Resistance of a binderless cemented carbide to abrasion and particle erosion

A binderless cemented carbide has been evaluated in abrasion and erosion tests. The binderless carbide was compared with: SiC, Al₂O₃ and two conventional cemented carbides with 6% Co and different WC grain sizes (1 and 7 μm). In the abrasion tests, the materials were ground with silica, silicon carbide and diamond particles in the size range of 5–15 μm. The erosion tests were performed with 80, 200 and 600 μm silicon carbide erodents. The angle of impingement was 45° and the erodent velocity 70 m/s. In all tests, the conventional cemented carbides showed the highest, the binderless cemented carbide an intermediate and the ceramics the lowest wear resistance. Scanning electron and atomic force microscopy of the abraded surfaces revealed that the binderless cemented carbide was worn by a preferential removal of TiC grains. In erosion, the wear mechanism was largely plastic for the cemented carbides, whereas the ceramics were worn by micro-fracture. The SEM analysis also showed an impact scaling effect for the cemented carbides in erosion. This revised version was published online in August 2006 with corrections to the Cover Date.     

The wear of ultrafine WC–Co hard metals

The wear performance of ultrafine-grained tungsten carbide–cobalt (WC–Co) hard metals during three-body abrasion and particle erosion has been evaluated and compared to that of similar conventional coarser grained hard metals. The tungsten carbide grain size varied between 0.5 and 3 μm with cobalt contents ranging from 6 to 15%. Silica particles were used in both forms of testing. Erosion was carried out at 60 ms⁻¹ at an impact angle of 75° and abrasion at a velocity of 0.5 ms⁻¹ and a load of 50 N.

The wear resistance of the ultrafine grades was found to be at least double that of the closest conventional fine grained hard metals. These increases in wear performance are considerably higher than any corresponding increase in hardness which is, at most, 25% and is not achieved at the expense of fracture toughness which is maintained at a similar level to that of conventional fine grained hard metals. The increase in wear resistance coincides with a change in the mechanism of material removal. Sub-micron materials experience ductile deformation and bulk removal of material whilst coarser grades display more localised response with extensive fragmentation of the WC grains.     

Effects of Co content and WC grain size on wear of WC cemented carbide

WC cemented carbides are used extensively to improve abrasion resistance. Co content and WC grain size influence the mechanical properties of the cemented carbides. In this study, the effects of Co content and WC grain size of cemented carbide on wear were examined. We prepared 13 different cemented carbides with different Co content and WC grain size. Wear tests were carried out against 0.45% carbon steel under dry condition at 98 N and 232 mm/s. From the results, we found that wear increased with both Co content and WC grain size. Specific wear rate of the cemented carbides tested was in the range of 10⁻⁷ mm³/(N m). We discussed the wear properties with hardness and the mean free path of the cemented carbide. These two parameters alone cannot explain the wear property.     

Abrasion of cemented carbides by small grits

The abrasion properties of a series of cemented carbides with different carbide grain sizes, different amounts and types of binder phases have been investigated under varied conditions. Abrasion results from other works are also incorporated for comparison reasons. The results are interpreted in the light of a previously published model for the abrasion properties of multiphase materials, although this is the first time this model is applied to materials with very high amounts of hardphase. It is confirmed that the abrasion resistance of tungsten carbide–cobalt materials may vary considerably, also for fixed amounts of metal and hardphase. Not only the wear resistance level but also the ranking depends both on the test conditions and on the microstructure. It is further showed that some nano-crystalline materials posses a wear resistance superior to those of the pure carbide material.     

Cemented carbide and cermet tooling for film-perforating

The tools used to perforate a particular photographic film started to wear at an unacceptable rate when the film base was changed from cellulose triacetate to polyester (PET). A laboratory investigation was initiated to screen candidate tool materials and identify ones with potential for 10 times life improvement over cemented carbide (WC/10% Co).

The screening tests started with abrasion and corrosion tests on various grades of cemented carbide, cermets and selected ceramics. Concurrent production trials indicated that the laboratory corrosion tests were not correlating with production results. To address this problem, a “nibbler” test was developed which simulates perforating and material removal on a punch after 10⁶ perforations (nibbles) became the screening test metric.

It was determined that abrasion tests do not accurately predict tool material behavior when chemicals are present on or in the materials being perforated. Static corrosion tests do not predict tool response under production conditions. The rubbing of the film on the tool surfaces removes protective films and there can be a significant corrosion component in tool erosion. The nibbler simulates real tool conditions because erosion is produced by actual cutting of coated webs. Nibbler tests in this study indicated that alumina/zirconia resisted film erosion better than cemented carbide, even cemented carbide with PVD coatings. The nibbler tests also indicated that leaving recast layers from electrical discharge machining on cemented carbide greatly increases erosion rates. It should be removed.

Production tests conducted since completion of these laboratory studies suggests that nibbler results correlate with production results. Coated cemented carbides are providing 3 times the service life of uncoated cemented carbides as predicted by the nibbler test.     

Assessment of the erosion resistance of steels used for slurry handling and transport in mineral processing applications

The wear environment of steels used for containing, transporting and processing erosive mineral slurries is often such that fluid borne particles form a layer moving at high speed across the wearing surface. Information on the performance ranking of such materials is limited, particularly with respect to the influence of steel hardness and microstructure on the resistance to erosion. This is particularly important for the oil sands industry of Northern Alberta where handling and processing of essentially silica-based solids results in extremely severe wear conditions. This paper presents slurry erosion data obtained on 11 commercially available wear resistant plate and pipeline steels with hardness values up to 750 HV. These data were obtained using a Coriolis erosion tester operated at 5000 rpm with an aqueous slurry containing 10 wt.% of 200–300 μm silica sand particles.

The Coriolis erosion tester was selected because it provides a low-angle scouring action that simulates the erosive conditions encountered in oil sands and tailings pipeline transport and in some related processing operations. Results show that this test method is able to discriminate clearly between the erosion resistance of these steels, expressed in terms of specific energy (the energy necessary to remove unit volume of test material), with the most erosion resistant steel being more than five times superior to the least resistant. A graphical relation between steel hardness and erosion resistance is given. A comparison is also made between slurry erosion data and the performance of the materials in the ASTM G65 dry sand rubber wheel (DSRW) sliding abrasion test. Comments on the influence of the macro- and microstructures of the steels on their wear behaviour are included.     

Effect of carbide fraction and matrix microstructure on the wear of cast iron balls tested in a laboratory ball mill

The effect of carbide volume fraction from 13 to 41% on the wear resistance of high chromium cast irons was evaluated by means of ball mill testing. Martensitic, pearlitic and austenitic matrices were evaluated.

The 50-mm diameter balls were tested simultaneously in a 40 cm diameter ball mill. Hematite, phosphate rock and quartz sand were wet ground. The tests were conducted for 200 h.

Quartz sand caused the highest wear rates, ranging from 6.5 to 8.6 μm/h for the martensitic balls, while the wear rates observed for the phosphate rock ranged from 1.4 to 2.9 μm/h.

Increasing the carbide volume fraction resulted in decreased wear rates for the softer abrasives. The almost complete protection of the matrix by carbides in eutectic microstructures caused the eutectic alloy to present the best performance against hematite or phosphate rock. The opposite effect was observed for the quartz sand. The quartz abrasive rapidly wears out the matrix, continuously exposing and breaking carbide branches. A martensitic steel presented the best performance against the quartz abrasive.

With phosphate rock, the wear rate of 30% carbide cast irons increased from 1.46 to 2.84 and to 6.39 μm/h as the matrix changed, respectively, from martensitic to austenitic and to pearlitic. Wear profiles of worn balls showed that non-martensitic balls presented deep subsurface carbide cracking, due to matrix deformation. Similar behavior was observed in the tests with the other abrasives.

In pin-on-disc tests, austenitic samples performed better than the martensitic ones. This result shows that pin tests in the presence of retained austenite can be misleading.     

WC-Ni硬质合金的研究与应用

作为传统硬质合金主要粘结剂的Co资源稀缺且价格昂贵,因此寻找Co的代用品具有重要意义。本文综述了以Ni代Co的WCNi系硬质合金的研究现状,包括其发展变革、制备方法、性能特点和应用领域,并指出了目前存在的问题。     

Coarse cemented WC particle ceramic-metal composite coatings produced by laser cladding

Coarse cemented WC particle (600–900 μm) ceramic-metal composite coatings with a thickness of 1.2–1.5 mm were cladded on 20Ni4Mo steel surfaces using a laser of power 2 kW, diameter 5 mm and traverse speed 4–20 mm s⁻¹. The weight fraction of WC particles was 67 wt%. Compared with the behaviour of cemented WC particles of the same size and ratio in atomic hydrogen welded coating (AHWCs), the WC particles in laser-cladded ceramic-metal coating (LCCCs) show a uniform distribution in the molten zone. The microhardness of WC particles in LCCCs is 13.7–16.2 GPa, and their sizes are almost unchanged, which indicates that little heat damage occurs during laser cladding. The abrasive wear results showed that LCCCs have superior wear resistance to AHWCs. The wear mechanisms for LCCCs and AHWCs are analysed and compared.     

Tribological behavior of select MAX phases against Al2O3 at elevated temperatures

The layered M_n+1AC_n ternary carbides – MAX phases – Ta₂AlC, Ti₂AlC, Cr₂AlC and Ti₃SiC₂ were tested under dry sliding conditions against alumina at 550 °C and 3 N load (for a stress of ≈0.08 MPa) using a pin-on-disk tribometer. Ta₂AlC and Ti₂AlC exhibited low specific wear rates, SWRs, (≤1 × 10⁻⁶ mm³/N m), while the coefficients of friction, μ, were 0.9 and 0.6, respectively. At 0.4, μ of Ti₃SiC₂ was the lowest measured, but the SWR, at ≈2 × 10⁻⁴ mm³/N m, was high. With a μ of 0.44 and a SWR of 6 × 10⁻⁵ mm³/N m the Cr₂AlC sample was in between. No visible wear of Al₂O₃ counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.     

Effects of composition and microstructure on the slurry erosion of WC-Co cermets

Cemented carbides of optimum composition and microstructure are the preferred materials for resisting the severe erosion encountered in components handling erosive slurries. They possess an attractive combination of erosion resistance and fracture toughness required for structural reliability. In this paper the results are presented of an investigation of the effects of composition and microstructure of well-characterized WC-Co cermets on their erosion wear as assessed in a slurry jet impingement test. The effects of binder volume fraction and microstructural parameters such as WC grain contiguity and mean carbide grain size are rationalized in terms of a phenomenological analysis of erosion in the two-phase microstructure. Quantitative predictions of the semiempirical analysis are shown to be consistent with the experimental observations.     

Dry sliding wear of fly ash particle reinforced A356 Al composites

In the present study aluminium alloy (A356) composites containing 6 and 12 vol. % of fly ash particles have been fabricated. The dry sliding wear behaviour of unreinforced alloy and composites are studied using Pin-On-Disc machine at a load of 10, 20, 50, 65 and 80 N at a constant sliding velocity of 1 m/s. Results show that the dry sliding wear resistance of Al-fly ash composite is almost similar to that of Al₂O₃ and SiC reinforced Al-alloy. Composites exhibit better wear resistance compared to unreinforced alloy up to a load of 80 N. Fly ash particle size and its volume fraction significantly affect the wear and friction properties of composites. Microscopic examination of the worn surfaces, subsurfaces and debris has been done. At high loads (>50 N), where fly ash particles act as load bearing constituents, the wear resistance of A356 Al alloy reinforced with narrow size range (53–106 μm) fly ash particles were superior to that of the composite having the same volume fraction of particles in the wide size range (0.5–400 μm).     

A tribotesting method for evaluating cemented carbide tribo-performance

The abrasive wear properties of materials in sliding contact with solid mineral particles during the comminution process have been studied. The equipment used can simulate the tribo-conditions inside coal pulverisers. Using this experimental apparatus, a number of different cemented tungsten carbides have been tested and classified according to their resistance to abrasive wear in rubbing contact with particulate coal. The paper shows that the wear results can be used to estimate the resistance of a material to brittle fragmentation and chipping of the edges during tribo-contact with solid particles. An equation is presented which enables calculation of the fracture resistance factor, K_WR, based on results from carefully controlled repeated abrasion tests.     

Fine-particle slurry wear resistance of selected tungsten carbide thermal spray coatings

The surface degradation of tungsten carbide based thermal spray coatings when exposed to fine-particle slurry abrasion has been investigated. The coatings that were studied contain binder-phase constituents consisting of either nickel or cobalt. The coatings were deposited onto test cylinders using a detonation gun device. After applying approximately 0.15 mm thickness of thermal spray coating, the coatings were ground, then diamond polished to achieve surface roughnesses of 0.03 μm Ra or less. The coatings were exposed to a three-body abrasive wear test involving zirconia particles (less than 3 μm diameter) in a water-based slurry. Results show that preferential binder wear plays a significant role in the wear of these tungsten carbide coatings by fine abrasives. In the comparison presented here, the coating containing nickel-based binder with a dense packing of primary carbides was superior in terms of retaining its surface finish upon exposure to abrasion. The coating containing a cobalt binder showed severe surface degradation.     

Slurry pump side-liner wear: comparison of some laboratory and field results

The current work compares some slurry pump lab wear results with the wear found across different field applications with d₈₅ particle size ranging from 100 to 4000 μm. Side-liner wear life data has been collected for two different impeller geometries and two different material classes (cast iron and natural rubber). Different field wear patterns have been photographed and categorised on the basis of particle size. The field wear patterns showed close similarity to the lab wear patterns particularly in the areas of localised gouging. Wear rates are also compared for the different geometries. Overall trend of wear with particle size for the white iron parts was similar to the grey iron lab tests albeit at significantly lower wear rates. In general, the wear with the rubber side-liner was less at smaller particle sizes but greater for particles larger than d₈₅ of about 700 μm.     

微织构(W,Mo)C基刀具和YG8刀具对钛合金干切削性能的影响

刀具切削钛合金时存在切削温度高、单位面积上切削力大等问题,微织构刀具可以有效减小摩擦力,减小切削力。通过正交实验法设计微织构参数,研究微织构参数对Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具以及YG8刀具切削钛合金实验的切削性能影响。实验结果表明,合适参数的沟槽型微织构能有效降低Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具和YG8刀具切削TC4钛合金的切削力,相同沟槽参数下,无黏结相硬质合金刀具的切削力明显低于YG8刀具的切削力;合适参数的沟槽型微织构能有效降低刀具刀屑界面的摩擦系数,相同沟槽参数下,无黏结相硬质合金刀具的摩擦系数大都低于YG8刀具的摩擦系数;沟槽深度10μm、沟槽间距100μm以及沟槽宽度30μm的沟槽参数下,切削钛合金时,无黏结相硬质合金刀具前刀面无明显磨损,后刀面只有边界磨损,YG8刀具发生崩刃,前刀面出现切屑的滞留。     

Comparison of the wear resistance of selected steels and cemented carbide cutting tool materials in machining wood

An experimental investigation is described where specimens of selected steels and cemented carbides are tested to simulate cutting green wood and cured wood. Extensive results are presented that show quantitatively the progressive wear of several Stellites, steels and cemented carbides as a function of time for sliding under wet and dry conditions.A simple theoretical analysis of tool wear that applies to cutting green wood with cemented carbide tools is described. The analysis, which indicates the important parameters in the wear process, is used to predict the effect of carbide particle size on wear rate. Comparisons are made between the predicted and experimentally determined wear rates for two groups of cemented carbide materials. Good agreement is found between experimental measurements and theoretical predictions. It is shown that wear depends on carbide particle size. Superior wear resistance of cemented carbides is attributed to the high hardness and low chemical reactivity of the carbide phase. The improved wear resistance of the Stellites is attributed to the low reactivity of the matrix.     

In-situ SEM observation of the fracture behaviour of titanium carbide/nickel aluminide composites

A range of experimental titanium carbide (TiC)/nickel aluminide (Ni₃Al) composites have been developed. The Ni₃Al content has been varied from 15 to 40 vol.%, for two different alloy compositions. The fracture behaviour of these composites was assessed in situ , within the chamber of a field emission gun scanning electron microscope. An applied moment double cantilever beam test geometry was employed, which allowed determination of the materials fracture resistance curve (or R -curve), while simultaneously monitoring crack–microstructure interactions. All of the tested materials exhibited a pronounced R -curve, with fracture resistance increasing with increasing crack length, up to a steady-state plateau value. The highest steady-state toughness values (up to 15 MPa m^−1/2) were obtained for composites prepared with the highest Ni₃Al binder content. In addition, these materials exhibited the highest strength and Weibull modulus. In-situ examination of the fracture process demonstrated considerable crack wake bridging by ductile Ni₃Al ligaments, with bridging zone length of >100 μm often observed. The use of a displacement mapping technique has demonstrated that Ni₃Al plastic deformation is highly localized around the crack, typically within one TiC grain width (i.e. ≈3–5 μm) away from the crack.     

Micro-scratch evaluation of rock types—a means to comprehend rock drill wear

Drilling, transportation and handling of rock always result in wear of the equipment that comes into contact with the rock and rock fragments. Rock is normally considered rather hard, and the contact leads to abrasion, erosion and point fatigue. However, the wear mechanisms of the tools are often complex and vary in character depending on the rock type.To understand the wear mechanisms of the cemented carbide used in rock drill bits, it is central to understand how different rock types respond to severe scratching from hard tips. A cemented carbide tip with radius 10 μm was used in a scratch tester at progressive loads of 0 to 20 N and at constant loads of 10 N. The tested rock types were calcite, two types of magnetite, hematite, leptite, mica schist, granite, sandstone and quartz spanning average hardness values from 190 up to 1220 HV. The scratches were investigated in SEM and the friction coefficient between rock and the tip was measured. In addition, the wear volume of the cemented carbide tip is measured.The rock types differed significantly with respect to damage mechanism and critical load for transition from a mild to a more severe damage. The friction behaviour correspondingly shifted from rather smooth to very fluctuant. The wear of the tip was found to be correlated to the hardness of the rocks, but was also influenced by the grain size, the quartz content and isotropy. The implications from the present results on full-scale rock drill wear are discussed.     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.