy with a die built for pressing in its bottom;

- the impossibility of evacuation of hydrogen reduction products of titanium oxides, as this is impeded by an airtight shell;

- high energy costs for cleaning the surface and the surface layer of granules from oxides by dissolving them in the volume of granules, as well as heating the collected preform for surface thermal hydrogen distillation, carried out by layerwise decomposition of titanium hydride in the collected preform;

- significant difficulties arise when optimizing the ratio of strength characteristics and ductility of the workpieces.

The proposed technical solution aims at creating an economically feasible and effective technology that provides improved mechanical properties of semi-finished products with the optimal combination of strength characteristics and ductility, which is achieved by creating a new composite material.

The essence of the claimed technical solution lies in the fact that in the method of manufacturing composite billets based on titanium, comprising preparing a mixture containing waste titanium alloys by adding particles of titanium powder with a ratio of waste and particles of titanium of 70/30 mass percent; subsequent deoxidation of the mixture, combined with hydrogenation up to 0.1 ... 1 wt. % hydrogen in titanium; grinding the components of the mixture is combined with mixing, while the operation is carried out at room temperature for the time required to obtain a uniform distribution of components and particle size distribution of particles not more than 1000 microns; heating the mixture to a pressing temperature; pressing the workpiece; removal of contaminants from the surface of the workpiece, coating it with grease and subsequent rolling; thermal dehydration.

The technical result of the claimed technical solution is to reduce the number of cyclically repeated operations, combining the processes of titanium deoxidation and hydrogenation, as well as combining the mixing and grinding operations of a mixture of highly plastic titanium powders and waste titanium high-strength alloys, as well as achieving the optimal composition of the charge to obtain a composite billet and optimize the modes high-temperature processing and heating temperatures for pressing blanks; the possibility of evacuation of hydrogen reduction products of titanium oxides is provided.

Operation deoxidation of the charge, combined with hydrogenation up to 0.1 ... 1 wt. % hydrogen in titanium is aimed at a simultaneous decrease in the oxygen concentration in the charge and hydrogenation, which contributes to the embrittlement of components during subsequent grinding at room temperature and plasticizes them during deformation processing at elevated temperatures. Embrittlement of the components leads to a significant reduction in labor costs and energy costs necessary for their grinding. Plasticization of the charge significantly facilitates deformation processing, leads to an increase in density and ultimately to an increase in the ductility of the material of composite billets.

Deoxidation involves the purification of titanium waste from oils and emulsions in an alkaline solution, the removal of surface oxides, and the hydrogen absorption by etching in an acidic solution. By eliminating the need for protection against oxidation of the processed material and the loss of hydrogen in comparison with the prototype, the need for the use of a pressurized shell made of a heat-resistant alloy is eliminated, the number of operations is reduced, and the technology is simplified. Eliminates the need to perform operations of compaction of a significant number of tablets from titanium waste and titanium hydride to fill the containment, which leads to a significant reduction in the number of cyclically repeated operations.

The mixture for the manufacture of composite billets includes a ratio of waste and particles of titanium of 70/30 mass percent. The combination of harder and softer charge components in the indicated ratio allows for more intensive flow of titanium into interparticle cavities during deformation processing. In this case, intense deformation of the interparticle contact layers is carried out, which contributes to the solid-phase welding of the components of the composite material being manufactured. Deviations from the specified ratio of titanium alloy and titanium waste to a greater or lesser extent leads to a decrease in mechanical properties and to a violation of the optimal combination of plastic and strength properties of the composite.

The operations of grinding waste and mixing them with titanium powder are combined. In this case, mechanical activation of the surface layers of powder particles is carried out, which intensifies surface diffusion and, as a result, increases the ductility of composite billets.

The mixture is crushed at room temperature for the time necessary to obtain a uniform distribution of components and particle size distribution of particles not more than 1000 microns. If the crushed particles will be large, it is impossible to achieve the necessary uniformity of the distribution of the components of the mixture and to ensure uniformity of the properties of the composite preform.

After pressing, the contaminants are removed from the surface of the workpiece, coated with grease, which allows for the subsequent rolling process.

Thermal dewatering of the composite billet is necessary to exclude the manifestation of the effect of hydrogen embrittlement of the composite billet during possible subsequent cold deformation processing and operation of products made from composite billets. Simultaneously with thermal dehydration, the processes of diffusion mass transfer are realized, the state of interparticle boundaries improves, continuity defects are healed, which favorably affects the mechanical properties of the composite material.

Pressing is carried out by a semi-continuous method, which allows us to produce composite blanks of unlimited length.

An example of a specific implementation.

For the manufacture of composite billets based on titanium, titanium alloy waste was taken in the form of oxidized shavings of VT22 alloy formed as a result of machining of rods. The waste of titanium alloy was cleaned of oils and emulsions in soda-phosphate (alkaline) solution. The mixture was prepared by adding particles of titanium powder grade PTM1 in fat-free waste. The mass percentage ratio of chips and particles of titanium powder was taken optimal, namely 70/30. A portion of the obtained mixture was etched in a fluoride chloride acid solution to remove oxides from the surface of the chip and to hydrogenate the chip and particles of the PTM1 titanium powder. A decrease in titanium losses was achieved due to the additional introduction of hydrogen peroxide into the composition of the solution. To prepare the etching solution, calculated amounts of hydrochloric acid with a density of 1.19 g / cm ^{3 of a} 30% solution of hydrogen peroxide (perhydrol) and sodium fluoride were added to a container filled with industrial water with a known volume. The mixture etching solution contained: hydrochloric acid 150 ... 180 g / l; sodium fluoride 1-1.5 g / l; hydrogen peroxide 30 ... 34 g / l. Substandard shavings of VT22 alloy were degreased by washing with hot and cold running water and loaded into an etching bath with a temperature of 55 ° C. The etching process was carried out with constant stirring of the etching solution for 25 min, after which the chips were removed, washed with hot water at a temperature of 70 ° C, and then with running water, and dried at 80 ° C. The composition of the etching solution was optimized, focusing on the color of the chips, minimizing the loss of titanium by mass and achieving the necessary hydrogen concentration in the chips and titanium powder.

At relatively low temperatures, short duration and depth of etching, a fairly complete removal of undesirable impurities was achieved (not more than% in the chips: 0.15 oxygen; 0.030 nitrogen; 0.035 carbon). Purified from oxides and other surface contaminants, the titanium shavings hydrogenated during etching and the PTM1 powder acquired brittle properties.

After etching, a sample of the charge was placed in a crusher and subjected to joint grinding of its components for one hour at room temperature in an inert atmosphere. At the same time, shavings and particles of titanium powder were simultaneously crushed and mixed. The size of the components of the mixture after grinding did not exceed 1000 microns.

After grinding, the mixture was heated to 350 ° C, which is below the titanium oxidation threshold of approximately 400 ° C. Then the heated charge was transferred to a uniaxial press container heated to 325 ° C.

A temperature of 325 ° С was chosen, since for hydrogen-doped titanium near 300 ° С, the phase eutectoid transformation α + γ → α + β occurs in the Ti-H system, which leads to a significant improvement in the deformation properties of titanium. Thus, at 325 ° C, the mixture consists of two uniformly mixed components: plastic hydrogen-doped titanium particles and solid particles of crushed chips.

The uniaxial press container was filled with a charge in an air atmosphere. In this case, the hole in the bottom of the uniaxial press container was hermetically sealed with a plug.

The compaction was carried out as follows: the plunger of the press was slowly lowered in order to evacuate the air from the porous mass. The presence in the batch of particles of hydrogen-doped titanium having a 1.2-fold decrease in comparison with pure titanium and deformation resistance made it possible to lower the relative porosity of the composite briquette from 7 to 4%.

The compacted billet had approximate calculated dimensions: diameter 45 mm and height 45 mm.

After obtaining the preform, the container of the uniaxial press was filled with the next portion of the mixture, without removing the previous compacted preform. In this case, the bottom plug of the uniaxial press container was replaced with a matrix. Carried out the extrusion of the workpiece; at the same time, the extrusion force of the compacted billet provided the necessary compaction of the next portion of the mixture. Thus, the blanks were pressed by a semicontinuous method, which ensured the absence of external porosity and minimal internal porosity. In this case, the drawing coefficient did not exceed a value of 2 and was determined by the pressure level necessary for the required degree of compaction of the second portion of the mixture and the formation of a negligible porosity emerging on the surface of the compacted workpiece extruded through the matrix. After squeezing the workpiece from the container, the process is repeated using the next portion of the mixture. After compacting and extruding from the container a uniaxial press with a drawing coefficient of 1.3, the workpiece from the mixture had a diameter of 31 mm, a length of 90 mm, and a relative density of ≈97%.

After compacting and pressing the workpiece in a semicontinuous method through a matrix with a drawing coefficient of not more than two, to facilitate the further rolling process and minimize tool wear, as well as to prevent the entry of atmospheric impurities, the resulting workpiece was coated with glass grease.

The billet was heated to 600 ° C for further hot rolling under atmospheric conditions since the applied glass grease protects the metal from oxidation at this temperature. The billet can be heated to any temperature in the range from 300 to 1000 ° С since in this range the phase transformation α + β → β takes place in hydrogen-doped titanium and its alloys, as a result of which the resistance of the composite billet to deformation decreases and its ductility increases. In the described example, the deformation processing of composite preforms obtained by compacting and squeezing particles of a mixture of hydrogen-doped titanium particles and crushed chips of VT22 alloy from a uniaxial press container was carried out at 600 ° C with pressing forces 1.3 times lower than those without hydrogen.

After the manufacture of the rods of the desired size and shape, heat treatment is performed to soften, sinter and remove hydrogen from them, for which the rods are held in a heated vacuum furnace in a vacuum of at least 2 * 10-2 mm Hg, in a mode that promotes sufficient recrystallization , sintering and softening, while the complete removal of hydrogen previously introduced into titanium is also carried out. Thus, during annealing in a vacuum furnace, the composite rod is softened simultaneously and hydrogen is removed from it. An experimental study of the mechanical properties of the composite billet showed that the achieved tensile strength of the billet was 920 MPa, while the elongation was 11%.

Thus, the application of the inventive method for the manufacture of titanium-based composite billets can reduce the number of cyclically repeated operations, combine the processes of titanium deoxidation and hydrogenation, as well as combine the mixing and grinding of a mixture of highly plastic titanium powders and waste titanium high-strength alloys, as well as optimize the temperature mode of heating for pressing blanks; to ensure the possibility of complete evacuation of the products of hydrogen reduction of titanium oxides, to obtain the optimal composition of the mixture for the manufacture of the composite, which allows to provide the optimal ratio of strength and ductility of the material of the composite billet. The method allows to use for the manufacture of composite billets waste machining of expensive high-strength titanium alloys.

Claims (3)

1. A method of manufacturing composite titanium-based preforms, comprising preparing a charge containing titanium alloy waste, compacting the charge into billets by pressing, characterized in that the charge is prepared by adding titanium powder to titanium alloy waste purified in an alkaline solution at a weight ratio of waste to powder titanium equal to 70/30, the resulting mixture is subjected to etching in an acidic solution with the provision of deoxidation and hydrogenation to 0.1-1 wt. % hydrogen in titanium, then the mixture is ground, combining with mixing, and heated to a pressing temperature, after pressing, contaminants are removed from the surface of the obtained workpiece, coated with grease, rolled and thermally dehydrated. 2. The method according to p. 1, characterized in that the grinding of the mixture is carried out at room temperature for the time required to obtain a uniform distribution of components and particle size distribution of particles not more than 1000 microns. 3. The method according to p. 1, characterized in that the pressing of the blanks is carried out by a semi-continuous method.