Volume Fraction Of Intermetallic Phases Research Articles

Effect of laser power and deposition sequence on microstructure of GRCop42 - Inconel 625 joints fabricated using laser directed energy deposition

The joining of Inconel 625 and GRCop42 using additive manufacturing is required for thermal management of high operating temperature components such as rocket combustion chambers. Though prior efforts have been made to use laser directed energy deposition to join these materials, the impact of laser power and deposition sequence on microstructure of these joints is not well understood. In this study, Inconel 625 onto GRCop42 and GRCop42 onto Inconel 625 joints are fabricated by powder directed-energy-deposition at various laser powers and subsequently subjected to characterization in terms of present defects, grain morphology, and phases. Results show lack-of-fusion free Inconel 625 onto GRCop42 joints can be fabricated by increasing the laser power in the first layer. Substrate remelting in GRCop42 onto Inconel 625 joints is found to result in a melt pool composition which induces liquid-state immiscibility, resulting in a Cu-deprived liquid solidifying to form crack prone islands. Increasing laser power decreases the embrittlement of these islands due to the precipitation of a lower volume fraction of intermetallic phases.

Microstructure and creep properties of cast hypereutectic Al-11Ce alloy with Si addition

This study systematically investigated the as-cast microstructure, heat and creep- resistance of Al-11Ce-xSi (x = 0, 0.9, 1.7 wt%) alloys. A tetragonal AlCeSi intermetallic compound was formed by adding Si. With the increase of Si content, the Chinese-script Al11Ce3/α-Al eutectics changed to rod-like structure and were gradually replaced by broad flaky AlCeSi/α-Al eutectics. The Al-11Ce alloy containing 0.9 wt% Si possessed the optimal tensile properties with an ultimate tensile strength of 129.2 MPa and an elongation of 4.3%, which were 8.4% and 65.4% higher than that of the based alloy, respectively. After aging at 400 ℃ for 1008 h, the microhardness of Si-containing alloys remained unchanged, indicating excellent coarsening resistance of the strengthening AlCeSi phases. Under tensile creep conditions at 300 ℃, the creep deformation of three alloys was the dislocation creep mechanism. Nevertheless, with the addition of 1.7 wt% Si, the steady-state strain rate of Al-11Ce alloy was decreased to 1/3 of its original value. The enhanced creep resistance was mainly attributed to the relatively high volume fraction of intermetallic phase, the reduced volume fraction of coarse primary phase, and the presence of AlCeSi precipitates that effectively hinder dislocations motion.

Modelling Effects of Copper on Microstructure and Properties of Al–Si–Cu Alloys

The combined impacts of copper content, cold working and homogenization in aluminium–silicon alloys were examined using microstructure study, thermodynamic modelling, image analysis and hardness measurement. Two aluminium alloys of varying copper contents were cast in a permanent mould using induction furnace. Microstructural observation revealed the formation of varying amount of intermetallic phases due to the presence of copper. Image analysis confirms the relative changes in percent phase fractions owing to presence of copper as intermetallic phases increases. Al2Cu phase was most favoured with increasing copper. Cold working was performed by reduction of 5%, 10% and 15% of the cast alloys by equal amounts of strain. Hardness measurements indicated increase in hardness values attributed to both higher amounts of copper and cold working. Al2Cu phase was predicted contribute compared to Al7Cu4Ni and Alpha phases. Homogenization at 300°C for 4 hr would suffice to obtain a uniform structure. The reasons for changes in microstructure and mechanical properties for different copper content were established by thermodynamic phase fraction calculation. Higher amounts of copper leads to greater volume fractions of intermetallic phases. Using solidification calculations, it is found that copper in liquid encourages dendrite formation which was also evident from microstructure.

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications.

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al11Ce3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al3Ni and Al11Ce3 fibers, (iii) large ternary eutectic colonies, where the binary Al3Ni and Al11Ce3 phases are alternating or intertwining within the individual, fine fibers (diameters of ∼60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al3Ni and Al11Ce3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. The alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al3Ni particles which engulf finer, more stable Al11Ce3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al3Ni and Al11Ce3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

Evolution of Phase Constitution, Morphology and Corrosion Behavior of ZnCo Coating Containing Graphene Oxide

The morphology, phase constitution and corrosion behavior of a pristine ZnCo coating (obtained from an acidic bath) and ZnCo composite coatings containing different amounts of graphene oxide were studied. To achieve this, electrochemical impedance spectroscopy, potentiodynamic polarization studies, scanning electron microscopy, X-ray diffraction, atomic force microscopy, contact angle measurement and weight loss measurements were conducted. It was observed that the morphology, phase constitution and corrosion resistance of the coatings were highly sensitive to the amount of graphene oxide contained in the coatings. For lower graphene oxide amounts, a compact and smooth morphology was observed, whereas higher graphene oxide content produced a non-uniform morphology with cracks on the coating surface essentially due to the deposition of agglomerated graphene oxide in the coating matrix. All the coatings contained a mixture of Zn phase and Zn10.63Co2.34 intermetallic phase. The volume fraction of the nobler intermetallic phase increased with an increase in the graphene oxide amount. The corrosion rate of the coatings decreased with the initial addition of graphene oxide to reach a minimum after which it increased with continued addition of graphene oxide. The initial reduction in the corrosion rate was attributed to the enhancement in the coating compactness and smoothness with the addition of graphene oxide, impermeability of the graphene oxide and enhancement of the relative volume fraction of the intermetallic phase. The enhancement of the corrosion rate after the optimum, which gave the lowest corrosion rate, was due to the increase in the morphologic roughness, cracks and surface defects in the coatings primarily due to non-uniform deposition of agglomerated graphene oxide in the coating matrix. Surface defects did not allow the formation of a continuous passive protection layer.

The Interesting Complicacy of the New Age Metallic Coatings with Carbonaceous Additives

Metallic coatings have been traditionally used to protect the underlying substrate against corrosion. Recent reports have illustrated that use of carbonaceous material such as graphene, graphene oxide, carbon nanotubes as additives in conventional coating have led to significant enhancement in the corrosion resistance behaviour of the composite coatings. In this talk, the author will discuss the evolution of microstructure, morphology, phase constitution and corrosion behaviour of electrodeposited ZnCo coatings as a function of the amounts of graphene oxide contained in them. The as-deposited ZnCo-graphene oxide composite coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). XRD based analysis of the coatings revealed that all the coatings contained Zn phase along with intermetallic phase (Zn10. 63Co2.34). A gradual increase in the volume fraction of the intermetallic phase was observed upon graphene oxide addition. Morphological characteristics and changes in the surface roughness were studied using SEM and AFM. A compact and smooth morphology was observed for initial graphene oxide additions while a higher graphene oxide concentration produced surface cracks due to graphene oxide agglomeration in the electrolytic bath. Weight loss measurements of control sample containing only the intermetallic phase revealed that the intermetallic was more corrosion resistant. The coatings were studied using electrochemical impedance spectroscopy (EIS) in 3.5 wt. % NaCl to understand the characteristics of corrosion product layer. Corrosion current in the coatings was found to decrease for initial graphene oxide addition while for higher additions a sudden increase in corrosion rate was observed. The impermeability of the graphene oxide and a relative increase in the volume fraction of nobler intermetallic phase lead to the initial reduction in corrosion rate. While, after an optimum graphene oxide addition which yielded the lowest corrosion rate, the incorporation of agglomerated graphene oxide lead to cracks and surface defects primarily due to non-uniform deposition. The surface morphology was analyzed using SEM after they were exposed to the electroactive media (3.5 wt.% NaCl). A continuous zinc dissolution was observed in the case of pristine ZnCo coatings while formation of pits was evident for maximum graphene oxide addition. Figure 1

Studies on the characterization and morphological features of the coating on interstitial free steel dipped in molten Al-Si-Mg alloy at 800 °C

Interstitial-free (IF) steel specimens were coated by hot-dip aluminizing process bearing bath composition as Al-6.9% Si-1.4% Mg and bath temperature at 800°C. Dipping time varied for 0.5, 1, 3 and 6min. The objective of the present study is to conduct a systematic investigation to identify and analyse the formation of various phases and compounds in the coating. Studies on aluminizing of steel had indicated the presence of an intermetallic layer adjacent to steel substrate. In this study, the morphological features obtained after hot dipping at 800°C were investigated. For the application of aluminized steel sheets in industry for manufacture of tubes and pipes, the adherence of the aluminized coating must be ensured. This property of the coating is influenced by the morphological features of the coating. Aluminizing being thought of a possible substitution of galvanizing owing to its promise to evolve lesser volume fraction of intermetallic phases and consequently known to generate a ductile coating. The entire coating consists of an outer Al-Si topcoat and a thin intermetallic layer which composed of an outer θ-FeAl3 and inner η-Fe2Al5 layers. The thickness of intermetallic layers was found to increase with the increase of dipping time in a near parabolic manner.The phases formed on the IF steel substrates were characterized by scanning electron microscopy with EDS, X-ray diffraction, EPMA and EBSD techniques.Interesting findings from XRD include the presence of Al3FeSi2 (τ4) and Al2FeSi (τ3) phases, which normally appear after annealing of aluminised sheet. A distinct elemental Si peak was found in XRD study. Presence of Mg in the form of Mg2Si was also found in XRD and supported by EPMA investigation. Presence of several ternary Al-Fe-Si (τ3, τ4, τ5) and binary FeAl3 and Fe2Al5intermetallic phases were identified by composition profile analysis from SEM based EDS and GDOES and further confirmed by EBSD. Presence of Si humps in the top and intermetallic layer attributed by the presence of Si-bearing phases or elemental pro-eutectic Si in Al-Si alloy were also indicated in SEM-EDS and GDOES study. Variation of surface topographical features of the HDA steel substrates with increasing dipping durations were examined and reported for the first time by using AFM. Formability tests were conducted by bending the samples 180° over a mandrel. None of the specimens showed any tendency of flaking exhibiting excellent bonding of the coating with IF steel substrate.

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.

Effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy

The effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy was investigated by thermal analysis. The different cooling rates were chosen in the present work, which were attained by a stepped sand mold, ranging from 0.3 to 3.5 °C s−1. The solidification parameters were determined from the cooling curve as well as its first and second derivative curves. The results show that the microstructure and solidification parameters of Mg–3Al–3Nd alloy are influenced by changing the cooling rate. The nucleation temperature, undercooling temperature, the range of solidification temperature all increase with increasing the cooling rate. The precipitated temperature of Al2Nd and Al11Nd3 phases, recalescence undercooling temperature and total solidification time all decrease with increasing the cooling rate. The grain size of Mg–3Al–3Nd alloy is refined, and the intermetallic phases are distributed more uniformly with increasing the cooling rate. Furthermore, the volume fraction of intermetallic phases and the number density of Al2Nd particle also increase with increasing the cooling rate.

Work hardening behavior of Ti/Al-based metal intermetallic laminates

Titanium- and aluminum-based in situ metal intermetallic laminate (MIL) composites were prepared by solid-state diffusion bonding. The transition joints between Ti/Al were made at temperatures 550 and 575 °C with different bonding time under uniaxial pressure of 4 MPa under high vacuum to achieve MILs with different volume fraction of intermetallic phase. The phase and elemental analyses revealed the presence of only TiAl3 intermetallic layer formed between Ti/Al diffusion couple. Also, the layer thickness of the intermetallic phase increased with the increase in both bonding time and temperature. Compression tests were conducted on these MILs at room temperature both parallel and perpendicular to intermetallic layers. The mechanical properties and the failure mode of these MILs were studied based on the volume fraction of intermetallic phase. Results showed that the strength along the parallel direction of the MILs were much higher than the perpendicular direction. The failure mechanism of the MILs also varied based on the volume fraction of the intermetallic phases. Fractography revealed that with high intermetallic content, cracks were formed only on the intermetallic layer irrespective of loading direction. MILs containing intermetallic phase fraction exhibited better work hardening rate and the hardening rate behavior varied with the loading orientation.

The Influence of Individual Rare Earth Elements (La, Ce, or Nd) on Creep Resistance of Die‐Cast Magnesium Alloy AE44

Three AE44 (Mg–4Al–4RE, wt%) alloys are prepared from individual RE elements, i.e., La, Ce, or Nd, by high‐pressure die casting and the creep resistance of these alloys is evaluated. It is shown that the choice of RE elements has a significant influence on the creep resistance of AE44, with the La‐containing alloy being the most creep‐resistant while the Nd‐containing alloy the least creep‐resistant. Microstructural examinations suggest that the observed difference in creep resistance cannot be accounted for by the thermal stability of the Al11RE3 phase, as reported previously, but can be related to the volume fraction of intermetallic phases and the content of manganese.

Polymer-derived Ceramics as Innovative Oxidation Barrier Coatings for Mo-Si-B Alloys

ABSTRACTThree phase Mo-Mo3Si-Mo5SiB2 alloys possess excellent mechanical properties over a wide temperature range. The Mo solid solution phase is needed for balanced mechanical properties at room temperature. However, this phase suffers from catastrophic oxidation behavior at high temperatures caused by the formation and evaporation of MoO3. The oxidation resistance of three phase alloys benefits from a high volume fraction of intermetallic phases. In particular Mo5SiB2 leads to the formation of a borosilicate protective glassy layer on the material’s surface while exposed to air at elevated temperatures. Hence, it is unlikely to identify alloy compositions that will yield both optimum mechanical and oxidation performance.Different coating systems and techniques, such as pack cementation, magnetron sputtering and plasma spraying are discussed in the literature to control the oxidation properties of Mo-based alloys. A different approach is to apply coating systems based on polymer derived ceramics (PDCs). Our present work introduces PDCs as a new type of promising and innovative oxidation-protective coatings for high temperature Mo-based alloys. After dip-coating with perhydropolysilazane (PHPS) and pyrolysis at 800 °C, dense and well-adhered SiNO ceramic layers could be achieved. These were investigated by scanning electron microscopy. Cyclic oxidation tests at 800 °C and 1100 °C were performed to investigate mass changes due to the thermal treatment. Indeed, even thin pyrolyzed PHPS layers with a thickness of around 70 nm to 175 nm protected the Mo-Si-B substrate during the initial stage of oxidation. By increasing the silicon oxide concentration at the material’s surface a first oxidation barrier was provided and thus, the strong initial mass loss could be decreased as compared to uncoated alloys. Furthermore, first results of the ongoing optimization process on PDC-coatings applied to Mo-Si-B alloys will be presented, involving the enhancement of the coating´s thickness or varying pyrolysis atmospheres.

Microstructure and Creep Resistance of Mg-Al-Ca-Sr Alloys

Abstract Microstructure and creep properties of cast Mg-Al-Ca-Sr alloys have been investigated. The microstructure was characterized using light microscopy, scanning and transmission electron microscopy. Phase identification was made by EBSD technique and by SAED analysis. The measurement of volume fraction of intermetallic phases was performed using quantitative metallography. Creep tests were performed at 180°C and at applied stress between 45 and 90 MPa. Microstructure of tested alloys composed of α-Mg grains and intermetallic compounds in the interdendritic regions. It was found that the addition of calcium and strontium improves creep resistance at 180°C.

The Thermal Diffusivity of Mg-Al-Sr and Mg-Al-Ca-Sr Sand Casting Magnesium Alloys

In the present study, the thermal diffusivity of four sand casting magnesium alloys: Mg-9Al-1Zn, Mg-6Al-2Sr, Mg-9Al-1.5Ca-0.3Sr and Mg-9Al-2.2Ca-0.8Sr were studied. Sand casting was performed at 730-780°C temperatures. Thermal diffusivity was measured by a LFA 427 Netzsch apparatus. The thermal diffusivity of the investigated alloys was chemical composition and temperature dependent and increased with increasing temperature. The thermal diffusivity of Mg-Al-Ca-Sr alloys was higher than that of Mg-Al alloy, because the total volume fraction of intermetallic phases in alloys containing calcium and strontium is larger than that in Mg-Al alloy. The formation of intermetallic phases caused the consumption of the solute element in the α-Mg matrix, and improved the thermal diffusivity of the Mg-Al-Ca-Sr magnesium alloy.

Impact Toughness of an Isothermally Treated Zeron®100 SDSS

The aim of the present study is to investigate the impact toughness of a UNS 32760 SDSS, in relation to the quantity of secondary phases precipitated after isothermal aging in the range of 850-950 °C and for different exposure times. The impact toughness has been investigated by means of instrumented impact testing, using Charpy V-notched specimens at room temperature. The impact testing results show that, for an amount of about 0.5% volume fraction of intermetallic phase, the impact toughness is reduced by over 50%. For volume fractions higher than 1.5-2%, the impact toughness is definitively compromised, and small entities of plastic deformations are enough to cause a prevailing brittle fracture mechanism. By increasing the precipitates’ amounts, the fracture mechanism shows an ever more prominent brittle behavior until 6% volume fraction, exceeding which the ductile component is totally absent.

Parameters controlling the microstructure of Al–11Si–2.5Cu–Mg alloys

This study investigated the effects of cooling rate during solidification, heat treatment, and the addition of Mn and Sr on the formation of intermetallic phases in Al–11Si–2.5Cu–Mg alloys. Microstructures were monitored using optical microscopy and EPMA techniques. The results reveal that the volume fractions of intermetallic phases are generally much lower in the furnace-cooled samples than in the air-cooled ones due to the dissolution of the β-AlFeSi and Al 2Cu phases during slow cooling at critical dissolution temperatures. Strontium additions increased the volume fraction of the Al 2Cu phase in the as-cast conditions at low and high cooling rates, as well as at varying ranges of Mn levels. Platelets of the β-AlFeSi phase were to be observed in the microstructure of the as-cast air-cooled samples with a DAS of 40 μm at both Mn levels, while none of these particles were to be found in the furnace-cooled samples with a DAS of 120 μm. Sludge particles were observed in almost all of the air-cooled alloys with sludge factors of between 1.4 and 1.9. These particles, however, were not observed in the furnace-cooled alloys with similar sludge factors. Solution heat treatment coarsens the Si particles in the non-modified alloys under both sets of cooling conditions studied. In the Sr-modified alloys, solution treatment has varied effects depending on the cooling rate and the level of Mn present.

Analysis of Aluminium Based Alloys by Calorimetry: Quantitative Analysis of Reactions and Reaction Kinetics

AbstractFor Abstract see ChemInform Abstract in Full Text.

The effect of intermetallics on the strength properties of diffusion bonds formed between Ti–5.5Al–2.4V and 304 stainless steel

Solid-state diffusion bonding was done to produce transition joints between Ti–5.5Al–2.4V and type 304 austenitic stainless steel in the temperature range of 850–950°C under uniaxial load for 1h. The diffusion-bonded couples thus produced were evaluated by optical microscopy, scanning electron microscopy, X-ray diffraction and tensile testing. Scanning electron microscopy in back scattered mode reveals the presence of different reaction bands in the diffusion zone. Chemical compositions of these reaction layers were determined by using energy dispersive spectroscopy. The study indicates the existence of σ, Fe2Ti, FeTi and Fe2Ti4O in the reaction zone. These compounds were confirmed by X-ray diffraction technique. It has been observed that with the rise in processing temperature, the width of diffusion zone as also volume fraction of intermetallic phases increases. Highest bond strength (∼272MPa) has been obtained for the diffusion-bonded assemblies processed at 850°C due to presence of thinner width of brittle intermetallics and the failure occurs in the region somewhere in between FeTi and β-Ti during tensile loading for all the diffusion-welded joints.

On the parameters affecting the formation of iron aluminides during pressure-assisted infiltration of aluminium into a preform of steel fibres

The parameters affecting the formation of iron aluminides during reactive infiltration of iron-based fibre preforms in a squeeze-casting equipment were investigated. The volume fraction of intermetallic phases was found to increase when the fibre volume fraction and size decreased. The increase of the temperatures of the die, aluminium and preform allowed avoiding premature chocking of the preforms, reducing the gradient of reaction and increasing the extent of exothermic reactions. As-infiltrated material with overall chemical composition corresponding to Fe 3Al was studied by SEM, X-ray diffraction and TEM. The unreacted iron fibres were surrounded by iron-rich FeAl phases. The single-phase grains adjacent to the boundary layer were identified as Fe 2Al 5 whereas the grains with lamellar morphology were identified as consisting of a mixture of FeAl and FeAl 2 lamellae. Heat treatment of such an as-infiltrated material resulted in the formation of a fine-grained structure composed of FeAl and Fe 3Al phases.