Effects of Ni addition and cyclic sintering on microstructure and mechanical properties of coarse grained WC–10Co cemented carbides

Coarse grained WC–10(Co, Ni) cemented carbides with different Ni contents were fabricated by sintering-HIP and cyclic sintering at 1450 °C. The effects of Ni addition and cyclic sintering on the microstructures, magnetic behavior and mechanical properties of coarse grained WC–10(Co, Ni) cemented carbides have been investigated using scanning electron microscope (SEM), magnetic performances tests and mechanical properties tests, respectively. The results showed that the mean grain size of hardmetals increases from 3.8 μm to 5.78 μm, and the shape factor Pwc decreases from 0.72 to 0.54, with the Ni content increases from 0 to 6 wt.%. Moreover, the W solubility reaches the highest value of 10.33 wt.% when the Ni content is 2 wt.%. The hardness and transverse rupture strength of WC–8Co–2Ni are 1105 HV₃₀ and 2778 MPa, respectively. The cyclic sintering is conducive to increase the WC grain size of WC–10(Co, Ni) and improves the transverse rupture strength of WC–10Co without compromising the hardness of alloys.     

Wear damage of cemented carbides with different combinations of WC mean grain size and Co content. Part I: ASTM wear tests

In the present work we made and examined cemented carbides characterized by very different WC grain sizes varying from near-nano with a WC mean grain size of about 200 nm to coarse-grain with a WC mean grain size of about 4.5 μm and Co contents varying from 3 to 24 wt.%. The major objective of the present work was to examine the wear damage, wear behavior and wear mechanisms of cemented carbides having nearly the same hardness but greatly varying with respect to their WC grain size and Co content in the high-load ASTM B611 test and low-load G65 test.Both the hardness and resistance to fracture and micro-fatigue of cemented carbides play an important role in the wear damage by use of the high-stress ASTM B611 test when the carbide surface is subjected to alumina particles at high loads. In this case, the wear-resistance increases with increasing the WC mean grain size and decreasing the Co content at nearly the same hardness of the different cemented carbides. The submicron and near-nano cemented carbides are characterized by lower wear-resistance in comparison with the coarse-grain grade due to their reduced fracture toughness, fracture resistance and resistance to micro-fatigue.The Co mean free path in the carbide microstructure plays an important role with respect to wear-resistance in the low-stress ASTM G65 test when the carbide surface is subjected to gentle scratching by abrasive silica particles. The predominant wear of the thick Co interlayers leaving unsupported WC grains plays the decisive role in the wear behavior of the coarse-grain grade resulting in its low wear-resistance. In contrast to the ASTM B611 test the wear rate decreases with decreasing the WC mean grain size and increasing the Co content due to the corresponding reduction of Co mean free path in the carbide microstructure. As a result, the wear-resistance of the near-nano grade in the ASTM G65 test is the best of all in spite of its reduced fracture toughness.Phenomena of micro-fatigue, micro-fracturing and micro-chipping are found to play a decisive role in the wear damage of cemented carbides if they are subjected to abrasion wear, high loads and severe fatigue.     

Effect of initial particulate and sintering temperature on mechanical properties and microstructure of WC–ZrO2–VC ceramic composites

Owing to improving the mechanical properties of cemented carbides in high speed machining fields, a new composite tool material WC–ZrO₂–VC (WZV) is prepared from a mixture of yttria stabilized zirconia (YSZ) and micrometer VC particles by hot-press-sintering in nitrogenous atmosphere. Commercial WC, of which the initial particle sizes are 0.2 μm, 0.4 μm, 0.6 μm and 0.8 μm, is mixed with zirconia and VC powder in aqueous medium by following a ball mill process. The sintering behavior is investigated by isostatic pressing under different sintering temperature. The relative density and bending strength are measured by Archimedes methods and three-point bending mode, respectively. Hardness and fracture toughness are performed by Vickers indentation method. Microstructure of the composite is characterized by scanning electron microscopy (SEM). The correlations between initial particles, densification mechanism, sintering temperature, microstructure and mechanical properties are studied. Experimental results show that maximum densification 99.5% is achieved at 1650 °C and the initial particle size is 0.8 μm. When temperature is 1550 °C and particle size is 0.4 μm, the optimized bending strength (943 MPa) is obtained. The best hardness record is 19.2 GPa when sintering temperature is 1650 and particle size is 0.8 μm. The indention cracks propagate around the grain boundaries and the WC particles fracture, which is associated with particle and microcrack toughening mechanism.     

Effect of Mo and Y2O3 additions on the microstructure and properties of fine WC-Co cemented carbides fabricated by spark plasma sintering

The effects of Mo and Y₂O₃ additions on the microstructure and properties of fine WC-6Co cemented carbides prepared by spark plasma sintering (SPS) were investigated. The microstructure, mechanical properties and corrosion behavior were analyzed by SEM, TEM, XPS, mechanical property tests and potentiodynamic polarization curve measurements. The results show that there are no significant differences in the microstructure and properties of alloys with 1.0% Y₂O₃ addition. However, the addition of Mo was beneficial for refining the WC grains. The hardness of alloys increased until the maximum value, and then followed a decreasing trend with the increase of Mo content. In addition, the relative density of alloys decreased with the increase of Mo addition, which caused to an obvious decline in fracture toughness. With the additions of Mo and Y₂O₃, the corrosion resistance of alloys improved significantly both in acid and alkaline solutions (0.1 M HCl and 0.1 M NaOH solutions). The adding amount of Mo should be controlled within a certain range and 1 wt% of Mo has the most positive effect on the comprehensive properties of WC-6Co alloys.     

Effect of Mo2C additions on the properties of SPS manufactured WC–TiC–Ni cemented carbides

The effect of spark plasma sintering (SPS) on the microstructure and mechanical properties of WC–Co and WC–Ni cemented carbides was studied, and compared to WC–Co produced by liquid phase sintering (LPS). There were finer WC grains with larger Co pools in the spark plasma sintered WC–Co, resulting in higher hardness and slightly lower fracture toughness than the liquid phase sintered WC–Co. The influence of the addition of 0.5–5 wt.%Mo₂C to WC-based cemented carbide containing 6.25 wt.%TiC and 9.3 wt.%Ni prepared by SPS was also studied. This addition improved the wettability between WC and Ni and lead to the improvements of microstructures, resulting in good combinations of hardness, fracture toughness and modulus of elasticity that were comparable to WC–Co based cemented carbides.     

Effect of ultra-fine TiC0.5N0.5 on the microstructure and properties of gradient cemented carbide

To increase the performance of cemented carbide, it was common to coat the wear surfaces with thin layers of hard materials. Cemented carbides with surface zone depleted of hard cubic phase and enriched in ductile binder phase were commonly used as the substrates. At the present, the so-called “gradient cemented carbides” were usually prepared by adding TiN or medium-sized TiCN, and a two-step sintering process including pre-sintering in nitrogen and gradient sintering in vacuum was usually adopted. In this paper, gradient cemented carbide based on WC–5.19 wt.%Ti–9.2 wt.%Co was prepared by simple vacuum sintering with the addition of 0.13 μm ultra-fine TiC_0.5N_0.5, compared with medium-sized TiN or TiCN. The result showed that gradient cemented carbide prepared with 0.13 μm ultra-fine TiC_0.5N_0.5 had better properties. With the increase of ultra-fine TiC_0.5N_0.5 content, the thickness of gradient surface zone decreased. TiCN coatings were deposited on gradient substrate and conventional substrate by moderate temperature chemical vapor deposition (MTCVD), respectively. Gradient substrate resulted in better adhesion and cutting performance.     

Comparison of the wear behavior of WC/(FeAl-B) and WC-Co composites at high temperatures

In this research, the sliding wear behavior of the hot pressed WC/40 vol%(FeAl-B) composites was investigated at temperatures ranging from the ambient one to those as high as 600 °C. The composites were then compared with hot pressed WC-40 vol%Co and commercial WC-16 vol%Co (H10F) in terms of their mechanical properties and high temperature wear behavior. It was found that the WC/(FeAl-B) composite recorded its maximum wear resistance at all the experimental temperatures, which was higher than that of WC-40 vol%Co at these same temperatures due to the higher hardness of the FeAl-B than that of the Co matrix. Also, WC/(FeAl-B) exhibited a higher wear resistance at lower temperatures and a more proper behavior at higher temperatures than did the commercial WC-16 vol%Co; this was attributed to the higher strength of the FeAl-B matrix at high temperatures. Examination of the wear surfaces revealed that abrasion was the wear mechanism in the commercial WC-16 vol%Co and WC/(FeAl-B) composites at both ambient temperature and 300 °C. At 400 °C, however, the wear mechanism was more of an adhesive one, while binder oxidation was observed at 600 °C.     

Effects of fine WC particle size on the microstructure and mechanical properties of WC-8Co cemented carbides with dual-scale and dual-morphology WC grains

Dual-scale and dual-morphology WC grained WC-8Co cemented carbides comprising triangular or hexagonal fine WC grains and plate-like coarse WC grains were synthesized by vacuum sintering using Co, flaky graphite, WC, and coarse W as the starting materials. The effects of fine WC particle sizes on microstructure, relative densities, and mechanical properties of the dual-scale and dual-morphology WC grained cemented carbides were investigated. The results revealed that the growth of plate-like coarse WC grains was further promoted with the decrease in the particle size of the added fine WC; hence, their aspect ratio increased. In addition, added fine WC led to the separation of plate-like coarse WC grains so as to break their oriented arrangement and prevent their face contact; hence, plate-like coarse WC grains were completely covered by the Co binder phase. Moreover, the addition of smaller particle size of fine WC contributed to more uniform Co binder phase. When 0.4-μm WC powders was added, the aspect ratio of plate-like coarse WC grains was greater than that of plate-like WC grained cemented carbides without the addition of fine WC. The dual-scale and dual-morphology WC grained cemented carbides by adding 0.4-μm fine WC exhibited good comprehensive mechanical properties, with a transverse rupture strength of 3645 MPa, a Rockwell hardness of 91.5 HRA, and a fracture toughness of 12.3 MPa∙m^1/2.     

The effect of submicron-sized initial tungsten powders on microstructure and properties of infiltrated W-25 wt.% Cu alloys

In the present work, several W-25 wt% Cu alloys have been prepared through combined processes of high-energy ball-milling, liquid-phase sintering and infiltration, using the precursors of industrial copper powders with an average particle size of 50 μm and tungsten powders with alternative average particle size of 8 μm, 800 nm, 600 nm or 400 nm. Microstructure characteristics, relative density, hardness and electrical conductivity of the WCu alloys were investigated to elucidate the effect of initial particle size of tungsten powders. EBSD was further utilized to reveal the orientation and grain size distribution in the WCu alloys prepared by 8 μm and 400 nm-sized tungsten powders. The results showed that the WCu alloy made by 400 nm-sized tungsten powders exhibited excellent homogeneity for both sintered tungsten powders and grains, together with the highest relative density of 98.9%, the highest hardness of 230 HB, and good electrical conductivity of 48.7% IACS. Moreover, it also showed highly improved arc erosion and mechanical wear resistances.     

Effect of Al2O3 ceramic binder on mechanical and microstructure properties of spark plasma sintered WC-Co cermets

This study investigates how the partial replacement of Co with Al₂O₃ ceramic binder has an effect on the sintering behaviour, microstructure, and final mechanical properties of WC-Co cermets via spark plasma sintering. To examine this, three batches (WC-6 wt%Co, WC-3 wt%Co-3 wt%Al₂O_3, and WC-6 wt%Al₂O₃) were mixed through high energy ball mill, and sintering was carried out at temperatures of 1350 °C and 1600 °C. The results showed nearly full dense WC-Co cermets at different temperatures. It was shown that WC-6 wt%Al₂O₃, in comparison to reference WC-6 wt%Co cermet, not only led to the rise in sintering temperature from 1350 °C to 1600 °C, but also reduced its strength and toughness. But replacing some part of Co with alumina (WC-3 wt%Co-3 wt%Al₂O₃) exhibited the combination of high strength (1095 MPa), hardness (17.62 GPa), and fracture toughness (19.46 MPa·m^1/2).     

Effect of VC and NbC additions on microstructure and properties of ultrafine WC-10Co cemented carbides

The nanocomposite WC-Co powders were prepared through planetary ball milling method. Effects of grain growth inhibitor addition and the vacuum sintering parameters on the microstructure and properties of ultrafine WC-10Co cemented carbides were investigated using X-ray diffractometer, scanning electron microscope and mechanical property tester. The results show that VC and NbC additions can refine the WC grains, decrease the volume fraction of Co₃W₃C phase in ultrafine WC-10Co cemented carbides, and increase the hardness and fracture toughness of the base alloys. After sintering for 60 min at 1400 °C, the average grain size and hardness of ultrafine-grained WC-10Co-1VC cemented carbide are 470 nm and HRA 91.5, respectively. The fracture toughness of cemented carbide WC-10Co-1NbC alloy is over 7 MN·m^?3/2.     

Influence of consolidation process and sintering temperature on microstructure and mechanical properties of near nano- and nano-structured WC-Co cemented carbides

In this paper the influence of the consolidation process and sintering temperature on the properties of near nano- and nano-structured cemented carbides was researched. Samples were consolidated from a WC 9-Co mixture by two different powder metallurgy processes; conventional sintering in hydrogen and the sinter-HIP process. Two WC powders with different grain growth inhibitors were selected for the research. Both WC powders used were near nanoscaled and had a grain size of 150 nm and a specific surface area of 2.5 m²/g. Special emphasis was placed on microstructure and mechanical properties; hardness and fracture toughness of sintered samples. Consolidated samples are characterised by different microstructural and mechanical properties with respect to the sintering temperature, the consolidation process used and grain growth inhibitors in starting powders. Increasing sintering temperature leads to microstructure irregularities and inferior hardness, especially for samples sintered in hydrogen. The addition of Cr₃C₂ in the starting powder reduced a carbide grain growth during sintering, improved microstructural characteristics, increased Vickers hardness and fracture toughness. The relationship between hardness and fracture toughness is not linear. Palmqvist toughness does not change with regard to sintering temperature or the change of Vickers hardness.     

Preparation of polycrystalline cubic boron nitride compact by high-pressure infiltration using cemented carbide

Polycrystalline cubic boron nitride (PcBN) compacts, using the infiltrating method in situ by cemented carbide (WC–Co) substrate, were sintered under high temperature and high pressure (HPHT, 5.2 GPa, 1450 °C for 6 min). The microstructure morphology, phase composition and hardness of PcBN compacts were investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The experimental results show that the WC and Co from WC–Co substrate spread into cubic boron nitride (cBN) layer through melting permeability under HPHT. The binder phases of WC, MoCoB and Co₃W₃C realized the interface compound of PcBN compact, and the PcBN layer formed a dense concrete microstructure. Additionally the Vickers hardness of 29.3 GPa and cutting test were performed when sintered by using cBN grain size of 10–14 μm.     

Optimization of Processing Parameters for WC-11Co Cemented Carbide Doped with Nano-Crystalline CeO2

Nine types of trace nano-CeO₂-doped WC-11Co cemented carbides designed by orthogonal method were prepared. The variance analysis results show that the relative density increases with increasing sintering temperature in the range of 1400-1450 °C; the hardness is highly dependent on grain size of WC which is closely related to the particle size of the initial WC powder and grain refinement produced by nano-CeO₂; the bending strength of WC-11Co cemented carbide with less than 0.15 wt.% of nano-CeO₂ is effectively improved because of its effect on the decreasing of porosity and inhibiting the grain growth of WC and martensitic phase transformation of Co; the fracture toughness rises at the beginning then drops later if the particle size of initial WC powder is in the range of 3-11 μm.     

Consolidation and properties of ultrafine binderless cemented carbide by spark plasma sintering

Owing to the absence of metal binder, binderless cemented carbides have higher wear, corrosion, and oxidation resistance. WC-0.3VC-0.5Cr3C2 powders with an average particle size of 200nm and a little amount of active element were consolidated by spark plasma sintering. The sintered microstructure revealed that the average WC grain size was 0.24μm, which was almost consistent with the initial fine powder. The results of XRD showed that W2C phase was formed. Nearly complete densification of ultrafine binderless cemented carbide was achieved by sintering at 1400℃ for 120s under 50MPa. The resulting hardness and the fracture toughness were 28.18 GPa and 6.05MPa·m1/2, respectively.     

Wear mechanism of CrN/NbN superlattice coating sliding against various counterbodies

Wear properties of CrN/NbN superlattice coating deposited on the WC-12Co substrate was investigated while using 100Cr6 steel, SiC and Al₂O₃ ball as counterbodies for friction pairs. The value of friction coefficient and wear rate was lowest at ~ 0.01 and 2.6 × 10^− 7 mm³/Nm, respectively, when coating slides against Al₂O₃ ball. In contrast, friction coefficient and wear rate were increased while sliding with steel and SiC ball. The deviation in friction coefficient was described by mechanical and chemical properties of these balls. Hardness of Al₂O₃ and SiC ball was comparable but significant deviation in friction coefficient was observed. That is related to oxidation resistance of these balls which is high for Al₂O₃ compared to SiC ball as evident by Raman analysis of the wear track. However, hardness and oxidation resistance were low for steel ball which shows oxidational wear mechanism.     

Microstructure and mechanical properties of 90WC-8Ni-2Mo2C cemented carbide developed by conventional powder metallurgy

In this paper, the microstructure and mechanical properties of a WC-Ni based cemented carbide with the addition of 2 wt% Mo₂C, processed by conventional powder metallurgy, was investigated. With the addition of only Mo₂C in the WC-Ni alloy system, the wettability between the WC and Ni binder phase was improved, which was confirmed by the increased density, hardness, fracture toughness and flexure strength of the cemented carbide obtained, which is superior than those observed in WC-10Ni cemented carbides and similar to those observed in WC-Co and WC-Ni-TiC-Mo₂C cemented carbides. Microstructural examinations of the developed cemented carbide 90WC-8Ni-2Mo₂C indicated that there was no excessive grain growth of the WC particles during sintering, confirming that Mo₂C is a grain growth inhibitor as effective as other carbides such as VC, TiC, Cr₂O₃, showing that the addition of only Mo₂C is able to improve the overall mechanical properties of the WC-Ni alloy system without sacrificing the toughness.     

The effect of volume fraction of WC particles on wear behavior of in-situ WC/Fe composites by spark plasma sintering

Tungsten carbide (WC) particles have been in-situ synthesized through the reaction between tungsten particles and carbide particles by spark plasma sintering (SPS). The composites with different WC content were comparatively observed by the techniques of scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction, hardness and pin-to-disc abrasive wear test. The results showed that the formed WC particles were homogenously distributed in the iron matrix with the size of smaller than 25 μm. Additionally, with the increasing of the WC content, the hardness of composites, the microhardness of matrix and the wear resistance increased, but there was no change significantly between 32 vol% WC/Fe composites and 42 vol% WC/Fe composites. The composites possessed excellent wear resistance comparing the specific wear rate determined in the present work to the martensitic wear-resistant steel under the load of 80 N after a sliding distance of ~ 950 m. The specific wear rate of the martensitic wear-resistant steel was a factor of 24 and 48 times higher than WC/Fe composites, when the content of WC was 32 vol% and 42 vol% in WC/Fe composites, respectively. The main wear mechanism was synthetic of abrasion wear and oxidation wear. The wear performance of 32 vol% WC/Fe composites didn't appear to be much different from 42 vol% WC/Fe composites, due to the WC particles in the 42 vol% composites produced stress concentration easily, which could ultimately induce the creak initiation around WC particles in the subsurface (near wear surface) and propagation to wear surface promoting the breakup of surface film.     

Effects of nano-alumina on mechanical properties and wear resistance of WC-8Co cemented carbide by spark plasma sintering

The effects of adding different nano-alumina on the structure, mechanical properties and wear resistance of WC-8Co cemented carbide during spark plasma sintering (SPS sintering) were investigated. The results show that the nano-alumina is dissolved in the Co phase, which results in a larger proportion of FCC-Co in the γ phase on the surface of the WC-Co cemented carbide. Under the scanning electron microscope, it is observed that the grains of cemented carbide are refined, and when the addition amount is 0.5 wt%, the effect of WC grain refinement is the most significan. The hardness, flexural strength and fracture toughness showed a trend of increasing first and then decreasingwith nano-alumina added. The peak value is reached when the nano-alumina content is 0.5 wt%, Which means that the alloy has the best combination of mechanical properties, that is, hardness reaches 1716 HV₃₀, bending strength reaches 2728 MPa, and fracture toughness is 12.95 MPa·m^1/2. Adding nano-alumina is beneficial to improve the wear resistance of cemented carbide. As a matter of course, when the content of nano-alumina is 0.5 wt%, the friction coefficient is the lowest, the wear rate is the smallest, and the wear resistance is the best.     

Effects of Ti addition on microstructure homogenization and wear resistance of wide-band laser clad Ni60/WC composite coatings

Ni60/WC composite coatings were fabricated by wide-band laser cladding. The effects of Ti addition on microstructure homogenization and coating properties were investigated. Coating microstructure, phase constitution, microhardness and wear resistance were studied and grading analysis of in-situ synthesized ceramic particles was carried out. Results indicated that ceramics particles of Cr₅B₃ and M₂₃C₆ (M represents for Cr and W) carbides were in-situ synthesized in original Ni60-20WC coatings. With Ti addition, dissolution of original WC was facilitated and lots of TiC particles were synthesized instead of M₂₃C₆ carbides. Furthermore, the block Cr₅B₃ particles were greatly homogenized due to the net structure formed by dispersive TiC particles. With Ti addition, D50 of particle size decreased from 8.94 μm to 4.45 μm and particle morphologies were transformed from star-like shapes to uniform square blocks. Microhardness distribution became more uniform with average value decreased from 799 ± 89 HV_0.2 to 744 ± 77 HV_0.2. Due to the homogenized ceramic particles, wear resistance of coatings with Ti addition was enhanced to 2.6 times that of the original coatings.