Effects of HfB2 and HfN Additions on the Microstructures and Mechanical Properties of TiB2-Based Ceramic Tool Materials

Abstract

The effects of HfB2 and HfN additions on the microstructures and mechanical properties of TiB2-based ceramic tool materials were investigated. The results showed that the HfB2 additive not only can inhibit the TiB2 grain growth but can also change the morphology of some TiB2 grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB2-HfB2 ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB2 and Ni. The decrease of the flexural strength and Vickers hardness of the TiB2-HfN ceramics was due to the increase of defects such as TiB2 coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB2 coarse grains. The toughening mechanisms of TiB2-HfB2 ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB2-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.

Microstructure and Mechanical Properties of ZrB2–HfC Ceramics Influenced by HfC Addition

“…In fabricating ZrB 2 –SiC–HfB 2 ceramics, Balak et al pointed out that Hf and Zr diffused each other in a way that resulted in the formation of a (Zr, Hf)B 2 solid solution [ 34 ]. Generally, when a new solid solution forms, twin peaks appear next to the standard XRD [ 35 , 36 ]. However, the peak position of ZrB 2 and HfC in Figure 1 was in line with their respective peak position in the standard XRD card.…”

Microstructure and Mechanical Properties of TiC0.7N0.3-HfC-WC-Ni-Mo Cermet Tool Materials

“…Fracture toughness ( K IC ) was measured via the direct indentation method [16,17]. Vickers hardness was measured on the polished surfaces using a diamond pyramid indenter (HVS-30, Shanghai Precision Instruments Co., Ltd., Shanghai, China) under a load of 196 N for 15 s by HV-120 based on Chinese National Standards GB/T 16534-2009 [18].…”