Properties and microstructure of WC–TiC–Co and WC–TiC–MO2C–Co(Ni) cemented carbides

Abstract

The present study is an attempt to observe the changes in microstructure and properties of modified WC–10Co cemented carbides from the viewpoint of the distinctive role played by modified binder phase. Introduction of TiC into WC–10Co cemented carbide results in microstructural non-uniformity, i.e. a wide range of grain size distribution, which in turn gives rise to a drastic drop in values of transverse rupture strength and toughness. The modification of binder and carbide phases by incorporating, respectively, nickel and M02C improves the microstructural uniformity, which ensures better mechanical properties. The present findings have been interpreted in terms of various quantitative microstructural parameters, with particular attention being given to the wettability factor.

MST/1363     

Microstructures and fracture toughness of directionally solidified Mo–ZrC eutectic composites

Microstructures and fracture toughness of arc-melted and directionally solidified Mo–ZrC eutectic composites were investigated in this study. Two kinds of directionally solidified composites were prepared by spot-melting and floating zone-melting. Microstructure of the arc-melted composite (AMC) consists of equiaxed eutectic colonies, in which ZrC particles are dispersed. The spot-melted composite (SMC) exhibits spheroidal colony structure, which is rather inhomogeneous in size and morphology. ZrC fibers in the eutectic colonies are aligned almost parallel to the growth direction. Well aligned, homogeneous columnar structure with thin ZrC fibers evolves in the floating zone-melted composite (FZC). Texture measurement by X-ray diffractometry revealed that the growth direction of Mo solid solution (Mo_SS) in FZC is preferentially 〈100〉, while that of SMC is scattered. Fracture toughness K_Q evaluated by three point bending test using the single edge notched beam method is >13 MPa m^1/2 for AMC, 20 MPa m^1/2 for SMC and 9 MPa m^1/2 for FZC. Intergranular fracture along colony boundaries is often observed in AMC. In contrast, transgranular fracture is dominant in SMC and FZC, although significant gaps caused by intergranular fracture are occasionally observed in SEM micrographs of SMC. Fracture surface in FZC is wholly flat. Pull-out of ZrC occurs owing to Mo/ZrC interfacial debonding in intergranularly fractured regions of AMC and SMC.Coarse elongated colonies in SMC and FZC induce transgranular fracture instead of intergranular fracture. Intergranular fracture and interfacial debonding in AMC and SMC causes frequent crack deflection accompanied by ligament formation and crack branching, which is responsible for the high fracture toughness of the composites. Preferred 〈100〉 growth of Mo_SS phase in FZC leads to brittle {100} cleavage fracture associated with low fracture toughness.     

Combustion synthesis and densification of large-scale TiC–xNi cermets

Large-scale TiC–xNi cermets with 240-mm diameter were fabricated by self-propagating high-temperature synthesis and combined with pseudo heat isostatic pressing. Combustion-synthesized products consisted of TiC phase and Ni binder phase. Spheroidal TiC particles were enveloped by nearly continuous Ni binder phases. Size of TiC particles decrease with Ni content increase. Synthesized products have excellent mechanical properties and the bending strength of TiC–20Ni and TiC–30Ni is close to K151A and K152B, respectively, produced by traditional powder metallurgy technology.     

机械合金化合成(ZrC+TiC)/Cu复合材料的研究

以Zr、Ti、Cu和C元素粉末为原料,用XRD、EPMA、SEM、力学性能检测等方法,研究机械合金化合成的ZrC/C和(ZrC FiC)/Cu复合材料的力学和电学性能.实验结果表明:可以用机械合金化合成TiC、ZrC粉末.力学性能方面,经ZrC弥散的Cu基复合材料抗拉强度为359.45MPa,布氏硬度为146.2,经(ZrC TiC)弥散的复合材料抗拉强度为377.3MPa,布氏硬度为166.5,说明ZrC作为第二相可以明显改善Cu基材料的力学性能,而且(ZrC TiC)两相强化效果更好.由断口形貌分析,复合材料主要发生沿界面脆性断裂.电学性能方面,由于致密度不够高以及其他杂质相的引入,材料的相对电导率(IACS标准)有待提高.     

Nanocrystalline matrix TiC–Al3Ti and TiC–Al3Ti–Al composites produced by reactive hot-pressing of milled powders

Mechanically alloyed nanocrystalline TiC powder was short-term milled with 40 vol.% of Al powder. The powders mixture was consolidated at 1200 °C under the pressure of 4.8 GPa for 15 s and at 1000 °C under the pressure of 7.7 GPa for 180 s. The bulk materials were characterised by X-ray diffraction, light and scanning electron microscopy, energy dispersive spectroscopy, hardness, density and open porosity measurements. During the consolidation a reaction between TiC and Al occurred, yielding an Al₃Ti intermetallic. The microstructure of the produced composites consists of TiC areas surrounded by lamellae-like regions of Al₃Ti intermetallic (after consolidation at 1200 °C) or Al₃Ti and Al (after consolidation at 1000 °C). The mean crystallite size of TiC is 38 nm. The hardness of the TiC–Al₃Ti and TiC–Al₃Ti–Al composites is 13.28 GPa (1354 HV1) and 10.22 GPa (1041 HV1) respectively. The produced composites possess relatively high hardness and low density. The results obtained confirmed satisfactory quality of the consolidation with keeping a nanocrystalline structure of TiC.     

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.     

Fabrication and mechanical evaluation of SiC–TiC nanocomposites by SPS

In the present study, the composites of SiC–TiC are prepared by spark plasma sintering (SPS) in vacuum without additive. The relationship of density and temperature of SiC–TiC composites with different content of TiC is studied. The maximum relative density reached was 98%. The mechanical properties of SiC–TiC composites with different content of TiC, which were sintered at 1800 °C, have been evaluated. From the fracture surface observation, two models of fracture mechanisms of the composites existed: transgranular and intergranular.     

Production and properties of steel–TiC composites for Wear applications

Abstract

Fe–(WTi)C composite granules containing up to 80 wt-% carbide have been produced by a selfpropagating high temperature synthesis reaction. These can be readily distributed in conventional steel melts. Additions up to 17 wt-% carbide have been made to a 0·4 wt-%C steel which was subsequently cast and hot rolled to plate. The microstructures of cast, rolled, and heat treated. samples display a homogeneous distribution of carbides which do not significantly affect the rolling performance of the steels. The carbides and grain refinement in heat treated samples result in a marked improvement in mechanical properties. The most significant improvement as a fraction of carbide additions is seen in abrasive wear performance.

MST/3196     

In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering

Using a new cast-sintering technique, iron-base surface composites reinforced by VC and TiC particles which were produced in situ and consisting of self-lubricant graphite and chromium-carbide, were sintered on the surface of cast steel during casting. The structure and composition of the surface composites were studied with the help of a SEM, an electron probe and XRD. From the outside in of the iron-based surface composites, the concentration of V and Ti was relatively stable and consistently retained a high level, while the concentration of Cr and Ni took on a gradient distribution and decreased gradually. The fine particles of VC and TiC measuring between 1 and 3 μm in diameter were uniformly dispersed in their matrices, and there was a perfect metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping with a heavy load, the Fe–VC and Fe–TiC surface composites offer virtually unique wear-resistance.     

Modification and control of TiC morphology by various ways in arc melted TiC/Ti–6Al–4V composites

Abstract

The effects of carbon sources, cooling rate, alloying elements and heat treatment on the morphology of TiC were investigated in arc melted TiC/Ti–6Al–4V composites. It was observed that different carbon sources of the composites led to different morphologies of TiC, and the carbon source of carbon powder was found to be more useful in restraining the dendritic growth of TiC. Increasing the cooling rate can reduce the size of TiC, and the refinement effect is more obvious in the composite with carbon powder as the carbon source. The addition of 0·3 wt-%Ni promotes the dendritic growth of TiC; however, the TiC particles become fine and dispersed when 0·3 wt-%Sn is added in the composites. TiC particles in the composites can be dissolved and gradually spheroidised with increasing holding time when heat treated at 1050°C.     

Microstructure and mechanical properties of Si3N4–TiC nanocomposites

Abstract

Si₃N₄–TiC nanocomposites are fabricated by hot press sintering from silicon nitride nanopowders and ultrafine TiC powders. The microstructure and mechanical properties are analysed and discussed. Scanning electron microscopy images show that the microstructure consists of equiaxed grains and grain boundary phase. The TiC added as a dispersed phase reacts with the nitrogen from Si₃N₄ during the liquid phase sintering, with the formation of TiC_0.7 N_0.3 , trace of SiC and N₂. The adding of a proper amount of TiC powders increases the flexural strength and has little influence on fracture toughness. The hardness increases with increasing TiC content.     

Sintered porous cermets based on TiB2 and TiB2–TiC–Mo2C

TiB₂ powder, with different binders (Ni and Ni/Mn), after milling were cold compacted (300 MPa) and sintered in H₂ at 1300 and 1350°C for 1 h. To improve the sintering behaviour, TiC/Mo₂C alloy carbide was added and the milled charge along with the same binders (Ni and Ni/Mn) was cold compacted and sintered under similar conditions. Sintered density, porosity, transverse rupture strength (TRS), grain size and lattice parameter of binder and hard phases were measured. Better densification was observed with Ni/Mn binder as compared to Ni binder for either hard phase based systems. Maximum value of TRS was noted for TiB₂–TiC–Mo₂C–40 wt.% Ni/Mn cermet. Melt exudation was observed for either hard phase based systems with Ni binder.     

Combustion Synthesis and Thermal Stress Analysis of TiC–Ni Functionally Graded Materials

Simultaneous combustion synthesis reaction and compaction of Ti, C, and Ni powders under a hydrostatic pressure was carried out to fabricate dense TiC–Ni functionally graded materials (FGMs) in a single processing operation. Scanning-electron microscope (SEM) and microprobe analysis (EPMA) was employed to investigate the microstructure and composition distribution. Experimental results demonstrate that Ni and Ti composition varies continuously and gradually along the thickness of the reacted sample, remarkably different from stepwise type prior to combustion synthesis. The constituents are continuous in microstructure everywhere and no distinct interaction occurs in TiC–Ni FGM. Moreover, the thermal physical and mechanical properties were measured as a function of composition. It was found that the properties of the FGMs were dependent on Ni content. The residual thermal stress of TiC–Ni FGM and dual-laminate non-FGM cooled to room temperature after combustion synthesis has been analyzed by finite element method. TiC–Ni FGM shows distortion and thermal stress relaxation, which is in striking contrast to the layered TiC–Ni non-FGM.     

Fabrication and oxidation behavior of a reaction derived graphite–ZrC composite for ultrahigh temperature applications

Graphite containing nominally 40 vol.% ZrC (graphite–ZrC) was prepared from commercially available ZrO₂ and graphite powders by hot pressing at 2000 °C in a vacuum. The oxidation behavior of the graphite–ZrC composite was carried out in dry stagnant air at the temperatures of 1200 and 2200 °C. Compared with the pure graphite, the graphite–ZrC composite exhibited good oxidation resistance because the mass loss of the composite powder was significantly lower than that of the pure graphite. The mass loss of graphite–ZrC at 2200 °C was lower than pure graphite at 1200 °C. Furthermore, the introduction of ZrC also improved the strength of the graphite–ZrC composite.     

Erosive–corrosive wear behaviour of Fe–TiC and cobalt based layers separately deposited on En31 steel

Abstract

Observations pertaining to the erosive–corrosive wear behaviour of samples of En31 steel hardfaced separately with Fe–TiC and a commercial cobalt based material are reported in the present investigation. Erosion–corrosion tests were carried out by the sample rotation technique in 3·5%NaCl solution for varying test durations of 8–32 h (corresponding traversal distances 136–544 km) at a fixed traversal speed of 4·71 m s^?1. The effect of the hardfaced layer on the wear behaviour was assessed through testing one set of each of the hardfaced and substrate steel samples under identical test conditions. The wear rate increased initially with traversal distance, attained the maximum and decreased thereafter. In the case of the steel substrate, the wear rate increased once again towards the final stage of testing. Hardfaced layers exhibited substantially decreasing wear rate compared with the substrate. Moreover, the performance of the Fe–TiC composite layer was intermediate between those of the cobalt based hardfacing material and the substrate. The observed response of the samples has been substantiated through their affected surface and subsurface characteristics.     

Phase relationships involving TiC and Ti3AlC (P phase) in Ti–Al–C system

Abstract

Titanium rich alloys of the Ti–Al–C system have been investigated to determine the constitution in the range 1250–750°C with particular reference to phase equilibria and transformations involving TiC and Ti₃AlC (P phase). Alloys with varying aluminium and carbon concentrations up to 15 at.-%Al and 15 at.-%C have been studied using scanning and transmission electron microscopy and X-ray diffraction. The isothermal sections at 1250, 1050, 1000, and 750°C reported by previous workers are reviewed. Equilibria involving the phases β-Ti, α-Ti, Ti₃Al (α ₂), TiC, and Ti₃AlC (P phase) have been investigated and partial isothermal sections at 1050 and 750°C are presented. A revision of the previously established Ti–Al–C isothermal section at 750°C is shown involving equilibria of α+α ₂+P and α+P+TiC. The orientation relationship between the P phase and Ti–Al (α/α ₂) matrix has been found to be (0001)_{α/α 2} ∥{111}_P and 〈12¯10〉_{α/α 2} ∥〈110〉_P.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

Mechanical Property,Oxidation and Ablation Resistance of C/C–ZrB_2–ZrC–SiC Composite Fabricated by Polymer Infiltration and Pyrolysis with Preform of C_f/ZrB_2

C/C–ZrB_2–ZrC–SiC composites were fabricated by polymer infiltration and pyrolysis(PIP) with a preform of C_f/ZrB_2. The carbon fibers and the resin carbon were coated with ceramic layer after PIP in the composites. The composite presents a pseudo-plastic fracture due to deflection of cracks and pullout of fibers.The composite has a higher bending strength by this method in comparison with the conventional PIP process due to fewer heat treatment cycles. The static oxidation test shows that the mass loss of the composites is no more than 1% after 20 min oxidation at 1100 °C. The "core–shell" structure between ZrC–SiC ceramic and other phases plays a positive role in preventing the inward diffusion of oxygen. The ablation resistance of the C/C–ZrB_2–ZrC–SiC composite samples was tested using a plasma generator. After ablation for 120 s, the mass and linear ablation rates of the composites are 4.65 mg cm~(-2)s~(-1) and 2.46 μm s~(-1), respectively. The short carbon layer shows a better ablation resistance than the nonwoven carbon fabric layer after the ceramic coating is peeled off because of its higher ceramic content.     

The thermal shock resistance of the ZrB2–SiC–ZrC ceramic

In the present work, the thermal shock resistance of the ZrB₂–SiC–ZrC ceramic was estimated by the water quenching method and the flexural strength of the quenched specimen was measured. The measured critical temperature difference of the ZrB₂–SiC–ZrC ceramic was significantly greater than that of the ZrB₂–15 vol.% SiC ceramic. The improvement in thermal shock resistance was attributed to its higher fracture toughness (6.7 MPa m^1/2) and lower flexural strength (526 MPa) relative to the ZrB₂–15 vol.% SiC ceramic (4.1 MPa m^1/2 and 795 MPa) based on Griffith fracture criterion. Furthermore, the temperature and thermal stress distributions in the specimen during instantaneous water quenching were simulated by Finite element analysis.