May/June_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 0 2 9 (a) (a) EBSD band contrast images and phase maps are shown in Figs. 2 and 3. In Fig. 2a, the angular, single crystal WC of the macrocrystalline WC in the TMS based material is apparent in the band contrast map. Figure 2b shows the dif- ferent phases more clearly, with the red binder material (Cu-Mn-Ni-Zn), blue single crystal WC from the macrocrys- talline WC, and the mix of W, WC, and W 2 C phases in chill cast carbide (yellow, blue, and green, respectively). The cast carbide within the material has a lamel- lar grain structure. Similarly, Figs. 3a and 3b show blend 2, which contains conventionally carburized WC based material. In both images, the polycrys- talline nature of the conventionally car- burized WC is shown. Also, binder, W, WC, and W 2 C are shown using the same color key in the EBSD phase map. Using optical and scanning elec- tron microscopy (Hitachi Flex SEM 1000), Figs. 4 and 5 show erosion scars after ASTM G65 testing. The apparent erosion damage varies by material sys- tem; however, damage to the cast car- bide particles in both material systems is rounded and unfractured. This phe- nomenon is attributed to the high hard- ness and lamellar grain structure of the chill cast carbide as it provides better erosion resistance than the convention- al or macrocrystalline WC particles. While the conventional and mac- rocrystalline carbide particles appear to provide less erosion resistance, these material families function to improve strength. Interestingly, the fracturing damage to the polycrystalline parti- cles in the conventionally carburized WC based material seems qualitative- ly more severe than the single crystal macrocrystalline WC (TMS) material (see Figs. 4d and 5d). The grain bound- aries of the conventionally carburized particles within blend 2 are apparent, while the TMS material appears more intact in its erosion scar. During original manufacturing as well as in repair, PDC cutters are manu- ally torch brazed. Great care is taken to minimize damage to the diamonds, as they are susceptible to graphitization and cracking due to thermal expansion between diamond and cobalt. Optical Fig. 4 — Erosion scars showing typical damage to Kennametal’s TMS formula (blend 1): (a) macro view; (b) low magnification; (c) typical damage to chill cast carbide (W 2 C) particle; and (d) typical damage to macrocrystalline WC. Fig. 5 — Erosion scars showing typical damage to the conventionally carburized formula (blend 2): (a) macro view; (b) low magnification; (c) typical damage to chill cast carbide (W 2 C) particle; and (d) typical damage to conventionally carburized WC. (d) (d) (c) (c) (b) (b)