“…Besides SiC whisker, Si 3 N 4 whisker is another most common ceramic whisker used as a toughening agent for ceramics. Zheng et al [153][154][155] investigated the effect of in situ growing β-Si 3 N 4 whiskers on toughening WC ceramics prepared by SPS. The formation of β-Si 3 N 4 whiskers significantly improved the toughness to 10.94 MPa m 1/2 for WC-Si 3 N 4 sample from 6.69 MPa m 1/2 for pure WC.…”
Section: Whiskers Tougheningmentioning
confidence: 99%
“… Fig. 12 SEM images of indentation cracks observed in the sintered WC–Si 3 N 4 composites: a Si 3 N 4 whiskers pullout, b crack-bridging by Si 3 N 4 whiskers [ 153 ]. Figure panels reproduced from Ref.…”
Section: Toughening Of Binderless Tungsten Carbidementioning
HIGHLIGHTS• Establish processing-composition-microstructure-property relationships governing binderless tungsten carbide (BTC).• Highlight the densification improving strategies and toughening methods for BTC.• Provide key challenges as well as the outlook for superior peformance associated with BTC.ABSTRACT WC-Co alloys have enjoyed great practical significance owing to their excellent properties during the past decades. Despite the advantages, however, recently there have been concerns about the challenges associated with the use of Co, i.e. price instability, toxicity and properties degeneration, which necessitates the fabrication of binderless tungsten carbide (BTC). On the other hand, BTC or BTC composites, none of them, to date has been commercialized and produced on an industrial scale, but only used to a limited extent for specialized applications, such as mechanical seals undergoing high burthen as well as high temperature electrical contacts. There are two challenges in developing BTC: fully densifying the sintered body together with achieving a high toughness. Thus, this review applies towards comprehensively summarize the current knowledge of sintering behavior, microstructure, and mechanical properties of BTC, highlighting the densification improving strategies as well as toughening methods, so as to provide reference for those who would like to enhance the performance of BTC with better reliability advancing them to further wide applications and prepare the material in a way that is environment friendly, harmless to human health and low in production cost. This paper shows that the fabrication of highly dense and high-performance BTC is economically and technically feasible. The properties of BTC can be tailored by judiciously selecting the chemical composition coupled with taking into careful account the effects of processing techniques and parameters.
“…Besides SiC whisker, Si 3 N 4 whisker is another most common ceramic whisker used as a toughening agent for ceramics. Zheng et al [153][154][155] investigated the effect of in situ growing β-Si 3 N 4 whiskers on toughening WC ceramics prepared by SPS. The formation of β-Si 3 N 4 whiskers significantly improved the toughness to 10.94 MPa m 1/2 for WC-Si 3 N 4 sample from 6.69 MPa m 1/2 for pure WC.…”
Section: Whiskers Tougheningmentioning
confidence: 99%
“… Fig. 12 SEM images of indentation cracks observed in the sintered WC–Si 3 N 4 composites: a Si 3 N 4 whiskers pullout, b crack-bridging by Si 3 N 4 whiskers [ 153 ]. Figure panels reproduced from Ref.…”
Section: Toughening Of Binderless Tungsten Carbidementioning
HIGHLIGHTS• Establish processing-composition-microstructure-property relationships governing binderless tungsten carbide (BTC).• Highlight the densification improving strategies and toughening methods for BTC.• Provide key challenges as well as the outlook for superior peformance associated with BTC.ABSTRACT WC-Co alloys have enjoyed great practical significance owing to their excellent properties during the past decades. Despite the advantages, however, recently there have been concerns about the challenges associated with the use of Co, i.e. price instability, toxicity and properties degeneration, which necessitates the fabrication of binderless tungsten carbide (BTC). On the other hand, BTC or BTC composites, none of them, to date has been commercialized and produced on an industrial scale, but only used to a limited extent for specialized applications, such as mechanical seals undergoing high burthen as well as high temperature electrical contacts. There are two challenges in developing BTC: fully densifying the sintered body together with achieving a high toughness. Thus, this review applies towards comprehensively summarize the current knowledge of sintering behavior, microstructure, and mechanical properties of BTC, highlighting the densification improving strategies as well as toughening methods, so as to provide reference for those who would like to enhance the performance of BTC with better reliability advancing them to further wide applications and prepare the material in a way that is environment friendly, harmless to human health and low in production cost. This paper shows that the fabrication of highly dense and high-performance BTC is economically and technically feasible. The properties of BTC can be tailored by judiciously selecting the chemical composition coupled with taking into careful account the effects of processing techniques and parameters.
“…But studies on the toughening effect of the porous fiber are rare yet. WC-Si 3 N 4 composites have been considered in detail with respect to the sintering process, phase transformation, microstructure, and mechanical properties using spark plasma sintering (SPS) (Li et al, 2013;Zheng et al, 2013aZheng et al, , 2015. In this study, the WC-10 wt.% Si 3 N 4 composites with addition of UPBNNF were prepared using SPS to investigate UPBNNF's effects on the overall mechanical properties.…”
WC-10 wt.% Si3N4 composites toughened with ultrafine porous boron nitride nanofiber (0, 0.01, 0.05, 0.1, and 0.15 wt.%) were prepared for the first time by spark plasma sintering. Compared with the WC-Si3N4 composite sintered in the same condition, the obtained WC-10 wt.% Si3N4 composites with ultrafine porous boron nitride were found to possess better hardness and fracture toughness. In addition, the Si3N4 phase in the UPBNNF toughened composites did not exhibit traditional catastrophic fracture as indicated in most investigations. In this study, the phenomena are discussed, and a probable mechanism is elucidated. It is deduced that the approach could be extended to materials with a feature of internal liquid phase during the sintering process and could improve hardness and fracture toughness.
“…A conventional method to improve the fracture toughness of binderless WC materials is to lower the grain size of sintered WC bulks . Other methods, which are based on the addition of zero‐ or one‐dimensional second phases such as Al 2 O 3 , ZrO 2 and Si 3 N 4 , have also been explored and found to be effective . These types of ceramic phase‐WC matrix combinations are typically considered to be a weak combination.…”
Porous fibers are widely used in catalysis chemistry and hydrogen storage but are rarely used in structural ceramics. In this study, spark plasma sintering was used to prepare an ultrafine porous boron nitride nanofiber-toughened WC composite for the first time. The obtained WC-0.05 wt% ultrafine porous boron nitride nanofiber composites exhibited better properties (ie, a 2.3% increase in hardness and a 19.6% increase in fracture toughness) compared to those of the pure WC specimen. The fiber porosity improved the second phase-WC matrix microstructural combination. The described approach is a novel preparation method for the WC composites.Furthermore, a new toughening mechanism, which is based on "pinning and stretching", was determined. These findings suggest that porous boron nitride fibers can be considered to be second phases for toughening the WC composites.
K E Y W O R D Sceramic composites, porous fibers, toughening mechanism, WC
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