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The laser implantation technique bases on a localized dispersing of ceramic particles in metallic surface layers for changing their micro geometry as well as their material properties. Using TiB2 and NbC hard particles, tailored microtextures consisting of elevated dome-, ring-, or line-shaped Features can be manufactured. Especially TiB2 implants feature high hardness values up to 1800 HV1 and ceramic particle contents up to 55 %, indicating superior wear resistant properties.
Improved wear resistant ceramics of metal incorporated NbC processed with gas pressure sintering
(2017)
Tungsten carbide (WC) dominates wear protection and machining since more than 90 years due to its hardness with an associated good toughness and high melting point.
It was recently demonstrated that Niobium Carbides are wear resistant and show a better performing under cutting than WC grades. In order to profit of the good properties of Niobium Carbide, specific processing techniques need to be developed. The density of NbC is half of WC and offers colloidal processing for perfectly mixing NbC with metallic binder (up to 15 vol.-% Ni) and secondary carbide-particles. The used NbC-powder has an average particle size d50 of 3 micron measured by laser granulometry analysis. The true density was 7.68 g/cm3. An Oxygen content of the used NbC of 0.4 % is caused by residual slag content.
It is possible to increase the stability of the NbC-suspensions and to reduce their viscosity by adding a specific dispersing agent.
This surface-modified NbC powders (containing Ni)were uniaxially pressed and then gas pressure sintered in vacuum or Argon atmosphere. All samples reached more then 98 % of there theoretical density. The micrographs showed a homogenius distribution of the Ni-binder in the product. The tribological behaviour under dry sliding and oscillating up to 600 °C and the mechanical properties were studied.
The process window and range of functional properties of NbC is wide, because micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, because Nb4C3, Nb6C5 and other short and long range ordered phases occur in the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary Phase diagram, and by the type of binder. Further improvements enable the addition of secondary carbides. Supporting results from literature and different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of these tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. NbC can be synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown in melts and leached out as coarse NbC cubes. NbC provides comparably lower friction in many relevant tribo-contacts and displays low wear. NbC and Nb2O5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO3 and Co3O4.
The present paper illuminates the metallurgical progress on niobium carbide based hard metal developments, which are characterized by: a.) the substitution of cobalt binder by nickel, b.) the change from SPS to conventional sintering and c.) by switching from lab to pilot scale. The toughness was increased in the frame of these developments without loosening the hardness level. The hardness-toughness profile of NbC grades match those of WC and cermet grades. Apart from the aforementioned parameters, the properties depend from the powder processing and sintering conditions.
The functional profile of nickel and NiMo bonded NbC versus cobalt bondedWC grades bonded by cobalt and nickel are benchmarked under dry sliding wear (T= 22/400°C; v= 0,1-10 m/s), abrasive wear (G65) and under dry turning and dry milling against different work piece alloys (C45E, 42CrMo4, 300WA, GG35, AlSi9Cu4Mg). The different elements explaining the wear resistance of NbC over WC will be illuminated.
The present paper illuminates the metallurgical progress on niobium carbide based hard metal developments, which are characterized by: a.) the substitution of cobalt binder by nickel, b.) the change from SPS to conventional sintering and c.) by switching from lab to pilot scale. The toughness was increased in the frame of these develop¬ments without loosening the hardness level. Stoichiometric and sub-stoichiometric, submicron NbC powders were used. The hardness-toughness profile of NbC grades match those of WC and cermet grades. Apart from the aforementioned parameters, the properties depend from the powder processing and sintering conditions. The functional profile of NbC and WC grades bonded by cobalt and nickel are benchmarked by 4-point bending strength, elastic moduli and hot hardness until 1000°C, dry sliding wear (T= 22/400°C; v= 0,1-10 m/s), abrasive wear (G65) and cutting performances under emulsion and coolant-free turning and milling against different alloys (C60, 100Cr6, 42CrMo4, X90CrMoV18, 300WA, GG35).