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:
AFINIDAD
ISSN:
0001-9704
Año:
2023
Vol.:
80
N°:
598
Págs.:
99 - 110
This article shows the results of solubility tests of keratin not only in basic media, close to the isoelec-tric point, but also in acidic media in the presence of different salts such as sodium and potassium halides, as well as several alkaline chlorides. The salt`s effect on the solubility of keratin or keratoses is described in terms of the law of matching water affinity, based on the distinct tendency of ions towards hydration. The application of this principle is focused on explaining the interaction`s competitiveness between inorganic salts` ions and ionized groups of keratin amino acids.
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.
Revista:
JOURNAL OF ALLOYS AND COMPOUNDS
ISSN:
0925-8388
Año:
2022
Vol.:
890
Págs.:
161631
Hot Isostatic Pressing (HIP) is a well-known technique that lately is gaining more interest because of its growing involvement in the Additive and Near-Net Shape manufacturing fields. When HIP is used for near net-shape manufacturing, the raw gas atomized powders assume the uttermost importance, and special attention should be given to their quality and characteristics. Based on this statement, the powder should be sieved directly after production to select only those that best suit the HIP process. Typically, a broad Particle Size Distribution is indicated for HIP purposes and looks economically advisable because it leads to a higher yield. Despite this, if the PSD is not strictly controlled, particles with high Oxygen content or chemical inhomogeneity could enter the production chain, leading to compacted components with insufficient mechanical properties. In this paper, Nickel-based superalloy Astroloy particles were assessed in depth both at their surface and in the core, dividing them into sub-batches via mechanical sieving. This procedure evidenced which contribution was brought to the final raw material by each sub-batch. Furthermore, physical properties such as flowability and tap density were studied as a function of the PSD. Next, a complete morphological assessment was conducted to understand the possible defects of each sub-batch better. Similarly, every particle group was chemically studied to determine the Oxygen, Carbon, Nitrogen, and Hydrogen content of each sub-batch. Micro and nano indentations combined with EBSD were used to understand how the particle size may affect the mechanical properties of the powders during the Hot Isostatic pressing. Furthermore, EDS and XRD analysis were used to thoroughly understand how Ti segregation starts forming and what effects are likely to develop. Based on these investigations, it was possible to rationally identify the upper and lower boundary for particle PSD without excessively limiting the overall process yield. (c) 2021 Elsevier B.V. All rights reserved.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2022
Vol.:
102
Págs.:
105719
The liquid phase formation temperatures of the quinary system W-C-Co-Fe-Ni with a ratio of Fe:Co:Ni = 40:20:40 were determined by means of DSC analysis. Besides, the experimental C-window of this system with a binder content of 14.3 +/- 2 wt% is accurately defined. Based on the experimental results, a thermodynamic modelling is carried out using the CALPHAD approach. Temperature-composition sections of the W-C-Co-Fe-Ni system with different binder contents are calculated to verify the rationality of the present modelling. There is a good correlation between the experimental and calculated results showing that the experimental data can be well reproduced by the present modelling.
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 °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:
POLYMER CHEMISTRY
ISSN:
1759-9954
Año:
2019
Vol.:
10
N°:
42
Págs.:
5726-5736
In this work, two novel polymeric semiconductors (D2 and D3), with perfluorinated side chains in their backbone, were developed. Moreover, a novel small molecule (D1), with a similar structure to polymers D2 and D3, was also designed for comparison purposes. Compounds D1-D3 were successfully synthesized, completely characterized and used as additives in perovskite solar cells (PSCs). The novel materials contain 26 fluorine atoms per unit, which is the largest amount of fluorine atoms reported for additives in PSCs. In this regard, D1-D3 were incorporated into the perovskite layer as additives and their effect on the film formation, stability and performance of PSCs was studied. As a result, D1-D3-based devices showed very good performances comparable to devices fabricated without additives and an increased stability. Thus, D1- and D2-fabricated devices retained 94 and 85% of their initial power, respectively, after 80 min under a bias, while the reference devices broke down completely. These results illustrate the extraordinary protective action of the perfluorinated polymers against humidity and oxygen, even at a low concentration of 2 mg ml(-1) used in our experiments.
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.
