J. M. Torralba

University Carlos III de Madrid IMDEA Materials Institute

The feasibility of sintering Portland cement clinker powders by Spark Plasma Sintering (SPS) has been studied. Different SPSed compacts have been successfully obtained by this technique. The compacts have been characterized by means of X-Ray Diffraction, InfraRed spectroscopy, Scanning Electron Microscopy, Raman Microscopy and Vickers hardness. It...

There is a general need for alternative structural materials to improve power plants' efficiency and reduce CO2 emissions. Within this framework, two new compositions of temperature-resistant sintered ODS ferritic steels (14Cr–5Al–3W), strengthened by a fine dispersion of precipitates (5·10²² ox./m³), have been developed. This work focuses on creep...

Nanocrystalline Cr-based-WC powders with different C contents (5.59, 6.03, and 6.69 wt% C) were sintered by four different sintering methods, including liquid phase sintering (LPS), hot pressing (HP), field-assisted hot pressing (FAHP), and spark plasma sintering (SPS). The densification, average WC grain size, phase composition, microstructure, an...

Powder Metallurgy (PM) is a forming technology that uses metallic (sometimes also in conjunction with ceramic) powders to develop parts, most of the time through a thermal process called sintering, which never reaches the melting point of the principal component of the alloy [...]

One of the main drawbacks of the powder metallurgy route for High-Entropy Alloys (HEAs) is the unavailability of fully pre-alloyed powders in the market. Using commodity powders (commercial Ni, Fe and Co base fully pre-alloyed powders, fully available in large quantities and at competitive prices) to produce HEAs presents a completely new and compe...

One of the main drawbacks of the powder metallurgy route for High-Entropy Alloys (HEAs) is the unavailability of fully pre-alloyed powders in the market. Using commodity powders (commercial Ni, Fe and Co base fully pre-alloyed powders, fully available in large quantities and at competitive prices) to produce HEAs presents a completely new and compe...

The Master-alloy (MA) alloy route to promote a liquid phase during sintering has great potential to reduce costs in low alloyed sintered steels, meanwhile enabling the introduction of innovative alloy systems with Cr, Mn and Si. However, in order to successfully modify the performance of steels, multi requirements must be met, including, for exampl...

This article covers the field of High Entropy Alloys (HEAs) consolidated by Powder Metallurgy (PM) collecting the last developments found in the literature with regard to powder development, PM consolidation and the associated properties in HEAs obtained by this processing route. In addition, potential opportunities for PM to produce “different” HE...

This article addresses the development of high-entropy alloys (HEAs) fabricated via Powder Metallurgy (PM) techniques. There are potential opportunities for PM techniques to produce ‘different’ HEAs and offer alternative routes to obtain special compositions. The potential for PM is vast, and the obtained properties are highly competitive with thos...

High entropy alloys have attracted much interest over the last 16 years due to their promising an unusual properties in different fields that offer many new possible application. Additionally, additive manufacturing has drawn attention due to its versatility and flexibility ahead of a new material challenge, being a suitable technology for the deve...

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently pr...

This work highlights the promising mechanical properties and oxidation resistance achieved by novel Cr-based WC hardmetals having nanosized tungsten carbide grains, designed by combining thermodynamic calculations and experimental evaluation. The hardmetals are processed by a powder metallurgy route including mechanical milling of powders and subse...

Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear perfo...

Polymer extraction is a key step of the metal injection moulding (MIM) process. An innovative method for extracting an organic binder involves the use of supercritical fluid instead of a regular solvent. The supercritical fluid selected was carbon dioxide due to its affinity toward polyethylene glycol. The supercritical carbon dioxide parameters we...

The aim of this work is to characterize the behavior of a novel multi‐use B‐free alloy that was designed as a liquid phase promoter and as a filler material for sintering and brazing steels in N2‐H2. Through thermodynamic calculations, a new Cu‐Fe‐Ni‐Si alloy (named LP) has been designed showing a proper melting point suitable for being used at tem...

Copper-graphite composites with 0-4 wt % graphite were fabricated by field-assisted hot pressing with the aim of studying the effect of graphite content on microhardness and tribological properties. Experimental results reveal that hardness decreases with the graphite content. Wear testing was carried out using a ball-on-disc tribometer with a norm...

High-entropy alloys (HEAs) have attracted a great deal of interest over the last 14 years. One reason for this level of interest is related to these alloys breaking the alloying principles that have been applied for many centuries. Thus, HEAs usually possess a single phase (contrary to expectations according to the composition of the alloy) and exh...

Abstract The development of duplex stainless steels produced by powder metallurgy represents an interesting alternative to conventional fabrication routes, since typical routes imply a strict control of composition and temperature during the processing path in order to avoid undesirable brittle phases. This work proposes a sintering route, designa...

A Co-based superalloy, Co-9Al-9W (at%), was processed by mechanical alloying by high-energy milling of elemental powders and consolidated by field assisted hot pressing (FAHP). The milled powder particles mainly consist of undissolved bcc-W as well as WC and an Al and W rich fcc-γ Co solid solution. After consolidation and heat treatment a fine gra...

This investigation analyzes the feasibility of processing a composite material comprising WC particles randomly dispersed in a matrix in which Cr is the main metallic binder. Thus, a new composite material is processed using a commercial, economic, and easily available Cr-based alloy, assuming that there is a certain Cr solubility in the WC particl...

The feasibility of processing duplex stainless steels with promising properties using a powder metallurgical route, including the consolidation by field-assisted hot pressing, is assessed in this investigation. The influence of the particle size and morphology of the raw austenitic and ferritic powders on the final microstructure and properties is...

The Zamak 2 alloy has the best mechanical properties of the Zamak alloys with respect to the tensile strength, creep resistance, and hardness. Zamak 2 is a commercial material widely used for the manufacturing of mechanical components. The presence of Cu in this alloy (3 wt. %) improves the mechanical properties through the formation of E (CuZn4) p...

Soft magnetic materials are used in a wide variety of electromagnetic devices such as motors, relays and sensors. Over the years, the devices are becoming smaller. Therefore, it is essential to produce small parts without compromising the final properties. Metal injection moulding (MIM) is a cost-effective technique to produce small and complex sof...

The success of the sinter-brazing technique depends on the control of the liquid phase of the brazing alloy. Therefore, it is necessary to design the composition of the brazer taking into account its wettability, infiltration capacity, chemical reaction with the base material and development of the final microstructure. The present work pretends to...

In this investigation, three different consolidation ways for Inconel 718 MIM samples are compared. The conventional sintering in a furnace is compared to field assisted hot pressing (FAHP) and microwave sintering. By accelerating the sintering kinetics, the thermal behaviour may be modified. Hence, the behaviour of the Inconel 718 sintered by fiel...

In this investigation on samples obtained by Metal Injection Molding (MIM), the conventional way of sintering in a furnace will be compared to Field Assisted Hot pressing (FAHP) sintering. The difficulty of this method is to be able to control the shrinkage of the sample and so its shape. It has yet not been investigated with a super alloy powder a...

In this investigation, three different ways of sintering Inconel 718 MIM samples are compared. The conventional way of sintering in a furnace will be compared to FAHP and microwave sintering. The difficulty of these two methods is to be able to control the shrinkage of the sample and so its shape. These methods have yet not been investigated with a...

Metal injection moulding (MIM) may be used to produce soft magnetic materials with optimal mechanical and magnetic properties. Unlike other techniques, MIM enables the production of complex and small Fe-Si alloy parts with silicon contents greater than 3% by weight. In MIM process development, it is critical to design a proper debinding cycle not o...

Liquid phase sintering is used for the consolidation of powder based materials to enhance densification by the activation of diffusion rates and sintering kinetics. However, an inappropriate interaction between the liquid and the solid powdered skeleton can promote excessive swelling instead of densification, and the purpose of the liquid phase pro...

A sintered 14Cr-5Al-3W oxide dispersion strengthened steel was produced by mechanical alloying and consolidated by field-assisted hot pressing. First, a nanostructured powder was developed thanks to the high-energy milling used for introducing 0.4Ti-0.25Y2O3-0.6ZrO2 into the prealloyed Fe-Cr-Al-W powder, and then the processed powders were consolid...

Brazing can be considered as an attractive method for joining sintered steel components since it can be integrated into the sintering process. The behavior and quality of the joint rely on the braze filler design. Among others, the interaction between the base material and the filler depends on the brazing temperature, wettability, infiltration abi...

The master alloy (MA) concept was brought up in the early 1970s as a means to introduce alloying elements with high oxygen affinity in low alloy sintered steels. Afterwards, it evolved to become what we currently understand: a MA as a powder that - admixed in very small amounts - can be used as a vehicle to efficiently tailor the microstructure and...

Introducing alloying elements through Master Alloy (MA) additions provides the unique opportunity of designing their composition to enhance sintering by forming a liquid phase. However, working with liquid phases poses important challenges like maintaining a proper dimensional control and minimizing the effect of secondary porosity on the final per...

The use of low melting point master alloy (MA) powders contributes beneficially to sintering by increasing the distribution rate of alloying elements, enhancing homogenisation and sometimes also promoting densification. However, working with liquid phases poses important challenges like maintaining a proper dimensional control and minimising the ef...

In the last 40 years, assessing the "copper swelling" effect that results from the interaction of copper with carbon, nickel, or other alloying elements during sintering has been a focus of interest of the powder metallurgy steel industry. Although wetting has been pointed out as a determinant parameter of the behavior of copper and its effect on t...

Carbon-based nanostructures involving carbon films and nanotubes (CNT) are currently in the spotlight for the development of highly efficient materials, useful in several applications (electronics, mechanical reinforcement, energy production/storage [1,2]). However, the production of those nanostructures find several issues relating process cost an...

An oxide dispersion strengthened (ODS) ferritic steel with nominal composition Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3-0.6ZrO2 was produced by mechanical alloying (MA), based on a prealloyed grade Fe-14Cr-5Al-3W steel with the addition of Ti element, Y2O3 and ZrO2, and subsequent consolidation by means of field assisted hot pressing (FAHP). The microstructur...

An oxide dispersion strengthened (ODS) ferritic steel with nominal composition Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3-0.6ZrO2 was produced by mechanical alloying (MA), based on a prealloyed grade Fe-14Cr-5Al-3W steel with the addition of Ti element, Y2O3 and ZrO2, and subsequent consolidation by means of field assisted hot pressing (FAHP). The microstructur...

New processing route has been developed for zircon based on powder injection moulding (PIM). Raw zircon powders, obtained from mineral sands, have been processed using a new water soluble binder system composed of PEG and CAB. Water solvent debinding stage has been studied in depth. On one hand, influence of some debinding parameters (temperature,...

A spherical carbonyl iron powder was consolidated by the field-assisted hot pressing technique using graphite tools at two different temperatures, both above the austenitizing temperature. The microstructures obtained exhibited a compositional gradient in carbon along the consolidated material. Thus, the outer rim of the cylindrical samples was com...

Oxygen-sensitive alloying elements such as Mn, Si, and Cr have a high potential for improving the properties of low alloyed sintered steels while reducing the alloying cost. However, it is necessary to find a way for avoiding, or at least minimizing, the oxidation of these elements especially during the early stages of the sintering cycle. In this...

Capillary rheology was used to determine the shear viscosities of low expansion alloy INVAR 36 feedstocks for powder injection moulding (PIM) based on gas atomized powders and cellulose acetate butyrate (CAB) and poly-ethylene glycol (PEG) binders. Different variables that describe the flow behaviour were analysed, in particular, the relationships...

Microstructural features of sintered steels, which comprise both phases and porosity, strongly condition the mechanical behaviour of the material under service conditions. Many research activities have dealt with this relationship since better understanding of the microstructure– property correlation is the key of improvement of current powder meta...

Oxide dispersion strengthened (ODS) Fe alloys were produced by mechanical alloying (MA) with the aim of developing a nanostructured powder. The milled powders were consolidated by spark plasma sintering (SPS). Two prealloyed high chromium stainless steels (Fe-14Cr-5Al-3W) and (Fe-20Cr-5Alz3W) with additions of Y2O3 and Ti powders are densified to e...

A γ-TiAl intermetallic alloy, Ti–45Al–2Nb–2Mn(at.%)–0.8vol.%TiB2, has been processed from gas atomized prealloyed powder by field assisted hot pressing (FAHP). An initial analysis of the prealloyed powder helped on the understanding of the intermetallic sintering behavior. Atomized powder consisted of α metastable phase that transformed into α2+γ e...

In recent years, many efforts have been made to obtain more environmentally acceptable powder injection moulding processes. In this sense, the purpose of this study is to optimise an eco-binder based on polyethylene glycol (PEG) as a water soluble component and cellulose acetate butyrate (CAB) as a natural backbone polymer derived from cellulose fo...

Powder Metallurgy (PM) is technology well known for mass production of parts at low cost but usually with worse mechanical properties than same parts obtained by alternative routes. But using this technology, high performance materials can be obtained, depending of the processing route and the type and amount of porosity. In this paper, a brief rev...

This work aims to contribute to a further understanding of the fundamentals of crystallographic slip and grain boundary sliding in the γ-TiAl Ti–45Al–2Nb–2Mn (at%)–0.8 vol%TiB2 intermetallic alloy, by means of in situ high-temperature tensile testing combined with electron backscatter diffraction (EBSD). Several microstructures, containing differen...

This study examined the hot deformation behavior and workability characteristics of nanocrystalline AZ91 Mg alloy by performing hot compression tests with a Gleeble-3800 machine. To this end, a nanocrystalline alloy powder with a crystallite size of 25 nm was synthesized via mechanical milling of a pre-alloyed AZ91 Mg alloy powder for 14 h. The mec...

Powder metallurgy (PM) is a metal-forming technology that uses powders (metallic and or ceramic) as raw materials which are formed into a specific shape and dimensions and subsequently sintered at high temperature. Using this technology, high performance materials can be obtained, but always depending of the processing route and the type and amount...

Micrometal injection moulding (m-MIM) is a promising alternative for fabricating micro parts. Low coefficient of thermal expansion Fex–Ni12x alloys are suitable to meet high dimensional stability with temperature keeping acceptable mechanical properties. However, these alloys are sensible of elements contamination during the debinding and sintering...

The present work concerns the processing of 7075 Al alloy by cold compaction and hot extrusion of a pre-mixed powder. To this end, a premixed Al-Zn-Mg-Cu powder, Alumix 431D, was uniaxially cold pressed at 600 MPa into cylindrical compacts 25 mm in diameter and 15 mm thick. Subsequently, selected green compacts were subjected to either a delubricat...

Spain is the second largest producer of PM (powder metallurgy) products in the EU, behind Germany. In traditional PM production, Spain has a number of specialized, highly productive plants embracing specialty parts, shock absorbers, synchronizing hubs, and bushings. Other Spanish PM products are specialty powders and hardmetals. In terms of product...

A water soluble binder system based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) is proposed and investigated to carry out a micro powder injection moulding (μPIM) process with an Invar 36 alloy powders. The overall process was optimised with an emphasis on the determination of the optimal solid loading. Several methodologies w...

Dilatometry experiments have been carried out to investigate the shrinkage kinetics on cold isostatic pressed iron specimens in the 550-730 degrees C temperature range, showing that dimensional contraction is much higher than that predictable on the basis of the shrinkage kinetics models, which neglect the effect of the prior cold compaction. The g...

The characteristics of the metallic powder surface play a critical role in the development of strong bonds between particles during sintering, especially when introducing elements with a high affinity for oxygen. In this study, Mn and Si have been combined in a Fe–Mn–Si–C master alloy powder in order to reduce their chemical activity and prevent ox...

Degradation kinetics and the thermal stability of Invar 36 powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA) and differential scanning calorimetry (DSC). The initial decomposition temperature (IDT) and the i...

Micronized natural zircon sand powders were used as a raw material to conduct low-pressure powder injection moulding (LPPIM) processes. PIM could lead to new technological applications for this mineral, which has very stable dimensional behaviour with changing temperature. Zircon powders that have unconventional attributes for PIM (in terms of size...

Mg alloys are characterised by several promising properties, including a good biocompatibility. In this work, a commercial AZ91 powder was used to produce cylindrical specimens by spark plasma sintering (SPS), and the specimens were further consolidated by hot extrusion. The SPS materials were found to be quite brittle because of the low bonding be...

The possibility of tailoring the characteristics of a liquid metal is an important asset in a wide number of processing techniques. For most of these processes, the nature and degree of the interaction between liquid and solid phases are usually a focus of interest since they determine liquid properties such as wettability and infiltration capacity...

The economic importance of the corrosion and wear of refractory materials is indisputable because these processes determine the viability of any high-temperature liner used in metallurgical processes. The degradation mechanism of lining materials (refractory bricks) in contact with corrosive gases can be studied by examining the penetration rate or...

High-energy milling is considered to be one of the most efficient techniques for producing materials that have a well-controlled chemical composition and microstructural features that are difficult to obtain using other synthesis routes. In this study, the mechanical alloying technique (MA) was used to develop special powder metallurgy (PM) steels...

This study examined the hot deformation behavior and workability characteristics of A291 Mg alloy powder compacts by performing hot compression tests with a Gleeble 3800 machine. To this end, powder compacts with a relative green density of 93% were hot-compressed at temperatures ranging from 150 degrees C to 500 degrees C and at true strain rates...

The effect of heat treatments on an as-HIPed γ-TiAl intermetallic alloy was examined. Duplex and fully lamellar microstructures were generated by annealing and subsequently characterized. The relationship between the microstructures and the deformation mechanisms of the intermetallic alloy was studied by means of in-situ tensile experiments perform...

Degradation kinetics and the thermal stability of zircon powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA). The initial decomposition temperature (IDT) and the integral procedure decomposition temperature (I...

This study analyzed the effect of high-energy milling (HEM) and subsequent isothermal annealing on the microstructural characteristics of a pre-alloyed AZ91 Mg alloy powder. To this end, the mentioned powder was milled for 14 h using a horizontal attritor. Then, the mechanically milled powder was isothermally annealed at temperatures ranging from 2...

The tolerances of parts produced for the automotive industry are so tight that any small process variation may mean that the product does not fulfill them. As dimensional tolerances decrease, the material properties of parts are expected to be improved. Depending on the dimensional and material requirements of a part, different production routes ar...

In conventional PM of low alloy steels various alloying routes are used (fully prealloyed powders, diffusion alloying, elemental powders), but always using powders that allow uniaxial pressing, i.e. acceptable compressibility and flow. Fully prealloyed gas atomised powders (including carbon content) have never been an option because their small siz...

Powder Injection Moulding (PIM), Metal Injection Moulding (MIM) when is limited to metals, is a fabrication route of parts with the final shape desired. This process combines the high capability of polymer injection moulding to produce complex shapes with the advantages of a powder route to process metallic, ceramic or composites materials. The pro...

Defining the proper conditions for sintering of steels containing oxidation-sensitive elements requires a deep understanding of the overall gas-gas and solid-gas reactions taking place especially during the heating stage of the sintering process. In this work, Mn and Si have been introduced in sintered steels in the form of a master alloy powder sp...

This study examined the effect of mechanical milling on the densification behavior of AZ91 Mg alloy powder during uniaxial cold compaction in the pressure range of 100 to 600 MPa. Both AZ91 and mechanically milled AZ91 (MM AZ91) powders exhibited good compressibility and reached relative green densities of 94 % and 91 %, respectively, at a compacti...

The objective of this work was to study the compressibility characteristics of a nanostructured 7075 Al alloy powder. To this end, the mentioned powder, which had previously been produced by the high-energy milling of a premixed Al-Zn-Mg-Cu powder (Alumix 431D), was uniaxially cold pressed into cylindrical compacts with diameters of 10 mm using com...