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Soft magnetic materials are characterized by achieving a high magnetic induction value in the presence of a small magnetic field. Common applications of these materials, such as transformers or sensors, are in constant evolution and new requirements are becoming more demanding. Nickel and its alloys are employed as smart materials taking advantage of their superior magnetoelastic properties. A metal injection molding (MIM) technique provides high-quality complex-shaped parts with a good density and controlled impurity levels, which are necessary for these applications, by carefully adjusting the sintering stage. Previous investigations have established a sintering cycle for pure nickel consisting of 1325 ∘C for 12 h within an N2-5%H2 atmosphere. Nevertheless, microstructural, mechanical and magnetoelastic responses can still be greatly enhanced. In this context, the effects of hot isostatic pressing (HIP), and sintering atmosphere have been investigated. The application of an adequate HIP treatment leads to significant improvements in comparison to the reference sintering process. It achieves almost complete densification while increasing field-dependent elastic modulus from 8.1% up to 9.6%. Additionally, the sintering atmosphere has been proven to be a key factor in reducing impurities and hence facilitating magnetic domain motion. Three different atmospheres have been studied: N2-5%H2 (with a higher gas flow), N2-10%H2-0.1%CH4 and low vacuum. Minimum carbon contents have been registered using more reducing atmospheres (N2-5%H2 and N2-10%H2-0.1%CH4) which has led to values of field-dependent elastic modulus higher than 10%. This value is 2.5 times higher than that obtained when nickel parts are processed via conventional techniques. Moreover, although minimizing carbon content has been shown to be easier and more beneficial than achieving complete densification, both strategies could be used in combination to improve and maximize magnetoelastic performance.

Producción Científica, Microstructural changes that result in relevant improvements in mechanical properties and electrochemical behavior can be induced by the use of different sintering conditions of ASTM F75 Cobalt alloys during their processing through powder metallurgy technique. It has been observed that the increase in carbon and nitrogen content improves corrosion resistance and mechanical properties as long as the precipitation of carbides and nitrides is avoided thanks to the use of rapid cooling in water after the sintering stage. In addition, the reduction of the particle size of the powder improves the hardness and resistance to corrosion in both acid media with chlorides and phosphate buffer medium that simulates the physiological conditions for its use as a biomaterial. These results lead to increased knowledge of the role of the carbon and nitrogen content in the behavior displayed by the different alloys studied., Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AGL2015-67482-R), Junta de Castilla y Leon - FEDER (project VA275P18), Junta de Castilla y León (project VA044G19)

Metal injection moulding (MIM) was used to process steel matrix composites reinforced with different amounts of vanadium carbide (VC) for tooling applications. The effects of adding VC on dry sliding wear behaviour have been investigated in detail using pin-on-disk and ball-on-flat tests. Final properties have been correlated with the microstructural analysis and XRD patterns. Increasing the amount of added VC has an inhibiting effect on the growth of the grains and larger amounts of particles are precipitated. These facts show that the microhardness and wear properties improve with higher amounts of additive. Thus, there is a tendency towards a better wear resistance with higher carbide additions. Additionally, better wear results have been obtained than those by conventional Powder Metallurgy (PM) using the same materials.

Solid oxide fuel cells (SOFCs) are one of the most promising and interesting devices for green energy production, especially for stationary applications, mainly because of their high efficiency in the development race to achieve the true energy transition in which hydrogen-related technologies are key. These devices operate at high temperatures and, therefore, several challenges related to the materials used need to be solved. Interconnectors are a significantly relevant part of SOFCs, as they allow the coupling of devices in series for power production in industrial quantities. This work presents meaningful comparisons between two Fe-based alloys with different Cr content, Crofer 22 and Crofer 30, and one Ni-based alloy, Inconel 718. The study presents the analysis of their processability by metal injection moulding (MIM) as the selected technique to combine the possibility of obtaining devices with high geometrical complexity and with realistic possibilities of industrialisation. The injection, debinding and sintering processes are optimized for each kind of material explaining the influence of the powder size distribution and shape. Additionally, functional properties of the interconnectors are analysed as the electrical resistivity and preliminary permeability tests proving the suitability of the properties obtained. Furthermore, different 3D printed inserts were used to facilitate possible interconnector designs, saving the costly development of MIM metal moulds. The work highlights the improvements that can be made in the development of interconnectors both by an adequate selection of raw materials and by an optimal performance of each stage of processing, opening up prospects for improvement that can soon be tackled.

The effects of chromium carbide on the microstructures and wear resistance of high speed steel were studied. Metal matrix composites (MMCs), based on M2 high speed steel reinforced with different percentages of Cr3C2, were produced following a metal injection moulding route: feedstock manufacturing, injection, debinding and sintering. The weight fraction of hard second phase particles in tool steels is limited by the formation of large interconnected carbides that embrittle the alloy. Additions of up to 14 wt-% Cr3C2 were successfully prepared. The influence of the chromium carbide content on the optimum sintering temperature was analysed. The mechanical properties of the sintered composites were obtained by measuring hardness and wear behaviour. Microstructure and wear mechanisms were investigated by means of scanning electron microscopic observations. These results, together with X-ray diffraction characterisation and EDS analysis, allow explanation of the mechanisms responsible for the wear beh...

Feedstock behaviour during processing via powder injection moulding (PIM) has a critical influence on the properties of the final parts. The objective of the present study is to analyze the effect of vanadium carbide (VC) addition (1, 3, 6, 10 and 14 wt.% VC) on the rheological response and stability of AISI M2 high speed steel PIM feedstocks. A binder system consisting of high density polyethylene (HDPE) and paraffin wax (PW) is proposed. The effects of VC concentration, powder loading, apparent viscosity and temperature have been investigated via capillary rheometer. The feedstocks with a 14 wt.% of VC, which exhibited a variable flow behaviour was discarded. The rest of the feedstocks showed a pseudoplastic behaviour which is suitable for injection moulding and in particular, those reinforced with 6 and 10 wt.% of VC exhibited the best rheological responses. In order to maximize the powder loading and ensure safety conditions, the feedstocks reinforced with 6 wt.% (5.9 vol.%) and 10 wt.% (9.8 vol.%) of VC with 68 vol.% of powder loading and 3 wt.% (2.8 vol.%) of VC with 62 vol.% of powder loading were selected to continue the rheological analysis. Rheological parameters such as flow behaviour index (n), yield stress (ơy), flow activation energy (Ea) and the general mouldability index (αstv) have been analyzed for the above mentioned feedstocks and showed suitable values for the injection moulding. The green parts produced using the three feedstocks have constant weights and dimensions, good mouldability, density, shape retention and stiffness. Therefore, the developed feedstocks are suitable for PIM.

Twinning Induced Plasticity (TWIP) steels are high manganese austenitic steels that have caused growing interest over the last decade due to their unique combination of strength and elongation. Nevertheless, the problems presented during their current fabrication process (continuous casting) complicate their production and commercialisation. Powder metallurgy may be an attractive alternative route of solving these problems in certain components. In this work, Metal Injection Moulding (MIM) is explored as an alternative fabrication method for TWIP steels, having the additional benefit of reaching a near-theoretical densification. The feedstock of this study is composed of a metallic prealloyed Fe–Mn–C–Al–Si powder and a binder system based on wax-HDPE. The feedstock was optimised by examining different metallic loads. A suitable powder–binder ratio was determined based on mixing torque and melt flow index measurements. It was optimised a two-stage debinding process and a sintering process in an argon atmosphere to obtain the correct microstructure.

The production of smart materials such as those with magnetoelastic properties is of increasing interest for some application as position transducers. The use of the metal injection moulding process permits the production of small parts with complex geometries as well as avoiding common defects produced by other processing techniques. In this study, a feedstock based on pure nickel and thermoplastic binder has been designed and moulded to have specific cylindrical geometry and defect-free green specimens. The parts were sintered changing several processing parameters that have influence on magnetoelastic effects. These effects were studied in terms of the field-dependent elastic modulus, which was estimated by subjecting the specimens to free longitudinal vibration while they remained within different magnetic fields from 0 to 2000 Oe. The optimal sintering parameters turned out to be 1325 °C for the temperature and 12 h for the holding time, whereas the estimated field-dependent elastic modulus variation (8%) was higher in comparison to variations in parts obtained by conventional processing (4%). Keywords: Metal injection moulding, Magnetomechanical properties, Smart materials, Sintering

A high-nitrogen, low-nickel powder metallurgy austenitic stainless steel was studied and compared with a conventional powder metallurgy austenitic stainless steel. Three different sintering processes were applied by controlling the sinter-cooling rate (furnace, gas, and water). Nitrogen was chosen as the sintering atmosphere. A microstructural study was performed and the corrosion behavior was evaluated in terms of anodic polarization measurements and an electrochemical potentiokinetic reactivation test. It was found that the water-cooling process is advisable for good corrosion behavior. The results were correlated with the microstructural features.

This investigation addresses sintering of AISI M2 high speed steel reinforced with vanadium carbide (VC) using concentrated solar energy (CSE). CSE allows significant reduction of processing times due to its enhanced activating effect and high heating rates achieved. The M2 steel powders were reinforced with 3, 6 and 10 wt% VC and sintered under a N2–5%H2 atmosphere at two solar installations: a Fresnel lens (FL) and a solar furnace (SF). The microstructures of the solar-sintered samples were studied and compared with other samples sintered using a conventional tubular furnace. Results show that the use of solar installations significantly reduces optimal sintering temperatures in more than 200 °C. Furthermore, the use of CSE allows a dramatic reduction of the treatment times from cycles longer than 10 h in tubular furnace (TF) to cycles of 15 min in solar furnace. Finally, the addition of VC increases hardness in most of the studied cases but in the samples processed in the solar installation the increase is higher achieving 987 HV in the sample reinforced with 10 wt% of VC without any additional thermal treatment. The microstructural analysis together with X-ray diffraction characterization allows explaining these results.

Mixtures of AISI M2 high speed steel and vanadium carbide (3, 6 or 10 wt.%) were prepared by powder metallurgy and sintered by concentrated solar energy (CSE). Two different powerful solar furnaces were employed to sinter the parts and the results were compared with those obtained by conventional powder metallurgy using a tubular electric furnace. CSE allowed significant reduction of processing times and high heating rates. The wear resistance of compacts was studied by using rotating pin-on-disk and linearly reciprocating ball-on-flat methods. Wear mechanisms were investigated by means of scanning electron microscopy (SEM) observations and chemical inspections of the microstructures of the samples. Better wear properties than those obtained by conventional powder metallurgy were achieved. The refinement of the microstructure and the formation of carbonitrides were the reasons for this., JCCM in the Spanish National Programme (Project PPIC10-0052-5968)

Electrical discharge machining (EDM) is one of the most widely used non-conventional machining processes for the production of moulds/dies, cutting tools and aero-engine parts, such as turbine/compressor blades. The paper details experimental research on the surface alloying/modification of chromium martensitic hot-work tool steel components (AISI H13, 55HRC) during EDM die-sinking operations using powder metallurgy (PM) tool electrodes, as a means of achieving enhanced workpiece wear resistance without resorting to a subsequent coating operation. Tool electrode performance of partially sintered WC/Co electrodes operating in a common hydrocarbon oil dielectric was assessed and subsequently compared with that of conventional electrode materials, such as Cu and Graphite. Surface/subsurface observations by optical and scanning electron microscopy (SEM) showed a recast solidified layer of ~ 8 µm when using WC/Co electrodes. Performed XRD and SEM-EDX analysis indicated that WC and Co contained in the PM tool electrodes, together with C decomposed from the hydrocarbon oil during sparking, were transferred and alloyed to the steel substrate surfaces. EDM surface alloyed layers were hardened over 1200 HK0.025. This hardening is related both to the formation of tungsten carbides with different stoichiometries and to the non-equilibrium microstructure evolution. Thickness of the hardened zone was shown to be dependent on EDM operating parameters, in particular peak-current (A) and pulse on-time (s).

In the present work, the injection moulding process of a Cu–10Sn bronze has been studied. Different formulations of binders based on high density polyethylene, paraffin wax and polyethylene glycol have been used. The optimisation of the metallic load is based on torque measurements and rheological studies. The optimum powder loading was 60 vol.-%. The moulding parameters are selected to obtain homogeneous specimens with three different geometries and without distortions. The green parts have an adequate strength for handling. The organic binder was eliminated by thermal debinding under N2/10%H2 atmosphere. The debinding process has been designed by means of thermogravimetrical analysis of binder and feedstock and considering the maximum heating rates at which the samples do not present cracks. The specimens were sintered at temperatures between 875 and 950°C in the same reducing atmosphere.

In this present investigation, Metal Injection Moulding (MIM) of M2 High Speed Steel (HSS) parts using a wax-High Density Polyethylene (HDPE) binder is shown. This work is focused on the examination of the sintering densification and microstructure evolution of the parts. The injection molding process of the feedstock has been optimized to obtain high quality green parts. The elimination of organic binder was carried out by thermal debinding under inert atmosphere. In order to keep carbon in the sample that could improve the sintering process, incomplete debinding was performed between 450 and 600 °C. The specimens were sintered at temperatures between 1210 and 1280oC in high vacuum atmosphere, obtaining the 98% of the theoretical density. A homogeneous distribution of fine M6C carbides was obtained as well as V-rich carbides (MX) during sintering which reinforced the HSS and hence increasing the mechanical properties of the parts. In the samples with higher residual carbon content, the sintering window was extended up to 20 degrees and the optimum temperature was lower.

Based on the comparison of structures and properties of the HS6-5-2 high speed steels made with the powder injection moulding method, pressureless forming, compacting and sintering, and commercial steels made with the ASEA-STORA method, fine carbides spread evenly in the steel matrix were found in the structure of all tested high-speed steels in the sintered state. The use of a nitrogen atmosphere in the sintering process, causes the formation of fine, spherical MX type carbonitrides, stable in high sintering and austenitizing temperatures. The steels made with the pressureless forming method are characteristic of the lowest sintering temperature and the highest density, resulting from the high carbon concentration coming from the binding agent degradation. Moreover, the higher carbon concentration causes an increase in the retained austenite portion and a lower hardness after quenching and tempering. The heat-treated injection moulded steel attains hardness comparable to the commercial ASP23 type one, demonstrating the well-founded reasons for using the powder-injection moulding method for manufacturing the high-speed steel. The powder-injection moulding makes manufacturing tools possible with their final shape, i.e., leaving out the plastic forming and machining which is necessary for instance in case of the ASP 23 type steel. Furthermore, the degradation and sintering process time of the injection moulded steels is approximately 10h shorter than for steels made with pressureless moulding, which is due to the use of a two-component binding agent.

In this communication, we present the powder injection moulding (PIM) of HS12-1-5-5 high-speed steel parts using a wax-HDPE based binder. The injection moulding process of the feedstock (68 vol.% of metal) has been optimized to obtain high quality green parts. The elimination of organic binder was carried out by thermal debinding under inert atmosphere. In order to keep carbon in the sample that could improve the sintering process, incomplete debinding were performed between 450 and 500 °C. In this study, we have studied the effect of different atmospheres on the debinding process. Debinding was performed under nitrogen and argon. The specimens were sintered at temperatures between 1200 and 1300 °C with steps of 10 °C in following mixture N 2 –10% H 2 atmosphere. The PIM parts present higher density than those obtained by conventional PM.

A new feedstock formulation for metal injection moulding (MIM) of M2 high speed steels has been developed. The binder is a multicomponent system based on high density polyethylene (HDPE) and paraffin wax (PW). The compatibility between binder constituents has been studied by dynamomechanical thermal analysis (DMTA) showing a partial miscibility between both components. Viscosity measurements of the different binder mixtures at different shear rates showed that the optimum formulation for MIM was 50 vol.-% HDPE. With this optimised binder, several mixtures were prepared with different powder loadings of M2 grade high speed steel. Torque measurements of the mixtures indicated that the maximum amount of metal to be used was 70 vol.-%. The wide distribution of the metal powder was homogeneously distributed into the polymer matrix. The polymeric part was driven off by thermal debinding using a thermal cycle designed on the basis of a thermogravimetric study of the binder. Finally the vacuum sintering ...

The control of carbon content is a key aspect of metal injection molding (MIM). This chapter describes the main systems in which carbon control is required to ensure high-quality components are produced. The main parameters used to control the carbon content during the industrial processing are discussed, especially for the debinding and sintering processes, together with the influence of the carbon content on final mechanical properties.

In this work we include valuable information about the way in which nickel may become a valuable smart material for some applications and we provide a better understanding of the influence of internal stresses on its magnetoelastic effects. The different states of internal stress are achieved via different heat treatments obtained by modifying three main parameters: the heating temperature, the heating time and the cooling method. Then, we carried out the next works: first, a microscopic analysis of the grain size of the samples under different heat treatments; second, all the tested specimens were subjected to an exhaustive internal stress analysis via X-Ray diffraction techniques; and third, the ∆Eand ∆Ψ-effects were estimated in order to link the internal stress state of the sample to its magnetoelastic response. The results can guide us in selecting the most suitable heat treatment in order to make nickel show the smart properties we desire.

Measurements of the #916;E-effect#916;E-effect and magnetomechanical damping are reported for crystalline pure nickel under several states of internal stresses. The different internal stresses are obtained by means of a wide variety of heat treatments and studied via microscopic examination and measurement. The influence of the heating temperature, the heating time and the cooling method on the magnetoelastic properties is studied. Our results make it possible to select the most suitable heat treatment for each application and to optimize the magnetoelastic response of nickel. Relative variations from 2% to 13% can be obtained in the #916;E-effect#916;E-effect, whereas relative variations from 40.0% to 99.9% are possible in magnetomechanical damping, in terms of specific damping capacity.