Evolution Of Intermetallic Phases Research Articles

Intermetallic phase evolution and strengthening mechanisms of the titanium and stainless steel lap joints welded by interrupted pulsed arc welding

The study is focused on analyzing the intermetallic phase evolution and strengthening mechanisms of the titanium alloy and stainless steel (Ti-SS) seam-welded joints using interrupted pulsed arc welding (IPAW). The precise adjustment of welding parameters for the IPAW technique allowed for the successful creation of two different joining modes for Ti-SS joints: contact reactive brazing and fusion modes. The homogeneous composition in the brazing joints was achieved by the formation of a diffusion-driven eutectic liquid phase at the joining contact, resulting in an unusual eutectic structure consisting of β-Ti and TiFe. The molten pool at high temperatures caused an uneven distribution of composition and energy throughout the fusion joints. The fusion joints consisted of a Ti-rich layer, containing β-Ti and TiFe phases near the TC4 side, and a Fe-rich layer, containing TiFe2/TiCr2 and α-Fe phases near the 304SS side. The shear-bearing capacity of the joints exhibited an initial increase and subsequent decrease as the heat input increased. The low heat input resulted in the formation of the unwelding zone, which significantly reduced the shear resistance of the joints. With the increase of the heat input, a reduction in shear strength occurred due to the accumulation of TiFe2 brittle phases associated with the shift of the joining mode from the brazing to the fusion. The shear force decreased after reaching its maximum value, despite the joints being fully joined and the joining area expanding.

Kinetics of Intermetallic Phase Precipitation in Manual Metal Arc Welded Duplex Stainless Steels.

The article presents the influence of heat treatment on the kinetics of transformations in lean duplex LDX2101 steel and a weld made of standard duplex 2209 material, which was welded by manual metal arc welding. Changes in the microstructure, hardness, and magnetic phase content were analyzed after heat treatment was conducted at a temperature of 800 °C for a period ranging from 15 to 1440 min. Light and scanning microscopy, Vickers hardness measurements, and magnetic phase content measurements using a ferritoscope were used for the research. In the LDX2101 steel, the presence of δ-ferrite and γ austenite was identified and additional Cr2N nitrides were observed in the heat-affected zone. After heat treatment, the decomposition of δ ferrite into γ2 austenite and Cr2N nitrides was observed in both areas. In the case of weld made by the coated electrode in 2209 grade, a ferritic-austenitic microstructure with allotriomorphic austenite (γA), Widmanstätten austenite (γW), and idiomorphic austenite (γI) and δ-ferrite area with "bee swarms" of fine precipitations of chromium nitrides Cr2N and non-metallic inclusions (NMIs) of slag, formed during the welding process, are observed in the as-welded state. After heat treatment, the presence of the χ phase (after 15 min of annealing) and the σ phase (after 120 min of annealing) was additionally identified. The kinetics of intermetallic phase evolution in welds made from 2209 material were presented. The obtained results of hardness measurements and metallographic tests were correlated, which allowed for a quick check of the precipitation processes on the used element.

Effect of high temperature annealing on the microstructure evolution and hardness behavior of the Inconel 625 superalloy additively manufactured by laser powder bed fusion

Additive manufacturing of Inconel 625 components attracts great interest due to its ability to produce parts with complex geometries that are needed for high-temperature applications in the aerospace, energy, automotive and chemical industries. To take full advantage of the potential of additive manufacturing, an in-depth understanding of the effects of prolonged high-temperature annealing on microstructure and hardness evolution is needed. Previous research in this field has mainly focused on a limited range of temperature and time. This study aims to determine the effect of prolonged high-temperature annealing on the evolution of intermetallic phases and carbides, as well as changes in the dislocation substructure of Inconel 625 superalloy additively manufactured by laser powder bed fusion subjected to stress relief annealing and subsequent isothermal annealing at a temperature up to 800 °C for 5–500 h. The microstructure development is correlated with hardness behaviour. It is determined that the microstructure evolution proceeds in four stages with temperature and time increase. In the initial stress-relieved condition, a cellular microstructure with nano-sized precipitates of the Laves phase and NbC carbides at the cell walls occurs, and hardness is equal to 300 HV10. In the 1st stage of the microstructure evolution, the γ'' phase particles precipitate on the cell walls, which results in hardening up to 383 HV10 in the specimen annealed at 700 °C for 5 h. The 2nd stage involves the precipitation of the γ'' phase both on the cell walls and inside the cells, as well as the formation of dislocation networks, which contribute to the softening effect and hardness drop to 319 HV10. In the 3rd stage, at temperature 700 and 800 °C, the δ phase, M23C6 carbides, and the Laves phase precipitate and grow, and the subgrain boundaries are formed. The hardness is in the range of 340–350 HV10 and is higher than in the 2nd stage. In the 4th stage, as the annealing time is increased at a temperature of 800 °C, the δ phase and M23C6 carbides coagulate, and the Laves phase particles spheroidize or partially dissolve. Very intense precipitation and growth of the hard δ phase particles provide an increase in hardness to 402 HV10. As a result of systematic studies, the various strengthening and softening mechanisms acting during high-temperature annealing are determined.Graphical abstract

Microstructure and Intermetallic Phase Evolution during the Homogenization of an Al–Zn–Mg–Cu–Zr–Nd Aluminum Alloy

The intermetallic phase evolution during the homogenization of an Al–Zn–Mg–Cu–Zr alloy with Nd addition is investigated. Large amounts of the eutectic interdendritic acicular‐state η (MgZn2) phase, primary phase T (AlZnMgCu), Al8Cu4Nd, and Al7Cu2Fe exist at the grain boundaries of the as‐cast Al–Zn–Mg–Cu–Zr–Nd alloy. The homogenized intermetallic phase evolves as follows: the η phase dissolves into the α (Al) matrix, most of the T phase is dissolved in 16 h, and the remaining part of the T phase is transformed into the S phase (Al2CuMg) after 24 h. The stable Al8Cu4Nd phase in the alloy captures Cu atoms and inhibits the further generation of the S phase during homogenization. The addition of Nd decreases the fraction of the S phase, and only Al7Cu2Fe, Al8Cu4Nd, and Al2CuMg remain after homogenization for 24 h. Homogenization kinetics analysis suggests that the Al–Zn–Mg–Cu–Zr–Nd alloy is suitably homogenized at 470 °C 24 h−1.

Characterizing the Al Si coating on 22MnB5 steel using Raman spectroscopy

Aluminum‑silicon (Al Si) coatings protect 22MnB5 steel blanks from oxidation and decarburization during hot stamping of ultra-high strength automotive parts. These coatings melt near 577 °C, and then react with iron from the base steel, eventually forming a solid mixture of aluminum‑iron‑silicon (Al-Fe-Si) and aluminum‑iron (Al Fe) intermetallic phases. This work is the first to investigate the evolution of intermetallic phases and oxides in the Al Si coating using variable-temperature Raman microscopy. The pairing of in-situ observations with ex-situ analysis of samples treated across the temperature range of interest enabled individual phases to be identified as a function of temperature, and, for the first time, Raman spectra are assigned to relevant Al-Fe-Si and Al Fe intermetallic phases. In-situ spectroscopic measurements readily elucidate the formation of specific phases as a function of heating schedule, which is difficult to do via ex-situ analysis of quenched specimens. • Analyzed the evolution of the Al Si coating using in-situ Raman microscopy. • Melting reactions at various temperatures were documented. • Individual phases could be identified as a function of time and temperature. • The first Raman spectra for relevant intermetallic compounds were assigned.

Effect of composition on microstructure and properties of as-cast 2196 Al–Cu–Li alloy

The influence of Li, Mg and Ag on microstructure and properties of Al–Cu–Li alloys attracted great attention, while few reports on casting state. In fact, the as-cast condition greatly influences the microstructure and performance during later treatments. This study conducts casting experiments on 2196-based Al–Cu–Li alloys with different Li, Mg and Ag additions. The grain refinement, evolution of intermetallic phases, and modification of properties caused by the composition are investigated by OM, EBSD, SEM, TEM characterisation and mechanical testing. In particular, microstructural, microchemical and crystallographic characteristics of intermetallic phases are identified. The mechanism based on the compositional effect on microstructure evolution is clarified, in combination with thermodynamic calculation. The mechanism of modification of properties is discussed in relation to the microstructure variations.

Influence of the evolution of heat-resistant phases on elevated-temperature strengthening mechanism and deformation behavior in Al–Si multicomponent alloys

Evolution of the heat-resistant phases and deformation behavior of α-Al matrix of four alloys have been characterized by SEM and EBSD. The strengthening mechanisms influenced by morphology and distribution of the heat-resistant phases were described. And the strain contouring of the α-Al matrix after deformation was rendered. The heat-resistant phases with block-like as reticular or semi-reticular network distribution exist in grain boundary can effectively provide elevated-temperature strength for alloys, while the strain contouring of α-Al matrix is mainly concentrated in the area with fewer intermetallic phases. It is shown that intermetallic phase evolution corresponds to extrusion treatment and the formation of eutectic Si and primary Si, highly interconnected networks of intermetallic phases exist in the alloy in which the primary Si and the eutectic Si are simultaneously present or disappeared. And only the disappearance of the primary Si and the extrusion treatment will destroy the network structure of the intermetallic phases. A reticular or semi-reticular microstructure is more capable of matching strength and plasticity and facilitating uniform deformation of the α-Al matrix. And the destruction of this microstructure is allowed to accommodate more plastic strain before failure.

The Effect of Heat Treatments on the Microstructural Evolution of Twin-Roll-Cast Al-Fe-Si Alloys

Dilute Al-Fe-Si alloys with different Fe-Si ratios were prepared by twin-roll casting, rolling and heat treatment. Tensile measurements, optical microscopic observations and electron microscopy observations were performed to investigate the effects of heat treatments on the properties and microstructure evolution of the Al-Fe-Si alloys. The results indicate that in twin-roll cast dilute Al-Fe-Si alloys, the β-AlFeSi, αc-Al12Fe3Si and α'-Al8Fe2Si phases coexist. Eutectic αc-Al12Fe3Si can be observed due to the higher Fe concentration in the center layer. In a twin-roll cast Al-0.36Fe-0.4Si alloy, annealing at temperatures of 400 °C or higher would lead to the refinement of intermetallic particles, which is due to the partial dissolution of intermetallic particles or the decomposition of Si-rich phases. During a slow cooling period after annealing, the coarsening of the α'-Al8Fe2Si phase occurred below 400 °C after partial dissolution. The recrystallized grain size is not obviously affected by the evolution of intermetallic phases. The morphologies and types of intermetallic phases in twin-roll cast Al-0.44Fe-0.24Si alloy are unaffected by the heat treatments.

Evolution of intermetallic phases in an Al–Si–Ti alloy during solution treatment

Abstract A cast Al–Si–Ti alloy was solution treated at 540 °C for different periods between 0 and 72 h to understand the evolution of intermetallic phases. Only an (Al,Si)3Ti intermetallic phase with a low Si content was found in the as-cast alloy. The (Al,Si)3Ti particles were converted partly into a lamellar structure, a eutectoid phase, consisting of a Si-rich phase and an Al phase during solution treatment. The amount of the lamellar structure increased with the solution treatment time, but the composition of either constitute was kept almost unchanged regardless of the solution treatment times. The lamellar Si-rich phase is (Al,Si)2Ti (τ2) with a TiSi2 (C49-type) structure based on thermodynamic calculations and high-resolution TEM analyses. FCC Al phase is the product residing between the τ2 lamellae after the completion of transformation from (Al,Si)3Ti to τ2 phase. A near-rational orientation relationship (OR) between the Al and τ2 phases is determined as Al [110]//τ2 [100], Al ( 1 1 ¯ 1 ¯ )//τ2 [060]. The phase transformation from (Al,Si)3Ti to τ2 being a result of the diffusion of Ti and Si within the original (Al,Si)3Ti particulates as well as the Si diffusion from the Al matrix during solution treatment is proposed. The formation of the lamellar structure in the microstructure is attributed mainly to the limited diffusivity of Ti element.

Formation of intermetallic phases during solidification in Al-Mg-Mn 5xxx alloys with various Mg levels

In the present study, four Al-Mg-Mn 5xxx alloys with different Mg levels (2-5 wt.%) were investigated for better understanding the evolution of intermetallic phases formed during solidification. Optical and scanning electron microscopes, electron backscattered diffraction and differential scanning calorimetry analyses in combination with thermodynamic calculation were used to identify various intermetallic phases. Results showed that the most dominant intermetallic phases are Al6(Mn,Fe), α-Al(Fe,Mn)Si, Al3Fe, Alm(Mn,Fe) and Mg2Si in experimental Al-Mg-Mn alloys, which is greatly dependant on the Mg levels. It is found that Chinese script α-Al(Fe,Mn)Si is the dominant iron-rich intermetallic phase for the alloys containing 2-3 wt.% Mg, while blocky Al6(Mn,Fe) and needle-like Al3(Mn,Fe) become the major phases for the alloy containing 4 wt.% Mg. Further increasing Mg content to 5 wt. %, the dominant phase transfers to blocky Al6(Mn,Fe) intermetallic. Meanwhile, the morphology of primary Mg2Si is changed from well-branched to plate-like with increasing Mg contents. In addition, β-Al3Mg2 and τ-Al6CuMg4 eutectic phases have been observed in the alloys with 3-5 wt. % Mg. A comparison on various intermetallic phases from the Scheil simulation and the actual as-cast microstructure is provided.

Phase transformation and dispersoid evolution for Al-Zn-Mg-Cu alloy containing Sn during homogenisation

Optical microscope (OM), field emission scanning electron microscope (FESEM), energy dispersive X-ray Spectroscopy (EDS), transmission electron microscope (TEM) differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were employed to investigate the evolution of intermetallic phases during homogenisation at 465°C for 0–48h for Al-Zn-Mg-Cu-Sn alloy. Evidentially, casting is accompanied by severe dendritic segregation. The primary phases appeared during casting consisted of α (Al), eutectic mixture of η (Mg (Zn, Cu, Al)2), θ (Al2Cu) and coarse Al7Cu2Fe particles. After 6h of homogenisation, two eutectic phases namely S (Al2CuMg) and Cu3Sn were formed. The appearance of dendrites and their consequent dissolution with the progress of homogenisation time was modelled using a kinetic equation taking interdendritic spacing and temperature as two variants. TEM micrographs revealed the presence of high density of fine dispersoids after 6h of homogenisation following almost complete dissolution of the dendrites into the matrix after 48h of homogenisation. Coarsening of the said dispersoids was observed with further homogenisation treatment following Ostwald ripening mechanism and consequently lowering of Zener pinning pressure (ZPP). Crystallographic texture analysis revealed the formation of strong γ fibre in both cast and homogenised samples. However, strong α fibre along with Goss, Brass, P, and Copper components was also noticed in the cast sample.

Hypoeutectic Fe-Cr-Ni-Mo-C alloys additionally strengthened by the Frank-Kasper phases – Design by means of the CALPHAD approach

In the present work, the concept of hypoeutectic Fe-Cr-Ni-Mo-C alloys additionally strengthened by the Frank-Kasper phases is shown. The alloys were designed using the CALPHAD approach in order to obtain a matrix with high corrosion resistance, similar to that of stainless steels, and good wear resistance at room and elevated temperatures, achieved by the precipitation of eutectic carbides and the Frank-Kasper phases. The main design strategy is to produce alloys with a narrow solidification range and precipitations of the Frank-Kasper phases within the dendrites after heat treatment in order to reduce the mean free path of the matrix. The effect of molybdenum on the evolution of intermetallic phases in the Fe-25Cr-xMo-0.8C system was determined. Additionally, the influence of nickel in the Fe-25Cr-5Mo-xNi-0.8C system on phase composition of the matrix, as well as the stability and volume fraction of intermetallic phases were investigated. Lever-Rule and the modified Scheil-Gulliver solidifications were simulated for selected five alloys in order to investigate the phase precipitation sequence. Particular emphasis during the discussion was placed on the influence of Mo and Ni on phase stability, as well as solidus and liquidus temperatures in the investigated systems.

Solidification behavior and elimination of undissolved Al2CuMg phase during homogenization in Ce-modified Al–Zn–Mg–Cu alloy

The solidification behavior and intermetallic phase evolution during homogenization annealing of an Al–Zn–Mg–Cu alloy with 0.12 wt% Ce addition were examined. The residual Al2CuMg phase is completely dissolved after homogenization and is replaced by a large number of dispersed micro/nanoscaled AlCuCe enrichment phases within Al matrix. This change occurs because of the formation of a large number of finer lamellar eutectic network structures which are more easily dissolved into Al matrix during the homogenization process. In addition, the trapping of Cu atoms in the stable AlCuCe phase also prevents the formation of Al2CuMg phase, leading to the complete dissolution of Al2CuMg phase in the Al–Zn–Mg–Cu alloy. The grain refinement behavior in Al alloy with Ce addition is similar to that in alloys with the addition of Sc, because of the formation of primary Ce-enriched Al11Ce3 phase as the nucleation agent of α(Al) during solidification.

Optimization of A354 Al-Si-Cu-Mg Alloy Heat Treatment: Effect on Microstructure, Hardness, and Tensile Properties of Peak Aged and Overaged Alloy

The aim of the present work is the study of T6 heat treatment of A354 (Al-Si-Cu-Mg) casting alloy. The heat treatment was optimized by maximizing mechanical strength of the alloy while keeping the treatment cost effective, reducing treatment time and temperature. Due to the presence of low melting compounds, a double stage solution treatment was proposed. The first stage was aimed at the homogenization and dissolution of the low melting phase while a second stage at a higher temperature was evaluated to foster dissolution of Cu/Mg rich intermetallics and keep the solution time and temperature as low as possible. Microstructural investigations were performed through optical and electronic microscopy, which allowed the assessment of the evolution of intermetallic phases during the solution treatment. Artificial aging was studied at different temperatures from 160 °C to 210 °C where the peak aging condition was identified. Over aging of the heat treated alloy was evaluated by soaking T6 samples at 200, 245, and 290 °C for up to 168 h. Tensile behavior of the T6 and over-aged alloy (i.e., after soaking at 210 °C for 50 h) was evaluated at room temperature. Results showed that the proposed treatment allowed the enhancement of mechanical properties of the alloy in comparison to industrial practice treatment, maintaining a good level of ductility and conferring a superior resistance to long-term high temperature exposure.

Intermetallic phase evolution and strengthening effect in Al–Mg2Si alloys with different Cu/Ni ratios

Microalloying of an Al–15%Mg2Si alloy (wt%) with Ni and Cu produced an enhanced strengthening response, increasing hardness whilst also improving tensile strength due to the formation and evolution of intermetallic phases. With the increase of Cu/Ni ratios, intermetallic phases translate from Al3Ni or Al3CuNi to Al7Cu4Ni, and the total volume fraction of Al3CuNi and Al7Cu4Ni increases to 3.51% (1%Ni and 5%Cu, Cu/Ni ratio = 5). The thermally stable Al3CuNi and Al7Cu4Ni phases are connected to each other forming chains and tend to build up a network. As a result, the ultimate tensile strength (at 350 °C) of the alloy (Cu/Ni ratio = 5) reached up to 132 MPa, 131.6% higher than that of Al–15%Mg2Si alloy.

Microstructure and kinetics of intermetallic phase growth of three-layered A1050/AZ31/A1050 clads prepared by explosive welding combined with subsequent annealing

The effect of annealing has been investigated with respect to interface microstructure and evolution of intermetallic phases in three-layered explosively welded A1050/AZ31/A1050 specimens. Both interfaces in the state after welding were characterized by wavy shape morphology with intermediate phases, which formed segmented structures. Two different morphologies consisted of equiaxed and columnar grains were observed within the Mg2Al3 phase, while the Mg17Al12 phase was built of only columnar grains. Furthermore, a small amount of Mg23Al30 was detected by X-ray synchrotron diffraction. Annealing at 350°C strongly induced the Mg23Al30 phase development in the form of discontinuous layer between Mg2Al3 and Mg17Al12 phases after 10h of annealing. Kinetics calculations indicated that, Mg2Al3 phase growth at 300°C was controlled by different mechanisms according to the location: volume diffusion and chemical reaction at the upper interface and solely by volume diffusion at lower one. The growth of Mg17Al12 was governed only by volume diffusion. Furthermore, the same mechanisms were observed during annealing at 400°C, however this heat treatment significantly changed the microstructure i.e. the grain size and shape. It was also established that the nanohardness of both Mg2Al3 and Mg17Al12 was about 350HV.

Evolution of Intermetallic Phases in Soldering of the Die Casting of Aluminum Alloys

Most die failures are resulted from chemical reactions of dies and molten aluminum in the die casting of aluminum. The formation of intermetallic phases between a steel die and molten aluminum is investigated by stationary immersion tests and compared to a real die casting process. Three intermetallic phases are identified in the stationary immersion tests: a composite layer and two compact layers. The composite layer is a mixture of α bcc, Al, and Si phases. The α bcc phase changes in morphology from rod-like to spherical shape, while the growth rate of the layer changes from parabolic to linear pattern with immersion time. The first compact layer forms rapidly after immersion and maintains a relatively constant thickness. The second compact layer forms after 4 hours of immersion and exhibits parabolic growth with immersion time. In comparison, only a composite layer and the first compact layer are observed in a real die casting process. The fresh molten aluminum of high growth rate washes away the second intermetallic layer easily.

In situ transmission electron microscopy investigation of the interfacial reaction between Ni and Al during rapid heating in a nanocalorimeter

The Al/Ni formation reaction is highly exothermic and of both scientific and technological significance. In this report, we study the evolution of intermetallic phases in this reaction at a heating rate of 830 K/s. 100-nm-thick Al/Ni bilayers were deposited onto nanocalorimeter sensors that enable the measurement of temperature and heat flow during rapid heating. Time-resolved transmission electron diffraction patterns captured simultaneously with thermal measurements allow us to identify the intermetallic phases present and reconstruct the phase transformation sequence as a function of time and temperature. The results show a mostly unaltered phase transformation sequence compared to lower heating rates.

Intermetallic phase evolution of 5059 aluminum alloy during homogenization

Intermetallic phase evolution of 5059 aluminum alloy during homogenization was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD). The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of Zn- and Cu-rich non-equilibrium β (Al3Mg2) phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si phase. During the homogenization, Zn- and Cu-rich non-equilibrium β (Al3Mg2) phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si gradually dissolve into matrix. Fine dispersed β(Al3Mg2) particles and rod-shaped Al6Mn particles form in the Al matrix after homogenization. The proper homogenization processing is at 450 °C for 24 h, which is consistent with the results of homogenizing kinetic analysis.

Intermetallic phase formation and evolution during homogenization and solution in Al-Zn-Mg-Cu alloys

The effects of major alloy element contents of Zn, Mg, Cu in Al-Zn-Mg-Cu alloys on the formation and evolution of intermetallic phases during casting, homogenization and solution treatment have been investigated through using X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Experimental results showed that a relatively higher Zn content with lower Mg and Cu contents was beneficial to the formation of MgZn 2 phase instead of the Al 2 CuMg phase, which resulted in the unicity of the intermetallics in the Al matrix, and that the MgZn 2 phase was easier for diffusion and dissolution during homogenization and solution than the Al 2 CuMg phase. Additionally, the results of the first-principles calculations gave support for explaining the experimental phenomena. A larger absolute value of formation enthalpy and a smaller value of binding energy of the MgZn 2 phase, as compared with the Al 2 CuMg phase, give it priority to precipitate during casting and make it easier to re-dissolve during homogenization and solution treatment. What's more, higher elastic constants with severe anisotropy of Young's modulus make undissolved blocks of Al 2 CuMg phase act as crack initiation, which degrade the performance of the materials.