Cr Si Research Articles

Effect of dual-scale FeCrSi phase on the strength and conductivity of Cu-2.5Fe-0.3Cr-0.2Si alloy

A new dual-scale (submicron and nanoscale) FeCrSi ternary second-phase has been successfully constructed in designed Cu-2.5Fe-0.3Cr-0.2Si alloy. The synergistic addition of Cr and Si promotes the transformation of the submicron Fe phase morphology from “square” to “flower” shape in as-cast alloys. The orientation relationship between nanoscale FeCrSi phase and Cu matrix is: [011] Cu//[01‾1] Fe11CrSi4 and the misorientation angle between the (200) of the Cu matrix and the (022) of the Fe11CrSi4 phase is about 4°. After three-stage thermomechanical treatment, the tensile strength and electrical conductivity of the alloy are 435 MPa and 70.52 %IACS, respectively. According to the calculated results, precipitation strengthening and substructure strengthening play an important role in the strengthening of Cu–Fe–Cr–Si alloys. With the addition of Cr and Si, the precipitation of the second phase in the alloy is promoted, which also leads to the improvement of the electrical conductivity and mechanical properties of the alloy.

Effects of Ti on microstructure and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

The effects of Ti on the microstructure and properties of Fe–20Mn–6Si–8Cr–5Ni shape memory alloy prepared by powder metallurgy were investigated. The results showed that trace Ti elements could improve the alloy's compressive yield strength and fracture strength. With the increase of Ti, a precipitated phase gradually appeared in the alloy, which adversely affected the mechanical properties of the alloy. The addition of Ti increased the lattice microstrain of the alloy, which provided the driving force for the martensitic phase transformation and facilitated the shape memory properties of the alloy. There was a relationship between the Ti content and the corrosion resistance of the alloy, with a small amount of Ti producing dispersion strengthening to improve the corrosion resistance of the alloy, and an excess of Ti causing composition segregation to make the alloy susceptible to corrosion. Ultimately, 0.5 wt% Ti was found to have good overall mechanical properties with a compressive yield strength of 1567 MPa and fracture strength of 2140MPa, its superelastic strain was 2.8% and 3.1% (at 10% and 15% pre-strain), respectively.

Effect of floating grains on the deformed microstructure of Mn- and Cr-containing Al-Mg-Si-Cu alloys

The effects of floating grains on the deformed microstructure of a Mn- and Cr-containing Al-Mg-Si-Cu alloy were first clarified based on a comparative study of the dispersoid precipitation and recrystallization behavior with and without floating grains. The presence of floating grains in the direct-chill casting billets resulted in inhomogeneous and sparse precipitation of the α-Al(Mn,Cr)Si dispersoids after homogenization. In response, the Zener drag force was significantly reduced and severe localized recrystallization occurred in the specimen containing floating grains after hot working. Whereas, the specimen without floating grains, which had dense and fine dispersoids, still had an ideal recovery microstructure after solution soaking. The innate reason consists in the special microscale features of floating grains, which significantly decreased the nucleation rate of the dispersoids-forming β′ precipitates.

Effect of thermomechanical treatment and microstructure on pseudo-elastic behavior of Fe–Mn–Si–Cr–Ni-(V, C) shape memory alloy

This study systematically investigated the effects of heat and thermomechanical treatments on the pseudo-elastic behavior of an Fe-based shape-memory alloy (Fe–17Mn–5Si–10Cr–4Ni-1(V, C) %wt.). First, samples were solution-annealed at 1000 °C for 2 h and aged at 760 °C for 6 h. A thermomechanical treatment was then applied to the heat-treated samples. The microstructure and mechanical properties (i.e., 0.1% yield stress and pseudo-elasticity) were characterized using X-ray diffraction, scanning and transmission electron microscopy, and uniaxial tensile tests. The results showed that decreasing the grain size and precipitation of VCs resulted in an improved pseudo-elasticity. The thermomechanical treatment decreased the number of thermal twins and developed a [111] texture in the austenite phase, which reduced the critical stress for inducing martensite. The presence of VC precipitates and texture formation in the thermomechanical-treated samples increased the pseudo-elastic strain more than twofold from 0.4 to 0.98%.

Enhanced carbon solubility in solvent for SiC rapid solution growth: Thermodynamic evaluation of Cr–Ce–Si–C system

The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal, which could determine the growth rate and quality of the products. However, the carbon dissolving ability of binary alloy solvent still needs to be improved. Here, we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr–Ce–Si ternary solvent, showing great potential for SiC solution growth. The phase relations of Cr–Ce–Si–C system were determined by using CALPHAD method based on thermodynamic parameters of CeCr2Si2C. It is indicated that the Cr–Ce–Si ternary solvent shows much larger carbon solubility in temperature range from 1700 to 2000 °C compared to Cr–Si binary one. Furthermore, the carbon supersaturation in solvent is also significantly increased in low temperature range after the addition of Ce, leading to a rapid growth rate. Our work not only demonstrates the feasibility of adding Ce in the alloy solvent for rapid growth of SiC crystal, but also provides an example for investigating the C solubility in ternary solvent.

Integrated phase equilibria experimental study and thermodynamic modeling of the Cr–Si–O, Fe–Cr–O and Fe–Cr–Si–O systems

Complete characterization of the Fe–Cr–Si–O system at high temperatures (700–2600 °C) is performed using integrated experimental and thermodynamic modeling research methodology. Experimental technique includes high-temperature equilibration, quenching and electron probe X-ray microanalysis (EPMA). Main challenges in the experiments are the choice of holding materials (substrate), fixing the oxygen partial pressure in a wide range, using the secondary standards for EPMA correction, overcoming slow reactions to achieve solid state equilibria. Thermodynamic modeling involves critical assessment of literature data, development of the mathematical models for the Gibbs energies of all phases in the system, and optimization of model parameters. The main modeling challenge is to obtain a self-consistent database, which requires a re-assessment of the Cr–Si–O and Fe–Cr–O sub-systems, and an accurate simultaneous description of all experimental data from literature and from the present study. There are several outcomes of the present study: a critical review of earlier work; a set of diagrams representing phase equilibria and distribution of elements among phases within the system; a set of thermodynamic model parameters for liquid and solid phases in the system. The results of the work will be applied to solve chemical engineering problems in pyrometallurgical production of copper, nickel and steel, recycling of waste electronics and designing refractory materials.

Improvement of mechanical properties through inhibition of oxidation by adding TiC particles in laser aided additive manufacturing of stainless steel 316L

Additive manufacturing has gained significant attention in recent years. However, oxidation is hard to be avoided especially for the directed energy deposition (DED) processes, which are normally operated in an open environment with inert gas shielding. Excessive oxidation will negatively affect the mechanical properties of the deposited materials. In this work, inhibition of oxidation was studied through adding TiC particles for laser aided additive manufacturing (LAAM) of stainless steel 316L. Notably, oxygen content can be reduced significantly, as TiC particles functioned as deoxidizers through chemical reaction with oxygen. Meanwhile, the large Si–Cr–Mn oxides can be changed into uniformly distributed fine TiO2 in the deposited stainless steel 316L. Consequently, ductility of the deposited stainless steel 316L was significantly improved by 54.1% with 5.6% increase in yield strength and 11.4% increase in ultimate tensile strength. This study shows a new way to overcome the negative effects of oxidation on the properties of the additively manufactured materials.

Evolution of shape memory effect with aging time during aging after pre-strain in Fe–Mn–Si–Cr–Ni–C shape memory alloys

The shape memory effect of Fe–Mn–Si–Cr–Ni–C shape memory alloys could be significantly improved by aging after pre-strain, because a high density of directional Cr23C6 particles is precipitated. However, the variation of shape memory effect under a large deformation-strain with aging time is not evident in the Fe–Mn–Si–Cr–Ni–C alloys subjected to aging after pre-strain. In order to clarify the above issue, the effect of aging time on the microstructures and the recovery-strain under a large deformation-strain of 7.5% for the Fe–Mn–Si–Cr–Ni–C alloy subjected to aging for 10–300 min after 10% pre-strain at room temperature was systematically investigated by XRD, SEM, EBSD, and EPMA. When the aging time was 30 min, the maximum recovery-strain of 5.4% was achieved. The recovery-strain increased from 4.9% to 5.4% when the aging time was extended from 10 min to 30 min. It is attributed to that the fraction of twin boundaries, inhibiting stress-induced ε martensitic transformation, decreased from 19.1% to 14.2%, as the precondition that the density of stacking faults, promoting stress-induced ε martensitic transformation, remained nearly constant. When the aging time was extended from 30 min to 180 min, the recovery-strain decreased from 5.4% to 4.6% due to both the decrement of stacking faults and the increment of twin boundaries.

Effect of contact time parameter on wettability and interface phenomena of B4C substrate by Ni–Cr–Si–Fe–B–C filler alloy

In the present research, the wettability of boron carbide ceramic by BNi-1 filler alloy at various contact times from 10 to 40 min has been studied. The results of sessile drop wetting tests showed that the BNi-1 filler alloy could spread well on the B4C surface at 10–40 min. With the increase of the contact time from the lowest time (10 min) to the highest time (40 min), the contact angle stably reduced, showing the enhancement of the spreading. However, by the increase of the contact time from 30 to 40 min, a slight change was observed in the wetting angle (from 21° to 19°). Overall, the appropriate spreading behavior of BNi-1 filler alloy on the B4C substrate can be attributed to the tendency of nickel for the reaction with B4C along with the simultaneous availability of silicon and chromium in the composition of this alloy. The maximum wetting angle of 48° was attained for the specimen with 10 min contact time and the minimum angle of 19° was achieved for the specimen with 40 min contact time. Due to the results, different compounds such as Ni4B3, CrB2, CrB, SiC, and Ni2Si have been observed at the system's interface. Moreover, the higher contact times can lead to the intensification of the system's interactions which can subsequently result in the higher penetration of the elements, the reacted area enlargement, and the formation of diverse microstructures and phases. The wetting experiments' results confirmed the spreading ratio calculations.

Study on Surface Modification of Fe–Si–Cr Alloy by Selective Oxidation Heat Treatment and its Corrosion Properties

Corrosion properties of the insulating oxide layer formed on the Fe–Si–Cr alloy through the selective oxidation heat treatment are evaluated to find out that the oxide layer can play a role as a barrier layer against corrosion. Preferential oxidation of Si and Cr during the selective oxidation heat treatment results in a two‐layered oxide layer. From the X‐ray photoelectron spectroscopy and transmission electron microscope results, it is revealed that the inner layer is SiO2 and the outer layer is Cr2O3, and they keep growing with the heat treatment time. The oxide layer formed by the selective oxidation heat treatment causes the ennoblement of the corrosion potential, but additional ennoblement does not occur with the growth of the oxide layer. However, the thickness of the oxide layer influences anti‐corrosion performance in terms of corrosion resistance and deterioration. The thicker the oxide layer is, the higher the corrosion resistance and the slower the deterioration become so that the protection property withstands for 3 h in the 3.5 wt% NaCl solution when the oxide layer has 44.3 nm thickness.

Microstructure and properties of Cu–Ni–Co–Si–Cr–Mg alloys with different Si contents after multi-step thermo-mechanical treatment

In this paper, a series of Cu-3.2Ni-0.6Co-xSi-0.2Cr-0.15 Mg (x = 0.62, 0.75, 0.92 and 1.09) (wt.%) alloys were fabricated and subjected to multi-step thermo-mechanical treatment (TMT), and the microstructure and properties of the alloys were investigated in detailed. The results showed that the alloys achieved the combination of high strengths and high conductivity, i.e. yield strengths of 809–913 MPa, tensile strengths of 849–951 MPa, and electrical conductivity of 33.4–42.0 %IACS. The good properties were due to nanoscale δ-(Ni,Co)2Si and Cr3Si precipitates, high-density dislocations, and even deformation twins. More importantly, it is found that the Ni, Co and Cr solute atoms decreased but the Si solute atoms increased with the Si contents in the alloys according to the principle of conservation of mass. For deformation, this change aggravated dislocation annihilation, reduced twinning propensity, and thus weakened the work-hardening effect. For precipitation, this change promoted the coarsening of nanoscale precipitates and the depletion of solute atoms, and thus weakened the precipitation-strengthening effect but benefited the electrical conductivity.

The effect of microstructures on the electrical properties of Cr–Si–C thin film resistors

The resistivity and temperature coefficient of the resistance (TCR) of Cr–Si–C films are investigated with various microstructures changed by annealing up to 1000 °C. The resistivity shows an abrupt change when the annealing temperature is between 450 °C and 600 °C, reaching its peak at 540 °C. In contrast, the TCR increases continuously and shifts from negative to positive values at around 510 °C. The crystal phase, microstructure and composition of the Cr–Si–C films are analyzed using X-ray diffraction, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The abrupt change in resistivity and TCR values above 450 °C annealing are attributed to the growth of Cr silicide crystals inside the amorphous Cr–Si–C film. The relationship between electrical properties and microstructures of Cr–Si–C film is discussed with the electrical current path model based on physical analysis.

Influence of the Oxygen Induced Surface Segregation Process of Solutes on the Anti-corrosion Properties of the Fe–Cr and Fe–Cr–Si Alloys

Influence of the Oxygen Induced Surface Segregation Process of Solutes on the Anti-corrosion Properties of the Fe–Cr and Fe–Cr–Si Alloys

Tailoring formation and proportion of strengthening phase in non-equiatomic CoCrFeNi high entropy alloy by alloying Si element

To adjust the formation and proportion of the strengthening phase in high entropy alloys (HEAs), the non-metallic Si element was added in non-equiatomic CoCrFeNi HEA. Co30Cr30(FeNi)40-xSix HEAs (x = 2, 4, 6, and 8 at.%, hereinafter, simplified as HSi2, HSi4, HSi6, and HSi8, respectively) were prepared. The phase evolution, tensile properties, and strengthening mechanisms were investigated. The results show that the phase structures are FCC, rich Cr–Si, and rich Ni–Si phases in HSi2 and HSi4. The rich Cr–Si phase disappears and the rich Ni–Si phase grows gradually with the increase of Si content. HSi6 presents an appropriate proportion of FCC and discontinuous rod-like rich Ni–Si phases. The mixing enthalpy (ΔHmix) is more suitable for the phase prediction in Co30Cr30(FeNi)40-xSix HEAs. With the increase of Si content, Ni atoms diffuse into the primary rich Cr–Si phase and replace Cr atoms to form a rich Ni–Si phase. The rich Ni–Si phase has a stronger binding force due to the Ni and Si atoms with more negative ΔHmix. The yield strength gradually increases from 215 MPa to 330 MPa with the increase of Si content. HSi6 has excellent tensile strength-ductility synergy with a tensile strength of 694 MPa and a fracture strain of 67.8%, which is attributed to high strain hardening ability. The discontinuous and rich Ni–Si phase plays an important role as a strengthening phase in the deformation process, reducing the free path of dislocation movement and delaying the occurrence of necking. The FCC phase with large plastic deformation ability leads to crack passivation and maintains a certain ductility. More rich Ni–Si phases will deteriorate the ductility of HSi8.

Core-loss reduction of Fe–Si–Cr crystalline alloy according to particle size in the high frequency band

We used different sizes of gas atomized Fe–Si–Cr alloy powder to produce soft magnetic composites (SMCs), this alloy has higher resistivity than existing materials used in SMCs. These powders were prepared by sieving raw materials which had an average size from less than 25 μm to over 63 μm. Our experiments show that as particle size decreases, the magnetic saturation tends to increase, the sample made from the powder with particles 25–38 μm in size recorded the highest magnetic saturation of 169.38 emu/g. Additionally, as particle size decreased, permeability increased. The sample made from powder with particles under 25 μm had a permeability of 20.7 H/m at 1 MHz. Also, the relationship between particle size and quality factor was found to be inversely proportional. Finally, the minimum core-loss was 187.26 kW/m3 at 1 MHz for the sample made from powder whose constituent particles are under 25 μm.

Radiation-induced segregation on dislocation loops in austenitic Fe-Cr-Ni alloys

Radiation-induced segregation of alloying elements to crystallographic defects is commonly observed in irradiated austenitic stainless steels. The interaction between solutes and radiation-induced defects changes the physical distribution of solutes and thus affects the formation and growth of defects. The change of the microstructure consequently affects the mechanical properties of the material. A qualitative and quantitative understanding of the interaction between solutes and defects is desirable to better predict the service lifetime of nuclear materials. We used atom probe tomography to measure the distribution of solutes at dislocation loops in 304L stainless steel, irradiated with 2 MeV protons up to 1.5 displacements per atom at 373 and 633 K. No segregation at dislocation loops was found in samples irradiated at 373 K, whereas Ni and Si enrichment and Cr depletion were detected at dislocation loops irradiated at 633 K. The experimentally observed perfect and faulted dislocation loops in vacancy and interstitial types were reproduced by molecular dynamics (MD). A hybrid MD/Monte Carlo method was used to predict the redistribution of alloying atoms at all possible types of dislocation loops in face-centered cubic Fe-Cr-Ni alloys at the same irradiated temperatures (373 and 633 K). The simulations show that, at both temperatures, Cr clusters were formed and distributed randomly, and Ni atoms enriched or depleted at interstitial or vacancy dislocation loops, respectively. The change of solute concentration reaches the highest at the edge of the loop. Ni profiles exhibit characteristic behavior in terms of the stress field of the loops: tension inside of vacancy loops showing depletion of Ni atoms compared with compression inside of interstitial loops showing enrichment of Ni atoms. In addition, the stress field is reduced after solute redistribution. The absence of alloying segregation observed in experiments at a lower temperature (373 K) is explained by a rate theory model: Low-temperature irradiation requires significantly longer irradiation time to see the same amount of segregation as at high temperatures because of the extremely low diffusion of vacancies at low temperatures.

Microstructure and Deformation Characteristics of Mn–Si–Cr Ultra-high Strength Steel

Microstructure and Deformation Characteristics of Mn–Si–Cr Ultra-high Strength Steel

Effect of Homogenization on Metallurgical Structure of Nicrofer 5520 (IN-617) Superalloy Joints Diffusion-Brazed Using a Ni–Cr–Si–B Interlayer

Effect of Homogenization on Metallurgical Structure of Nicrofer 5520 (IN-617) Superalloy Joints Diffusion-Brazed Using a Ni–Cr–Si–B Interlayer

Electronic and magnetic properties of MAX phase Cr2SiC with GGA+U approximation

In this work, we investigate the magnetic stability of Cr2SiC and electronic properties using the linear enhanced plane wave method (FP-LAPW) at full potential in generalized gradient approximation (GGA) and (GGA ​+ ​U). An anti-ferromagnetic spin order of Cr atoms is shown to be the ground state of this compound. Based on its electron band structures and state density (DOS), Cr2SiC has a metallic character and from the analysis of the projected site and of the moment densities, it follows that the bond is obtained by hybridization of Cr-3d with C -2p and Cr-3d with Si-3p states. Also note that the Cr–C bond is more covalent than Cr–Si. In the ferromagnetic phase (FM), the calculation of the polarized spin indicates that the total magnetic moment of Cr2SiC increases from 1.99 to 2.34 μB. Finally, we expect that the theoretical study of this material will give an idea for experimenters in the future.

Surface Plasmonic Lasing in Micro-Nanostructures of Silicon Excited by using Pulsed Infrared Lasers

Surface plasmon is a possible candidate to break the diffraction limit and open the door for developing nanolasers on silicon chips. A new step in this development involves the choice of the structures and compositions for better surface plasmonic emission. The micro-nanostructures were fabricated by using a nanosecond pulsed laser on silicon surface, in which the surface plasmonic emission is stronger. The group of emission peaks with multiple-longitudinal-mode occurs in the optical gain curve. Interestingly, the quantum energy of surface plasmon with 140[Formula: see text]meV has been measured at first, which is related to the peak interval (about 62[Formula: see text]nm) of longitudinal modes in the surface plasmonic lasing spectra. The surface plasmonic lasing near 865[Formula: see text]nm was observed in the Purcell cavity with Si–Cr–Si layers excited by using pulsed lasers at 1064[Formula: see text]nm. Surface plasmonic structure induced with photons was observed by using the reflection Talbot effect image, in which the mechanism of the surface plasmonic lasing can be explored. The physical model of the surface plasmonic laser has been built on the energy levels of the micro-nanostructures of Si.