Revistas
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2024
Vol.:
119
Págs.:
106552 - *
TiC-FeCrMo cermets have been obtained in fully dense form by Sinter HIP at 1400 degrees C. Significant microstructural changes have been observed in these materials for relatively small variations in their carbon content after sintering. In the cermets with higher carbon content Cr-rich likely M7C3 carbides are observed to precipitate at the (Ti1-x,Mo-x)(y)C-z - metal interface. In addition, these cermets present a significant amount of retained austenite as part of the metal matrix. No retained austenite and many fewer M7C3 carbides are found in alloys with a reduction of 0.2 wt% in the total C content. Continuous cooling diagrams have been obtained from an austenitizing temperature of 950 degrees C. Hardness increases by 30% with respect to that of as sintered specimens after cooling at 1 degrees C/s confirming that these TiC-FeCrMo cermets are suitable for hardening by air-quenching. At this cooling rate, it is observed that the relatively small carbon changes mentioned before have a significant effect on the bainitic transformation, displacing its onset to higher temperatures as the C content is reduced. Slower cooling rates result in complex microstructures, in which, in addition to martensite, ferritic bainite, M7C3 and M23C6 carbides are also found. Microstructure and hardness of TiC-FeCrMo materials can be modified by the use of standard heat treatments to obtain a wide variety of mechanical properties suitable for certain hot rolling applications.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2024
Vol.:
118
Págs.:
106442 - *
Laser induced periodic surface structures (LIPSS) have been produced at the surface of a WC-Co turning insert by femtosecond pulsed laser ablation. Wavelengths of approx. 500 nm have been obtained with a 1030 nm incident radiation and with a spot size of 30 mu m. No thermal damage is induced by following this procedure, although a slight surface stress relaxation is detected as fluence increases. The higher material removal needed for chamfering operations requires accumulated fluences over 1 kJ/cm2. At lower energy densities, material removal is not completed. If fluence is increased by reducing the laser spot size, material removal is also inefficient since signicant amount of debris is accumulated on the irradiated areas. Best chamfering strategy involves the combination of relatively large spot sizes and fluences. Form factors (Kappa) of the chamfered cutting edges range from 4 to 10 although the laser is oriented at 45 degrees of the rake face. Lower K values can be obtained by adjusting the laser focus along the machining process.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2023
Vol.:
110
Págs.:
105994
Shrinkage, liquid formation and mass losses of WC-19 vol% FeNiCoCr alloys during sintering have been inves-tigated in compositions either with coarse or submicron WC powders. Mass losses detected by thermogravimetry are compatible with carbothermal reduction of the different oxides present in the powder mixtures. Hardness and fracture toughness of materials based on submicron WC powders are within tolerances of those reported for WC -Co materials with similar microstructures. However, fracture strength is approx. 25% lower.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2023
Vol.:
114
Págs.:
106262
TiC-Fe-Cr3C2-Mo and TiC-Fe-Cr3C2-Mo2C powder mixtures have been consolidated by liquid phase sintering under different vacuum conditions. Densification is improved by reducing the pressure of the furnace chamber from 10-2 to 10-5 mbar. This is due to a more efficient carbothermal reduction of powder oxides, which en-hances the diffusion phenomena needed for good wetting of ceramic grains by the liquid phase. Cermets based on fine Mo2C powders exhibit higher densities than those based on coarse Mo additions. This is associated to higher C losses after sintering suggesting that diffusion kinetics and removal of oxide layers from starting powders are key for successful liquid phase sintering of TiC-Fe-Cr-Mo cermets. Ar injection in the sintering chamber at 1300 degrees C, used for avoiding the evaporation of the binder phase, leads to residual porosity due to Ar entrapment in pores open to the sintering atmosphere. Compositional gradients found at the surface of cermets sintered at 10-2 mbar are not present at 10-5 mbar. This is likely associated to the slight surface oxidation once the close porosity state is reached. The hardness of TiC-Fe-Cr-Mo cermets can be modified by applying standard heat treatments, leading to values in the range of those used for certain hot rolling applications.
Autores:
Guzmán, D. (Autor de correspondencia); González, F.; Muranda, D.; et al.
Revista:
MATERIALS
ISSN:
1996-1944
Año:
2023
Vol.:
16
N°:
10
Págs.:
3618
This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Lambda g-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO2-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 +/- 1.5% IACS). This fact would be related to the reaction of Zn2SnO4's formation on the material's surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2022
Vol.:
109
Págs.:
105965
Ultrahard WB4-B and WB4-TaB2 based materials have been obtained by applying glass encapsulated HIPing to mixtures comprised of WB4 and free boron with and without metallic tantalum additions. Porosity removal is more efficient in the alloy containing metallic tantalum, achieving near full density at temperatures 300 ? lower than those reported so far for these materials. The WB4 phase is better stabilished by HIPing at 1350 ? than at 1100 ?. This is due to the formation of TaB2, which, at 1100 ?, likely occurs by direct reaction between metallic Ta and the surrounding WB4 particles. At 1350 ?, diffusion is enhanced and the reaction between free B and Ta particles becomes more probable. The hardness of hipped specimens ranges from 43 GPa to 24 GPa depending on the applied load. K-1c values calculated from indentation cracks reach 5.6 MPa.m(1/2), assuming Palmqvist type crack shape.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2022
Vol.:
103
Págs.:
105748
Hardness and fracture strength of WC-Ni-Co-Cr-Ti-Al cemented carbides have been measured at room temperature in as-HIPed and solution-aged conditions. These treatments are applied to modify the size of gamma prime precipitates, which are intrinsically formed within the metallic binder of these ceramic-metal composites during the sintering process. Compositions containing approx. 28-29 vol% metal content exhibit hardness values in the range of those reported for similar grades of WC-Co hardmetals. Optimized aluminum additions lead to materials with fracture strength values only 15% lower than those reported for the same WC-Co commercial references. These results suggest gamma prime precipitation hardening as a potential strategy for improving the performance of WC-Co materials at high temperatures. Regarding Fe-Ni-Co-Cr alloys are potential candidates for partial substitution of Co content in WC-based hardmetals. It has been investigated WC coarse grade with 15 wt%(FeNiCoCr). The Cr content has been adjusted in order to avoid the precipitation of M7C3 carbides. Within the corresponding carbon windows, fracture strength values range from 2.8 GPa to 3.0 GPa. These values are within the range of standard WC-Co grades with similar binder contents and WC grain sizes.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2021
Vol.:
95
Págs.:
105427
Cemented carbides processed from WC-Ni-Co-Cr3C2-TiAl3 powder mixtures by HIP after sintering present a homogeneous precipitation of gamma prime in their metallic binder phases. Other reaction products include alumina precipitates and (Ti-x,W1-x)C mixed carbides. The formation of these phases is consistent with the highly exothermic reactions detected by DSC during the heating ramp of the sintering cycle. The amount of alumina and gamma prime phases present in the sintered materials depends on the oxygen content of the powder mixtures. Refinement of gamma prime precipitates depends critically on the cooling rate after HIPing. Nanoindentation experiments have confirmed the presence of age hardening effects of samples which were previously solution treated. As expected, gamma prime precipitation is induced at lower temperatures in compositions with higher Al contents in the binder phase.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2020
Vol.:
87
Págs.:
105164
The sintering behaviour of cemented carbides based on WC-ZrC-Co-Cr3C2 powder mixtures have been analyzed by dilatometric and calorimetric methods for different cobalt contents and WC/ZrC ratios. As expected, powder oxide reduction in these compositions is mainly of carbothermic nature. However, depending on the milling conditions, some highly stable Zr-rich oxides are retained in the binder phase after sintering. Hot isostatic pressing (HIP) cycles have been successfully applied for closing residual porosity after vacuum sintering. For a fixed amount of binder phase and a WC/ZrC ratio, the hardness of these materials depends on the amount of residual porosity and WC grain growth control. The best combination of hardness and toughness is found for alloys with 8 wt%Co and WC/ZrC wt. ratios of 6.46. HIP treatments induce the formation of a compact and well adhered layer mainly comprised of Zr oxides and WC grains. The cobalt binder phase migrates from this layer towards the sample bulk likely due to the loss of wettability on these Zr rich oxides. Hot hardness is higher for the alloy with higher WC/ZrC ratio suggesting that this property depends on both the volume fraction of (ZrxW1-x)C and WC phases and their degree of contiguity.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
WC-Fe-Ni-Co-Cr cemented carbides have been obtained by liquid phase sintering from WC-Fe-Ni-Co-Cr3C2 powder mixtures. Taking the 40wt%Fe-40wt%Ni-20wt.%Co alloy as a reference, new binder phases has been prepared by introducing controlled amounts of Cr and C, via Cr3C2 and C black powders respectively. As described for WC-Co-Cr materials, Cr additions are observed to reduce the eutectic temperatures of the WC-Fe-Ni-Co system. First liquids detected on heating exhibit wide temperature melting ranges, which become narrower and are displaced to higher temperatures on repeated heating and cooling cycles. Apart from the decarburization associated to the carbothermal reduction of powder oxides, this phenomenon could be also associated to the homogeneization of the chemical composition of these multicomponent binder phases, which is faster as C content decreases. Correlation between experimental melting and solidification temperature ranges and those predicted by Thermocalc (R) is better as Cr content increases. Experimental C windows, defined in this work by the absence of free C or. phases, are located at C contents higher than those estimated by Thermocalc (R). Although the 40wt.%Fe-40wt.%Ni-20wt.%Co alloy is austenitc, BCC phases are partially stabilized at low C and high Cr contents. Although these compositions are free from. phases or free C, a precipitation of Cr-rich carbides is found at the WC-metal interface. These precipitates are not observed in the alloy with 0.75 wt% Cr (i.e. 5 wt% of the nominal metal content) and 5.39 wt%C. This C content is 0.17 wt% higher than that predicted for precipitation of M7C3.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2020
Vol.:
88
Págs.:
105202
The binder phase of WC based cemented carbides has been alloyed by adding two different aluminium compounds, AlN and TiAl3, to mixtures comprised of WC, Ni, Co and Cr3C2 powders. A more efficient alloying effect is obtained by TiAl3 additions likely due to its higher dissolution rate during liquid phase sintering. Shrinkage and melting phenomena are strongly affected by the energy of the milling process and the amount of metallic additions. The use of higher milling rotation speed induces higher oxidation of the powder mixtures and the subsequent formation of a higher volume fraction of alumina particles after sintering. Densification and WC grain growth are hindered by increasing the Al addition. Thus, full densification of alloys with higher Al additions require the use of HIP after standard vacuum sintering cycles. As-HIPed WC-Ni-Co-Cr-Al-Ti samples present a binder phase with precipitation of gamma prime similar to that found in as-cast Ni superalloys. The size, volume fraction and morphology of these precipitates has been modified by applying a standard solution treatment (1150 degrees C-2 h) followed by fast air cooling and subsequent aging at 600 degrees C and different dwelling times. Age hardening effects have been confirmed in the composition consisting of WC-12 wt% Co-12 wt% Ni-1.7 wt% Cr3C2-5 wt% TiAl3 after 100 h at this temperature.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2020
Vol.:
88
Págs.:
105202
The binder phase of WC based cemented carbides has been alloyed by adding two different aluminium compounds, AlN and TiAl3, to mixtures comprised of WC, Ni, Co and Cr3C2 powders. A more efficient alloying effect is obtained by TiAl3 additions likely due to its higher dissolution rate during liquid phase sintering. Shrinkage and melting phenomena are strongly affected by the energy of the milling process and the amount of metallic additions. The use of higher milling rotation speed induces higher oxidation of the powder mixtures and the subsequent formation of a higher volume fraction of alumina particles after sintering. Densification and WC grain growth are hindered by increasing the Al addition. Thus, full densification of alloys with higher Al additions require the use of HIP after standard vacuum sintering cycles. As-HIPed WC-Ni-Co-Cr-Al-Ti samples present a binder phase with precipitation of gamma prime similar to that found in as-cast Ni superalloys. The size, volume fraction and morphology of these precipitates has been modified by applying a standard solution treatment (1150 °C-2 h) followed by fast air cooling and subsequent aging at 600 °C and different dwelling times. Age hardening effects have been confirmed in the composition consisting of WC-12 wt% Co-12 wt% Ni-1.7 wt% Cr3C2-5 wt% TiAl3 after 100 h at this temperature.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2018
Vol.:
72
Págs.:
89 - 96
The damage induced by thermal shock in WC-43 vol%Co and WC-40.7 vol%Co-Ni-Cr cemented carbide grades has been analyzed by measuring the loss of fracture strength after repeated water quenching experiments from temperatures ranging from 400 °C to 700 °C. At 500 °C and lower temperatures, damage is more severe for the WC-Co-Ni-Cr alloy, this being associated to its lower toughness compared to that of the WC-Co grade. However, the opposite is found when the temperature step used in quenching experiments reaches 700 °C. In this case, the relative loss of strength is much higher for the WC-Co material. Microstructural analyses confirm that this phenomenon is likely associated to the precipitation of very fine W-rich intermetallics in the binder phase of this alloy, which are not observed in the WC-Co-Ni-Cr grade. Toughness is critical since thermal shock damage is characterized by the formation of microcracks at distances ranging from 10 to 20 ¿m from the sample surface. These cracks are preferentially located at the WC-metal interfaces. Results obtained from cylindrical samples allow to separate microstructural damage from that induced by stress concentrators present in the prismatic ones.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2018
Vol.:
77
Págs.:
44 - 53
Cemented carbides with Ni-Co-Cr-Al-W binder phases have been obtained from WC-Ni-Co-Cr3C2-TiAl3 powder mixtures by using standard hardmetal processing routes. Dilatometric and DSC experiments confirm that melting events and shrinkage in these materials are shifted towards higher temperatures as the Al content increases. It is also shown that sintering in Argon is enhanced at very low Al levels (0.63 wt%), which is likely due to the efficient reduction of powder oxides via direct reaction with TiAl3. For higher Al additions, HIP treatments are needed in order to remove the residual porosity left after vacuum sintering. Microstructural characterization confirms that Al additions induce two types of precipitation phenomena in the metallic binder phase of these hardmetals: one consisting of very fine Al-rich oxides (product of the aforementioned powder oxide reduction) and the other comprising even finer gamma' type cuboids (similar to those found in Ni superalloys). As confirmed by TEM-EDS analyses, the binder phase of these cemented carbides is a multicomponent alloy incluiding Co, Ni, Cr, W and increasing amounts of Al as TiAl3 addition increases. About 0.5 wt% Al is lost to the powder oxides reduction process. TiAl3 additions have a significant hardening effect on WC-Ni-Co-Cr3C2 alloys. This is due to its effective role as WC grain growth inhibitor. Although, solution-aging treatments induce a finer and more homogeneous precipitation of the gamma' phase in these materials, their hardness is slighlty reduced if compared to that of as-HIPed samples.
Autores:
Guzman, D.; Muñoz, P.; Aguilar, C.; et al.
Revista:
APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING
ISSN:
0947-8396
Año:
2014
Vol.:
117
N°:
2
Págs.:
871 - 875
Nowadays, Ag-CdO alloys are widely used in electrical contact applications, because of their good electrical and thermal conductivity is as well as high resistance to arc erosion and contact welding. Considering the restricted use of Cd due to its toxicity, it is necessary to find a material that can replace those alloys. The objective of this work was to study the possibility of obtaining an Ag-ZnO alloy from an Ag-Zn solid solution powders by means of a mechanochemical method. The mechanochemical process was carried out in a SPEX 8000D mill, under air and with ethanol as a reaction agent. Based on the results obtained, it can be concluded that an Ag-ZnO alloy with a fine and uniform ZnO distribution in the Ag matrix can be obtained by applying the mechanochemical process for 25 h.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2012
Vol.:
548
Págs.:
189 - 194
This work studied the structural evolution of Cu-xMo (x = 5 and 8 wt.%) alloys processed by mechanical alloying using x-ray diffraction profiles, scanning electron microscopy, differential scanning calorimetric and microhardness. X-ray diffraction analysis was done using the modified Williamson-Hall and Warren-Averbach methods. These were used to determine structural properties, such as crystallite size, stacking fault probability and energy, dislocation density of metallic powder as a function of the amount of Mo and milling time. The main results obtained for both alloys were higher dislocation density and Vickers microhardness values were measured and crystallites sizes of around 10 nm were measured for both systems at 50 h of milling. Lattice defects increase the free energy and the free energy curves shift upwards, therefore the solubility limits change and Cu-Mo solid solution is formed. (C) 2012 Elsevier B.V. All rights reserved.