A review on fabrication and characterization of WC–graphene self-lubricant tool prepared by spark plasma sintering

Semi-empirical relationship between the hardness, grain size and mean free path of WC–Co

Nano-grained WC-10Co hardmetal can be made by doping a new invented VC-based multi-grain-growth-inhibitor and suitable technical processing. The specifications for quantitative measurement of the grain size of WC in the alloy were investigated. It is very important to obtain the SE images of the alloy with good contrast and clear profile of WC grains by FESEM; then the linear intercept (LI) method was used to quantitatively measure the intercepts of WC grains. When the surveyed intercept numbers of WC grain exceeded 200, the statistic data for the mean grain size of WC were reproduced. The discriminative minimal grain size of used LI method was 12 nm; the maximum intercept of WC grain was 109 nm; the average intercept of WC grains was 45 nm and the corresponding 3D mean grain size of WC was 70 nm which is agreeable with the XRD outcome.

Nano-grained WC-10Co hardmetal can be made by doping a new invented VC-based multi-grain-growth-inhibitor and suitable technical processing. The specifications for quantitative measurement of the grain size of WC in the alloy were investigated. It is very important to obtain the SE images of the alloy with good contrast and clear profile of WC grains by FESEM; then the linear intercept (LI) method was used to quantitatively measure the intercepts of WC grains. When the surveyed intercept numbers of WC grain exceeded 200, the statistic data for the mean grain size of WC were reproduced. The discriminative minimal grain size of used LI method was 12 nm; the maximum intercept of WC grain was 109 nm; the average intercept of WC grains was 45 nm and the corresponding 3D mean grain size of WC was 70 nm which is agreeable with the XRD outcome.

Effects of nanocomposite grain growth inhibitors and multi-walled carbon nanotubes on the microstructure and mechanical properties of ultrafine cemented carbides

Spark plasma sintering on nanometer scale WC–Co powder

The present authors previously reported that the high-strength WC-Co cemented carbide could be obtained by milling (WC+Co+Zn) powders and subsequently sintering the WC-Co-Zn mixture. In this report the effects of the amount of Zn mingled, sintering conditions and mean grain size of WC on the strength of Zn-added WC-10% Co medium-carbon alloys were first investigated. Secondly Second by the strengthening mechanism in the alloy was in detail studied in relation to the defects (such as pores, coarse WC grains and Co pools), which were observed on the ruptured surface as the origin of fracture.Results obtained were as follows: (1) The strength was not sensitive to sintering conditions. (2) The effect of Zn addition decreased with increasing mean grain size of WC. (3) In Zn-added alloy with usual grain size of WC (1.5-1.8μ), the fracture rate starting from coarse WC grains (<-15 μ) increased, leading to the fact that the high strength of the alloy was caused by the decrease in density of large pores which are in general more responsible for the fracture than coarse WC grains.

Effects of TiC0.4 on microstructure and properties of WC composites

Based on the backscattered electron (BSE) images and IMAGEJ image analysis software, the average grain size of WC in ultrafine grained WC-Co cemented carbides was measured. The result shows that BSE images of the polished surface not be etched are suitable for quantitative evaluating the grain size of WC in the ultrafine grained hardmetals. Both linear intercept method and equivalent circle diameter method can be used to accurately measure the grain sizes of WC in ultrafine grained hadmetals by using IMAGEJ software. Measurement results of WC grain sizes coincide with the conclusion of X-ray diffraction method

In this work, to explore potential substitutions for the Co binder phase, ultrafine-grain WC-based cermets with various binder phases of Co, Ni and AlCoCrNiFeCu HEA were prepared using the SPS method. Based on SPS, WC-based cermets were fabricated at higher speed, showing fine carbide particles less than 410 μm. The microstructure, mechanical properties and wear properties were systematically evaluated. By comparison, the grain size of WC was the lowest for WC-10Co, while WC-10 HEA cermet held the coarsest WC particles. The hardness and fracture toughness of WC-10 HEA were the best among all three samples, with values of 93.2 HRA and 11.3 MP·m1/2. However, the bending strength of WC-10HEA was about 56.1% lower than that of WC-10Co, with a value of 1349.6 MPa. The reduction in bending strength is attributed to the lower density, formation of a newly Cr-Al rich phase and coarser WC grains. In dry sliding wear conditions, WC-10 HEA showed the lowest wear rate (0.98 × 10−6 mm3/(N·m)) and coefficient of friction (0.19), indicating the best wear resistance performance. This reveals that WC-based cermet with a HEA binder phase has superior wear performance due to the higher hardness and good self-lubricating effect of the wear products.

Effects of Al2O3–ZrO2 content on the densification, microstructure, and mechanical properties of cemented tungsten carbides

This paper concerned with SPS (spark plasma sintering), hot pressing of sinter nanometer WC-Co powder and discussed the density, hardness, microstructures and grain sizes of the alloys sintered by different styles. The results showed that SPS could lower the sintering temperature, increased the density and circumscribed the growth of grain size of WC. Hot pressing sintering could produce high density alloys and play well on the grain growth, but its sintering temperature and sintering time were larger than SPS. Besides, the hardness of the sintered cemented alloys that was dependent on the grain size and densification could also be improved by SPS and hot pressing.

The mixing phenomena of WC and Co powders have not yet been made clear enough in spite of their importance in the Cemented Carbide industry. Therefore, in this paper the crushing of WC powders and the behaviour of their grain growth during sintering were examined using variousWC powders, i.e., coarse single crystal, coarse polycrystalline and medium single crystalline WC powders.The obtained results were as follows;(1) Coarse single crystal WC powders were crushed markedly by chipping in the early ball milling stage. There-after, average grain size of WC continued to decrease with the appearance of fine chipping powders. Therefore, the grain size distribution of the coarse single crystal WC powder grew wider with the increase of ball milling time.(2) Polycrystalline WC powders were crushed in the same way as the above mentioned (single crystal) in the early ball milling stage. However, the grain boundary destruction seemed to be caused after having been WC crushed into the definite size.(3) Single crystal WC powder of medium size were more difficult to be crushed with chipping than the coarse one.(4) The grain growth of coarse single crystal WC during sintering is more rapid than polycrystalline one because the size distribution of the former was wider than that of the latter. Moreover the average grain size of WC in alloys formed medium single crystal WC powders in coarser than that from coarse one, because the former was less crushed than the latter.(5) In sum, the crushbility of WC in ball milling and its grain growth in sintering did not only depend upon WC grain size, but also the manufacturing process.

Tungsten carbides are very attractive because of their superior properties, e.g., high thermal and electrical conductivities, high melting point, high hardness, and relatively high chemical stability. Tungsten carbides with a binder metal, for example Ni or Co, are mainly used to fabricate nozzles, molds and cutting tools in the composite form. Al has been reported as an alternative binder in Tungsten carbide since Al shows a higher oxidation resistance than Ni or Co and is less expensive. Nanostructured WC-Graphene-Al composites were sintered rapidly using pulsed current activated sintering (PCAS). The mechanical properties (hardness and fracture toughness) and microstructure were investigated using scanning electron microscopy and Vickers hardness tester. The PCAS method successfully obstructed grain growth, resulting in nanostructured materials, and induced a very fast consolidation nearly at the level of theoretical density. The grain size of WC in WC-Graphene-Al composite decreased with the addition of Al content. The fracture toughness and hardness of the WC-5vol.% graphene-x vol.% Al (x=0, 5, 10, 15) were 4.7, 5.5, 5.9, 7.9 MPa·m&lt;sup&gt;1/2&lt;/sup&gt; and 2008, 1961, 1883, 1731 kg/mm&lt;sup&gt;2&lt;/sup&gt;, respectively. The fracture toughness was improved without remarkable decrease of hardness due to the small dimensions of the WC grain and the consolidation facilitated by adding Al to WC-Graphene matrix.

Ultrafine binderless WC-based cemented carbides with varied amounts of AlN nano-powder fabricated by spark plasma sintering

Ultrafine grained WC-10FeCoCu cemented carbides doped with La2O3 prepared by spark plasma sintering