Abstract
Ternary borides possess remarkable properties, including high melting points, exceptional hardness, excellent wear resistance, and impressive corrosion resistance. Among them, WCoB, stands out with its superior hardness and excellent oxidation resistance. The sintering mechanism for WCoB, which encompasses different raw powders and sintering processes, has attracted significant attention due to its unique advantages in comparison to other ternary borides.
Researchers have previously delved into the properties and applications of WCoB-based materials. Despite the significant body of research on WCoB, the effects of Cu and Ni additions to WCoB cermet remain relatively unexplored. This study aims to fill this knowledge gap by investigating the impact of Cu and Ni additions on the phase compositions, microstructure, microhardness, and transverse rupture strength of WCoB cermet, as well as elucidating the distribution of Cu and Ni within the WCoB cermet. In this study, two distinct steps were involved in preparing the composite powders. First, a raw powder mixture was created, consisting of WC (59 wt.%), TiB2 (21 wt.%), and Co (20 wt.%). Next, four different compositions of powders were developed by adding Cu and Ni to the raw powder mixture. These compositions included: (A1) 50 wt.% raw powder + 30 wt.% Cu + 20 wt.% Ni, (A2) 50 wt.% raw powder + 25 wt.% Cu + 25 wt.% Ni, (A3) 50 wt.% raw powder + 20 wt.% Cu + 30 wt.% Ni, and (A4) 50 wt.% raw powder + 15 wt.% Cu + 35 wt.% Ni. The resulting ball-milled composite powders were then transferred into the mold press, and subsequently placed into a vacuum sintering furnace to complete the sintering process.
The addition of Cu and Ni results in significant alterations to the microstructure and mechanical properties of WCoB cermet. The grain’s morphology of WCoB cermet changed from like-spherical to polygon with the decrease of Cu (30 wt.% to 15 wt.%) and increase of Ni (20 wt.% to 35 wt%). X-ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) result demonstrate that Cu and Ni forms a ternary phase, Ti2CuNi, within the WCoB cermet, predominantly located at the grain boundaries of the hard phases. The alteration of Cu and Ni content leads to a noteworthy shift in grain size, with an increase in Ni content and decrease in Cu content resulting in expanded grain dimensions. This, in turn, contributes to a decrease in microhardness and transverse rupture strength. The ceramic with a composition of 30 wt.% Cu + 20 wt.% Ni displayed the most promising properties, featuring an average grain size of just 2.02 μm, with ceramic hardness reaching 1477.8 HV0.5 and transverse rupture strength reaching 1356 MPa. In comparison, the microhardness and transverse rupture strength of WCoB (30 wt.% Cu + 20 wt.% Ni) outperformed WCoB (15 wt.% Cu + 35 wt.% Ni) by 2.7% and 6.9%, respectively. This notable improvement is attributed to the grain refinement driven by Cu addition and the grain boundary strengthening, primarily due to solid solution strengthening and dispersion strengthening facilitated by the formation of Ti2CuNi. Interestingly, despite the inherently brittle nature of WCoB ceramics, the addition of Cu and Ni led to a marked increase in fracture surface smoothness, the occurrence of grain pull-out phenomena, and a reduction in plastic deformation capacity. This intriguing combination of factors contributes to the improved mechanical properties observed in these cermet materials.
In summary, this research provides valuable insights into the synergistic effects of Cu and Ni additions to WCoB cermet. These alloying elements impact the phase compositions, microstructure, microhardness, and transverse rupture strength of the material, providing insight into the distribution of Cu and Ni within the cermet. The findings open up new avenues for optimizing the performance of WCoB-based materials, making them promising candidates for a range of industries requiring high-performance, wear-resistant materials with superior mechanical properties.
