Fine WC-Co Research Articles

Flow phenomenon of micron-sized particles during cold spray additive manufacturing: High-speed optic observation and characterization

A high-speed laser shadowgraph observation of the particles flow during cold spraying enables a good phenomenological characterization. The particles in-flight behaviour develops a kinematics with two regimes regardless the powder nature. When leaving the nozzle, the particles form a regime of uniform jet over a certain distance along the flow direction, and then a regime of sparse jet while particles deviate in the radial direction. This dispersion increases away from the nozzle exit and exhibits thereby an event of oblique collision during an additive route process. Under such conditions, kinematic deficiency prevails since oblique collision has shown to alter the deposition efficiency, in the literature. Albeit these particles flow regimes represent a generic behaviour, there are differences in the powder’s response depending of their features that can be combined using the parameter ρpDp. The variance ρpDp in cold spraying is scaled through a few cases of powders (copper, aluminium, magnesium, cermet, and PEEK). The powders dispersion becomes more and more important as ρpDp decreases from high value (large Cu powders) down to low value (case of Mg powders). However, this tendency cannot be extrapolated to lightweight powders represented by the fine PEEK powders (low ρpDp) which are more stable over a larger distance due to a higher sensitivity to the axial component of the gas velocity. They get unstable later in the jet since they become sensitive to the radial component of the gas velocity due to a progressive decrease of the axial gas velocity. The fine WC-Co powders adopt similar behaviour since they are lightweight as the PEEK powders due to their porous structure.

Effect of Mo and Y2O3 additions on the microstructure and properties of fine WC-Co cemented carbides fabricated by spark plasma sintering

The effects of Mo and Y2O3 additions on the microstructure and properties of fine WC-6Co cemented carbides prepared by spark plasma sintering (SPS) were investigated. The microstructure, mechanical properties and corrosion behavior were analyzed by SEM, TEM, XPS, mechanical property tests and potentiodynamic polarization curve measurements. The results show that there are no significant differences in the microstructure and properties of alloys with 1.0% Y2O3 addition. However, the addition of Mo was beneficial for refining the WC grains. The hardness of alloys increased until the maximum value, and then followed a decreasing trend with the increase of Mo content. In addition, the relative density of alloys decreased with the increase of Mo addition, which caused to an obvious decline in fracture toughness. With the additions of Mo and Y2O3, the corrosion resistance of alloys improved significantly both in acid and alkaline solutions (0.1M HCl and 0.1M NaOH solutions). The adding amount of Mo should be controlled within a certain range and 1wt% of Mo has the most positive effect on the comprehensive properties of WC-6Co alloys.

The effects of fine WC contents and temperature on the microstructure and mechanical properties of inhomogeneous WC-(fine WC-Co) cemented carbides

Inhomogeneous WC-(fine WC-Co) cemented carbides with improved hardness and toughness were successfully prepared through the addition of fine WC using planetary ball milling combined with sinter isostatic hot pressing (SHIP) technology. The inhomogeneous microstructure of the alloys consisted of coarsened WC grains and WC-Co consisting of fine WC dispersoids and Co binder phase. The increase of temperature and the addition of fine WC enhanced the sintering process. The morphologies of the coarsened WC and of the fine WC consisted of triangular and near-hexangular prisms, respectively. Due to crack path deflection and crack bridging, the prism-like coarsened WC crystals efficiently hindered cracks propagation. Intergranular fracture became predominant when adding fine WC. However, the excessively coarsened WC and some pores in alloys with 20wt% fine WC could decrease the mechanical properties. The inhomogeneous WC-(fine WC-Co) cemented carbides with 10wt% fine WC, sintered at 1430°C for 40min, could provide a combination of superior hardness and toughness.

Wear Performance of the Plasma Sprayed Fine WC-Co Composite Powders Coatings

WC/Co; Composite coating; Plasma spraying; Friction and wear Abstract: WC- Co composite powders were synthesized by direct mechanical grinding in a rotary-vibration mill under 8h, and then analyzed by SEM and XRD. WC and WC/Co composite coatings were prepared by supersonic plasma spraying fine WC-Co composite powders. The wear and friction properties of both coatings were evaluated. The results showed that the wear resistance of the WC/Co composite coating was superior to that of the WC coating. The improvement in wear resistance of the WC/Co composite coating was attributed to its higher fracture toughness and adhesion strength as well as better thermal diffusivity. As for the WC/Co composite coating, the mechanism was mainly adhesion with micro-abrasion and fatigued-induced brittle fracture within splats, and the delamination along splat boundaries only occurred at high load. However, the failure of the WC coating was predominantly detachment of transferred film and brittle fracture within the splats and delamination along splat boundaries, which were enhanced with the increasing load.

Wear Performance of the Plasma Sprayed Fine WC-Co Composite Powders Coatings

Wear Performance of the Plasma Sprayed Fine WC-Co Composite Powders Coatings

Fabrication and Mechanical Properties of ultra fine WC-6wt.%Co by Spark Plasma Sintering Process

Using the spark plasma sintering process (SPS process), the WC-6wt.%Co hard materials were densified using an ultra fine WC-Co powder. The WC-Co was almost completely dense with a relative density of up to 100% after the simultaneous application of a pressure of 60 MPa and the DC pulse current for 3 min without any significant change in the grain size. The average grain size of WC that was produced through this experiment was about 0.2~0.8 μm. The hardness and fracture toughness were about 1816 kg/mm and 15.1 MPa·m, respectively, for 60 MPa at 1200°C. (Received September 30, 2010)