Microstructure and Wear Behavior of Conventional and Nanostructured Plasma-Sprayed WC-Co Coatings

Abstract

WC-12%Co coatings were deposited by atmospheric plasma spraying using conventional and nanostructured powders and two secondary plasmogenous gases (He and H 2 ). Coating microstructure and phase composition were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction techniques (XRD) techniques. This study examined wear and friction properties of the coatings under dry friction conditions. SEM was used to analyze abraded surface microstructure. Coating microhardness and fracture toughness were also determined. All coatings displayed strong decarburization as a result of WC decomposition, which gave rise to the formation of secondary phases (W 2 C and W). A very fine undissolved WC crystalline dispersion coexisted with these new phases. TEM observation confirmed that the matrix was predominantly amorphous and filled with block-type, frequently dislocated crystallites. Wear was observed to follow a three-body abrasive mechanism, since debris between the ball and the coating surface was detected. The main wear mechanism was based on subsurface cracking, owing to the arising debris. WC grain decomposition and dissolution were concluded to be critical factors in wear resistance. The level of decomposition and dissolution could be modified by changing the plasmogenous gas or feed powder grain size. The influence of the plasmogenous gas on wear resistance was greater than the influence of feedstock particle size.

Influence of Post-treatment on the Microstructural and Tribomechanical Properties of Suspension Thermally Sprayed WC–12 wt%Co Nanocomposite Coatings

“…During spraying of WC-Co powders, significant changes in the chemical and phase compositions can occur [1]. The past two decades have seen extensive research in optimizing the feedstock powder characteristics, process parameters and post-treatments of wear-resistant hardmetal coatings [2][3][4][5][6][7][8][9][10][11][12][13][14]. Most research, however, has related to the coatings sprayed from agglomerated and sintered powders, with the typical particle size ranging from 10 to 50 lm and WC grain size ranging from 0.8 to 3.5 lm [2][3][4][5][6][7].…”

“…Most research, however, has related to the coatings sprayed from agglomerated and sintered powders, with the typical particle size ranging from 10 to 50 lm and WC grain size ranging from 0.8 to 3.5 lm [2][3][4][5][6][7]. Optimization of these coatings has resulted in coating microstructures with negligible porosity, high fracture toughness and minimization of secondary carbide phases [2][3][4][5][6][7][8][9][10][15][16][17][18].…”

“…These coatings have the potential to provide further improvement in their tribomechanical performance. Previous researchers have used conventional thermal spray systems to deposit coatings from nanostructured WC-Co feedstocks [9,10,[19][20][21]. In these previous investigations, agglomerated and sintered nanosized particles have been used for the deposition of nanostructured thermal spray coatings, generally resulting in a predominantly bimodal coating structure, where the coating architecture exhibits micrometer-sized zones with nanometer-sized structure [19].…”

Sliding wear investigation of suspension sprayed WC–Co nanocomposite coatings

“…Tribomechanical properties such as hardness, wear resistance, and strength are influenced primarily by the size and distribution of WC grains, the porosity, the volume fraction and thermo-mechanical properties of the metal matrix, and post-treatments of the composite hardmetal coating [1][2][3][4][5][6][14][15][16][17][18][19][20][21][22]. Both room temperature and higher temperature investigations have been conducted [23][24][25][26].…”

Tribological Characteristics of Tungsten Carbide Reinforced Arc Sprayed Coatings using Different Carbide Grain Size Fractions

“…For various thermal spray techniques, numerous studies emphasized the enhanced wear resistance of WC reinforced coatings against sliding wear [1], abrasive wear RESEARCH [2] as well as erosion [3] and erosion-corrosion [4]. For high velocity oxy fuel [5,6], plasma [7,8] and suspension flame [9] sprayed coatings, several authors investigated the tribological characteristics of stressed surfaces by employing different tungsten carbide grain-sized feedstocks. It was found that a decreased carbide grain size possesses a higher resistance against abrasion, sliding, or erosive wear.…”