Metal Binder Content Research Articles

Synergic Effects of Nanosecond Laser Ablation and PVD-Coating on Cemented Carbides: Assessment on Surface and Mechanical Integrity

Emerging laser precision machining, particularly using pulsed lasers, enlightens the innovation and functionalization of cemented carbides. These backbone materials of the tooling industry are usually considered difficult to machine or shape using conventional mechanical approaches. The coating of cemented carbide tools, deemed to improve their mechanical and thermal properties, is a common supplementary surface treatment prior to their application. This work aims to study the synergic effects of nanosecond laser ablation and coating deposition on the surface, as well as the mechanical integrity of cemented carbides. In this regard, two plain WC–Co grades with different metallic binder content (10%wtCo and 15%wtCo) were first processed by a short-pulsed nanosecond laser. Subsequently, an AlTiN film was physically vapor-deposited on the laser-processed surfaces. The resulting surface integrity was assessed in terms of topographical, morphological, and microstructural changes. Mechanical integrity was evaluated in terms of indentation and sliding contact responses using Vickers hardness and scratch tests, respectively, the latter including frictional, penetrating, and sliding performances under selected surface processing conditions. In general, the nanosecond laser ablation proved to be beneficial for the mechanical integrity of coated cemented carbides in most studied cases, as it increased surface hardness, reduced penetration depth, and hindered damage during sliding. This was the case despite a slight increase in surface roughness, as well as minor morphological and microstructural changes at the coating–substrate interface, discerned.

Microstructural and mechanical properties at the submicrometric length scale under service-like working conditions on ground WC-Co grades

The unique combination of hardness, toughness, and wear resistance exhibited by heterogeneous hard materials, particularly cemented carbides (WC-Co), has made them preeminent material choices for extremely demanding applications, such as metal cutting/forming tools. The grinding post-processing of WC-Co induces changes in their surface integrity by modifying both constitutive phases through cracking the WC ceramic phase, introducing compressive residual stresses and/or inducing phase transformations (from face-centered cubic to hexagonal compact phase) in the metallic Co binder. A systematic micro- and nanomechanical study of different ground WC-Co grades (with distinct metallic Co binder content and WC particle size) is presented. In general, three different aspects are investigated: (1) assessment of the intrinsic hardness of the deformed layer from room temperature up to 600 °C, (2) correlation of the compressive residual stresses with hardness and elastic modulus maps by using high-speed indentation tests, and (3) evaluation of the oxidation process as a function of the testing temperature for the different ground WC-Co grades. It was found that the mechanical properties of the deformed ground layer for the different WC-Co grades slightly decrease at temperatures ranging between 400 and 500 °C, being this temperature non depending on the amount of metallic binder or WC grain size. This is attributed to different effects which take place simultaneously when the testing temperature increases: dislocation motion, reduction of compressive residual stresses and particularly, the generation of a heterogeneous oxide layer formed of CoWO4, WO3 and Co3O4.

Low temperature synthesis of bulk Boron Nitride Nanoplatelets with and without metallic binder

Boron Nitride Nanoplatelets (BNNP) are consolidated into a bulk form using a low energy processing route that consisted of cryogenic milling, cold isostatic pressing, and a short, mild heat treatment. X-ray diffraction analysis was performed to confirm the presence of the secondary metallic constituent and the different phases of Boron Nitride (BN). Unique features of BNNP such as platelet stacking and kinking are retained. A secondary metallic constituent is also included to improve processability and to enhance structural support in the bulk structure. Mechanical properties were evaluated using microhardness testing and nanoindentation. Relative density, elastic modulus, and hardness increased with the incorporation of Al binder contents of as low as 10 vol %. A high degree of load transfer efficiency is demonstrated in higher metallic binder content composites (50 vol % Al) by comparing theoretical and experimentally measured microhardness values. This study presents a novel template for manufacturing bulk 2D nanomaterials using simple and low energy processing.

RESEARCH OF THE MECHANISM OF SEALING POWDER MIXTURES BASED ON SILICON CARBIDE IN EXPLOSIVE PRESSING

The effects of the metal binder content and parameters of shock-wave compression on the compaction of SiC-Ti powder mixtures under explosive loading were investigated; microstructure of the obtained materials; The prevailing mechanisms of compaction of powder mixtures of silicon carbide with titanium during explosive pressing are revealed.

Effects of metal binder content and carbide grain size on the microstructure and properties of SPS manufactured WC–Fe composites

In the research, an investigation has been carried out on the microstructure and mechanical properties of WC–Fe composites, with various Fe content and either fine- or coarse-grained WC. The WC/Fe composite powders were processed by powder metallurgy method and consolidated to high density by spark plasma sintering (SPS). According to the thermodynamic calculations, the sintering temperature was selected to be 1050 °C. The experimental results indicated that there existed two main phases of WC, α-Fe and one minor Fe3W3C phase in the WC–Fe composites, which was consistent with the thermodynamic calculations. Besides, the relative densities of the composites increased with the Fe binder content, while exhibited different trends for the fine- and coarse-grained composites. Among the WC–Fe hard alloys, the composite with fine-grained WC and 30 wt % Fe binder possessed the highest hardness of 60.5 HRC. The maximum bending strength of 1851 MPa was attained for the composite with coarse-grained WC and 70 wt % Fe binder. The fracture mechanism of the composites was a combination of transgranular failure, intergranular failure, and Fe binder plastic tearing.

Problems of Development and Application of Metal Matrix Composite Powders for Additive Technologies

The paper considers the problem of structure formation in composites with carbide phase and a metal binder under self-propagating high-temperature synthesis (SHS) of powder mixtures. The relation between metal binder content and their structure and wear resistance of coatings was studied. It has been shown that dispersion of the carbide phase and volume content of metal binder in the composite powders structure could be regulated purposefully for all of studied composites. It was found that the structure of surfaced coating was fully inherited of composite powders. Modification or coarsening of the structure at the expense of recrystallization or coagulation carbide phase during deposition and sputtering does not occur.

Effect of titanium on the rheological properties of MoSi2-based materials prepared by SHS

We have studied the moldability of molybdenum disilicide-based materials using free self-propagating high-temperature synthesis (SHS) compression, a method that combines combustion and high-temperature deformation processes. As a moldability criterion, we used strain. The strain of the synthesized materials has been determined experimentally as a function of the time delay before high-temperature deformation, compaction pressure, heating temperature, and metallic binder content of the starting mixture. To improve the plasticity of the synthesized material, 1–2 wt % titanium was added to the starting mixture as a metallic binder.

Silicide Ceramic Synthesis Based on Molybdenum Disilicide in a Combustion Regime Under High-Temperature Deformation Conditions

A fundamental possibility is demonstrated of using SHS-extrusion and SHS-compression methods, combining combustion and high-temperature deformation, for preparing compact materials and objects of silicide ceramics based on MoSi2. Formability of silicide ceramic by free SHS-compression is studied. The effect of holding time before high-temperature deformation, heating temperature, and metal binder content in an original charge workpiece, on the degree of synthesized material deformation is studied. Specimen macro- and microstructure, prepared by SHS-extrusion is provided, and the effect of high-temperature heating on specific electrical resistance is also studied.

Effects of metal binder on the microstructure and mechanical properties of Ti(C,N)-based cermets

To optimize the mechanical properties of Ti(C,N)-based cermets used as tool materials, the cermets with different Ni–Co binder contents and Co/(Ni+Co) weight ratios were prepared. The effects of metal binder content and Co/(Ni+Co) ratio on the microstructure and mechanical properties of Ti(C,N)-based cermets were investigated by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and measuring the transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (KIC). The experimental results reveal that increasing Ni–Co binder content can increase the thickness of rim phases by improving the solid solution reaction and the wetting of hard phases. The cermets with 25wt.% binder addition present good comprehensive mechanical properties, which is attributed to the moderate rim phases and uniformly distributed Ti(C,N) grains. The Co/(Ni+Co) weight ratios in binder have a great influence on the grain sizes and microstructure features of Ti(C,N)-based cermets, in virtue of the synergic effects between the wettability of Co and the solubilizing capacity of Ni on hard phases. The cermets with pure Co as binder exhibit optimal mechanical properties with a TRS of 1767±81MPa, a hardness of 12.26±0.10GPa and a KIC of 8.40±0.47MPam1/2, which meet the requirements for tool materials. And the cermets with a Co/(Ni+Co) ratio of 0.2 have the second best mechanical properties with a TRS of 1848±201MPa, a hardness of 11.12±0.40GPa and a KIC of 9.43±0.54MPam1/2, in which the lower hardness can be further improved by optimizing the compositions and sintering process.

Effects of Ni/Co Metal Binder Phase on Mechanical Properties of Ti(C,N)-Based Cermets

Ti(C,N)-based cermets were prepared by pressureless sintering using micron-sized TiC and TiN powders as main starting materials and Ni and Co as metal binders. The fracture micrographs of Ti(C,N)-based cermets were observed by SEM. The effects of metal binder phase content on porosity and mechanical properties of Ti(C,N)-based cermets were investigated. The results show that when sintering at 1450 °C for 50min, typical core/rim microstructure is observed in the cermets, which is compact and distributed homogeneously, the density and relative density are 5.9 g/cm3 and 95.6%, respectively. Intergranular fracture is the main crack propagation mode, with a few of the transgranular fracture, and there are more dimples and tearing ridges in the fracture surface. Using the same sintering process, Ti(C,N)-based cermets with metal binder content of 10%Ni5%Co has a compact microstructure and fine grains, the metal binder phase is dispersed more evenly, the best vicker hardness, bending strength and fracture toughness of Ti(C,N)-based cermets are 15.8 GPa, 885.5MPa and 9.7 MPa·m1/2, respectively. However, Ti(C,N)-based cermets with Ni replaced of high Co content will generate some brittle intermetallic compound, its toughness is inferior to the metal binder phase, which reduces the strength and toughness of Ti(C,N)-based cermet materials.

The effects of metal binder content and carbide grain size on the aqueous corrosion behaviour of TiC–316L stainless steel cermets

The room temperature electrochemical response of TiC-based cermets, with 10 to 30vol.% 316L stainless steel binder and either fine- or coarse-grained TiC, has been investigated in an aqueous 3.5wt.% NaCl solution. The assessment methods included Tafel extrapolation, in combination with potentiodynamic and potentiostatic polarisation. Corroded samples were characterised using SEM, with post-corrosion solutions analysed using ICP-OES. The highest corrosion resistance was achieved at the lowest binder contents, while those with a more coarse-grained structure generally showed superior resistance, due to a reduced TiC–316L interfacial area. Preferential dissolution of the steel binder was observed, leaving the TiC essentially unaffected.

Induction brazing of cermets to steel

The paper considers the induction brazing of TiC based cermets with Ni-Mo and Fe-Ni binder phase and Cr3C2 based cermets with Ni binder to structural and stainless steels under vacuum and air conditions. Commercially available traditional filler metals and experimental amorphous filler foils were tested. Possibility of mechanical metallizing of cermet surfaces with rotating Ti brushes prior to the brazing process was studied. Increase in the surface roughness after mechanical metallizing and non-uniform distribution of Ti on the treated surfaces were observed. Positive influence of electrochemically deposited Ag and Ni coatings on the shear strength of joints was found when optimal filler metals were used. Maximum shear strength up to 200-250 MPa was achieved with Ti- and Ni-based amorphous filler foils. Brazing in air by optimal fluxes and Ag- and Cu-based conventional brazing fillers can be used for brazing of cermets. Shear strength up to 150-190 MPa was achieved. The shear strength of vacuum brazed joints increases with the increase of the metal binder content in the cermet. Diffusion of the filler metal to base metal and to joint interface was studied by EPMA and SEM. It was found that cermets are successfully brazed with amorphous filler metals and the strength of the joints was not affected by the rapid heating during the induction process and relatively low vacuum.

Mechanical Characterization and Wear Performance of WC – ZrO<sub>2</sub> – Ni Cermets Produced by Hot Isostatic Pressing

Microstructure analysis and mechanical characterization were performed on newly developed WC based and yttria stabilized tetragonal zirconia (ZrO2) doped cermets with nickel metal binder produced by hot isostatic pressing. The cermets have reached higher than 99% of theoretical density after processing at 1700 0C and 206 MPa for 1 hour. Zirconia has appeared to form agglomerates of about 1 µm and suppressed carbide grains growth. Hardness of zirconia doped materials was of the same magnitude and fracture toughness was slightly higher as compared to conventionally produced WC-Co hardmetals of the same metal binder content while wear resistance in conditions of erosion and abrasion in silica media is increased by two fold.

Effect of liquid phase composition on the microstructure and properties of (W,Ti)C cemented carbide cutting tools

The microstructure and properties of (W,Ti)C cemented carbides with a different metal binder composition of Ni and Co fabricated by powder technology were investigated. The densifications of the prepared materials were accomplished by using vacuum sintering at 1450 °C. Nearly fully dense (W,Ti)C cemented carbides were obtained with a relative density of up to 99.7% with 30 wt% Co and 99.9% with 30 wt% Ni. The average grain size of carbides for the (W,Ti)C–Co and the (W,Ti)C–Ni was decreased with increasing the metal binder content. The hardness of the dense (W,Ti)C–15 wt%Co and (W,Ti)C–15 wt%Ni, was greater than the hardness of other different compositions of (W,Ti)C–Co and (W,Ti)C–Ni cemented carbides respectively; in addition, the (W,Ti)C–Co cemented carbides had greater hardness values than the (W,Ti)C–Ni cemented carbides. The magnetic properties, which were measured at an applied field of 0.8 T, indicate that the (W,Ti)C–Co cemented carbides have ferromagnetic properties with a higher magnetic saturation with higher cobalt content as well as higher coercivity with lower cobalt content. On the other hand, the (W,Ti)C–Ni cemented carbides are non-magnetic on account of the very low magnetic saturation and they have lower coercivity values than the (W,Ti)C–Co cemented carbides.

(W,Ti)C계 초경합급의 미세조직 및 경도에 미치는 금속 결합재 조성의 영향

The microstructure and hardness of (W,Ti)C cemented carbides with a different metallic binder composition of Ni and Co fabricated by powder technology were investigated. The densifications of the prepared materials were accomplished by using vacuum sintering at <TEX>$1450^{\circ}C$</TEX>. Nearly full dense (W,Ti)C cemented carbides were obtained with a relative density of up to 99.7% with 30 wt.% Co and 99.9% with 30 wt.% Ni as a metallic binder. The average grain size of the (W,Ti)C-Co and the (W,Ti)C-Ni was decreased by increasing the metallic binder content. The hardness of the dense (W,Ti)C-15 wt%Co and (W,Ti)C-15 wt%Ni, was greater than that of the other related cemented carbides; in addition, the cobalt-based cemented carbides had greater hardness values than the nickel-based cemented carbides.

Modelling of metal-binder migration during liquid-phase sintering of graded cemented carbides

Sintering of cemented carbides with graded metal binder content is modelled in this article. Production of graded cemented carbides by traditional liquid-phase sintering is hampered by high rate of liquid-binder migration with inevitable subsequent homogenisation of binder content in specimens. The driving forces of the migration are analysed. It is shown that the migration is governed not only by capillary forces but also by additional stresses that arise due to surface tension at solid–liquid interfaces. As a result, the migration takes place even in pore-free graded specimens. A numerical approach for the prediction of binder flow with coupled deformation of the refractory skeleton during liquid-phase sintering is put forward. Calculations predict that complete densification of specimens with retention of graded-binder distribution can be achieved by sintering with long solid-state sintering stage ended by comparatively short high temperature liquid-phase stage.

Effect of metallic binder content on the microhardness of TiCN-based cermets

Microhardness testing was conducted on a series of TiCN-based cermets with different contents of metallic binders in the applied load range from 0.49 to 9.8 N. Significant indentation size effect (ISE) in the measured microhardness was observed for each test sample. The traditional Meyer's law and the modified proportional specimen resistance (MPSR) model were employed to analyze the load-dependence of the measured hardness. It was found that the Meyer's exponent n increases with the metallic binder content, implying that increasing the metallic binder content would restrain the ISE. The load-independent hardness was found to decrease with the increasing metallic binder content. This can be attributed to the fact that the hardness of metallic binder is lower than that of the TiCN matrix.

Liquid-phase sintering and properties of Cr 3C 2/NiCr cermets

Liquid-phase sintering of Cr 3C 2/NiCr cermets was investigated as a function of Cr 3C 2 content (55–95 wt%) at a constant Ni-to-Cr ratio of 4. Specimens cold-isostatically pressed at 230 MPa were sintered in a vacuum and in the presence of a liquid phase, at 1300°C for 15 and 30 min. Specimens with a carbide content of <75% were heavily distorted due to excessive liquid phase formed during sintering, but those with a higher carbide content were densified to near theoretical density (>98%) within 15 min. The density of the succesfully sintered specimens decreases slightly with inreasing carbide content and sintering time. Using X-ray diffraction analysis and scanning electron micrographs, it was revealed that the microstructures consisted of a prismatic Cr 3C 2 phase and a metallic binder phase. The hardness of the samples increased with increasing carbide content, whereas the transverse rupture strength decreased. The decrease in strength is attributed to the reduction in the metallic binder content and to poor densification. It was shown that almost fully-densified Cr 3C 2/NiCr cermets with carbide contents of 75–95 wt% could be produced in a vacuum through the liquid-phase sintering process at a low temperature, such as 1300°C, for a sintering time as short as 15 min.

Dependence of erosion–corrosion on carbide/metal matrix proportion for HVOF Cr3C2–NiCr coatings

A series of erosion–corrosion (EC) tests was carried out on HVOF Cr3C2–NiCr cermet coatings with different fractions of NiCr metal binder phase. Testswere conducted using a nozzle type elevated temperature erosion tester at test temperatures up to 450°C. Bed and fly ash retrieved from operating fluidised bed combustor boilers as well as SiO2 angular quartz were used as the erodent materials for tests at both shallow and steep impact angles. The fly ash contained chemically active compounds and a corrosive environment was involved. The morphology of the specimens was examined by scanning electron microscopy. It was found that the cermet coatings were eroded by SiO2 quartz and fly ash at a low velocity with peak wastage occurring at an intermediate value of carbide content at both the shallow and the steep impact angles. Erosion caused by the bed ash at a high velocity resulted in no peak wastage at either the shallow or the steep angles. Instead, the EC thickness loss increased with increasing metal binder content. The EC behaviour of the coatings is related to the morphology of the coatings and the characteristics of the erodent particles.

Rolling contact fatigue failure mechanisms in plasma and HVOF sprayed WC-Co coatings

The rolling contact fatigue (RCF) behaviour of thermally sprayed WC-Co coatings with nominal compositions of WC-12%Co, WC-10%Co-4%Cr and WC-17%Co was studied with a two-roll configuration roll-against-roll testing apparatus under 420–600 MPa Hertzian contact stresses in unlubricated pure rolling conditions. The coatings were prepared by atmospheric plasma spray (APS) and two high-velocity oxyfuel (HVOF) spray processes. In the APS sprayed WC-12%Co coating the RCF damage was dominated by an increased surface roughness due to spallation of flakes and a formation of a network of cracks within the coating layer. HVOF sprayed WC-12%Co and WC-10%Co-4%Cr coatings were damaged either by the formation of vertical, linear cracks or pitting of the contact surface. The formation of pits in the HVOF sprayed coatings was significantly less than that found in the APS sprayed coatings. The HVOF sprayed WC-17%Co coating showed the best RCF behaviour among the studied coatings with unchanged surface roughness, no formation of cracks and only a few pits were found on the contact surface. The good resistance of this coating against formation of failure in the RCF testing is caused by its higher ductility and fracture toughness due to a higher metallic binder content in comparison with the other coatings. Other characteristics such as a low amount of brittle Co-W-C carbides and a dense microstructure are also believed to be beneficial for a RCF resistant coating.