Flexural strength behavior of a ZrB2–TaB2 composite consolidated by non-reactive spark plasma sintering at 2300 °C

A bulk zirconium–tantalum diboride ceramic composite was consolidated by non-reactive spark plasma sintering (SPS) at 2300 °C. In order to consolidate the ZrB₂–44 wt% TaB₂ composite and restrict grain-growth, a special loading procedure was used. Pressure was applied and released at 2150 °C and 1250 °C, respectively. These SPS conditions allowed us to obtain a crack-free bulk composite with a grain size of 4–8 μm. Flexural strength at temperatures up to 1800 °C was measured for the ZrB₂–TaB₂ composite. Importantly, at 1600 °C, the strength was 336 ± 23 MPa, which is superior to that of monolithic ZrB₂. Moreover, the ZrB₂–TaB₂ composite only showed plastic behavior at 1800 °C, a finding that is atypical for ZrB₂-based ceramics.     

Sintering of WC-Co powder with nanocrystalline WC by spark plasma sintering

A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering （SPS） at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.     

Reactive spark plasma sintering of TiB2–SiC–TiN novel composite

The effects of adding SiC as a reinforcement and TiN as an additive on TiB₂-based composites fabricated by the spark plasma sintering (SPS) technique were investigated. SPS was implemented at the sintering conditions of 1900 °C temperature, 7 min holding time and 40 MPa pressure. Adding these two secondary phases had noticeable effects on the microstructure of TiB₂-based composites. A relative densities of 99.9% was obtained for TiB₂–SiC–TiN composite. Detection of in-situ formed phases and investigation on them were done using SEM, XRD, EDS and thermodynamic assessment. These evaluations proved the formation of in-situ phases of TiC, BN nano-platelets, TiSi and B₄C in the TiB₂-based composite codoped with SiC and TiN. Formation of these in-situ phases had fascinating effects on the sinterability and ultimate microstructure of titanium diboride.     

Thermophysical properties of TiB2SiC ceramics from 300 °C to 1700 °C

In the present work, high-frequency induction heating is used to fabricate TiB₂SiC ceramics and the relative density was more than 97%, and then the thermophysical properties of TiB₂SiC ceramics were investigated in detail. The specific heat showed the weak dependence on the test temperature due to the presence of the interface gap because the relative density was not 100%. As the sintering temperature increased, the thermal diffusivity of TiB₂SiC ceramics increased, which was due to the increase of relative density and grain growth. The thermal conductivity of TiB₂SiC ceramics showed a marked increase with increasing grain size and relative density. This could be attributed to a reduction in the number of grain boundaries that interrupt the heat flow path, resulting in an increase in the mean free path of the phonons. Larger grains led to an increase of mean free path of the phonons and thus contributed to a further increase in thermal conductivity.     

Intergranular glassy phase free SiC ceramics retains strength at 1500 °C

We report SiC ceramics sintered with AlN and Sc₂O₃ (or Lu₂O₃) that retain room temperature strength to 1500 °C. The intergranular glassy phase has not been observed in the ceramics due to a designed-sintering additive and, thus, the unsatisfactory effect of glassy phases on the high temperature strength is eliminated.     

A comparative study of spark plasma sintering and hybrid spark plasma sintering of 93W–4.9Ni–2.1Fe heavy alloy

Mixed 93W–4.9Ni–2.1Fe powders were sintered via the spark plasma sintering (SPS) and hybrid spark plasma sintering (HSPS) techniques with 30 mm and 60 mm samples in both conditions. After SPS and HSPS, the 30 mm and 60 mm alloys (except 60 mm-SPS) had a relative density (> 99.2%) close to the theoretical density. Phase, microstructure and mechanical properties evolution of W–Ni–Fe alloy during SPS and HSPS were studied. The microstructural evolution of the 60 mm alloys varied from the edge of the sample to the core of the sample. Results show that the grain size and the hardness vary considerable from the edge to the core of sintered sample of 60 mm sintered using conventional SPS compared to hybrid SPS. Similarly, the hardness also increased from the edge to the core. Furthermore, the 60 mm-HSPS alloy exhibited improved bending strength of 1115 MPa when compared to that of 60 mm-SPS, 920 MPa. The intergranular fracture along the W/W grain boundary is the main fracture modes of W–Ni–Fe, however in the 60 mm-SPS alloy peeling of the grains was also observed which diminished the properties. The mechanical properties of SPS and HSPS 93W–4.9Ni–2.1Fe heavy alloys are dependent on the microstructural parameters such as tungsten grain size and overall homogeneity.     

Fe–B–C composites produced using spark plasma sintering

Fe–B–C composites were produced using iron and boron carbide powders. The powders were mixed to produce various compositions, ranging from 1 vol.% Fe to 80.1 vol.% Fe. Spark plasma sintering (SPS) was used to densify the composite powder green compacts. The sintering temperatures used ranged from 900 °C for the composites with a high iron content to 2000 °C for those with a high boron carbide content. It was evident that during the sintering process the iron reacted with the boron carbide. XRD analysis showed the presence of FeB, Fe₂B, Fe₃C, Fe₃(B_0.6C_0.4), Fe₂₃(B,C)₆ and residual carbon as reaction products. The composites were found to have hardness values between 9.8 and 33.1 GPa with the higher hardness being associated with the higher boron carbide contents. The fracture toughness values determined were in the range of 2.8–5.3 MPa m^0.5. With increasing iron content from 1 to 5 vol.%, it is evident that the FeB formed begins to embrittle the material rather than increase the fracture toughness as a result of the high residual stresses between the B₄C and FeB phases.     

Effect of wear debris of Al2O3, ZrO2 and WC balls on Y-α/β-SiAlON ceramics consolidated by spark plasma sintering

Three types of Y-α/β-SiAlON powders were prepared by mixing and milling the raw materials for 20 h using Al₂O₃, ZrO₂, and WC balls, thereafter denoted as SNA, SNZ and SNW, respectively. The three types of specimens were sintered using spark plasma sintering (SPS) at 1510 °C for 5 min under 30 MPa in a vacuum. α-phases (SiAlON and Si₃N₄) and β-SiAlON phase were observed in the SNA and SNZ specimens, but only the β-SiAlON phase existed in the SNW specimen. The wear debris of the WC balls affected the grain boundary properties and eventually promoted the full phase transformation of α-Si₃N₄ into α- and β-SiAlON phases. However, SNA and SNZ were partially transformed into α- and β-SiAlON phases. The Vickers hardness of SNA was the highest (18.7 GPa), due to its having the highest content of α-phase, but its fracture toughness was the lowest (4.09 MPam^1/2) due to its having the lowest content of β-SiAlON phase. The wear debris and secondary phases existed at the grain boundary, mostly at the triple junction, and also affected the color. The color of the sintered specimen was quite different depending on the milling media.     

Air-oxidation of a Co-based amorphous ribbon at 400–600 °C

The oxidation behavior of a commercial Co₆₉B₁₂Si₁₂Fe₄Mo₂Ni₁ amorphous ribbon (Co6-AR) was studied over the temperature range of 400–600 °C in dry air. The results showed that virtually no oxidation occurred at 400 °C. On the other hand, the oxidation kinetics of the Co6-AR alloy at 450–600 °C generally followed a multi-stage parabolic-rate law, and the parabolic-rate constants (k_p values) tend to increase with increasing temperature. It was found that the oxidation rates of the glassy alloy are slower than those of pure Co, indicative of a better oxidation resistance. An exclusive scale of CoO was observed after the oxidation of the glassy alloy in the temperature range of interest, and several crystalline phases formed on the substrate beneath the scale, consisting of pure Co (both FCC and HCP structures), Co₃B, Co₂Si, CoFe, and Co₂B (absent at 450 °C), which indicated the occurrence of crystallization.     

Mechanical alloying and characteristics of spark plasma sintering of Ti-A1 composite powders

The mechanical alloying process of Ti-Al composite powders were carried out by use of high energy ball-milling machine. Structure variations of powder mixtures during mechanical alloying and characteristic of spark plasma sintering were investigated. The results show that during milling, TiAl, Ti3Al and Ti2Al phase intermetallic compounds are formed, simultaneously with powder refinement for the （TiH2-45Al-0.2Si-SNb） and （TiH2-45Al-0.2Si-7Nb） mixtures. The particle sizes of two powder mixtures are less than 300 nm after milling for 30 h. Sintering process of the milled powder can be completed in a short time by spark plasma sintering, and the sintering microstructure is composed of fine and homogeneous TiAl and Ti3Al phase.     

Microstructure and thermoelectric properties of β-FeSi2 ceramics fabricated by hot-pressing and spark plasma sintering

The microstructure and thermoelectric properties of β-FeSi₂ ceramics by hot pressing (HP) and spark plasma sintering (SPS) are investigated. With increasing hot-pressing temperature, the density, electronic conductivity and thermal conductivity of the samples increase significantly, the thermoelectric figure of merit is improved slightly. The microstructure study indicates that the sizes of the β-FeSi₂ and ?-FeSi phases in the sample sintered by the SPS process are smaller than that by the HP process. The SPS sample shows excellent thermoelectric performance due to the low thermal conductivity.     

Heat treatment process of new NdFeB magnet prepared by spark plasma sintering

1　INTRODUCTIONTraditionallysinteredNdFeBmagnetcanmeettherequirementofdimensional precisionthroughpost machining ,whichusuallyresultsin 4 5 %ofma terialloss.Post machiningnotonlywastestherareearthresources ,butalsoincreasesthe productioncost .Moreover ,itisdifficulttopreparehomogeneousworkpieceswithlargedimensionandcomplicatedshapeduetosomeuncontrollablefactorsinthecon ventionalsintering process .Ontheotherhand ,al thoughthebondedNdFeBmagnethasbetterforma bilityanddimensionalprecision ,…     

Effect of Al addition on SiC–B4C cermet prepared by pressureless sintering and spark plasma sintering methods

SiC–B₄C–Al cermets containing 5, 10 and 20 wt.% of Al were fabricated by high-energy planetary milling followed by conventional sintering and spark plasma sintering (SPS) techniques separately. The average particle size reduced to ~ 3 μm from an initial size of 45 μm after 10 h of milling. The as-milled powders were conventionally sintered at 1950 °C for 30 min under argon atmosphere and SPS was carried out at 1300 °C for 5 min under 50 MPa applied pressure. The formation of Al₈B₄C₇ and AlB₁₂ phases during conventional sintering and SPS were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The formation of Al₈B₄C₇ at 700 °C and AlB₁₂ at 1000 °C was well supported by XRD and differential scanning calorimetry (DSC). The maximum relative density, microhardness and indentation fracture resistance of SiC–B₄C–10Al consolidated by SPS are 97%, 23.80 GPa and 3.28 MPa·m^1/2, respectively.     

Creep- and coarsening properties of Al–0.06 at.% Sc–0.06 at.% Ti at 300–450 °C

Upon aging at 300–450 °C, nanosize, coherent Al₃(Sc_1−xTi_x) precipitates are formed in pure aluminum micro-alloyed with 0.06 at.% Sc and 0.06 at.% Ti. The outstanding coarsening resistance of these precipitates at these elevated temperatures (61–77% of the melting temperature of aluminum) is explained by the significantly smaller diffusivity of Ti in Al when compared to that of Sc in Al. Furthermore, this coarse-grained alloy exhibits good compressive creep resistance for a castable, heat-treatable aluminum alloy: the creep threshold stress varies from 17 MPa at 300 °C to 7 MPa at 425 °C, as expected if the climb bypass by dislocations of the mismatching precipitates is hindered by their elastic stress fields.     

Fireside corrosion degradation of ferritic alloys at 600 °C in oxy-fired conditions

This paper reports the results of a study carried out to investigate the effects of simulated coal/biomass combustion conditions on the fireside corrosion. The 1000 h deposit recoat exposure (5 × 200 h cycles) was carried out at 600 °C. In these tests ferritic alloys were used 15Mo3, T22, T23 and T91. Kinetics data were generated for the alloys exposed using both traditional weight change methods and metal loss measurements. The highest rate of corrosion based on EDX results occurred under D1 deposit where provoke mainly by the formation of alkali iron tri-sulphate phase.     

Comparative study of the fabrication of ultrafine Ti（C,N）-based cermets by spark plasma sintering and conventional vacuum sintering

Spark plasma sintering (SPS) and conventional vacuum sintering (VS) were employed to fabricate ultrafine Ti(C,N)-based cermets. The shrinkage behavior, microstructure, and porosity and mechanical properties of the samples fabricated by SPS were compared with those of the samples sintered by VS using optical microscopy, scanning electron microscopy, universal testing machine, and rockwell tester. The results are as follows: (1) The shrinkage process occurred mainly in the range of 1000-1300℃ during the VS process, and only a 0.2% linear shrinkage ratio appeared below 800℃；during the SPS process, a 60% dimensional change occurred below 800℃ as a result of pressure action. (2) By utilizing the SPS technique, it is difficult for obtaining fully dense Ti(C,N)-based cermets. Due to the much existence of pores and uncombined carbon, the mechanical properties of the sintered samples by SPS are inferior to sintered ones by VS. (3) grain size of the samples sintered by SPS is still below 0.5μm, but not by VS; because of low sintering temperature, there are no typical core/rim structures formed in the sintered samples by SPS1; the main microstrures of the sintered samples by SPS2 are a white core/grey shell sstructure, whereas by VS show a typical black core.grey shell structure.     

Fabrication of W–Cu functionally graded material by spark plasma sintering method

Three-layered (W–25Cu/W–50Cu/W–75Cu, volume fraction) W/Cu functionally graded material (FGM) was synthesized by spark plasma sintering (SPS) at different temperatures for 5 min under a load of 40 MPa. The influences of different sintering processes on relative density, hardness, thermal conductivity and microstructure at various layers of sintered samples were investigated. The experimental results indicated that the graded structure of the composite could be well densified after the SPS process. The relative density increased with the increment of sintering temperature and it was up to 96.53% as sintered at 1050 °C. In addition, the thermal conductivity reached 140 W/m·K at room temperature and 151 W/m·K at 800 °C, which could be ascribed to the specific structure that W particles enwrapped by net-like Cu. And the Vickers hardness was converted from 4.11 to 4.68 GPa.     

Experimental isothermal section at 1200 °C of V–Cr–Si system

In the present work, the isothermal section at 1200 °C of the V–Cr–Si phase diagram was experimentally studied. The samples were prepared by arc melting and characterized using scanning electron microscopy/energy-dispersive spectroscopy and electron probe microanalyzer. The continuous solution phases (Cr,V)₃Si, (Cr,V)₅Si₃ and (Cr,V)Si₂ were confirmed. The solubilities of Cr in V₆Si₅ and of V in CrSi have been measured. A ternary phase (Cr,V)₁₁Si₈ was observed and its homogeneity range, which is at constant Si ratio, was determined at 1200 °C.     

Phase equilibria in the Fe-Mo-Ti ternary system at 1000 °C

An isothermal section of the Fe-Mo-Ti ternary system at 1000 °C has been constructed using data acquired from a series of seven alloys. The limit of solubility of Fe in the continuous A2 phase field between Ti and Mo has been determined, as have the extents to which Mo may be accommodated in the B2 TiFe phase, and Ti in the D8₅ Fe₇Mo₆ phase. The B2, D8₅ and C14 Fe₂ (Ti, Mo) intermetallics were found to have limited tolerance for non-stoichiometric compositions. The positions of the A2 + B2 + C14 and A2 + C14 + D8₅ three-phase fields were determined, along with the extents of the A2 + B2, A2 + D8₅, A2 + C14, C14 + B2 and C14 + D8₅ two-phase fields. No ternary phases were observed in any of the alloys studied.