Effects of Boron Addition on the Microstructure and Mechanical Properties of (Ti,Ta)(C,N)-Co Based Cermets

In this work, a titanium–tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i.e., (Ti,Ta)B2 and (Ti,Ta)3B4, was observed. Moreover, the nature of the binder was also modified, from the (Ti,Ta)Co2 brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti,Ta)Co3 and -Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets.Fondo Europeo de Desarrollo Regional MAT2014-52407-

Kinetics of high-temperature oxidation of (Ti,Ta)(CN)-based cermets

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.Gobierno de España European Regional Development MAT2011- 2298

High temperature oxidation resistance of (Ti,Ta)(C,N)-based cermets

Cermets based on titanium–tantalum carbonitride were oxidized in static air between 800 °C and 1100 °C for 48 h. The thermogravimetric and microstructural study showed an outstanding reduction in the oxidation of more than 90% when the Ta content was increased. In cermets with low Ta content, the formation of a thin CoO/Co3O4 outer layer tends to disappear by reacting with the underlying rutile phase, which emerges at the surface. However, in cermets with higher Ta content, the formation of an external titanate layer, observed even at a low temperature, appears to prevent the oxygen diffusion and the oxidation progressionGobierno de España European Regional Development MAT2011- 2298

Liquid-phase sintering of Ti(C,N)-based cermets. the effects of binder nature and content on the solubility and wettability of hard ceramic phases

Different commercial TiC-TiN/Co/Ni mixtures were used as raw materials for Ti(C,N) cermets, and the effects of the sintering parameters (binder content, binder nature, sintering time and additives) on the final hard ceramic phase were studied at the sintering temperature of 1400 °C. When Co is used as the binder medium, it is possible to completely convert the starting commercial TiC-TiN mixture into TiCxN1-x. When Ni is used, which exhibits lower solubilising capacity than Co, the total conversion can never be reached and the metallurgical reactions between TiC and TiN during the liquid-phase sintering are more dependent on the sintering time than on the binder content. However, the use of Co-Ni mixtures, showing a synergic effect between the wettability capacity of Ni and the solubilising capacity of Co, enhances the metallurgical reactions at short sintering times. © 2013 Elsevier B.V. All rights reserved.Gobierno de España No. MAT2011- 2298

Characterization and Monitoring of Titanium Bone Implants with Impedance Spectroscopy

Porous titanium is a metallic biomaterial with good properties for the clinical repair of cortical bone tissue, although the presence of pores can compromise its mechanical behavior and clinical use. It is therefore necessary to characterize the implant pore size and distribution in a suitable way. In this work, we explore the new use of electrical impedance spectroscopy for the characterization and monitoring of titanium bone implants. Electrical impedance spectroscopy has been used as a non-invasive route to characterize the volumetric porosity percentage (30%, 40%, 50% and 60%) and the range of pore size (100–200 and 355–500 mm) of porous titanium samples obtained with the space-holder technique. Impedance spectroscopy is proved to be an appropriate technique to characterize the level of porosity of the titanium samples and pore size, in an affordable and non-invasive way. The technique could also be used in smart implants to detect changes in the service life of the material, such as the appearance of fractures, the adhesion of osteoblasts and bacteria, or the formation of bone tissue

Development of multicomponent-multiphase materials based on (Ti, Ta, Nb)CxN1-x carbonitride solid solutions

A set of powdered cermets based on (Ti,Ta,Nb)C xN 1-x carbonitride solid solutions were synthesized from mixtures of elemental powders by a mechanically induced self-sustaining reaction (MSR) method and subsequently sintered using a pressureless method. Differing nominal compositions of the hard phase were used, and the nature of the metallic-binder phase (Co, Ni, or Co-Ni) was varied. For comparative purposes, the design of the material was performed using two different synthesis pathways. The composition and microstructure of the ceramic and binder phases before and after sintering were analyzed and related to the microhardness of the material, which was found to increase with increasing contiguity of the hard phase and with decreasing particle size.The samples synthesized in one step (SERIES 2) showed higher microhardness and a more homogeneous microstructure with smaller particle size of the hard phase due to the presence of Ti, Ta, and Nb in the molten binder that hindered ceramic growth during liquid phase sinteringGobierno de España No. MAT2010- 1704

Development of a novel fcc structure for an amorphous-nanocrystalline Ti-33Nb-4Mn (at.%) ternary alloy

[EN] In this work, a novel amorphous-nanocrystalline titanium-niobium-manganese solid solution ternary alloy with a Ti-33Nb-4Mn (at.%) nominal composition was developed by a High-Energy Mechanical Alloying. Nb and Mn were added to the elemental Ti as a beta-phase (bcc) stabilizer and an amorphization promoter, respectively. The system evolved from the elemental Ti, Nb and Mn raw materials to a body centred cubic (bcc) TiNbMn alloy and, finally, to the formation of an original and stable face centred cubic (fcc) nanocrystalline TiNbMn alloy, not reported until now, at short milling time (20 h). This alloy remains invariant until 120 h. In turn, the partial amorphization of the system occurs and increases until at intermediate milling time (80 h). The production of both original fcc and the amorphous TiNbMn alloy may be beneficial for reducing the Young's modulus and improving the mechanical strength pursued for the Ti alloy. The optimal milling time respect to the amorphization, nanocrystalline size and Fe mount from milling media was 60 h and 80 h (TiNbMn60h and TiNbMn80h), with > 50 wt% of an amorphous phase and a crystalline domain size of approximately 5 nm.This work was supported under postdoctoral grant no. 3150060, which is financed by the FONDECYT fund (Government of Chile).Chicardi, E.; García-Garrido, C.; Sayagués, M.; Torres, Y.; Amigó, V.; Aguilar, C. (2018). Development of a novel fcc structure for an amorphous-nanocrystalline Ti-33Nb-4Mn (at.%) ternary alloy. Materials Characterization. 135:46-56. https://doi.org/10.1016/j.matchar.2017.11.021S465613

TiTaCN-Co cermets prepared by mechanochemical technique: microstructure and mechanical properties

Microstructure and mechanical characterization of (Ti,Ta)(C,N)-Co based solid solution cermets prepared by two mechanochemical synthesis processes (one- and two-step milling) and a pressureless sintering in protective helium atmosphere. Materials with composition of TixTa1- xC0.5N0.5-20%Co with two different Ti/Ta ratios (x = 0.9 and x = 0.95) were developed to prepare four groups of experimental materials. Microstructures were observed using confocal microscopy and grain size was evaluated using image analysis. Mechanical testing was carried out using nanoindentation equipment and nanohardness and indentation Young´s modulus were obtained. Mechanical properties of individual phases were measured using single load/unload method with 20 mN maximum load (40 mN/min loading rate and maximum 10 s holding time for each indent). Mechanical properties of each material as a bulk were obtained also by single load/unload method with 300 mN maximum load (600 mN/min loading rate and maximum 10 s holding time). The resulting mechanical properties were comparable to that of typical industrial hardmetal cermets. Two-step milling resulted in finer microstructure but a wider range of grain size distribution. No significant dependence between mechanical properties and number of milling steps was found. However, the materials with higher amount of Ta showed slightly higher indentation elasticity modulusConCer APVV-0108-1

Influence of the Test Configuration and Temperature on the Mechanical Behaviour of WC-Co

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths ( Co), was studied. The mechanical strength was measured at 600º C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of theWeibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600ºC due to oxidation phenomena, but higherWeibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.Junta de Andalucía P12-TEP-262

Inverse core-rim microstructure in (Ti,Ta)(C,N)-based cermets developed by a mechanically induced self-sustaining reaction

Cermets with a nominal composition (Ti 0.8Ta 0.2C 0.5N 0.5- 20 wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400 °C and 1600 °C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core-rim structure and a Ti-Ta-Co intermetallic phase that acted as the bindeGobierno de España No. MAT2010-1704