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 8 (a) (b) (a) (b) a significant impact on the erosion re- sistance and TRS of the bit body due to the powder’s underlying charac- teristics including stoichiometry, size, and particle size distribution (PSD). The current commercial landscape of matrix materials includes a vari- ety of WC powders, as highlighted in Table 1 [5,6] . Due to their intricacies, the high upfront manufacturing costs associ- ated with PDC matrix bit bodies re- quires that manufacturers choose a material that is suitable for refurbish- ment and reuse. PDC cutters are often replaced or rotated to expose a new cutting edge, which exposes the body material to high and nonuniform tem- peratures. Thus, to get the greatest eco- nomic use out of a bit body, a matrix material must not only have appropri- ate strength and erosion resistance, but also be resistant to damage from ther- mal cycling mechanisms present in the repair process. EXPERIMENTAL PROCEDURES Two material combinations were blended with fractions of chill cast W 2 C and either macrocrystalline WC or con- ventional carburized WC using standard dry blending equipment. The first ma- terial was based on Kennametal’s newly formulated, macrocrystalline based To- tal Matrix Solution (TMS) matrix powder material. The second used convention- ally carburized WC as the base material (30% chill cast W 2 C, 65% WC, and nickel powder for the balance). Lab coupons of the two matrix ma- terials were infiltratedwith commercial- ly available Macrofil 53 (Cu-Ni-Mn-Zn) at 1200°C in an air atmosphere to near 100% densification. Samples were eval- uated for ASTM B406 transverse rup- ture strength, modified ASTM G76 wet erosion resistance, and subjected to a subsequent thermal cycle greater than 1200 o C meant to be an exaggerated simulation from braze cycling. The ero- sion test uses water as the carrier and ASTM G65 silica sand (50/70 mesh) as the erodent. Scanning electron microscopy (SEM) was used to characterize ero- sion scars and electron backscatter dif- fraction (EBSD) was used to evalu- ate phases in the microstructure. All EBSD work was performed on a Jeol JSM7100F with an Oxford Instruments XMax EBSD detector. Data was collected at 28 kV with a 350-nm step size. Sub- sequent data mapping and post pro- cessing were accomplished with HKL Tango mapping software from Oxford Instruments. RESULTS AND DISCUSSION Table 2 shows the erosion re- sistance, volume loss per unit mass of erodent, and transverse rupture strength. TABLE 1 – COMMERCIAL MATRIX MATERIALS Base material Chill cast carbide Macrocrystalline carbide Conventionally carburized Stoichiometry WC/W 2 C WC WC Morphology TABLE 2 – EROSION RESISTANCE AND TRANSVERSE RUPTURE STRENGTH Blend WC type Modified ASTM G76 (mm 3 /kg) ASTM B406 (MPa) 1 Macrocrystalline blend (Kennametal TMS) 11.1 1207 2 Conventionally carburized blend 10.4 1145 Fig. 2 — (a) Band contrast map, blend 1; and (b) phase map, blend 1. Fig. 3 — (a) Band contrast map, blend 2; and (b) phase map, blend 2.