ASTM G132 testing for evaluating abrasion resistance of WC-Co hardmetal

The current test method experimentally simulates two-body abrasive wear of WC-6wt% Co hardmetal using modified pin abrasion tester configuration (ASTM G132). Silicon carbide (SiC) and alumina (Al2O3) with different sizes ranging from 22μm to 200 μm were used as abrasives in this test. Experiments were performed for different normal force from 4 to 16 N with constant sliding speed of 150 mm/s for 30 m sliding distance. Worn surface morphology and topography were characterized through SEM and white light interferometry. The obtained results clearly highlights the potential of pin abrasion tester for characterizing two body abrasion of hardmetals

Effect of carbon content on the microstructure and mechanical properties of NbC-Ni based cermets

The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content were prepared by conventional liquid phase sintering for 1 h at 1420 degrees C in vacuum. Microstructural analysis of the fully densified cermets was performed by electron probe microanalysis (EPMA) to assess the effect of carbon and VC or Mo additions on the NbC grain growth and morphology. A decreased carbon content in the starting powder mixtures resulted in increased dissolution of Nb, V, and Mo in the Ni binder and a decreased C/Nb ratio in the NbC based carbide phase. The Vickers hardness (HV30) and Palmqvist indentation toughness were found to decrease significantly with an increasing carbon content in the Mo-free cermets, whereas an antagonistic correlation between hardness and toughness was obtained as a function of the Mo-content in Mo-modified NbC cermets. To obtain optimized mechanical properties, methods to control the total carbon content of NbC-Ni mixtures were proposed and the prepared cermets were investigated in detail

Exceptional appendage and soft-tissue preservation in a Middle Triassic horseshoe crab from SW China

Abstract Horseshoe crabs are classic “living fossils”, supposedly slowly evolving, conservative taxa, with a long fossil record back to the Ordovician. The evolution of their exoskeleton is well documented by fossils, but appendage and soft-tissue preservation is extremely rare. Here we analyse details of appendage and soft-tissue preservation in Yunnanolimulus luopingensis, a Middle Triassic (ca. 244 million years old) horseshoe crab from Yunnan Province, SW China. The remarkable preservation of anatomical details including the chelicerae, five pairs of walking appendages, opisthosomal appendages with book gills, muscles, and fine setae permits comparison with extant horseshoe crabs. The close anatomical similarity between the Middle Triassic horseshoe crabs and their recent analogues documents anatomical conservatism for over 240 million years, suggesting persistence of lifestyle. The occurrence of Carcinoscorpius-type claspers on the first and second walking legs in male individuals of Y. luopingensis indicates that simple chelate claspers in males are plesiomorphic for horseshoe crabs, and the bulbous claspers in Tachypleus and Limulus are derived

Powder synthesis and densification of ultrafine B₄C-ZrB₂ composite by pulsed electrical current sintering

Submicrometer sized B₄C-30 vol% ZrB₂ ceramic composites were made both by one-step in situ pulsed electric current sintering (PECS) of a B₄C, ZrO₂ and carbon black powder mixture or by PECS of B₄C-ZrB₂ powder mixtures synthesized by thermal treatment in vacuum at 1100–1400 °C for 2 h. The influence of the processing temperature on the phase evolution and chemical composition of the mixtures were investigated in detail by Rietveld XRD and SEM analysis. Conventional vacuum thermal treatments allowed to synthesize homogeneous and submicrometer sized B₄C-ZrB₂ powder mixtures at 1300 and 1400 °C for 2 h, whereas 37 and 11 wt% (m + t)-ZrO₂ was present in the mixtures processed at 1100 and 1200 °C respectively. Subsequent PECS treatment at 2000 °C for 5 min allowed to obtain B₄C-ZrB₂ composites from these thermally treated B₄C + ZrO₂ + C powder mixtures. In the one-step in situ process, a PECS temperature of 1900 °C was necessary to complete the conversion of the in situ formed B₂O₃ to B₄C to form B₄C-ZrB₂ composites. The composites prepared by both routes exhibited a Vickers hardness (HV₁₀) of 30–32 GPa, a modest fracture toughness of 2.4–2.9 MPa m¹/² and a good flexural strength of 630–730 MPa.publisher: Elsevier articletitle: Powder synthesis and densification of ultrafine B4C-ZrB2 composite by pulsed electrical current sintering journaltitle: Journal of the European Ceramic Society articlelink: http://dx.doi.org/10.1016/j.jeurceramsoc.2014.01.022 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Effect of Al2O3 Addition on Mineralogical Modification and Crystallization Kinetics of a High Basicity BOF Steel Slag

Basic oxygen furnace (BOF) steel slag is a main byproduct that is produced during the converter steelmaking process. The volume instability and fast crystallization of BOF slag limits its added-value application. This article aims to understand the effect of Al2O3 on the mineralogical modification and crystallization kinetics of a high basicity BOF steel slag. Continuous cooling transformation and time-temperature-transformation curves were constructed to determine the crystallization characteristics of BOF slag. The critical cooling rate to vitrify the slag was experimentally obtained. The crystallization sequence was clarified by integrating in situ and post-mortem observations with thermodynamic calculations. The results suggest that the addition of Al2O3 can effectively remove free lime, decrease the melting point, and improve the glass formation ability of the high basicity BOF slag. Undercooling the slag is enhanced by increasing the cooling rate and/or adding Al2O3. By steering the addition of Al2O3 and the cooling rate, BOF slag can be modified to obtain a more amorphous phase, presenting an enhanced potential to be a binder for added-value applications

Potentials of niobium carbide (NbC) as cutting tools and for wear protection

© 2018 The American Ceramic Society. The existence of different pseudo-cubic phases beside NbC, like Nb4C3, Nb6Cs, define a large range of homogeneity of NbCx(0.75≤ x ≤1.0) in the binary phase diagram and enable a large process window. Properties, like micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, the addition of secondary carbides and the type of binder. The initial NbC grade was substoichiometric, SPS sintered and cobalt bonded (NbC0.88-12Co SPS). So far, NbC and Nb2O5do not have a REACH (Registration, Evaluation, Authorisation and Restriction of Chemical substances programme) classification related to human toxicology and are not listed as substances of very high concern contrary to WO3and Co3O4. The NiMo-bonded stoichiometric NbC1.0grades enable the substitution of cobalt by nickel, SPS by conventional sintering and NbC0.88by NbC1.0in view of functional properties. Nickel bonded NbC grades have improved toughness versus cobalt bonded NbC grades, but exhibit lower hardness. NiMo and N1Mo2C bonded NbC1.0grades compensated for the loss in hardness while keeping the toughness. The tool lifes of uncoated NiMo- and NiMo2C-bonded stoichiometric NbC1.0grades under dry turning 42CrMo4and C45E were between +30% to +100% higher and up compared to WC-6Co (fine grain). Niobium is today largely available. NbC grades displayed lower dry sliding friction over WC grades. The softer Ni- and NiMo-bonded NbC1.0-grades have a higher abrasive wear resistance (ASTM G65), even with lower toughnesses, than the tougher WC-Co grades and harder NbC-Co grades.status: publishe

Optimization of Mineralogy and Microstructure of Solidified Basic Oxygen Furnace Slag Through SiO2 Addition or Atmosphere Control During Hot-Stage Slag Treatment

Valorization of basic oxygen furnace (BOF) slag is of significant importance for mitigation of the steel production's environmental impact. The present work aims to investigate the influence of SiO2 addition and oxygen partial pressure on the mineralogical modification of a typical industrial BOF slag. The slag basicity (mass ratio of CaO/SiO2) was varied from 1.8 to 4.4 by mixing specific amounts of SiO2 with the master BOF slag. The original and modified slags were remelted and solidified under argon or air atmosphere followed by slow cooling. The experimental observations were then compared with the results of thermodynamic modeling to achieve a thorough understanding. With decreasing the basicity, free lime was eliminated, as it forms dicalcium silicate (Ca2SiO4). With increasing oxygen partial pressure, wustite was oxidized to hematite, which combined with free lime to form calcium aluminoferrite (C(2)AF). The effects of SiO2 addition and oxygen partial pressure were finally evaluated with respect to the energy consumption for the BOF slag valorization. The modified slag is suitable as a precursor for construction applications as binders

Densification and tribological profile of niobium oxide

The origin of the intrinsic wear resistance of NbC-based materials is investigated through an assessment of the tribological performance of fully dense, crack-free spark plasma sintered Nb₂O₅ (here as a reduced polymorph: monoclinic Nb₁₂O₂₉ or NbO₂.₄₁₆). The most likely wear mechanism on NbC is the tribooxidation to Nb₂O₅. The unlubricated (dry) friction and wear behavior of alumina (99.7%) mated against rotating disks of crack-free niobium(V)oxide (Nb₂O₅) under unidirectional sliding (0.03–10 m/s; 22 °C and 400 °C) and oscillation (ƒ = 20 Hz, dx = 200 mm, 2/50/98% rel. humidity, n=10⁵ /10⁶ cycles) will be presented. The microstructure and mechanical properties of the crack-free Nb₂O₅ are assessed. The tribological data obtained are benchmarked with different NbC grades, ceramics, cermets and thermally sprayed coatings.publisher: Elsevier articletitle: Densification and tribological profile of niobium oxide journaltitle: Wear articlelink: http://dx.doi.org/10.1016/j.wear.2016.02.003 content_type: article copyright: Copyright © 2016 Elsevier B.V. All rights reserved.status: publishe

NbC-BASED CERMETS: INFLUENCE OF SECONDARY CARBIDE

The influence of Al metal and WC, Cr3C2, VC, TiC and Mo2C secondary carbide additions on the microstructure and mechanical properties of Fe, Co and Ni bonded NbC cermets was investigated. Powder mixtures were fully densified by pressureless liquid-phase sintering for one hour at 1420 °C in vacuum. Microstructural and compositional analysis, as well as the elemental distribution in the dense cermets, was performed by electron probe microanalysis (EPMA) to assess the effect of the additions on the NbC grain growth, NbC morphology and metal binder composition, allowing correlation of the microstructure with the fracture toughness and hardness of the cermets. The substitution of WC with 40 wt.%NbC in WC-12 wt.%Co cemented carbides resulted in a significant improvement of hardness when adding 0.9-3.6 wt.%VC or Cr3C2 as WC grain growth inhibitors. Compared to pure NbC-Ni, a limited NbC grain growth and homogeneous grain size distribution were obtained upon adding secondary phase carbides or Al metal. WC and Mo2C significantly enhanced the hardness and toughness of NbC-Ni cermets. The Vickers hardness (HV 10) of 976 kg/mm2 and indentation toughness of 9.2 MPa m1/2 of a NbC-15 vol.%Ni could be increased to 1357 kg/mm2 and 10.1 MPa m1/2 respectively upon adding both 8.5 vol.%WC and 8.5 vol.%Mo2C. The addition of 25-50 at.%Al in Fe binder also increased the hardness of NbC-Ni/Fe cermets, but with decreased toughness. The maximum hardness of the investigated cermets was obtained for a 40 wt.%NbC substituted WC-12 wt.%Co cemented carbide, exhibiting a Vickers hardness of 1697 kg/mm2 and toughness of 7.8 MPa m1/2, whereas the WC and Mo2C added NbC-Ni cermets exhibited the optimum combination of hardness and fracture toughness.status: publishe