SYNTHESIS OF WC-12wt%Co NANOCOMPOSITES BY HIGH ENERGY BALL MILLING AND THEIR MORPHOLOGICAL CHARACTERIZATION

Abstract

In this work micrometric particles of WC and Co were processed by high energy ball milling in a planetary ball mill. We evaluated the phase formation and changes in microstructure of WC-12wt%Co as a result of the following milling parameters: ball-to-powder weight ratio, milling time and speed. The material was characterized by X-ray diffraction (crystalline phases and crystallite size), particle size analysis (average grain diameter), the BET method (surface area), and scanning electron microscopy (powder morphology). The average particle size (D50) and crystallite size were respectively 1.63µm and 13.8nm, for a surface area of 4.709 m 2 /g, using a ball-to-powder weight ratio of 1:20, a milling time of 5h and a milling speed of 500 rpm.

Comparative study of the fatigue performance of the micro and nanometric Cr3C2-25NiCr coating sprayed by HVOF on ASTM A516 steel substrate

“…Parameters used were 40 kV and 40 mA, 10 mm window, 1º slot, angle between 5 0 and 75º. The diffractograms were treated and analyzed through the software WinFit 1.2, employing the Single -Line method to calculate the mean diameter of the crystallites [13]. Scanning electron microscope (SEM JOEL Carry Scope JSM-5700) and energy dispersive spectroscopy (EDS) techniques were applied for the powders and coating analysis.…”

“…Therefore, it can be assumed that the nanometric powder may consist of amorphous structures and crystal dispersions. The XRD analysis ( Figure 2 ) explains the presence of Cr 3 C 2 [13,15,20,27,29], and Cr 7 C 3 in the micrometric powder. The intensity of the peaks decreases, while they expand as a function of milling time.…”

“…Coatings obtained from milled powders down to the nanometer level, whose structure contains nanometric crystallites, provide coating with greater adhesion to the substrate, significantly lower porosity and higher surface quality, lower roughness, in addition to the increased hardness and wear resistance [11]. The high energy milling (HEM) is a technique where powder mixtures of different metals are ground together to obtain a homogeneous alloy [13]. This process causes intense plastic strain of the powders, leading the particles to hardening, fracture and subsequent cold welding in successive stages [14].…”

“…The structure undergoes intense multiplication of dislocations, which leads to the reduction of its long-range order, promoting particles fracture up to the nanometer scale, although they remain as crystallites. The HEM allows nanostructured materials to be synthesized easily in a short time [13]. Moreover, the main objectives of the HEM for the synthesis of Cr 3 C 2 -25NiCr coating powder are: i) to reduce the granulometry of the composite; ii) to ensure that the carbide particles will be surrounded by the precursor constituent of the NiCr binder phase; iii) to create new active surfaces and structural defects in the composite [15].…”

“…The size of sprayed powders intimately effects the physical and mechanical properties of the coating. Structure formed by nanometer crystallites of the coating and high volumetric fraction of atoms in the layer's grain boundaries can improve mechanical properties [13]. Coatings obtained from nanometric powders have been researched more recently, and their use enhances coating performance gains [1,10,22,24].…”