ABSTRACT The present work is a continuation of the research carried out in a previous work, with the aim of improving the production of Ti35Nb alloy by reducing the particle size of Ti (from 50–149 Μm to < 53 Μm) and Nb (from 31–500 Μm to < 62 Μm) powders. Micro (MI) and Macroporous (MA) Ti35Nb alloy samples were processed by powder metallurgy. Ammonium bicarbonate (AB) was utilized as pore former additive for processing MA samples. The powders were mixed, uniaxially pressed and then sintered at 1300 ºC for 2 hours under argon atmosphere. The samples were characterized by SEM/EDS, XRD, profilometry, and Vickers hardness test. The porosity levels were determined by geometric method, Archimedes’ principle and quantitative metallographic analysis. The results showed that the processing parameters used in this work successfully produced porous Ti35Nb alloys with completely stabilized β-Ti phase, indicating an enhancement in the methodology when compared with those reported in previous work. Smaller particle sizes influenced positively on the chemical-physical properties of MI and MA samples, since they demonstrated an improvement in the their characteristics, such as: more homogeneous microstructure; better particle consolidation; homogeneous elemental distribution with no relevant chemical contamination; porosity values in accordance with literature; presence of low amounts of titanium oxides on the surfaces which can improve the biocompatibility features; suitable surface roughness parameters for bone implant applications and favouring adhesion of bioceramic coatings; more uniform microhardness values for both samples which make the material with a further predictable mechanical behavior.

Abstract In this work, CoCrMo-base alloys specimens were produced by additive manufacturing using selective laser melting (SLM) as well as CAD/CAM milling. For SLM specimens, spherical particles were laser processed at 1320°C under argon atmosphere and submitted to thermal stress relieving at 750°C–45min. Specimens from CoCrMo blocks were milled by CAD/CAM machining and sintered at 1300°C–60min. The materials from both techniques were characterized by relative density, dilatometry, SEM/BSE, OM and XRD analysis. The mechanical properties were determined by Vickers hardness and tensile tests. The specimens from both techniques exhibited single phase γCo (FCC) and CTE of 14 x10-6 °C-1. Relative density of 95.4%/ 85.6%, hardness values near 400HV/ 350HV and UTS of 905MPa/ 780MPa were measured for SLM and CAD/CAM specimens, respectively. Higher relative density is the main factor for increased mechanical properties of SLM specimens. On the other hand, both SLM and CAD/CAM specimens present properties in accordance with ISO-22674 recommendations, compatible with dental applications such as bridges containing four or more elements as well as fully dense pontics.

The development of β-metastable titanium alloys that combine low Young’s modulus, good mechanical properties, corrosion resistance and biocompatibility has attracted industry interest. This type of alloy is an alternative to commercial alloys such as Ti-6Al-4V, avoiding the cytotoxic effect that occurs with Al and V in the human body in the manufactured orthopedic prostheses. In this scenario, the present work aims to characterize the effect of Nb concentration in the properties of Ti alloys based on the Ti-12Mo-xNb stoichiometry (x = 0, 3, 8, 13, 17 and 20). All alloys were produced by arc melting with non-consumable tungsten electrode in an argon atmosphere and the ingots were characterized by x-ray diffraction (XRD), optical microscopy (OM), Vickers microhardness and Young’s modulus was measured by impulse excitation and density was measured using the Archimedes’ principle. The Ti-12Mo alloy and the Ti-12Mo-20Nb alloy showed the lowest Young’s modulus. The best hardness/modulus was found for the Ti-12Mo-3Nb alloy. All the alloys studied in this work showed hardness/modulus ratio above the traditional Ti-6Al- 4V alloy (2.85), presented great potential for the biomedical application.

In this work a re-investigation of the solubility limits of the (Nb), Nb3Al, Nb2Al and the Nb-rich side of the NbAl3 phases on the Nb-Al system is presented. Alloys in the binary fields ((Nb)+Nb3Al, Nb3Al+Nb2Al and Nb2Al+NbAl3) were arc-melted, and then equilibrated at 1000, 1200 and 1400 ºC. The phases were confirmed via X-ray powder diffractometry, and their compositions were determined via EPMA measurements. The results showed agreement with the literature concerning the solubility limits of (Nb), Nb3Al and NbAl3 phases, while important differences in the values were found for the Nb2Al phase. In addition, the lattice parameters of the Nb2Al phase were determined via Rietveld refinement. This new set of more accurate experimental information indicates that a thermodynamic reassessment is necessary to precisely describe this system.

Boron added steels in quenched and tempered condition have been widely used in applications where good mechanical properties and low cost are required. In this study, impact resistance of DIN 39MnCrB6-2 steel grade was investigated due to its criticality in automotive components. Metastable phase diagrams were built to guide heat treatments. The influence heat treatment parameters and initial microstructure were evaluated. Impact toughness results showed low absorbed energy (<30J) for all tempering temperatures. CVN impact toughness was substantially increased in samples submitted to solution treatment. Microscopic observation showed coarse borocarbides in surface fracture of Q&T samples. It was concluded that the formation of borocarbides is inherent in boron steels and their coarse morphology should be avoided in order to reduce embrittlement.

CA6NM steel is widely used in the manufacture of hydraulic turbines metallic parts, due to its resistance to corrosion and cavitation damage, combined with good weldability and fatigue properties. However, welding of this type of steel is complex and to ensure a minimum residual stress after welding it is necessary perform a post welding heat treatment (PWHT) of the part. This study aims to analyze the effect of a PWHT on the microstructure and mechanical properties of CA6NM steel weld joint produced by the FCAW process and compare it with the characteristics of an as-welded joint. A martensitic microstructure has been present in both materials. However, the PWHT material has shown finely dispersed retained austenite, in an amount near 10 vol.%. Vickers microhardness values of all regions of PWHT welded joint present lower hardness values compared to those of the as-welded joint. Despite nearly identical toughness values of the weld metal from AW and PWHT samples, results of fracture analysis have shown distinct features in appearance of the fractures.

Metastable β-type Ti alloys with non-toxic addition elements such as Mo, Zr, Sn, Ta and Nb were developed as an alternative to the widely used Ti-6Al-4V alloy for biomedical applications. These alloys possess enhanced biocompatibility and reduced elastic modulus in comparison with Ti-6Al-4V. Moreover, for orthopedic implants, low Young's modulus is required in order to avoid the stress shielding phenomenon. This study analyzes the microstructure and mechanical properties of a new Ti-12Mo-8Nb alloy after hot swaging, annealing at 950 ºC for 1h and water quenching. The alloy was characterized by X-ray diffraction, optical microscopy and transmission electron microscopy. Tensile tests were performed at room temperature. Young's modulus and hardness values were also measured. The structural characterization reveals a metastable β structure containing only a small amount of α and ω phases. Exhibiting a lower Young's modulus than Ti-6Al-4V and other previously studied Ti-Mo-Nb alloys, the Ti-12Mo-8Nb alloy can be a promising alternative for orthopedic application.

Alloys containing Me-Si-B (Me - Refractory Metal) are of great interest for high temperature structural applications and accurate knowledge of its low order systems (binaries and ternaries) is important to predict the phase relations in the multicomponent alloys. Recent reevaluations of binaries containing Me-Si found out that the accuracy of the description of this type of systems could be improved. Knowing this, a reevaluation of the invariant reactions in the V-Si system via microstructural characterization of as-cast alloys is presented. Alloys of key compositions were prepared by arc melting pure V (min. 99.75%) and Si (min. 99.998%) and characterized via scanning electron microscopy (SEM) using back-scattered electron (BSE) mode, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results of this study confirmed the solid phases, the nature of the invariant reactions and determined new compositions for the liquid participating in certain invariant reactions.

β-metastable titanium alloys with high strength to Young’s modulus ratio have been developed by different authors aiming their use as biomaterials for hard tissue replacement. However, it is not easy to combine low elastic modulus with high mechanical strength. In this work, a β-Ti alloy (Ti-10Mo-20Nb) was produced by arc-melting, then homogenized, cold swaged and aged in order to obtain fine α-Ti precipitates in a β-Ti matrix. The microstructures were characterized by transmission electron microscopy and X-ray diffraction. Mechanical properties characterization was based on Vickers microhardness tests and Young’s modulus measurements. The cold swaged material subjected to an ageing treatment at 500 °C for 4 h showed the highest hardness/ Young’s modulus ratio, associated to very fine α phase precipitates in a β-Ti matrix.

Beta titanium alloys were developed for biomedical applications due to the combination of its mechanical properties including low elasticity modulus, high strength, fatigue resistance, good ductility and with excellent corrosion resistance. With this perspective a metastable beta titanium alloy Ti-12Mo-13Nb was developed with the replacement of both vanadium and aluminum from the traditional alloy Ti-6Al-4V. This paper presents the microstructure, mechanical properties of the Ti-12Mo-13Nb hot swaged and aged at 500 °C for 24 h under high vacuum and then water quenched. The alloy structure was characterized by X-ray diffraction and transmission electron microscopy. Tensile tests were carried out at room temperature. The results show a microstructure consisting of a fine dispersed α phase in a β matrix and good mechanical properties including low elastic modulus. The results indicate that Ti-12Mo-13Nb alloy can be a promising alternative for biomedical application.

The focus of this work was to determine microstructural features in commercial Ni-Cr alloys which could be used to identify indirectly the presence of beryllium. Thus, eight commercial alloys were characterized by chemical analysis, thermal analysis, X-ray diffraction (XRD), scanning electron microscopy - back-scattered electron images (SEM/BSE), energy-dispersive spectroscopy (EDS). The results indicate that the presence of beryllium can be inferred from microstructural analysis via XRD and SEM/BSE. The X-ray diffractograms of the beryllium-containing alloys showed clearly the existence of the NiBe intermetallic phase. SEM/BSE images of these alloys show a very characteristic eutectic microstructure which also indicates the presence of this element. These characteristics are not observed in the beryllium-free alloys.

A partial isothermal section (Ti-TiSi2-TiB2 region) of the ternary Ti-Si-B system at 1250 ° C was determined from heat-treated alloys prepared via arc melting. Microstructural characterization has been carried out through scanning electron microscopy (SEM), x-ray diffraction (xRD) and wavelength dispersive spectrometry (WDS). The results have shown the stability of the near stoichiometric Ti6Si2B phase and a negligible solubility of boron in the Ti-silicides as well as of Si in the Ti-borides. The following three-phase equilibria have been observed in the Ti- TiSi2-TiB2 region: Ti ss+TiB+Ti6Si2B, Ti ss+Ti6Si2B+Ti5Si3, Ti5Si3+Ti6Si2B+TiB, Ti5Si3+TiB+Ti3B4, Ti5Si3+Ti3B4+TiB2, Ti5Si3+TiB2+Ti5Si4, Ti5Si4+TiB2+TiSi and TiSi+TiB2+TiSi2.

An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8%) and boron (minimum 99.5%) slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.

This study has investigated the niobium (Nb) additions effect on both microstructure and heat-treated Ti-10Mo-xNb (x = 3, 6 and 9) alloys mechanical properties. The microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy. The mechanical characterization was carried out by Vickers microhardness test and Young's modulus measurements. The outcomes show that the addition of Nb in alloys decreased the proportion of ω and α' phases. The Ti-10Mo-3Nb alloy presented the best hardness and elastic modulus combination among the three developed alloys and also with respect to Ti-6Al-4V alloy and commercially pure Ti.