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Metals, Volume 6, Issue 12 (December 2016)

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Open AccessArticle The Structural Evolution and Segregation in a Dual Alloy Ingot Processed by Electroslag Remelting
Metals 2016, 6(12), 325; https://doi.org/10.3390/met6120325
Received: 28 November 2016 / Revised: 15 December 2016 / Accepted: 16 December 2016 / Published: 21 December 2016
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Abstract
The structural evolution and segregation in a dual alloy made by electroslag remelting (ESR) was investigated by various analytical techniques. The results show that the macrostructure of the ingot consists of two crystallization structures: one is a quite narrow, fine, equiaxed grain region
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The structural evolution and segregation in a dual alloy made by electroslag remelting (ESR) was investigated by various analytical techniques. The results show that the macrostructure of the ingot consists of two crystallization structures: one is a quite narrow, fine, equiaxed grain region at the edge and the other is a columnar grain region, which plays a leading role. The typical columnar structure shows no discontinuity between the CrMoV, NiCrMoV, and transition zones. The average secondary arm-spacing is coarsened from 35.3 to 49.2 μm and 61.5 μm from the bottom to the top of the ingot. The distinctive features of the structure are attributed to the different cooling conditions during the ESR process. The Ni, Cr, and C contents markedly increase in the transition zone (TZ) and show a slight increase from the bottom to the top and from the surface to the center of the ESR ingot due to the partition ratios, gravity segregation, the thermal buoyancy flow, the solutal buoyancy flow, and the inward Lorentz force. Less dendrite segregation exists in the CrMoV zone and the transition zone due to a stronger cooling rate (11.1 and 4.5 °C/s) and lower Cr and C contents. The precipitation of carbides was observed in the ingot due to a lower solid solubility of the carbon element in the α phase. Full article
(This article belongs to the Special Issue Alloy Steels) Printed Edition available
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Open AccessArticle Effects of Multi-Phase Reinforcements on Microstructures, Mechanical and Tribological Properties of Cu/Ti3SiC2/C/BN/GNPs Nanocomposites Sintered by Vacuum Hot-Pressing and Hot Isostatic Pressing
Metals 2016, 6(12), 324; https://doi.org/10.3390/met6120324
Received: 18 October 2016 / Revised: 11 December 2016 / Accepted: 14 December 2016 / Published: 21 December 2016
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Abstract
Cu/Ti3SiC2/C/BN/GNPs nanocomposites were prepared by vacuum hot-pressing (HP) sintering and hot isostatic pressing (HIP) sintering methods. Microstructures, mechanical and tribological properties of Cu/Ti3SiC2/C/BN/GNPs nanocomposites were investigated. Microstructures were examined by optical microscopy (OM), X-ray diffraction
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Cu/Ti3SiC2/C/BN/GNPs nanocomposites were prepared by vacuum hot-pressing (HP) sintering and hot isostatic pressing (HIP) sintering methods. Microstructures, mechanical and tribological properties of Cu/Ti3SiC2/C/BN/GNPs nanocomposites were investigated. Microstructures were examined by optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscope (SEM). Mechanical properties were determined by the relative density, micro-Vickers hardness, as well as tensile strength, compressive strength and shear strength. Tribological behavior of the Cu/Ti3SiC2/C/BN/GNPs composite against the GCr15 steel ring was evaluated using an M-2000 wear tester with high tangential sliding velocity. Results demonstrated that BN and graphene nano-platelets (GNPs) have an impact on the microstructures and mechanical properties of Cu/Ti3SiC2/C/BN/GNPs nanocomposites. Based on microstructures, and mechanical and tribological properties of Cu/Ti3SiC2/C/BN/GNP nanocomposites, strengthening, fracture and wear mechanisms for synergistic enhancement by multi-phase reinforcements were analyzed. Full article
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Open AccessArticle Effect of Finish Rolling Temperature on the Microstructure and Tensile Properties of Nb–Ti Microalloyed X90 Pipeline Steel
Metals 2016, 6(12), 323; https://doi.org/10.3390/met6120323
Received: 12 October 2016 / Revised: 27 November 2016 / Accepted: 9 December 2016 / Published: 20 December 2016
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Abstract
The relationship between microstructure and tensile properties of an Nb–Ti microalloyed X90 pipeline steel was studied as a function of finish rolling temperature using a Gleeble 3500 simulator, an optical and scanning electron microscope, electron back scattered diffraction (EBSD), a transmission electron microscope
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The relationship between microstructure and tensile properties of an Nb–Ti microalloyed X90 pipeline steel was studied as a function of finish rolling temperature using a Gleeble 3500 simulator, an optical and scanning electron microscope, electron back scattered diffraction (EBSD), a transmission electron microscope (TEM) and X-ray diffraction. The results indicate that the microstructure is primarily composed of non-equiaxed ferrite with martensite/austenite (M/A) constituent dispersed at grain boundaries for the specimens with different finish rolling temperatures. With a decrease in the finish rolling temperature, the yield strength increases, following a significant increase in the grain refinement strengthening contribution and dislocation strengthening contribution, although the precipitation strengthening contribution decreases. The increasing yield ratio (YR) shows that the strain hardening capacity declines as a result of the microstructure evolution when decreasing the finish rolling temperature. Full article
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Open AccessArticle Structural and Corrosion Study of Uncoated and Zn-Cu Coated Magnesium-Based Alloy
Metals 2016, 6(12), 322; https://doi.org/10.3390/met6120322
Received: 31 October 2016 / Revised: 29 November 2016 / Accepted: 14 December 2016 / Published: 19 December 2016
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Abstract
Zn-Cu alloy was deposited onto AZ63 substrate, and the corrosion behaviour of resulting modified electrodes was investigated in 3 wt % NaCl solution in comparison with uncoated AZ63. Electrochemical, structural, and morphological study of the coating is presented. SEM images reveal that the
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Zn-Cu alloy was deposited onto AZ63 substrate, and the corrosion behaviour of resulting modified electrodes was investigated in 3 wt % NaCl solution in comparison with uncoated AZ63. Electrochemical, structural, and morphological study of the coating is presented. SEM images reveal that the surface morphology of the films is uniformly small spherical grain distributions. The XRD patterns illustrate polycrystalline structure and the formation of peaks corresponding to hexagonal close-packed ε-phase of Zn-Cu with various crystallographic orientations. Cyclic voltammetry was used to determine the potential ranges where the various redox processes occur. Linear sweep voltammetry results illustrate that longer exposure of uncoated AZ63 in NaCl solution produces a greater corrosion potential shift because of the formation of an oxide layer that did not prevent the progression of corrosion attack. The corrosion resistivity of Zn-Cu coated AZ63 is approximately two orders of magnitude greater than that of uncoated AZ63. Full article
(This article belongs to the Special Issue Selected Papers from ICWET16)
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Open AccessArticle The Effect of Ultrafast Heating on Cold-Rolled Low Carbon Steel: Formation and Decomposition of Austenite
Metals 2016, 6(12), 321; https://doi.org/10.3390/met6120321
Received: 11 November 2016 / Revised: 5 December 2016 / Accepted: 8 December 2016 / Published: 19 December 2016
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Abstract
The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM)
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The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 °C/s to 1500 °C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite. Full article
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Open AccessFeature PaperArticle Laser-Driven Ramp Compression to Investigate and Model Dynamic Response of Iron at High Strain Rates
Metals 2016, 6(12), 320; https://doi.org/10.3390/met6120320
Received: 14 October 2016 / Revised: 2 December 2016 / Accepted: 8 December 2016 / Published: 18 December 2016
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Abstract
Efficient laser shock processing of materials requires a good characterization of their dynamic response to pulsed compression, and predictive numerical models to simulate the thermomechanical processes governing this response. Due to the extremely high strain rates involved, the kinetics of these processes should
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Efficient laser shock processing of materials requires a good characterization of their dynamic response to pulsed compression, and predictive numerical models to simulate the thermomechanical processes governing this response. Due to the extremely high strain rates involved, the kinetics of these processes should be accounted for. In this paper, we present an experimental investigation of the dynamic behavior of iron under laser driven ramp loading, then we compare the results to the predictions of a constitutive model including viscoplasticity and a thermodynamically consistent description of the bcc to hcp phase transformation expected near 13 GPa. Both processes are shown to affect wave propagation and pressure decay, and the influence of the kinetics of the phase transformation on the velocity records is discussed in details. Full article
(This article belongs to the Special Issue Laser Shock Processing on Metal)
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Open AccessArticle Corrosion Fatigue of Austenitic Stainless Steels for Nuclear Power Engineering
Metals 2016, 6(12), 319; https://doi.org/10.3390/met6120319
Received: 21 September 2016 / Revised: 5 December 2016 / Accepted: 8 December 2016 / Published: 16 December 2016
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Abstract
Significant structural steels for nuclear power engineering are chromium-nickel austenitic stainless steels. The presented paper evaluates the kinetics of the fatigue crack growth of AISI 304L and AISI 316L stainless steels in air and in corrosive environments of 3.5% aqueous NaCl solution after
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Significant structural steels for nuclear power engineering are chromium-nickel austenitic stainless steels. The presented paper evaluates the kinetics of the fatigue crack growth of AISI 304L and AISI 316L stainless steels in air and in corrosive environments of 3.5% aqueous NaCl solution after the application of solution annealing, stabilizing annealing, and sensitization annealing. Comparisons were made between the fatigue crack growth rate after each heat treatment regime, and a comparison between the fatigue crack growth rate in both types of steels was made. For individual heat treatment regimes, the possibility of the development of intergranular corrosion was also considered. Evaluations resulted in very favourable corrosion fatigue characteristics of the 316L steel. After application of solution and stabilizing annealing at a comparable ∆K level, the fatigue crack growth rate was about one half compared to 304L steel. After sensitization annealing of 316L steel, compared to stabilizing annealing, the increase of crack growth rate during corrosion fatigue was slightly higher. The obtained results complement the existing standardized data on unconventional characteristics of 304L and 316L austenitic stainless steels. Full article
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Open AccessArticle Influence of Microstructure on Strength and Ductility in Fully Pearlitic Steels
Metals 2016, 6(12), 318; https://doi.org/10.3390/met6120318
Received: 24 October 2016 / Revised: 29 November 2016 / Accepted: 5 December 2016 / Published: 15 December 2016
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Abstract
This article deals with the relationship between the microstructure and both strength and ductility in eutectoid pearlitic steel. It is seen how standard mechanical properties and fracture micromechanisms are affected by heat treatment and the resulting microstructure in the material. The yield stress,
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This article deals with the relationship between the microstructure and both strength and ductility in eutectoid pearlitic steel. It is seen how standard mechanical properties and fracture micromechanisms are affected by heat treatment and the resulting microstructure in the material. The yield stress, the ultimate tensile strength and the ductility (measured by means of the reduction in area) exhibit a rising trend with the increasing cooling rate (associated with smaller pearlite interlamellar spacing and a lower pearlitic colony size), while the strain for maximum load shows a decreasing tendency with the afore-said rising cooling rate. With regard to the fracture surface, its appearance becomes more brittle for lower cooling rates, so that the fracture process zone exhibits a larger area with observable pearlite lamellae and a lower percentage of microvoids. Full article
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Open AccessFeature PaperArticle Detection of the Magnetic Easy Direction in Steels Using Induced Magnetic Fields
Metals 2016, 6(12), 317; https://doi.org/10.3390/met6120317
Received: 30 September 2016 / Revised: 25 November 2016 / Accepted: 8 December 2016 / Published: 15 December 2016
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Abstract
Conventional manufacturing processes cause plastic deformation that leads to magnetic anisotropy in processed materials. A deeper understanding of materials characterization under rotational magnetization enables engineers to optimize the overall volume, mass, and performance of devices such as electrical machines in industry. Therefore, it
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Conventional manufacturing processes cause plastic deformation that leads to magnetic anisotropy in processed materials. A deeper understanding of materials characterization under rotational magnetization enables engineers to optimize the overall volume, mass, and performance of devices such as electrical machines in industry. Therefore, it is important to find the magnetic easy direction of the magnetic domains in a simple and straightforward manner. The Magnetic easy direction can be obtained through destructive tests such as the Epstein frame method and the Single Sheet Tester by taking measurements in regions of irreversible magnetization usually called domains. In the present work, samples of rolled SAE 1045 steel (formed by perlite and ferrite microstructures) were submitted to induced magnetic fields in the reversibility region of magnetic domains to detect the magnetic easy direction. The magnetic fields were applied to circular samples with different thicknesses and angles varying from 0° to 360° with steps of 45°. A square sample with a fixed thickness was also tested. The results showed that the proposed non-destructive approach is promising to evaluate the magnetic anisotropy in steels independently of the geometry of the sample. The region studied presented low induction losses and was affected by magnetic anisotropy, which did not occur in other works that only took into account regions of high induction losses. Full article
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Open AccessArticle Effective and Environmentally Friendly Nickel Coating on the Magnesium Alloy
Metals 2016, 6(12), 316; https://doi.org/10.3390/met6120316
Received: 19 October 2016 / Revised: 17 November 2016 / Accepted: 2 December 2016 / Published: 11 December 2016
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Abstract
The low density and good mechanical properties make magnesium and its alloys attractive construction materials in the electronics, automotive, and aerospace industry, together with application in medicine due to their biocompatibility. Magnesium AZ91D alloy is an alloy with a high content of aluminum,
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The low density and good mechanical properties make magnesium and its alloys attractive construction materials in the electronics, automotive, and aerospace industry, together with application in medicine due to their biocompatibility. Magnesium AZ91D alloy is an alloy with a high content of aluminum, whose mechanical properties overshadow the low corrosion resistance caused by the composition of the alloy and the existence of two phases: α magnesium matrix and β magnesium aluminum intermetallic compound. To improve the corrosion resistance, it is necessary to find an effective protection method for the alloy surface. Knowing and predicting electrochemical processes is an essential for the design and optimization of protective coatings on magnesium and its alloys. In this work, the formations of nickel protective coatings on the magnesium AZ91D alloy surface by electrodeposition and chemical deposition, are presented. For this purpose, environmentally friendly electrolytes were used. The corrosion resistance of the protected alloy was determined in chloride medium using appropriate electrochemical techniques. Characterization of the surface was performed with highly sophisticated surface-analytical methods. Full article
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Open AccessArticle Ultrasonic Guided Wave Propagation through Welded Lap Joints
Metals 2016, 6(12), 315; https://doi.org/10.3390/met6120315
Received: 30 September 2016 / Revised: 30 November 2016 / Accepted: 6 December 2016 / Published: 10 December 2016
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Abstract
The objective of the research presented here is the investigation of ultrasonic guided wave (UGW) propagation through the lap joint welded plates used in the construction of a storage tank floors. The investigations have been performed using numerical simulation by finite element method
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The objective of the research presented here is the investigation of ultrasonic guided wave (UGW) propagation through the lap joint welded plates used in the construction of a storage tank floors. The investigations have been performed using numerical simulation by finite element method (FEM) and tested by measurement of the transmission losses of the guided waves transmitted through the welded lap joints. Propagation of the symmetric S0 mode in the welded stainless steel plates in the cases of different lap joint overlap width, operation frequency, and additional plate bonding caused by corrosion were investigated. It was shown that the transmission losses of the S0 mode can vary in the range of 2 dB to 8 dB depending on the ratio between lap joint width and wavelength. It was also demonstrated that additional bonding in the overlap zone caused by corrosion can essentially reduce transmission losses. Full article
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Open AccessArticle The Effects of Fe-Particles on the Tensile Properties of Al-Si-Cu Alloys
Metals 2016, 6(12), 314; https://doi.org/10.3390/met6120314
Received: 16 September 2016 / Revised: 11 November 2016 / Accepted: 5 December 2016 / Published: 10 December 2016
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Abstract
The effect of Fe-rich particles has been a topic for discussion in the aluminum casting industry because of the negative impact they exert on the mechanical properties. However, there are still contradictions on the effects of various morphologies of Fe-particles. In this study,
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The effect of Fe-rich particles has been a topic for discussion in the aluminum casting industry because of the negative impact they exert on the mechanical properties. However, there are still contradictions on the effects of various morphologies of Fe-particles. In this study, microstructural characterization of tensile tested samples has been performed to reveal how unmodified and modified Fe-rich particles impact on the tensile behavior. Analysis of additions of Fe modifiers such as Mn and Cr, showed higher amounts of primary Fe-rich particles (sludge) with increased porosity and, as result, degraded tensile properties. From the fracture analysis of tensile tested hot isostatic pressed (HIPed) samples it could be concluded that the mechanical properties were mainly governed by the Fe-rich particles, which were fracturing through cleavage, not by the porosity. Full article
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Open AccessArticle Morphology Analysis of a Multilayer Single Pass via Novel Metal Thin-Wall Coating Forming
Metals 2016, 6(12), 313; https://doi.org/10.3390/met6120313
Received: 30 June 2016 / Revised: 22 November 2016 / Accepted: 24 November 2016 / Published: 9 December 2016
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Abstract
Through using a novel micro-coating metal additive manufacturing (MCMAM) process in this study, the forming characteristics of the multilayer single-pass specimens were investigated. The forming defects including the porosity and the bonding quality between layers were analyzed. Moreover, we also attempted to study
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Through using a novel micro-coating metal additive manufacturing (MCMAM) process in this study, the forming characteristics of the multilayer single-pass specimens were investigated. The forming defects including the porosity and the bonding quality between layers were analyzed. Moreover, we also attempted to study the effect of process parameters such as flow rate, deposition velocity, and layer thickness on the forming morphology. Based on the results, the optimization of process parameters was conducted for the fabrication of thin-wall MCMAM. Finally, estimation criteria for the integrity of the interfacial bond were established. Full article
(This article belongs to the Special Issue 3D Printing of Metals) Printed Edition available
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Open AccessArticle Fretting Behavior of SPR Joining Dissimilar Sheets of Titanium and Copper Alloys
Metals 2016, 6(12), 312; https://doi.org/10.3390/met6120312
Received: 18 October 2016 / Revised: 2 December 2016 / Accepted: 2 December 2016 / Published: 9 December 2016
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Abstract
The fretting performance of self-piercing riveting joining dissimilar sheets in TA1 titanium alloy and H62 copper alloy was studied in this paper. Load-controlled cyclic fatigue tests were carried out using a sine waveform and in tension-tension mode. Scanning electron microscopy and energy-dispersive X-ray
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The fretting performance of self-piercing riveting joining dissimilar sheets in TA1 titanium alloy and H62 copper alloy was studied in this paper. Load-controlled cyclic fatigue tests were carried out using a sine waveform and in tension-tension mode. Scanning electron microscopy and energy-dispersive X-ray techniques were employed to analyze the fretting failure mechanisms of the joints. The experimental results showed that there was extremely severe fretting at the contact interfaces of rivet and sheet materials for the joints at relatively high loads levels. Moreover, the severe fretting in the region on the locked sheet in contact with the rivet was the major cause of the broken locked sheet for the joints at low load level. Full article
(This article belongs to the Special Issue Titanium Alloys 2017)
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Open AccessArticle Effect of Remelting Duration on Microstructure and Properties of SiCp/Al Composite Fabricated by Powder-Thixoforming for Electronic Packaging
Metals 2016, 6(12), 311; https://doi.org/10.3390/met6120311
Received: 30 August 2016 / Revised: 28 November 2016 / Accepted: 2 December 2016 / Published: 8 December 2016
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Abstract
In this work, a novel processing method called powder thixoforming was proposed to prepare composites reinforced with 50 vol % of SiC particles (SiCp) that were used for electronic packaging in order to investigate the effects of remelting duration on its
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In this work, a novel processing method called powder thixoforming was proposed to prepare composites reinforced with 50 vol % of SiC particles (SiCp) that were used for electronic packaging in order to investigate the effects of remelting duration on its microstructure and properties. Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods were applied for the material characterization and the corresponding physical and mechanical properties were examined in detail. The obtained results indicate that the remelting duration exerted a large effect on the microstructure as well as the SiCp/Al interfacial reaction. The density and hardness of the composite continuously increased with increasing remelting duration. The thermal conductivity (TC) and bending strength (BS) first increased during the initial 90 min and then decreased. The remelting duration exerted a limited influence on the coefficient of thermal expansion (CTE). The optimal TC, BS, and hardness of these composites were up to 135.79 W/(m·K), 348.53 MPa, and 105.23 HV, respectively, and the CTE was less than 6.5 ppm/K after the composites were remelted at 600 °C for 90 min. The properties of the composites could thus be controlled to conform to the application requirements for electronic packaging materials. Full article
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