Effect of Ti(C,N) addition on sintering behaviour and properties of binder-modified WC-10Co cemented carbide

In the present investigation the microstructure and mechanical properties of WC-10Co, WC-8.3Ti(C,N)-12Co, WC-8.3Ti(C,N)-6Co-6Ni and WC-7Ti(C,N)-2Mo₂C-6Co-6Ni cemented carbides were studied. Introduction of Ti(C,N) in WC-10Co cemented carbide imposed sintering difficulties and hot isostatic pressing was required to obtain fully dense material. The modification of the binder cobalt with nickel and molybdenum did not noticeably affect the sintered microstructure. In general the mechanical properties of Ti(C,N)-containing cemented carbides were inferior to those of WC-10Co cemented carbide.     

Use of Ti in hard metal alloys – Part II: mechanical properties

WC‐Co hard metal is a material of high hardness, high compressive strength and wear resistance while maintaining good toughness and thermal stability. Samples of nanosized WC powders with 10 wt% Co, WC‐10 wt% Ti, WC‐9 wt% Ti‐1 wt% Co were cold pressed at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar. The characterization of the sintered materials was performed by the measurements of densification, HV30 hardness, fracture toughness and compression strength. The results showed that it is possible to process a hard metal through a Powder Metallurgical conventional route from nanoscaled WC grains, using Ti (or a Ti‐Co mixture) as a binder phase, with good mechanical properties.     

Microstructure and properties of the sintered composite prepared by hot pressing of TiN-coated alumina powder

Alumina powders (average grain size: 50 m) coated with TiN film of thickness 0.5 and 1.2 m were prepared by rotary powder-bed chemical vapour deposition for 15 and 90 min, respectively. These Al₂O₃-TiN composite powders were hot-pressed at 1800 °C and 40 MPa for 30 min. The microstructure of the Al₂O₃-TiN sintered composite was composed of a TiN network homogeneously distributed on the grain boundaries of alumina. The mechanical properties (hardness, bending strength and fractured toughness) and thermal conductivity of the sintered composite were found to depend on the composition and microstructure of the sintered composite, even with a small content (3–7 wt%) of TiN. The resistivity of the sintered composite was 10^–1-10^–3 cm. The relatively high electrical conductivity of the Al₂O₃-TiN composite was caused by the grain boundary conduction of TiN.     

Deposition of TiN films on Co–Cr for improving mechanical properties and biocompatibility using reactive DC sputtering

This study reports the deposition of TiN films on Co–Cr substrates to improve the substrates’ mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N₂) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co–Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N₂)1:1, Ti/TiN-(Ar/N₂)1:1, and Ti/TiN-(Ar:N₂)1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co–Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co–Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co–Cr alloys.     

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.     

Use of Ti in hard metal alloys – Part I: structural and microstructural analysis

Nanosized WC, and binders Co, Ti and Ti‐Co, are used to process hardmetals. Titanium (Ti) was proposed to reduce and even replace the Co in these composites, verifying the effectiveness of the new binders. Samples of nanosized WC with 10 wt% Co, 9 wt% WC 1 wt% Ti – Co, WC‐10 wt% Ti were cold compacted at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar for the processing of hardmetal were performed. The structural characterization by X‐ray diffraction and microstructure by scanning electron microscopy (SEM) and EDS microanalysis of the sintered material. We observed the presence of the W₂C phase in the sintered samples, and Co₃W phases in the samples with Co content and a good distribution of binder phase, leading to formation of small “pool” of Co and Ti and small porosity and well distributed. It was proved that using Ti as binder phase, the neta phase formation was avoided.     

Liquid-Phase Sintering and Properties of Si3N4–TiN Composites

Densification during liquid-phase sintering of Si₃N₄–TiN was studied in the presence of Y₂O₃. The content of TiN was varied from 0–50 mass%. During the densification Y-silicate was formed. The amount of silicate increased with both decreasing fraction of TiN and increasing isothermal heating time. Density, fracture toughness, and electrical resistivity were measured as a function of TiN content. It was found that the density and fracture toughness increased with increasing TiN content. The electrical resistivity drops drastically, from 10¹⁰ m for sintered Si₃N₄ to 10^–3 m for sintered Si₃N₄–TiN composite containing 30 vol% TiN.     

Characterization of wurtzitic boron nitride compacts

Characterization of sintered polycrystalline wurtzitic boron nitride compacts was carried out regarding the different crystalline phases that are formed at high temperature and high pressure, composition, particle size distribution of BN and binder and hardness. Wurtzitic boron nitride, cubic boron nitride, TiC/TiN solid solution, TiB and TiB₂ were the crystalline phases that have been observed in sintered wurtzitic boron nitride compacts. The particle size distribution of BN and the binder was found to be comparable (1 to 5m), with about 80% of the particles lying between 2 and 3m. Weight percentages of different elements present in these compacts were determined. The average Knoop hardness values under 500 g load were measured, and the variation of hardness as a function of position on the specimen surface was studied.     

Paper‐Derived Ferroelectric Ceramics: A Feasibility Study

Preceramic paper may serve as a preform to manufacture single sheet as well as multilayer porous ferroelectric ceramic products. In this article, the authors discuss the formation, microstructure, and properties of preceramic papers highly loaded with BaTiO₃ filler ranging from 70 to 80 vol% and their conversion into ceramic materials. In order to increase the density of the single sheets, post calendering is applied. These sheets are used for the fabrication of multilayer ceramics using warm lamination technique. After binder burnout and sintering up to 1300 °C for 2 h in air, porous paper‐derived multilayer BaTiO₃ is obtained. The effect of ceramic filler content and calendering on the residual porosity in sintered samples is studied. Furthermore, the influence of porosity on the microstructure, mechanical, dielectric, and piezoelectric properties of the sintered BaTiO₃ ceramics is investigated.

     

两种AC-HVAF喷涂WC涂层微观组织以及耐蚀性研究

利用AC-HAVF喷涂技术在0Cr13Ni5Mo不锈钢上制备了WC-10Co-4Cr,WC-12Co涂层,并利用XRD,SEM,电化学以及盐雾实验分析了涂层的微观组织以及耐蚀性.结果表明:两种涂层相组成与其粉末一致,未出现其他喷涂技术普遍存在的W2C以及W,AC-HAVF喷涂技术可以有效的抑制WC的分解;两种涂层都很致密且与基体结合良好,孔隙率低;电化学以及盐雾实验发现,WC-10Co-4Cr涂层的耐蚀性好于WC-12Co涂层,并较基体0Cr13Ni5Mo不锈钢有较大的提高,粘结相中Cr元素的加入以及孔隙率低是WC-10Co-4Cr涂层耐蚀性优异的重要原因.     

Precursor routes to Group 4 metal borides, and metal boride/carbide and metal boride/nitride composites

Precursor routes to Group 4 metal borides, as well as metal-boride/carbide and metal-boride/nitride composites, that employ metal-oxide/polymer and metal/polymer dispersions are described. The metal boride precursors were initially obtained by dispersing metal oxides in a decaborane-dicyanopentane polymer, but better results have now been achieved using a newly developed polyhexenyldecaborane polymer. Subsequent pyrolyses of the metal-oxide/polymer dispersions afford metal borides, including TiB₂, ZrB₂, and HfB₂ in high chemical and ceramic yields. On the other hand, pyrolyses of hafnium/polyhexenyldecaborane dispersions provide an efficient route to hafnium-boride/carbide composites. Metal-boride/nitride composites, including TiB₂/TiN and HfB₂/HfN materials, are also readily obtained by pyrolyses of metal dispersions in the boron-nitrogen polymer polyborazylene, (B₃N₃H₄) _X . The high ceramic yields of the metal-boride/nitride systems (98%), enable their use for the controlled formation of shaped monolithic TiB₂/TiN or HfB₂/HfN materials by pyrolysis of pressed precursor green bodies.     

Mechanical properties of reaction sintered TiN ceramics with B4C addition

Reaction sintering of TiN with B₄C addition was developed to densify the composite without the application of external pressure. The process utilizes high affinity of B for Ti which leads to the formation of extremely fine highly active TiB₂. The addition of 6–8 wt% B₄C is sufficient to increase the sintered density to over 96% theoretical density, fracture toughness to 3.5 MPa·m^1/2, flexural strength to 415 MPa, and hardness to 14 GPa. The major toughening mechanism was identified to be the crack deflection caused by the presence of hard and tough TiB₂ particles. The large improvements in mechanical properties make this in situ produced composite viable material for applications requiring higher level of reliability.     

Synthesis of WC hard materials using coated powders

Nickel and cobalt were used as binder materials for tungsten carbide powders (WC) hard materials. Ni and Co binder were added individually to the WC powder by two different methods namely, mechanical mixing and chemical electroless coating. In this study WC powders of grain sizes 0.3–1.0 μm were electroless coated with either nickel or cobalt. The loading of either Ni or Co coating was 13 wt.%. The electroless-coating method conditions of both Ni and Co on WC powders are described. The coated powders were cold compacted and sintered in vacuum at different sintering temperatures. For comparison, identical materials compositions were prepared by mixing the powders constituents mechanically, compacted and sintered under the same conditions.The prepared powders and sintered materials were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that coated WC materials have smaller values of porosity and more homogeneous microstructure while other properties, such as transverse rupture strength, and hardness exhibit greater values than those produced using mixing elemental powders. It is possible to outline the benefits of coated powder approach in the following: high homogeneity and better distribution of binder materials within WC hard materials, higher density and good interfacial bonding, capability of using fine powders, and possibility of using small alloying and/or reinforcement additions in a more uniform manner.     

Studies on Cobalt(II) Complexes with Benzenesulfonate: Synthesis,Crystal Structure,and Spectroscopic and Magnetic Properties

Two novel transition metal benzenesulfonate complexes with a formula [Co(H₂O)₆][C₇H₅O₃SO₃]₂?2H₂O (1) and Na₄[Co(H₂O)₂ Cl₄][C₇H₅O₃SO₃]₂?4H₂O (2), have been synthesized and characterized by single-crystal X-ray diffraction technique; thermal analysis was done and spectroscopic and magnetic properties were studied. The [Co(H₂O)₆][C₇H₅O₃SO₃]₂?2H₂O (1) complex crystallizes in the triclinic system; however, the (2) complex crystallizes in the monoclinic crystal system with the C2/c space group. Each Co(II) atom in (1) and (2) is octahedrally coordinated. A hydrogen bond links the complex cation and anion, forming one-dimensional hydrogen-bonded supramolecular chains. The complexes exhibit different decomposition characteristics. Magnetic susceptibility measurement shows that complexes have weak anti-ferromagnetic intermolecular interactions between many local spins. The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures, and they are compared with those reported for related systems. Magnetic moments of both compounds at room temperature are characteristic of high-spin complexes Co(II).     

Preparation of TiB2 sintered compacts by hot pressing

A sintered compact of titanium diboride (TiB₂) was prepared by hot pressing of the synthesized TiB₂ powder, which was obtained by a solid-state reaction between TiN and amorphous boron. Densification of the sintered compact occurred at 20 MPa and 1800° C for 5 to 60 min with the aid of a reaction sintering, including the TiB₂ formation reaction between excess 20 at % amorphous boron in the as-synthesized powder (TiB₂ + 0.2B) and intentionally added 10 at % titanium metal. A homogeneous sintered compact of a single phase of TiB₂, which was prepared by hot pressing for 30 min from the starting powder composition [(TiB₂ + 0.2B) + 0.1 Ti], had a fine-grained microstructure composed of TiB₂ grains with diameters of 2 to 3 m. The bulk density was 4.47 g cm^–3, i.e. 98% of the theoretical density. The microhardness, transverse rupture strength and fracture toughness of the TiB₂ sintered compact were 2850 kg mm^–2, 48 kg mm^–2 and 2.4 MN m^–3/2, respectively. The thermal expansion coefficient increased with increasing temperature up to 400° C and had a constant value of 8.8 x 10^–6 deg^–1 above 500° C.     

A study of Nd2Fe14B and a neodymium-rich phase in sintered NdFeB magnets

The microstructure and properties of NdFeB sintered permanent magnets were analysed by different methods. Samples analysed were sintered and thermally treated. The hard magnetic Nd₂Fe₁₄B phase and amorphous neodymium-rich phase were observed by TEM. The neodymium-rich phase contained iron and boron, in elemental and in B₂O₃ form, which is known as a glass former. At the sintering temperature, Nd₂Fe₁₄B and the neodymium-rich phase are supersaturated with iron, which should be dissolved at the annealing temperature to react with neodymium and boron and form additional Nd₂Fe₁₄B phase. Iron precipitates of size up to 2 nm were detected in the Nd₂Fe₁₄B phase. These superparamagnetic precipitates of -Fe could affect the hard magnetic properties of NdFeB magnets.     

In Situ synthesis of TiN-reinforced Si3N4 matrix composites using Si and sponge Ti powders

Dense Si₃N₄-TiN composites from Si and sponge Ti (0–40 wt %) powders were produced by in situ reaction-bonding and post-sintering under N₂ atomosphere. The fracture strength and toughness of Si₃N₄-17% TiN composite were found to be 537.9 MPa and 10.4 MPam^1/2, respectively. In the reaction-bonded bodies, Si₃N₄ grains were constructed with - and -Si₃N₄ structure as well as TiN and some amounts of residual Si phase. After post-sintering, the residual Si and -Si₃N₄ grains were transformed to -Si₃N₄ grains with rod-like shape. No intermetallic compounds (e.g., TiSi₂, Ti₅Si₃ and Ti₅Si₄) were formed at the interfaces between Si₃N₄ and TiN grains. The main toughening mechanisms were crack deflection and crack bridging caused by rod-like Si₃N₄ grains which were randomly dispersed in sintered body. Microcracking due to the dispersion of in situ formed TiN particles also contributed to the toughening of the sintered body.     

Nitride and carbonitride layers of titanium formed under high energy ion irradiation

Titanium nitride and carbonitride films were formed by evaporating titanium while simultaneously irradiating with energetic nitrogen ions in an atmosphere of N₂ and C₂H₂+N₂, respectively. The physical and chemical properties, such as composition, purity, hardness, adhesion and corrosion resistance behaviour, were examined with respect to the process parameters such as nitrogen ion current density and the process pressure of the reactive gases. Nitride and carbonitride phases can be obtained over a wide range of process parameters. Oxygen contamination strongly depends on the ion current density. Deposits of TiN were prepared with hardness values of up to 2800 kgmm^–2 and adhesion values of up to 15 N critical load in the scratch test. For TiCN the values were 4000 kgmm^–2 and 10 N. Even a thin layer of only 1 m of either TiN or TiCN reduced the corrosion rate of stainless steel in sea water by about an order of magnitude over a period of one month.     

The microstructure of WC and WC-4.3 wt% Co sintered at high pressure

WC and WC-4.3 wt% Co were sintered at 1400° C under the condition of 5.8 GPa by using a modified belt-type high pressure apparatus. Their microstructures were observed with a transmission electron microscope, in order to clarify the structural features and sintering mechanisms of the materials. As a result, a stacking-fault vector and mobile dislocations during sintering were determined. Also, it is concluded that the sintering mechanisms of WC and WC-4.3 wt% Co are plastic deformation and solution precipitation through the liquid binder phase, respectively.     

A transmission electron microscopy study of WC-10Co cemented carbides with modified hard and binder phases

The alloy design of WC-10Co cemented carbide, modified with addition of a hard carbide phase, TiC, and with Ni and Mo in the binder phase, has been highlighted by the authors in a number of publications. The present article deals with the fine microstructural features of various phases in such cemented carbides. WC grains in all the investigated cemented carbide compositions appear to develop straight facets during sintering because of their anisotropic nature. In contrast, the TiC phase is characterized by its rounded shape. Dislocations are present in both WC and TiC grains, being of lesser density in the latter. The binder phase is always associated with stacking faults. The nature of the hard phase/binder interfaces has been found to be dependent on the binder phase chemistry. The observed changes in microstructures and mechanical properties have been correlated with the wettability and solubility of the hard phases in the binder melt, and with the different strengthening mechanisms in the binder phase.