RU2013137739A - METHOD FOR ACHIEVING THE COMBINATION OF HIGH QUANTITIES OF HARDNESS AND CRACK RESISTANCE OF HIGH-DENSITY NANOSTRUCTURAL PRODUCTS FROM TUNGSTEN CARBIDE - Google Patents

Abstract

1. A method of achieving a combination of high hardness and fracture toughness of high-density nanostructured products of tungsten carbide, comprising using tungsten carbide obtained with acceptable characteristics of the powder structure and electropulse plasma sintering of workpieces from the specified powder under vacuum pressing at optimal speeds heating and heating temperature depending on the combination of the required high hardness and crack resistance of high-density products, x characterized by the fact that they carry out technological selection of the initial tungsten carbide powder based on the control of its dispersion level and the content of tungsten monocarbide in it, provided that its particle size R≤110 nm and the volume fraction of tungsten monocarbide particles is not less than ~ 99%, and sintering is performed from such a powder with an optimal heating rate, which is selected from the interval of 25-2400 ° C / min, taking into account an increase in its value in the specified interval to increase the hardness of the sintered preform or reduce its value in in the same interval, in order to increase the crack resistance of this preform, choosing the desired heating rate to achieve a given combination of the indicated properties, the preforms are heated to the optimum sintering temperature T, the value of which is refined depending on the particle size R of the initial tungsten carbide powder using the following formula where α is numerical coefficient of accounting for the volume fraction of tungsten monocarbide and the composition of the phases remaining in the tungsten carbide powder after plasma chemical synthesis and reductive annealing; Q- e

Claims (5)

1. A method of achieving a combination of high hardness and fracture toughness of high-density nanostructured products of tungsten carbide, comprising using tungsten carbide obtained with acceptable characteristics of the powder structure and electropulse plasma sintering of workpieces from the specified powder under vacuum pressing at optimal speeds heating and heating temperature depending on the combination of the required high hardness and crack resistance of high-density products, x acterized in that the selection process is performed starting powder of tungsten carbide-based control level and its dispersion contained tungsten monocarbide, subject to its particle size R _o ≤110 nm and a particle volume fraction of tungsten monocarbide is not less than about 99%, and produce sintering preforms of such a powder with an optimal heating rate, which is selected from the range of 25-2400 ° C / min, taking into account an increase in its value in the specified interval to increase the hardness of the sintered preform or reduce its value in the same interval, to increase the crack resistance of this billet, selecting the desired heating rate to achieve a given combination of these properties, the billets are heated to the optimum sintering temperature T _diff , the value of which is specified depending on the particle size R _{o of the} initial tungsten carbide powder using the following formulas

where α is the numerical coefficient for taking into account the volume fraction of tungsten monocarbide and the composition of the phases remaining in the tungsten carbide powder after plasma chemical synthesis and reductive annealing; Q _b is the activation energy of the process of grain boundary diffusion; k is the Boltzmann constant; δ is the width of the grain boundary; D _bo - preexponential factor in the expression for the coefficient of grain boundary diffusion $$D_b=D_{bo}\exp (-\raisebox{1ex}{$Q_b$}\!\left/ \!\raisebox{-1ex}{$k{T}_m$}\right.)$$

; T _m is the flow temperature of grain boundary diffusion, which is the current sintering temperature; τ _diff is the heating time. 2. The method according to claim 1, characterized in that the starting material is tungsten carbide powder obtained by plasma-chemical synthesis from tungsten oxide and hydrocarbon in a stream of reducing gas generated by an arc plasmatron with a powder particle size of R _o = 60 nm and a volume fraction of the powder of tungsten monocarbide particles is 99.7%, and the billet is sintered from such a powder under compression conditions at a pressure of 60 MPa at an optimal sintering temperature T _diff = 1800 ° C in a vacuum of 4 Pa, heating the billet to the specified sintering temperature with about the heating rate of 2400 ° C / min and getting after such heating without holding it with natural cooling in the workpiece, hardness H _v = 34 GPa and crack resistance K _1C = 4.3 MPa · m ^1/2 or sintering of the workpiece from the same powder under its conditions pressing with a pressure of 60 MPa at an optimal sintering temperature T _diff = 1550 ° C in a vacuum of 4 Pa, heating the preform to the specified sintering temperature at a heating rate of 25 ° C / min and obtaining hardness H _v = 24 after such heating without holding it with natural cooling in the preform , 2 GPa and crack resistance K _1C = 6.7 MPa · m ^1/2 in both cases teas at a relative density of the processed workpiece of 99.5-99.7% of the density of pure tungsten monocarbide and an average grain size of 0.1 μm. 3. The method according to claim 1, characterized in that the starting material is tungsten carbide powder obtained by plasma-chemical synthesis from tungsten oxide and hydrocarbon in a stream of reducing gas generated by an arc plasmatron with a powder particle size of R _o = 55 nm and a volume fraction of particles tungsten monocarbide 100% and produce sintering of such a powder preform under conditions of the pressing pressure of 60 MPa at an optimum sintering temperature T _diff = 1800 ° C in a vacuum of 4 Pa, heating said preform to the sintering temperature at a rate of heating to 500 ° C / min to afford, after such heating without exposure to natural cooling in the workpiece hardness H _v = 28,5 GPa and a fracture toughness K _1C = 5.4 MPa · m ^1/2 at a relative density of 98.2% obtained by the workpiece the density of pure tungsten monocarbide and an average grain size of 0.1 microns. 4. The method according to claim 1, characterized in that the starting material is tungsten carbide powder obtained by plasma-chemical synthesis from tungsten oxide and hydrocarbon in a stream of reducing gas generated by an arc plasmatron with a powder particle size of R _o = 55 nm and a volume fraction of particles tungsten monocarbide 100% and produce sintering of such a powder preform under conditions of the pressing pressure of 60 MPa at an optimum sintering temperature T _diff = 1800 ° C in a vacuum of 4 Pa, heating said preform to the sintering temperature at a rate of heating 100 ° C / min to afford, after such heating without exposure to natural cooling in the workpiece hardness H _v = 27,4 GPa and a fracture toughness K _1C = 6.0 MPa · m ^1/2 at a relative density of 98.9% obtained by the workpiece the density of pure tungsten monocarbide and an average grain size of 0.15 microns. 5. The method according to claim 1, characterized in that the starting material is tungsten carbide powder obtained by plasma-chemical synthesis from tungsten oxide and hydrocarbon in a stream of reducing gas generated by an arc plasmatron with a powder particle size of R _o = 113 nm and a volume fraction of particles 99.7% tungsten monocarbide and produce sintering of such a powder preform under conditions of pressing pressure of 60 MPa at an optimum sintering temperature T _diff = 1550 ° C in a vacuum of 4 Pa, heating said preform to the sintering temperature at a rate nd heating 25 ° C / min to afford, after such heating without exposure to natural cooling in the workpiece hardness H _v = 19,5 GPa and a fracture toughness K _1C = 6.0 MPa · m ^1/2 at a relative density of 98.0% obtained preform the density of pure tungsten monocarbide and an average grain size of 0.3 microns.