Ti6Al4V/Al2O3 vacuum brazed joints were successfully processed at 830 °C using Ag-Cu eutectic foil as filler alloy. Scanning electron microscopy and energy dispersive spectroscopy were used to characterize the brazed joints microstructure and chemical composition. Studies focusing the electrochemical behavior of the base Ti6Al4V alloy and of the brazed joints were performed in 3.5 wt.

Joining cemented carbides and steels is particularly challenging due to the very dissimilar thermal properties that lead to high residual stresses at the interface, where in addition, brittle phases can be formed. An effective carbide-steel joint can unleash the creation of multi-material parts for several applications, and in this sense, it is of utmost importance to develop efficient methods for their fabrication. This work proposes a novel approach, using the high fabrication freedom of laser powder bed fusion technology to additively manufacture 316L stainless steel on a WC-Co substrate, to obtain complex multi-material cutting tools, with dissimilar materials in different locations. Results showed a good bonding between materials, since a dense, well-defined, and capable of withstanding cutting forces interface was obtained. The 316L stainless steel hardness ranges from 238 HV to 302 HV, with a direct correlation being found between the energy density used during laser powder bed fusion and the obtained hardness. This approach was found effective to produce multi-material WC-Co/316L stainless steel cutting tools with good metallurgical bonding and mechanical strength, without the need of adding an interfacial material.

Ti6Al4V and Al 2 O 3 were successfully vacuum brazed at 980 °C using TiCuNi filler foil. The microstructure and the chemical composition of the interface were analysed by SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy), respectively. The hardness profile across the interface and the mechanical strength of joints were assessed by Vickers microhardness tests and shear tests, respectively. The fracture surfaces were analysed by SEM, EDS and XRD (X-ray diffraction). The corrosion behaviour of joints was evaluated by OCP (open circuit potential), potentiodynamic polarisation tests and EIS (electrochemical impedance spectroscopy). Brazing produced a layered interface, free of pores and cracks, essentially composed of α-Ti, Ti 2 (Cu,Ni) and Ti x O y . The shear strength of joints was 168 ± 13 MPa, and fracture occurred partially through the hardest zone of the interface (1261 HV 0.01 .), located in the vicinity of the Al 2 O 3 sample, and partially through the ceramic sample. The brazed joint did not significantly affect the corrosion behaviour of Ti6Al4V.

The joining of zirconia (ZrO2) to Ti6Al4V using Ag-Cu sputter-coated Ti brazing filler foil was investigated. Brazing experiments were performed at 900, 950, and 980 °C for 30 min under vacuum. The microstructural features of the brazed interfaces were evaluated by optical microscopy (OM) and by scanning electron microscopy (SEM). The chemical composition of the brazed interfaces was analyzed by energy dispersive X-ray spectroscopy (EDS). Room temperature shear tests and Vickers microhardness tests performed across the interfaces were used to evaluate the mechanical strength of the joints. Multilayered interfaces were produced for all brazing temperatures, consisting essentially in α-Ti + Ti2(Ag, Cu), TiAg. Joining to ZrO2 was promoted by the formation of a hard layer, reaching a maximum of 1715 HV0.01, possibly consisting mainly in α-Ti and Ti oxide(s). Joining to the Ti6Al4V was established by a layer composed of a mixture of α-Ti and Ti2(Ag, Cu). The highest shear strength (152 ± 4 MPa) was obtained for brazing at 980 °C and fracture of joints occurred partially across the interface, throughout the hardest layers formed close to ZrO2, and partially across the ceramic sample.

In this work, low volume reinforcement ex-situ Ti-B4C composites were produced using two different routes: conventional powder metallurgy (PM) and hot-pressing (HP). The effect of reinforcement phases and processing method on corrosion and tribocorrosion behaviour were studied. Composites processed by PM lost the typical passive behaviour of Ti matrix, while composites processed by HP presented similar behaviour to unreinforced Ti. Tribocorrosion tests showed that both composite groups presented two times decrease in corrosion kinetics under sliding compared to pure titanium. An antagonistic effect between wear and corrosion was observed for composites with at least two times decrease in wear volume compared to titanium. (C) 2021 Elsevier B.V. All rights reserved.

The properties of the joints are dictated by the nature, distribution, and morphology of the phases formed at the interface. The mechanical properties of brazed joints are well documented in the literature, contrarily to their electrochemical behaviour. Thus, the main objective of this study was to understand the influence of the phases formed at the interface on the corrosion behaviour of commercially pure Ti brazed joints, produced by using TiCuNi, eutectic AgCu, and Ag filler foils. The electrochemical behaviour of the Ti joints was accessed by open circuit potential and potentiodynamic polarization tests in phosphate buffer saline solution electrolyte at body temperature. Results showed that Ag-based fillers induced susceptibility to micro-galvanic corrosion between the Ag-rich and Ti phases formed at the interface and commercially pure Ti base metal. However, no significant differences were observed between the joint system and the base material when brazing with TiCuNi filler.

The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazing filler foil, was investigated. Brazing experiments were performed at 980 °C for 30 min in vacuum. The microstructure and chemical composition of the brazed interfaces were analyzed by scanning electron microscopy and by energy dispersive X-ray spectroscopy, respectively. A microstructural characterization of joints revealed that sound multilayered interfaces were produced using this novel brazing filler. Both interfaces are composed mainly of α-Ti, along with Ti2(Ag,Cu) and TiAg intermetallics. In the case of the brazing of γ-TiAl alloys, α2-Ti3Al and γ-TiAl intermetallics are also detected at the interface. Bonding to Al2O3 is promoted by the formation of a quite hard Ti-rich layer, which may reach a hardness up to 1872 HV 0.01 and is possibly composed of a mixture of α-Ti and Ti oxides. Hardness distribution maps indicate that no segregation of either soft or brittle phases occurs at the central regions of the interfaces or near the base Ti alloys. In addition, a smooth hardness transition was established between the interface of Al2O3 to either γ-TiAl or Ti6Al4V alloys.

Corrosion behavior of joined Ti-B4C composites was evaluated in 9 g/L NaCl solution using cyclic polarization and electrochemical impedance spectroscopy. Tribocorrosion behavior was investigated by sliding against an alumina ball under open-circuit potential and potentiodynamic polarization. The results showed that joining did not negatively affect the corrosion behavior of the composites. Regarding tribocorrosion, while joining did not significantly influence the coefficient of friction and total wear volume loss, it resulted in slightly increased electrochemical activity under sliding. These results showed that brazing may be considered as a simple and low-cost technique for joining Ti-B4C composites to be operated in tribocorrosive environments.

The Argemela microgranite is a late- to post-tectonic granite (305–300 Ma), and is an example of a late Variscan small intrusion of W-enriched granite with magmatic cassiterite, columbite and Li-micas. The occurrence of this type of magmatism is very rare in the European Variscan Belt. A quarry where this microgranite intrusion has been exploited for ceramic applications revealed the border of an aplite cross-cut by two types of quartz veinlets: type I with quartz, K-feldspar ± amblygonite; and type II with quartz and wolframite mineralization, thus allowing the study of a W-mineralization which is intimately associated with a highly-differentiated magmatic system. In this work, detailed mineralogical, geochemical and fluid inclusion studies are presented, in an attempt to reconstruct the P–T-x conditions responsible for different stages of fluid evolution. We have found magmatic and hydrothermal aqueous-carbonic fluids (H2O–CO2–CH4–N2–NaCl) associated with the late crystallization of the Argemela microgranite, and also responsible for the later formation of the two types of veinlets. The Argemela fluid system is characterized by an increase of CO2 in the volatile phase and a decrease in salinity throughout the transition from magmatic to hydrothermal stage. Most importantly, the late stages correspond to the period of tungsten deposition at pressures below 100 MPa.

Joining γ-TiAl alloy to Ni-based superalloy Hastelloy using Ag-Cu sputtered coated Ti foil as brazing filler was investigated in this study. Brazing experiments were performed at 900, 950, and 980 °C with a dwelling stage of 10 min in vacuum. The microstructure and the chemical composition of the resulting interfaces were analyzed by scanning electron microscopy (SEM) and by energy dispersive X-ray spectroscopy (EDS), respectively. Sound joints were produced after brazing at 980 °C, presenting a multilayered interface, consisting mainly of Ti-Al and Ti-Ni-Al intermetallics close to the γ-TiAl alloy, and of Ti-rich, Ti-Ni, and Cr-Ni-Mo rich phases near Hastelloy. The hardness of the interface, ranging from around 300 to 1100 HV0.01, is higher than both base materials, but no segregation of either Ag solid solution or coarse intermetallic particles was observed. Therefore, the developed brazing filler also avoids the need to perform post-brazing heat treatments that aim to eliminate detrimental extensive segregation of either soft phases or of hard and brittle compounds.

Across Europe, small scale deposits of critical materials and/or strategic elements, such as W, Li and Sn, are not viable to mine and process using the traditional large scale mining and processing technologies due to their geological characteristics. Project FAME (Flexible And Mobile Economic Processing Technologies, EC Horizon 2020 Grant Agreement No. 641650) was created in order to specifically address the technical and environmental challenges to the sustainable processing of low sulphide ores from pegmatites, greisens and skarns deposits. One of the deposits, Alvarrões-Gonçalo, is a Li pegmatite located at the Gonçalo pegmatite field (Central Portugal) that is being investigated on the scope of the concerned project. Currently, the pegmatites are only being exploited for ceramics, aggregates and ornamental purposes, however, there is exploitation potential for Li2O-rich ores. Froth flotation is being tested to produce a lepidolite concentrate. Results showed the feasibility to obtain a Li2O grade adequate for the metallurgical production of lithium compounds as Li2CO3. The lepidolite flotation rejects, normally stored in tailings dumps, are mainly composed by a mixture of feldspars, quartz and non-recovered lepidolite (though a very low content), which is, by itself, a very interesting raw material for ceramic purposes. Consequently, mining exploitation of lepidolite, as Li2O ore, from pegmatite could comply with the standards of green mining, reaching an almost zero waste exploitation, as it can be accomplished in the case of the mineral processing of the Alvarrões-Gonçalo lithium ore. This basic scenario could be improved by applying froth flotation also for feldspars/quartz separation, aiming at obtaining a high content feldspars concentrate (floated) and a quartz product (non-floated): the feldspars concentrate can be used to produce blends with different ratios feldspars/quartz for sanitary ware and tiles and quartz for other uses, such as glasses and silica flour.

This study aims to demonstrate, by a detailed fundamental analysis, an alternative for the production of rare earth elements, including yttrium and scandium (REY + Sc), from the historic bottom ash deposit at Ceplea Valley (Romania). Twenty-five samples representing 20% of this deposit were studied using a combination of chemical (proximate and elemental analysis), mineralogical and petrographic techniques. This analysis also included, for the first time, a scanning electron microscopy with X-ray microanalysis SEM/EDS point-count method for tracking REE-bearing minerals. The results showed that the bulk REY + Sc concentration is consistent throughout the landfill, and a bottom ash composite sample was made to assess the chemical composition of several size fractions. Based on Seredin-Dai's criteria (Seredin and Dai, 2012), the plot of the outlook coefficient of REY ores (C-outl) versus the percentage of critical REY of the deposit samples (278 ppm in average) and of the composite sample size fractions shows that this ash is a potentially promising source of REY. However, Gd seems to be the most promising element, especially in the 0.090-0.125 mm and < 0.063 mm size fractions. Finally, the SEM/EDS results show that the only REE-bearing minerals (except one case with Y, Gd, Er, Dy) are micrometre-sized phosphate grains with Ce, La and Nd, with an average diameter of 4.85 mu m, which do not entirely account for the total REE determined by ICP-MS and indicates that a fraction of these elements must be dispersed in the glassy aluminosilicate matrix.

Abstract The aim of this study is to evaluate the potential use of titanium foil coated with sputtered silver and copper films as a novel brazing filler for joining TiAl alloys. For this purpose, a detailed microstructural characterization of the resulting brazing interfaces was carried out. The development of brazing fillers that allow the joining of TiAl alloys without compromising the service temperature is a fruitful prospect. Brazing experiments were performed in a vacuum at 900, 950, and 980°C, with a dwell time of 30 min. Microstructural characterization reveals that brazing joints can be obtained successfully at 950 and 980°C. The interface consists of a large central region of α-Ti with an amount of Al and Ti–Ag compound and thin layers, mainly composed of intermetallic compounds, formed close to the base material. A novel brazing filler consisting of Ti foil coated with sputtered Ag and Cu films inhibits the extensive formation of soft (Ag) zones or coarse brittle Ti–Al–(Cu,Ni) particles. Hence, the need for post-brazing heat treatments for the joining of TiAl alloys was avoided.

In this paper we reply to the criticisms advanced by Narkiewicz (2017) on the paper by Schito et al. (2017). We clarify the issues related to the stratigraphic and thermal maturity constraints used for reconstructing burial and thermal models of the two blocks of the Holy Cross Mountains. We also show how geological evidences brought by Narkiewicz (2017) as a proof of elevated Variscan heat flow are not conclusive or at least suggest the occurence of a localized thermal anomaly only along the, area of the Holy Cross Fault. In the end, we performed new burial and thermal models in the Kielce region demonstrating that stratigraphic thickness variations between Schito et al. (2017) and Narkiewicz et al. (2010) produce only negligible differences in levels of thermal maturity of Paleozoic rocks. In addition, we outline that levels of thermal maturity for Silurian rocks can be matched only by using constant heat flow values through the Paleozoic and point to a decisive role for the absence of regional high Variscan heat flow in the area. (C) 2017 Elsevier Ltd. All rights reserved.

Poland is considered the most prospective country for shale gas production in Europe. Hydrocarbon generation/expulsion scenarios, drawn in the latest intensive exploration phases, tend to overestimate maturation levels when compared with brand new data acquired after recent drillings. We tested an integrated workflow to correlate published and original thermal maturity datasets for the Paleozoic to Jurassic successions cropping out in the Holy Cross Mountains. These successions, when preserved in subsurface, host the major source rocks in the area. The application of the workflow allowed us to highlight the burial and thermal evolutionary scenarios of the two tectono-stratigraphic blocks of the Holy Cross Mountains (Łysogòry and Kielce blocks) and to propose this approach as a tool for reducing levels of uncertainty in thermal maturity assessment of Paleozoic successions worldwide. In particular, published datasets including colour alteration indexes of Paleozoic microfossils (conodont, acritarchs) and vitrinite and graptolite reflectance data, show differences in levels of thermal maturity for the Łysogòry (mid mature to overmature) and Kielce (immature to late mature) blocks. Original data, derived from optical analysis, pyrolysis, and Raman spectroscopy on kerogen, and X-Ray diffraction on fine-grained sediments, mostly confirm and integrate published data distribution. 1D thermal models, constrained by these data, show burial and exhumation events of different magnitude, during the Late Cretaceous, for the Łysogòry (maximum burial depths of 9 km) and Kielce (burial depths of 6 km) blocks that have been related to the Holy Cross Fault polyphase activity. In the end, Palynomorph Darkness Index and Raman spectroscopy on kerogen, for Llandoverian and Cambrian rocks, turned out to be promising tools for assessing thermal maturity of Paleozoic organic facies devoid of vitrinite macerals.

A new vitrified bonded abrasive composite for grinding wheels and a reference material used in the industrial production of grinding wheels were compared in terms of mechanical properties and wear behaviour. The new formulation abrasive samples were processed using different sintering temperatures. With the new composite, it was possible to, simultaneously, obtain similar mechanical properties and increase the open porosity, at a lower sintering temperature. The results demonstrated that the grinding performance of vitrified bonded abrasives can be optimized varying the heat treatment maximum temperature. The best combination of results was achieved with a sintering temperature of 1000 degrees C.

Poor wear resistance of titanium is a major concern since relative movements due to the cyclic loads in body environment cause wear between the bone and the implant material leading to detachment of the wear debris and release of metal ions due to the simultaneous action of corrosion and wear, defined as tribocorrosion. In order to increase the tribocorrosion resistance, Grade 2 Ti matrix 24vol% B4C particle reinforced composites were processed by hot pressing. Corrosion behaviour was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 9g/L NaCl solution at body temperature. Tribocorrosion tests were performed under open circuit potential, as well as under potentiodynamic polarization using a reciprocating ball-on-plate tribometer. Results suggested that the addition of B4C particles provided lower tendency to corrosion and lower corrosion kinetics under sliding, along with significantly reduced wear loss, mainly due to the load carrying effect given by the reinforcement particles.

Journal Article Influence of the Brazing Filler on the Microstructure of Ti6Al4V Joints Get access L Gomes, L Gomes University of Minho, Department of Mechanical Engineering, MEMS-UMinho, Campus de Azurém, 4800-058 Guimarães, Portugal Search for other works by this author on: Oxford Academic Google Scholar A Guedes A Guedes University of Minho, Department of Mechanical Engineering, MEMS-UMinho, Campus de Azurém, 4800-058 Guimarães, Portugal Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S4, 1 March 2016, Pages 40–41, https://doi.org/10.1017/S1431927616000398 Published: 14 March 2016

Poor wear resistance of titanium is a major concern since relative movements due to the cyclic loads in body environment cause wear between the bone and the implant material leading to detachment of the wear debris and release of metal ions due to the simultaneous action of corrosion and wear, defined as tribocorrosion. In order to increase the tribocorrosion resistance, Grade 2 Ti matrix 24 vol.% B4C particle reinforced composites were processed by hot pressing. Corrosion behaviour was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 9 g/L NaCl solution at body temperature. Tribocorrosion tests were performed under open circuit potential, as well as under potentiodynamic polarization using a reciprocating ball-on-plate tribometer. Results suggested that the addition of B4C particles provided lower tendency to corrosion and lower corrosion kinetics under sliding, along with significantly reduced wear loss, mainly due to the load carrying effect given by the reinforcement particles.

This study presents a methodology to evaluate the drying mechanism of grinding wheels production, along the depth of a specimen, during the drying thermal cycle. The thermal and moisture gradients along the specimens were determined. The adopted experimental methodology allows obtaining precise moisture contents along the cross section of a component. Results showed that two steps of drying are present and that the drying kinetics is affected by the compaction pressure, which in turn alters the open porosity level. A critical compression pressure (17–23 MPa) was determined for the change on the drying characteristics, for the tested material.