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.

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.

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.

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.

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.

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.

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.

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.

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.

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.