Revistas
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2020
Vol.:
63
N°:
2
Págs.:
75 - 79
Thermochemical treatments like plasma nitriding or surface carburizing are commonly used to enhance surface hardness of steel components. An important difference between these treatments is the temperature at which they are carried out. In the present paper, the surface carburizing was carried out following a recently reported non-isothermal low pressure carburizing (LPC) treatment. In order to gain a comparative view of the effect of different treatments on the microstructure, microhardness, fatigue and impact properties, materials with distinct hardenability and widely used in the industrial production were evaluated. Tests were also carried out using industrially processed components aimed to an application demanding high wear resistance. The microstructural evolution during case hardening was studied by optical and electron microscopy.
Autores:
Gabilondo, M.; Fraile, I. (Autor de correspondencia); Burgos, Nerea; et al.
Revista:
CERAMICS INTERNATIONAL
ISSN:
0272-8842
Año:
2019
Vol.:
45
N°:
17
Págs.:
23149 - 23156
Piezoelectric materials are used in several applications, including sensors and actuators. Perovskite type ferroelectrics, specially, lead zirconate titanate (PZT), due to its excellent dielectric, piezoelectric and ferroelectric properties are usually employed. In this work, a series of Spin Coated PZT thick films were deposited on alumina and stainless steel substrates. These PZT-based films were obtained using inks containing either pArtículos or a precursor that were synthesised using a chemical method. In order to consolidate the deposit as a thick film, a thermal treatment is required after deposition on a substrate. Under temperature exposure, the PZT pArtículos tend to sinter after the elimination of the organic vehicle. Moreover, the PZT precursor transforms to crystalline PZT. Films based on the PZT precursor exhibited many cracks after treatment, while those constituted by PZT pArtículos required sintering temperatures higher than 1000 degrees C which resulted in unstable PZT structures. As an alternative, slurries forming mixtures of PZT precursor and pArtículos, varying their relative proportions, were studied to improve the properties of the films. Films generated in this study were characterized by SEM and X-ray diffractometry.
Autores:
Sundaram, M. V. (Autor de correspondencia); Surreddi, K. B. ; Hryha, E. ; et al.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2018
Vol.:
49A
N°:
1
Págs.:
255 - 263
Reaching high density in PM steels is important for high-performance applications. In this study, liquid phase sintering of PM steels by adding gas-atomized Ni-Mn-B master alloy was investigated for enhancing the density levels of Fe- and Mo- prealloyed steel powder compacts. The results indicated that liquid formation occurs in two stages, beginning with the master alloy melting (LP-1) below and eutectic phase formation (LP-2) above 1373 K (1100 A degrees C). Mo and C addition revealed a significant influence on the LP-2 temperatures and hence on the final densification behavior and mechanical properties. Microstructural embrittlement occurs with the formation of continuous boride networks along the grain boundaries, and its severity increases with carbon addition, especially for 2.5 wt pct of master alloy content. Sintering behavior, along with liquid generation, microstructural characteristics, and mechanical testing revealed that the reduced master alloy content from 2.5 to 1.5 wt pct (reaching overall boron content from 0.2 to 0.12 wt pct) was necessary for obtaining good ductility with better mechanical properties. Sintering with Ni-Mn-B master alloy enables the sintering activation by liquid phase formation in two stages to attain high density in PM steels suitable for high-performance applications. (C) The Author(s) 2017. This article is an open access publication
Revista:
CERAMICS INTERNATIONAL
ISSN:
0272-8842
Año:
2018
Vol.:
44
N°:
13
Págs.:
15603 - 15610
Lead zirconate titanate (PZT) Pb(ZrxTi1-x)O-3 is one of the most studied perovskite type ferroelectric materials due to its excellent dielectric, piezoelectric and ferroelectric properties. PZT particles and a PZT precursor were synthesized using a chemical method. A vehicle was added to the synthesized particles and precursor for obtaining two inks with appropriate rheological properties to be printed by Inkjet Printing. The use of an 80 mu m diameter nozzle made necessary the utilization of an energetic ball milling for assuring the dispersion of small PZT particles in the ink. After ball milling nanoparticles of 150 nm diameter were obtained. These inks were deposited on alumina and steel substrates followed by sintering using a pulsed laser of 1064 nm wavelength. The work shows the effect laser sintering has on, both inks, the one containing PZT nanoparticles and that one based on the PZT precursor. Laser processing was optimized in order to generate suitable films to be subsequently poled. The effect of poling on these films was also studied and their piezoelectric properties were measured by a compression test. The microstructural characteristics of these films were obtained by SEM and X ray diffractometry.
Revista:
METAL ADDITIVE MANUFACTURING
ISSN:
2057-3014
Año:
2017
Vol.:
3
N°:
1
Págs.:
112 - 115
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2016
Vol.:
59
N°:
2
Págs.:
128 - 141
Present empirical correlations to predict the median particle size of water atomised powders have a validity restricted to a particular atomiser and alloy family. This work proposes a mathematical function that takes into account the influence of the heat transfer coefficient and, therefore, of the solidification time on the median particle size. This equation is applied in combination with previously proposed empirical correlations to extend their validity to a broader range of alloys. Experiments were conducted with alloys of different melting point (Fe base, Cu base and Sn). Quantitative measurements of the median particle size, tap density and several shape factors, and qualitative observations of the particle shape confirmed the importance of the heat transfer rate. It is shown that the inclusion of the solidification time effect results in a better agreement between calculated and experimental data when both low and high melting temperature alloys are taken together.
Revista:
INTERNATIONAL JOURNAL OF POWDER METALLURGY
ISSN:
0888-7462
Año:
2016
Vol.:
52
N°:
2
Págs.:
47 - 55
Despite the high oxygen sensitivity of manganese, its attractiveness as an alloying element in powder metallurgy steels is mainly cost but also accompanied with performance. Manganese is still scarcely used in industry, but research over many years has led to the development of manganese steels as lean alternatives for nickel- and copper-steels. Based on adding manganese in prealloyed form, or through a specially designed master alloy, the differences in microstructure, tensile strength, and hardness after sintering are discussed in terms of the overall chemical composition and alloying method. A detailed study of microstructural evolution is presented, based on interrupted sintering experiments from temperatures associated with the changes observed in the corresponding dilatometry traces.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2015
Vol.:
58
N°:
5
Págs.:
328 - 334
Powder blends within the Fe-Cu-C system are extensively used by the Powder Metallurgy industry. Based on the optimisation of mechanical properties the purpose of this work is to further understand the dimensional changes produced in the powder compact during sintering. Green compacts containing copper and carbon within ranges 0.5-3.5% Cu and 0.3-0.9% C were die pressed and sintered under different conditions varying processing parameters, including compaction pressure, temperature and time. Better understanding of the effect of different Cu/C combinations on dimensional changes was approached using the results obtained from dilatometry studies combined with interrupted sintering experiments. For selected specimens the effect of elemental Ni additions, at 1 and 4%, on dimensional changes was studied along with a detailed description of microstructural development. It was clearly observed that swelling due to copper melting and grain boundary diffusion is diminished as graphite additions were increased. The impact of Cu-C-Ni additions on hardness was also evaluated.
Autores:
Sarasketa, E.; Otaegi, L.; Rodriguez, L.M.; et al.
Revista:
SOLID STATE IONICS
ISSN:
0167-2738
Año:
2012
Vol.:
222 - 223
Págs.:
16 - 22
Porous Crofer Fe22Cr stainless steel supports for tubular Solid Oxide Fuel Cells (SOFC) were developed and tested successfully under hydrogen fuel with 50% humidification at 800 degrees C. Corrosion resistance and stability as a function of operation lifetime, porosity and thermal cycling were studied through the investigation of oxide growth and microstructure. Oxidation reactions followed subparabolic kinetics and substrates with porosities between 25 and 40% showed long-term stability over 4500 h and suitable properties for metal-supported SOFC technology application. (C) 2012 Elsevier B.V. All rights reserved.
Autores:
Bueno, S.; Saccarola, S.; Karuppannagounder, A.; et al.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2012
Vol.:
55
N°:
2
Págs.:
92 - 94
Ecological and economic demands are driving PM markets to incorporate less expensive, yet effective, alloying elements in iron based powders. To investigate their potential for this purpose recently developed sinter-hardening iron powders containing Cr and smaller amounts of Mo and Ni were industrially sintered at 1120 and at 1240 degrees C under laboratory conditions. One set of samples, containing 0.8% graphite additions, was cooled so to obtain sinter-hardened steels. A second set of samples, containing 0.3% graphite, was cooled under normal conditions and subjected to a secondary carburising treatment. The microstructures and mechanical properties developed were compared.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2012
Vol.:
548
Págs.:
189 - 194
This work studied the structural evolution of Cu-xMo (x = 5 and 8 wt.%) alloys processed by mechanical alloying using x-ray diffraction profiles, scanning electron microscopy, differential scanning calorimetric and microhardness. X-ray diffraction analysis was done using the modified Williamson-Hall and Warren-Averbach methods. These were used to determine structural properties, such as crystallite size, stacking fault probability and energy, dislocation density of metallic powder as a function of the amount of Mo and milling time. The main results obtained for both alloys were higher dislocation density and Vickers microhardness values were measured and crystallites sizes of around 10 nm were measured for both systems at 50 h of milling. Lattice defects increase the free energy and the free energy curves shift upwards, therefore the solubility limits change and Cu-Mo solid solution is formed. (C) 2012 Elsevier B.V. All rights reserved.
Revista:
SOLID STATE PHENOM
ISSN:
1012-0394
Año:
2011
Vol.:
172-174
Págs.:
1164 - 1170
Autores:
Rodriguez-Martinez, L.; Rivas, M.; Otaegi, L.; et al.
Revista:
ECS TRANSACTIONS
ISSN:
1938-5862
Año:
2011
Vol.:
35
N°:
1
Págs.:
445 - 450
Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. The most significant results to date include successful thermal cycling of the cell and anodic connection during 450 cycles and 2000 hours, oxidation testing of the metal support for more than 2500 hours and a comparison of influence of porosity during 100 hours oxidation of metal porous substrates under high water vapour atmospheres.
Autores:
Antepara, I.; Rivas, M.; Villarreal, I.; et al.
Revista:
JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY
ISSN:
1550-624X
Crofer can be considered as the reference interconnect material in solid oxide fuel cells (SOFCs) working under 800 degrees C. Thanks to its thermal expansion coefficient, it is suitable to replace ceramic components, such as the interconnect and the metal support, and it can be cost effective. Several research groups, including Ikerlan, have used porous substrates with the same composition as Crofer (PM from H. C. Starck GmbH, Goslar, Germany) as the metal support for their SOFC cells. The aim of this study is to determine the effect of certain variables (time, temperature, vapor content, cycling, porosity, and current flow), while other aspects are constant (sample composition and particle size and shape). [DOI: 10.1115/1.4001764]
Autores:
Saccarola, S.; Belin, G.; Bueno, S.; et al.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2010
Vol.:
53
N°:
3
Págs.:
184 - 187
A group of high strength, cost effective PM steels has been generated by combining alloying elements (e. g. Cr, Mo, Ni, Cu, Mn) in predetermined concentrations. The main aim was to optimise the balance between compressibility, hardenability and properties. Special efforts were devoted to identifying compositions and processing conditions giving specific proportions of transformation products (martensite, bainite, etc.) in an attempt to correlate microstructural characteristics with the mechanical properties of the sintered steels after tempering. Measuring dimensional changes after sintering as well as properties such as yield stress and hardness allowed processing conditions to be optimised for the composition and characteristics of the powder mixture.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2010
Vol.:
527
N°:
16-17
Págs.:
3949 - 3966
The present paper focuses on the initial stage of the liquid phase sintering (LPS) of a commercially available P/M Al-Si alloy, with nominal composition A1-14Si-2.5Cu-0.5Mg (in wt%). The microstructural examination of the as-received powder showed that it is constituted by pure Al particles and master alloy particles with composition Al-28Si-5Cu-1 Mg (in wt%). Its compressibility is lower than for the conventional elemental P/M aluminium premixes, but it is still better than for prealloyed Al powders and other P/M powders. Thermogravimetry experiments showed that the elimination of the organic lubricant takes place between 275 and 490 degrees C during heating to the sintering temperature. The phase transformations leading to the formation of the liquid phase were studied by differential scanning calorimetry (DSC). The dimensional changes associated with the generation of the liquid were measured by dilatometry. Samples quenched into water from different temperatures (between 450 and 575 degrees C) and times (between 0 and 30 min) were studied to reveal the microstructural evolution of the alloy. The first liquid is formed inside the master alloy particles at around 505 degrees C. This liquid spreads across the compact, enhancing the chemical homogenization of the material. The alloying elements diffuse from the liquid inside the originally pure Al particles, reducing their melting temperature. This alloying process is almost concluded at around 535 degrees C. When the temperature is increased the liquid starts to be formed also in the originally pure Al particles. The melting of the FCC Al-rich phase finishes around 575-590 degrees C. The full melting of the alloy occurs at about 635-645 degrees C. After analyzing the different possible causes, it is concluded that the main swelling mechanism is the volume change associated with the melting of a fraction of the material when the temperature is increased. The phases detected by X-ray diffraction (XRD) in the as-received powder and in the sintered compact are FCC Al-rich solid solution, Si, theta-phase (CuAl(2)), and Q-phase (Cu(2)Mg(8)Si(6)Al(5)). (C) 2010 Elsevier B.V. All rights reserved.