Preparation Of Multi-element WC-based Composites By Spark Plasma Sintering

WC cemented carbide has the characteristics of high hardness,high strength,high wear resistance and good toughness,and is widely used in various fields such as aerospace,mechanical processing,and oil drilling.However,cemented carbide prepared by traditional sintering has been unable to meet the rapid development needs of high-tech industrial technology.At present,the preparation of traditional sintered cemented carbide mainly has problems:high sintering temperature,long reaction time,waste of energy and other shortcomings,and the overall performance of cemented carbide needs to be further improved.This thesis mainly uses spark plasma sintering to synthesize multi-element WC-based cemented carbide test blocks through two preparation methods.The first is to use nano-tungsten carbide and nano-cobalt as raw materials,and mainly study composite inhibitor(nano-chromium carbide and nano-vanadium carbide),carbon nanotubes,graphene,etc.on the phase composition,microstructure and mechanical properties of the synthesized products under discharge plasma conditions.The second is to use nano tungsten oxide,nano cobalt oxide and nano carbon black as raw materials,The main research is the effects of nano-chromium oxide,nano-vanadium oxide and carbon nanotubes,etc.on the phase composition,microstructure and mechanical properties of multi-element WC-based cemented carbide in-situ synthesized by SPS under discharge plasma conditions.The results show that:(1)The addition of compound inhibitors of chromium carbide and vanadium carbide can effectively inhibit the growth of WC grains,and the grains are fine and distributed more uniformly.And the best sintering conditions of spark plasma sintering multi-element WC-based cemented carbide:sintering temperature is 1350?,holding time is 8 min,sintering pressure is 50 MPa.At this time,the structure of the multi-element WC-based composite is relatively uniform,the density is 14.43 g/cm³,the Vickers hardness is 2439.57 N/mm² and the fracture toughness is 12.05 MPa·m^1/2.(2)Under the optimal conditions of spark plasma sintering,the performance of the multi-element WC-based composite material increases first and then decreases with the increase of the carbon nanotube content.When the content of carbon nanotubes is 0.4%,the performance of the multi-element WC-based composite material is the best.At this time,the WC-based cemented carbide has finer grains,with an average grain size of 200-400 nm,the density is14.21 g/cm³,the Vickers hardness is 2520.85 N/mm²,and the fracture toughness is 13.26MPa·m^1/2.(3)Under the optimal conditions of spark plasma sintering,the comprehensive performance of the multi-element WC-based cemented carbide test block shows a trend of first increasing and then decreasing with the increase of the graphene content.When the graphene content is 0.6%,the comprehensive performance of the multi-element WC-based cemented carbide test block is the best.At this time,the density of the multi-element WC-based cemented carbide is 13.54 g/cm³,the Vickers hardness is 2008.53 N/mm² and the fracture toughness is 11.72 MPa·m^1/2.(4)When spark plasma sintering is used to synthesize WC-Co cemented carbide in situ,when the sintering temperature is 1320?,holding time is10 min,and sintering pressure is 50 MPa,the reaction product is mainly composed of WC and Co,the density of the alloy is 13.72 g/cm³,the Vickers hardness is 1458.90 N/mm² and the fracture toughness is 10.03 MPa·m^1/2.(5)Under the conditions of spark plasma sintering,adding different contents of nano-chromium oxide,the reaction product is mainly composed of WC and Co.When the content of nano-chromium oxide is 0.8%,the cemented carbide has the best performance,the density is 12.57 g/cm³,the Vickers hardness is 1864.88 N/mm²and the fracture toughness is 10.85 MPa·m^1/2.(6)Under spark plasma sintering conditions,adding different contents of nano vanadium oxide,the reaction product is mainly composed of WC and Co.When the content of nano vanadium oxide is 1.2%,the cemented carbide has the best performance,the density is 13.01 g/cm³,the Vickers hardness is 1639.79 N/mm²and the fracture toughness is 10.36 MPa·m^1/2.(7)The multi-element WC based cemented carbides were prepared by SPS in-situ synthesis using nano tungsten oxide,nano vanadium oxide,nano chromium oxide,nano cobalt oxide and carbon nanotubes as raw materials,the raw material ratio was determined on the basis of WC-0.4(V₈C₇-Cr₃C₂)-0.4CNTs-6Co.At this time,the density of the alloy is 13.62 g/cm³,the Vickers hardness is 2396.74 N/mm² and the fracture toughness is 13.15 MPa·m^1/2.