Solidification microstructures and mechanical properties of high-vanadium Fe–C–V and Fe–C–V–Si alloys

Fe–C–V and Fe–C–V–Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VC_x carbides. Depending on the alloy composition the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite + granular pearlite-like or granular pearlite-like + lamellar pearlite. In addition, it is shown that in Fe–C–V alloys the C/V ratio influences (a) the type of matrix, (b) the fraction of vanadium carbides, f_v and (c) the eutectic cell count, N_F. In Fe–C–V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by where C_e and V_e are the carbon and vanadium composition of the eutectic. Moreover, in the Fe–C–V alloys (depending on the alloy chemistry), the primary VC_x carbides crystallize with non-faceted or non-faceted/faceted interfaces, while the eutectic morphology is non-faceted/non-faceted with regular fiber-like structures, or it possesses a dual morphology (non-faceted/non-faceted with regular fiber-like structures + non-faceted/faceted with complex regular structures). In the Fe–C–V–Si system, the primary VC_x carbides solidify with a non-faceted/faceted interface, while the eutectic is non-faceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe–C–V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility.     

The effect of aluminum on the microstructure and phase composition of boron carbide infiltrated with silicon

Reaction-bonded boron carbide is prepared by pressureless infiltration of boron carbide preforms with molten silicon in a graphite furnace under vacuum. The presence of Al₂O₃ parts in the heated zone, even though not in contact with the boron carbide preform, causes aluminum to appear in the liquid silicon. The formation of aluminum sub-oxide (Al₂O) stands behind the transport of aluminum into the composite. The presence of aluminum in the boron carbide–silicon system accelerates the transformation of the initial boron carbide particles into B_x(C,Si,Al)_y and Al_1.36B₂₄C₄, newly formed carbide phases_. It also leads during cooling to the formation of some Si–Al solid solution particles. The effect of Al on the microstructural evolution is well accounted for by the calculated isothermal section of the quaternary Al–B–C–Si phase diagram, according to which the solubility of boron in liquid silicon increases with increasing aluminum content. This feature is a key factor in the evolution of the microstructure of the infiltrated composites.     

High-temperature stability of the mechanical and optical properties of Si–B–C–N films prepared by magnetron sputtering

Quaternary Si–B–C–N materials are becoming increasingly attractive due to their possible high-temperature and harsh-environment applications. In this work, amorphous Si–B–C–N films with two compositions (Si₃₄B₉C₄N₄₉ and Si₃₆B₁₃C₇N₄₀) and low contamination level (H + O + Ar < 4 at.%) were deposited on silicon substrates by reactive dc magnetron co-sputtering using two different targets and gas mixtures. Thermal stability of these films was investigated in terms of composition, bonding structure, as well as mechanical and optical properties after annealing in helium up to a 1300°C substrate limit. Films with a high nitrogen content (Si₃₄B₉C₄N₄₉, i.e. N/[Si + B + C]~ 1.0) were found to be stable up to 1300°C. After annealing, the hardness and elastic recovery of those films slightly increased up to 27 GPa and 84%, respectively, and the reduced Young's modulus remained practically constant (~ 170 GPa). The refractive index and the extinction coefficient at 550 nm were evaluated at 2.0 and 5 × 10^− 4, respectively, and the optical band gap was approximately 3.0 eV. In contrast, films with a lower nitrogen content (Si₃₆B₁₃C₇N₄₀, i.e. N/[Si + B + C]~ 0.7) were stable only up to 1200°C. Both Si–B–C–N materials studied here exhibited extremely high oxidation resistance in air up to the 1300°C substrate limit.     

Effects of thermo-mechanical processing and trace amount of carbon addition on tensile properties of Cu–2.5Fe–0.1P alloys

The effects of thermo-mechanical processing, including intermediate aging treatment and/or solution heat treatment, and a trace amount of carbon (C) addition were studied on tensile behavior of Cu–2.5Fe–0.1P alloys. In this study, Cu–2.5Fe–0.1P alloy sheets without and with a carbon content of 0.05 wt.% were cast and subsequently rolled and thermo-mechanically treated following various processing routes. The introduction of intermediate aging treatment between cold rolling improved the tensile strength of Cu–2.5Fe–0.1P alloys. Solution heat treatment prior to aging was proved to be detrimental on the tensile strength, probably due to recovery and recrystallization causing the complete loss of work hardening during previous cold rolling. The present study also suggested that two-step aging is more effective in improving the strength of Cu–2.5Fe–0.1P alloys than one-step aging. The effect of C addition on improving the tensile strength of Cu–2.5Fe–0.1P alloys was real but marginal, probably due to the limited solubility of C in Cu–2.5Fe matrix. The effects of intermediate heat treatments between cold-rolling processes on tensile properties of Cu–2.5Fe–0.1P specimens with and without C addition are discussed based on optical, scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs, and SEM fractographs.     

Characterization of transient-liquid-phase-bonded joints in a duplex stainless steel with a Ni–Cr–B insert alloy

Transient liquid-phase bonding of a duplex stainless steel was performed with a Ni–Cr–B insert alloy. The microstructure of the joint region was investigated by cross-sectional and layer-by-layer characterization. According to the experimental studies, prior to completion of isothermal solidification, the bond microstructure can be expressed as γ-Fe + δ-Fe/γ-Fe + δ-Fe + BN/γ-Ni(Fe) + BN/γ-Ni + Cr-rich borides/γ-Ni + Ni₃B + Cr-rich borides (CrB, CrB₂, Cr₂B₃, Cr₃B₄, Cr₅B₃ and CrB₄), from the base metal side to the bonded-interlayer side. Complete isothermal solidification occurred at 1090 °C within 3600 s. Only the γ-Ni solid solution phase was present in the bonded interlayer, and BN precipitates were not removed after isothermal solidification. The formation of secondary-phase precipitates might be responsible for the presence of peak microindentation hardness in the bond region.     

Synergistic Effects of B4C and Sn on the Coupled Growth Pattern and Mechanical Properties of Mg–Y–Zn–Mn Alloy Containing LPSO and W Phases

The effect of boron carbide (B₄C) particles and Sn on the microstructure and mechanical properties of Mg₉₄Y_2.5Zn_2.5Mn₁ alloy is mainly studied in this work. The results show that separated addition of B₄C and Sn could not achieve very good results. The separated addition of Sn significantly promotes the formation of LPSO phase, but it cannot change the growth pattern of LPSO phase and W phase. Adding B₄C changes the growth pattern of LPSO phase, but cannot effectively promote the formation of LPSO phase. The addition of B₄C and Sn in combination achieves the growth pattern transformation of α‐Mg from irregular dendrite to equiaxed dendrite and refines the grain size, which makes LPSO phase and W phase no longer grow by coupled growth. When 0.02 wt% B₄C and 0.35 wt% Sn is added, the Mg₉₄Y_2.5Zn_2.5Mn₁ alloy's growth pattern is changed and grains are refined, and thus exhibit superior mechanical properties. (Ultimate tensile strength of 255 MPa and elongation of 8.8%).

     

Wetting behavior of liquid Fe–C–Ti alloys on sapphire

Wetting behavior in the (Fe–C–Ti)/sapphire system was studied at 1823 K. The wetting angle between sapphire and Fe–C alloys is higher than 90° (93° and 105° for the alloys with 1.4 and 3.6 at.% C, respectively). The presence of Ti improves the wetting of the iron–carbon alloys, especially for the alloys with carbon content of 3.6 at.%. The addition of 5 at.% Ti to Fe–3.6 at.% C provides a contact angle of about 30°, while the same addition to Fe–1.4 at.% C decreases the wetting angle to 70° only. It was established that the wetting in the systems is controlled by the formation of a titanium oxicarbide layer at the interface, which composition and thickness depend on C and Ti contents in the melt. The experimental observations are well accounted for by a thermodynamic analysis of the Fe–Ti–Al–O–C system.     

A study of tensile properties in Al–Si–Cu and Al–Si–Mg alloys: Effect of β-iron intermetallics and porosity

The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al₅FeSi platelet size and porosity values obtained.     

Mobility of small clusters of self-interstitial atoms in dilute Fe–Cr alloy studied by means of atomistic calculations

Atomistic simulations have been used to characterize the interaction and mobility of small clusters of self-interstitial atoms (SIAs) in dilute Fe–Cr alloys. The variety of migration mechanisms for Di- and Tri-SIA clusters in the bcc Fe matrix were studied using the nudged elastic band method. The corresponding binding and migration energies for the SIA clusters interacting with isolated Cr atoms and Cr–Cr close pairs were calculated using the two-band model interatomic potential. The obtained results are discussed in the light of available experimental data for dilute Fe–Cr alloys and are compared with results obtained using ab initio calculations.     

Densification behaviour and mechanical properties of pressureless-sintered B4C–CrB2 ceramics

B₄C based ceramics composites with 0–25 mol% CrB₂ were fabricated by pressureless sintering in the temperature range 1850°C to 2030°C. The CrB₂ addition enhanced the densification of B₄C due to the CrB₂–B₄C eutectic liquid phase formation. Both a high strength of 525 MPa and a modest fracture toughness of 3.7 MPa m^1/2 were obtained for the B₄C–20 mol% CrB₂ composite with a high-relative density of 98.1% after sintering at 2030°C. The improvement in fracture toughness is thought to result from the formation of microcracks and the deflection of propagating cracks resulting from the thermal expansion mismatch of CrB₂ and B₄C.     

Structure, microstructure and mechanical properties of PM Fe–Cu–Co alloys

Fe–Cu–Co alloys are the new generation of metal matrix for diamonds in powder metallurgy processed cutting tools. These alloys were created with the purpose of reducing the cobalt content in diamond tools. Nevertheless, little have been published, once this is a matter of industrial interest. In this work, samples of Fe–(15-30-45-60)wt.%Cu–20 wt.%Co alloys were processed by cold pressing at 350 MPa, followed by sintering at 1150 °C/25 min/10⁻² mbar. Structures formed during sintering were studied by XRD and EDS. Micro-structural aspects were observed by SEM. Densification, hardness and wear tests were also performed. The alloy Fe–60 wt.%Cu–20 wt.%Co presented the best global results, suitable for use in diamond cutting tools.     

The effect of Fe addition on processing and mechanical properties of reaction infiltrated boron carbide-based composites

Dense metal-ceramic composites based on boron carbide were fabricated using boron carbide and Fe powders as starting materials. The addition of 3.5–5.5 vol% of Fe leads to enhanced sintering due to the formation of a liquid phase at high temperature. Preforms, with about 20 vol% porosity were obtained by sintering at 2,050 °C even from an initial boron carbide powder with very low sinterability. Successful infiltration of the preforms was carried out under vacuum (10⁻⁴ torr) at 1,480 °C. The infiltrated composite consists of four phases: B₁₂(C, Si, B)₃, SiC, FeSi₂ and residual Si. The decrease of residual Si is due to formation of the FeSi₂ phase and leads to improved mechanical properties of the composites. The hardness value, the Young modulus and the bending strength of the composites fabricated form a powder mixture containing 3.5 vol% Fe are 2,400 HV, 410 GPa and 390 MPa, while these values for the composites prepared form iron free B₄C powder are 1,900 HV, 320 GPa and 300 MPa, respectively. The specific density of the composite was about 2.75 g/cm³. The experimental results regarding the sintering behavior and chemical interaction between B₄C and Fe are well accounted for by a thermodynamic analysis of the Fe–B–C system.

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Influence of additives on the microstructure and tensile properties of near-eutectic Al–10.8%Si cast alloy

The continuing quest for aluminum castings with enhanced mechanical properties for applications in the automotive industries has intensified the interest in aluminum–silicon alloys. In Al–Si alloys, the properties are influenced by the shape and distribution of the eutectic silicon particles in the matrix, as also by the iron intermetallics and copper phases that occur upon solidification. The detailed microstructure and tensile properties of as-cast and heat-treated new experimental alloy belonging to cast Al–Si near-eutectic alloys have been investigated as a function of Fe, Mn, Cu, and Mg content. Microstructural examination was carried out using optical microscopy, image analysis, and electron probe microanalysis (EPMA), wavelength dispersive spectroscopic (WDS) analysis facilities. Tensile properties upon artificial aging in the temperature range of 155–240 °C for 5 h were also investigated. The results show that the volume fraction of Fe-intermetallics increases as the iron or manganese contents increase. Compact polygonal or star-like particles form when the sludge factor is greater than 2.1. The Al₂Cu phase was observed to dissolve almost completely during solution heat treatment of all the alloys studied, especially those containing high levels of Mg and Fe, while Al₅Cu₂Mg₈Si₆, sludge, and α-Fe phases were found to persist after solution heat treatment. The β-Al₅(Fe,Mn)Si phase dissolved partially in Sr-modified alloys, and its dissolution became more pronounced after solution heat treatment. At 0.5% Mn, the β-Fe phase forms when the Fe content is above 0.75%, causing the tensile properties to decrease drastically. The same results are obtained when the levels of both Fe and Mn are increased beyond 0.75%, because of sludge formation. On the other hand, the tensile properties of the Cu-containing alloys are affected slightly at high levels of Mg as a result of the formation of Al₅Cu₂Mg₈Si₆ which decreases the amount of free Mg available to form the Al₂CuMg phase. The results also show that, for the heat-treated alloys, peak aging is achieved at 180 °C, although the highest quality index corresponds to 155 °C aging temperature, for all the alloys investigated. Accordingly, 155 °C may be considered as the optimal aging treatment. It is also consistent with this observation that quality index is more sensitive to variations in tensile ductility than in tensile strength.     

Microstructural investigations on as-cast and annealed Al–Sc and Al–Sc–Zr alloys

Al–Sc and Al–Sc–Zr alloys containing 0.05, 0.1 and 0.5 wt.% Sc and 0.15 wt.% Zr were investigated using optical microscopy, electron microscopy and X-ray diffraction. The phase composition of the alloys and the morphology of precipitates that developed during solidification in the sand casting process and subsequent thermal treatment of the samples were studied. XRD analysis shows that the weight percentage of the Al₃Sc/Al₃(Sc, Zr) precipitates was significantly below 1% in all alloys except for the virgin Al0.5Sc0.15Zr alloy. In this alloy the precipitates were observed as primary dendritic particles. In the binary Al–Sc alloys, ageing at 470 °C for 24 h produced precipitates associated with dislocation networks, whereas the precipitates in the annealed Al–Sc–Zr alloys were free of interfacial dislocations except at the lowest content of Sc. Development of large incoherent precipitates during precipitation heat treatment reduced hardness of all the alloys studied. Growth of the Al₃Sc/Al₃(Sc, Zr) precipitates after heat treatment was less at low Sc content and in the presence of Zr. Increase in hardness was observed after heat treatment at 300 °C in all alloys. There is a small difference in hardness between binary and ternary alloys slow cooled after sand casting.     

Microstructure and texture of rolled and annealed β titanium alloy Ti–10V–4.5Fe–1.5Al

This work describes the evolution of texture during cold rolling and annealing of a hot rolled and solution treated sheet of a low cost β titanium alloy Ti–10V–4.5Fe–1.5Al. The alloy was cold rolled up to 60% reductions and then annealed in β phase field at different temperatures to study the re-crystallisation textures. The rolling and re-crystallisation textures obtained in this study are compared with those of other β titanium alloys and bcc metals and alloys such as tantalum and low carbon steel.     

Effect of Cr atoms on the formation of double kinks in screw dislocations in Fe and its correlation with solute hardening and softening in Fe–Cr alloys

In this work, we employed atomistic simulations to study the formation of a double kink (DK) on a screw dislocation in bcc Fe and to investigate how the presence of Cr affects it, using one of the most recent and reliable interatomic potentials for Fe and Fe–Cr systems (i.e. from Refs. [G.J. Ackland, M.I. Mendelev, D.J. Srolovitz, S. Han, A.V. Barashev, J. Phys.: Condens. Mat. 16 (2004) 1, P. Olsson, J. Wallenius, C. Domain, K. Nordlund, L. Malerba, Phys. Rev. B 72 (2005) 214119]). The formation energy of a DK of different lengths and structures, as well as the formation energies of each single kink and the interaction energies between them, have been obtained by performing large scale atomistic simulations and compared with the results obtained from elasticity theory. We show that the presence of Cr atoms, particularly Cr–Cr pairs, affects, sometimes significantly, the formation energy of DKs. The obtained results suggest a strong dependence of the effect of solute Cr atoms on dislocation motion in Fe–Cr alloys, depending on the actual Cr distribution, which in turn depends strongly on concentration and temperature. A possible framework to understand solute softening and hardening experimentally observed in Fe–Cr alloys is accordingly discussed.     

Magnetic properties of Nd–Fe–B/FeMn multilayer films

[Nd–Fe–B(x nm)/FeMn(d nm)]_n thin films were deposited by magnetron sputtering on Si (100) substrates heated at 650 °C. The influence of the composition and thickness of FeMn layer on the structure and magnetic properties of Nd–Fe–B films are investigated. The Nd–Fe–B/FeMn multilayer films present an enhanced coercivity and a reduced saturation magnetization, in comparison with those of a Nd–Fe–B single layer. The coercivity of [Nd–Fe–B(x nm)/FeMn(5 nm)]_n films increases with increasing the period number of FeMn layer for the same thickness of magnetic layer, while the coercivity in [Nd–Fe–B(50 nm)/FeMn(5 nm)]_n films increases with decreasing the period number of Nd–Fe–B/FeMn bilayers. The coercivity H_c of about 17.2 kOe is achieved in the Nd–Fe–B(50 nm)/FeMn(5 nm) film.     

Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al–20Si–5Fe alloys

The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al–20Si–5Fe–2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 10⁵ K/s and 5 × 10⁷ K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated. Results showed a profound effect of the cooling rate, consolidation stage, and transition metals on the microstructure and mechanical strength of Al–20Si–5Fe alloys. While microstructural refining was obtained at both cooling rates, the microstructure of the atomized powder exhibited the formation of fine primary silicon (~ 1 μm), eutectic Al–Si phase with eutectic spacing of ~ 300 nm, and δ-iron intermetallic. Supersaturated Al matrix containing 5–7 at.% silicon and nanometric Si precipitates (20–40 nm) were determined in the microstructure of the melt-spun ribbons. The hot consolidation resulted in coarsening of Si particles in the atomized particles, and precipitation of Si and Fe-containing intermetallics from the supersaturated Al matrix in the ribbons. The consolidated ribbons exhibited higher mechanical strength compared to the atomized powders, particularly at elevated temperatures. The positive influence of the transition metals on the thermal stability of the Al–20Si–5Fe alloy was noticed, particularly in the Ni-containing alloy.     

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Assessment of B4C reaction with liquid iron alloys

The degree of reaction achieved when B₄C powders are brought into contact with liquid iron alloys has been assessed by a levitation dispersion test. Reaction occurs rapidly, leading to boron carbide dissolution and iron boride formation. In carbon-free iron alloys borocarbide, Fe₂₃(C, B)₆, also forms and in low-carbon iron alloys free graphite was also formed. Highcarbon alloys reacted to form both Fe₃(C, B) and free graphite. Attempts to provide protection for the B₄C by forming a TiC coating on its surface byin situ reactions with liquid Fe-Ti and Fe-Ti-C alloys proved unsuccessful, with TiC forming as a dispersed phase throughout the iron matrix