scholarly journals Production of Ultrafine Grained Hardmetals by Electrical Resistance Sintering

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 159 ◽  
Author(s):  
Jesús Cintas ◽  
Raquel Astacio ◽  
Francisco Cuevas ◽  
Juan Montes ◽  
Thomas Weissgaerber ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Electrical Resistance ◽  
Processing Parameters ◽  
Medium Frequency ◽  
Main Achievement ◽  
Processing Times ◽  
Ultrafine Grained ◽  
Protective Atmospheres ◽  
Optimal Values

In this work, powders of cemented ultrafine WC-6 wt.% Co were consolidated. The feasibility of the medium frequency electrical resistance sintering (MF-ERS) technique were studied to prevent WC grain growth during consolidation. Porosity and hardness were measured at different zones of the MF-ERS compacts. The compacts showed a slight inhomogeneity in their properties across their section, but it was controlled by choosing suitable values of the processing parameters. The optimal values for the material studied were current intensities between 7 and 8 kA and sintering times between 600 and 800 ms. The main achievement using this consolidation method was that sintered compacts essentially maintained the initial WC grain size. This was attained to processing times of less than 2 s, and without the need for using protective atmospheres.

scholarly journals Relevance of processing parameters for grain growth of metal halide perovskites with nanoimprint

2021 ◽  
Vol 127 (9) ◽  
Author(s):  
Andre Mayer ◽  
Tobias Haeger ◽  
Manuel Runkel ◽  
Johannes Rond ◽  
Johannes Staabs ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Secondary Growth ◽  
Processing Parameters ◽  
Post Processing ◽  
Perovskite Layer ◽  
Processing Step ◽  
Similar Preparation ◽  
Materials Used ◽  
Log Normal

AbstractThe quality and the stability of devices prepared from polycrystalline layers of organic–inorganic perovskites highly depend on the grain sizes prevailing. Tuning of the grain size is either done during layer preparation or in a post-processing step. Our investigation refers to thermal imprint as the post-processing step to induce grain growth in perovskite layers, offering the additional benefit of providing a flat surface for multi-layer devices. The material studied is MAPbBr3; we investigate grain growth at a pressure of 100 bar and temperatures of up to 150 °C, a temperature range where the pressurized stamp is beneficial to avoid thermal degradation. Grain coarsening develops in a self-similar way, featuring a log-normal grain size distribution; categories like ‘normal’ or ‘secondary’ growth are less applicable as the layers feature a preferential orientation already before imprint-induced grain growth. The experiments are simulated with a capillary-based growth law; the respective parameters are determined experimentally, with an activation energy of Q ≈ 0.3 eV. It turns out that with imprint as well the main parameter relevant to grain growth is temperature; to induce grain growth in MAPbBr3 within a reasonable processing time a temperature of 120 °C and beyond is advised. An analysis of the mechanical situation during imprint indicates a dominance of thermal stress. The minimization of elastic energy and surface energy together favours the development of grains with (100)-orientation in MaPbBr3 layers. Furthermore, the experiments indicate that the purity of the materials used for layer preparation is a major factor to achieve large grains; however, a diligent and always similar preparation of the layer is equally important as it defines the pureness of the resulting perovskite layer, intimately connected with its capability to grow. The results are not only of interest to assess the potential of a layer with respect to grain growth when specific temperatures and times are chosen; they also help to rate the long-term stability of a layer under temperature loading, e.g. during the operation of a device.

Recrystallization and Grain Growth due to Annealing of an Ultrafine-Grained Al Alloy

2013 ◽  
Vol 753 ◽  
pp. 303-306
Author(s):  
Aicha Loucif ◽  
Roberto B. Figueiredo ◽  
Thierry Baudin ◽  
François Brisset ◽  
Terence G. Langdon
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Vickers Microhardness ◽  
High Pressure Torsion ◽  
Al Alloy ◽  
Size Refinement ◽  
Ultrafine Grained ◽  
Different Temperatures ◽  
Deformed State ◽  
Misorientation Angles

The evolution of the recrystallization microstructure at different temperatures and the related change in the microhardness were studied in an Al-6061 alloy after 2 turns of high-pressure torsion (HPT) by means of Vickers microhardness and EBSD analysis. The corresponding results show that HPT processing introduces a significant grain size refinement for the deformed state by comparison with the 150 µm grain size in the initial material. The microstructure after annealing at 200°C is relatively close to the as-processed one and the distribution of misorientation angles remains essentially unchanged. However, significant microstructural changes are produced with increasing annealing temperature and at the highest temperature (400°C) there is an abnormal grain growth. The variation of Vickers microhardness (Hv) after the different annealing treatments show a gradual decrease when the temperature increases.

Relationships between Processing Parameters and Properties of PZT Ceramics

2008 ◽  
Vol 55-57 ◽  
pp. 57-60
Author(s):  
C. Puchmark ◽  
Gobwute Rujijanagul
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Lead Zirconate Titanate ◽  
Sintering Temperature ◽  
Processing Parameters ◽  
Lead Zirconate ◽  
Growth Equation ◽  
Sintering Process ◽  
Pzt Ceramics ◽  
Linear Fit

In present work, lead zirconate titanate (PZT) ceramics, having the composition near morphotropic phase boundary were prepared by conventional mixed oxide method. The sintering process was performed at various sintering temperatures ranging from 1100 to 1300 oC. Relationships between phase and sintering temperature, and phase and structure were reported. An increase sintering temperature affected the increase in grain size. The grain growth rate was found to have a linear fit with the phenomenological kinetic grain growth equation. Tetragonal relative fraction increased with increasing sintering temperature. In addition, dielectric constant at dielectric peak increased with increasing grain size which consistent with the trend of tetragonality.

scholarly journals Structural evaluation and mechanical properties of AZ31/SiC nano-composite produced by friction stir welding process at various welding speeds

2017 ◽  
Vol 233 (5) ◽  
pp. 831-841 ◽  
Author(s):  
A Abdollahzadeh ◽  
A Shokuhfar ◽  
H Omidvar ◽  
JM Cabrera ◽  
A Solonin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Friction Stir Welding ◽  
Grain Growth ◽  
Welding Process ◽  
Processing Parameters ◽  
Nano Particles ◽  
Homogeneous Distribution ◽  
Friction Stir ◽  
The Matrix

A metal matrix composite made of AZ31 containing SiC nano-particles was successfully produced by friction stir welding (FSW), and the effect of processing parameters such as rotational and transversal speeds on the microstructure (grain size) and mechanical properties (tensile and hardness tests) were investigated. Prior to friction stir welding, nano-sized SiC particles were incorporated into the joint line and then different rotational (600, 800 and 1000 r/min) and transversal speeds (25, 75, 125 and 175 mm/min) were tested. The results indicated that the grain size of the matrix and SiC nano-particles are two key parameters controlling different characteristics of the developed composite. Both parameters, in turns, are dependent on the heat generated during the FSW process. The increase of rotational speed and decrease of transversal speed result in high amount of heat and homogeneous distribution of SiC nano-particles. The former leads to grain growth and decrease of strength and hardness, while the latter causes grain refinement and increases of strength and hardness. Accordingly, the heat input has opposite effects on matrix grain growth and homogeneous distribution of particles. Therefore, optimum values of rotational and transversal speeds were found (800 r/min and 75 mm/min) to produce the best microstructure and mechanical properties.

Effects of NbC/VC Addition on Mechanical Properties of Ultrafine Grained Cemented Carbides

2014 ◽  
Vol 602-605 ◽  
pp. 420-423
Author(s):  
Ai Min Jiang ◽  
Xian Quan Jiang ◽  
Zi Peng Zhao ◽  
Jin Yang ◽  
Rong Yu
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Growth ◽  
Sintered Sample ◽  
Cemented Carbides ◽  
Vacuum Sintering ◽  
Ultrafine Grained ◽  
Effective Reduction ◽  
Co Alloys ◽  
Co Doped

The samples are prepared by vacuum sintering technology, and the effects of VC/NbC combined addition on the mechanical properties of the WC-8% Co alloys with superfine grain are investigated. The results show that: with the transformation of Co-doped inhibitors content, the grain growth is inhibited and the grain size 460nm at 0.4%NbC/0.4%VC. The mechanism that Co-doped NbC/VC on the effective reduction of ultrafine WC-8%Co cemented carbides was analyzed. The 0.4%NbC/0.4%VC addition equipped with the best integrated properties was obtained in this study. And sintered sample were investigated with SEM.

Medium-Frequency Electrical Resistance Sintering of Highly Oxidized Iron Powder

2018 ◽  
Vol 772 ◽  
pp. 113-117
Author(s):  
Raquel Astacio ◽  
Fatima Ternero ◽  
Eduardo Sanchez Caballero ◽  
Juan Manuel Montes ◽  
Francisco Gomez Cuevas
Keyword(s):  
Electrical Resistance ◽  
Processing Parameters ◽  
High Energy ◽  
Heating Time ◽  
Current Intensity ◽  
Medium Frequency ◽  
Consolidation Process ◽  
Oxidized Iron ◽  
Hardness Change ◽  
Compression Resistance

Highly oxidized iron powders were consolidated by means of the medium-frequency electrical resistance sintering technique (MF-ERS). In order to activate the powders and to disperse the oxides coating the particles, prior to the consolidation process, powders were milled in a high-energy mill for 7 minutes. Structural and mechanical characterisations of electrically consolidated compacts were carried out in order to study the effect of two main processing parameters (current intensity and heating time). The compact properties resulted to be very sensitive to these parameters, especially to the current intensity. A change from 5 kA to 10 kA in the current intensity makes the porosity to fall from 30% to 8%. Moreover, using a higher current intensity (10 kA) increases the mechanical properties of the final compacts: micro-hardness change in almost 50 HV, up to 104 HV 1, and compression resistance by around 500 MPa, up to 569 MPa.

Medium-Frequency Electrical Resistance Sintering and Electrical Discharge Consolidation of Metallic Powders

2018 ◽  
Vol 772 ◽  
pp. 123-127
Author(s):  
Fatima Ternero ◽  
Raquel Astacio ◽  
Francisco Gomez Cuevas ◽  
Jesus Cintas ◽  
Juan Manuel Montes
Keyword(s):  
Electrical Resistance ◽  
Electrical Discharge ◽  
Mechanical Characterization ◽  
Processing Parameters ◽  
Ultrafine Grain ◽  
Medium Frequency ◽  
Iron Powders ◽  
Uniform Microstructure ◽  
Sintering Time ◽  
Ultrafine Grain Size

Compacts of iron powders were prepared by medium-frequency electrical resistance sintering (MF-ERS) and electrical discharge consolidation (EDC). Structural and mechanical characterization was carried out in order to study the effect of the main processing parameters (current intensity and sintering time in MF-ERS and voltage and capacity in EDC). The compact properties resulted to be quite sensitive to the consolidation method and parameters. Porosities around 8% and microhardness of about 120 HV were reached. It is concluded that the MF-ERS process can be a best option for the consolidation of cemented carbide composites with composition WC-6wt.%Co. MF-ERS compacts of this composite show a very low porosity and reasonable uniform microstructure, preserving the original ultrafine grain size and an adequate hardness with a very quick processing cycle of the order of one second.

On the Stability of Defects and Grain Size in Ultrafine-Grained Copper during Cyclic Deformation and Subsequent Ageing at Room Temperature

2005 ◽  
Vol 475-479 ◽  
pp. 4055-4058 ◽  
Author(s):  
Cun Xin Huang ◽  
S.C. Wang ◽  
Shi Ding Wu ◽  
Cheng Bao Jiang ◽  
G.Y. Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Internal Stress ◽  
Grain Growth ◽  
Cyclic Deformation ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
The Stability ◽  
Pure Cu

Ultrafine-grained (UFG) pure Cu processed by equal channel angular pressing (ECAP) was subjected to cyclic deformation and subsequent ageing treatment at room temperature (RT) in order to investigate the stability of defects and grain size. Cyclic deformation for 1000 cycles at RT leads to a large decrease of internal stress. X-ray diffraction (XRD) shows that the stability of defects and grain size at RT in as-cyclic deformed sample is lower than that in as-processed sample and that a reduction of internal stress takes place prior to grain growth. TEM observations show that the microstructural evolution during ageing is characterized by normal grain growth accompanied with recovery within grain interior.

Microstructural Design and Control of Silicon Nitride Ceramics

MRS Bulletin ◽  
1995 ◽  
Vol 20 (2) ◽  
pp. 38-41 ◽  
Author(s):  
Mamoru Mitomo ◽  
Naoto Hirosaki ◽  
Hideki Hirotsuru
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Grain Growth ◽  
Processing Parameters ◽  
Microstructural Development ◽  
Nitride Ceramics ◽  
Microstructural Design ◽  
And Control

The improvement of mechanical properties by microstructural control has been one of the main topics of interest in the development of silicon nitride ceramics. Toughening, by developing an in situ composite or self-reinforced microstructure, has attracted particular attention.Microstructural design is a key factor in the optimization of processing parameters. The microstructures of sintered materials are composed of silicon nitride grains and grain boundaries, which can be either crystalline, amorphous, or partially crystalline, depending on the composition, amount of sintering additives, and processing parameters. Silicon nitride ceramics have been fabricated with an addition of metal oxides and rare-earth oxides that form a liquid phase during sintering and accelerate grain boundary diffusion. The effect of composition of the glassy phase on the mechanical properties of ceramics is presented by Becher et al. and Hoffmann elsewhere in this issue. This article focuses specifically on the design and control of grain size.As it is well recognized, many processing parameters affect grain growth behavior and the resulting microstructure. During sintering, the α- to β-phase transformation leads to a self-reinforcing microstructure on account of the anisotropic grain growth of the stable hexagonal β- Si3N4 phase. Therefore, α-rich powders are widely used for starting materials. Phase transformation accelerates anisotropic grain growth, resulting in an increase in the fracture toughness of Si3N4 ceramics. Kang and Han discuss the effect of phase transformation on nucleation and grain growth in an article in this issue. The effect of the grain-size distribution on microstructural development is described in this article, based on studies conducted mostly with β-Si3N4 powders.

scholarly journals Characterization of ultrafine-grained copper joints acquired by rotary friction welding

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
M. Ciemiorek ◽  
Ł. Morawiński ◽  
C. Jasiński ◽  
M. Orłowska ◽  
T. Chmielewski ◽  
...  
Keyword(s):  
Grain Size ◽  
Heat Input ◽  
Friction Welding ◽  
Uniform Elongation ◽  
Weld Zone ◽  
Base Material ◽  
Processing Parameters ◽  
High Energy ◽  
Ultrafine Grained ◽  
Rotary Friction Welding

AbstractCopper rods with ultrafine-grained microstructure, obtained by multi-turn ECAP processing, were subjected to Direct Drive Rotary Friction Welding using various processing parameters, such as rotational speed and pressure, which resulted in different energy and heat input. Even though friction welding is a high energy process, by a proper selection of processing parameters it was possible to maintain grain size at around 0.7 µm in the weld zone and preserve the UFG microstructure. These microstructural features translated into mechanical properties: the YS for those specimens was around 330 MPa. Processing parameters that resulted in a larger heat input caused an increase in grain size to around 2 µm; this, however, increased ductility and led to a uniform elongation exceeding 5%. Corrosion resistance in the stir zone increased, as was evident in the higher open circuit potential and higher corrosion potential in comparison with base material; the observed differences were about 50 mV. These changes can be explained by the higher fraction of HAGBs in the SZ.

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