Rich Intermetallic Phase Research Articles

Correlation of microstructure, hardness, and electrical conductivity of hypereutectic Al-Si/B4C composites manufactured by hot pressing technique and subjected to hot extrusion

ABSTRACT B4C (5, 10 and 15 wt %) particles were added to hypereutectic Alumix-231® metal powders to produce composite material. The mixed powders were blended in a triaxial mixer. The production of compact samples was carried out by a hot press process. A hot extrusion secondary treatment was applied to some of the produced samples. Density measurements, microstructure examinations, and measurements of hardness and electrical conductivity were conducted on the samples. Primary Si particles and Cu-, Mg- rich intermetallic phases were observed within the microstructure of the sample produced from pure Alumix-231®. B4C particles seemed to be concentrated at the grain boundaries in the hot press samples. Through the secondary process of extrusion, primary Si particles and B4C particles exhibited mechanical fiberization-like dispersion. The samples with a density of over 97% were produced. The hardness of the samples increased with increasing wt % B4C particle ratio. The measured hardness values of the extruded samples were higher than the hot press samples. The extruded samples also showed high electrical conductivity values.

Hot dip aluminization of 304L SS and P91 ferritic-martensitic steel – Comparison of interface morphology and growth kinetics of reaction zones

P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 °C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2–3 μm sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 ± 5 μm vs 120 ± 15 μm at 800 °C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 °C-2 min and 800 °C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.

Effects of Al on Precipitation Behavior of Ti-Nb-Ta-Zr Refractory High Entropy Alloys

Addition of Al can decrease density and improve oxidation resistance of refractory high entropy alloys (RHEAs), but may cause complicated precipitation and further affect mechanical properties. The present work studied the microstructural evolution of Al-contained RHEAs at elevated temperatures. The effects of Al on precipitation behavior were discussed. Results show that, TiNbTa0.5ZrAlx alloys (x ≤ 0.5) have single BCC (Body Centered Cubic) structure, but the primary BCC phase is supersaturated. Precipitation of BCC2(Nb,Ta)-rich solid solution phase, HCP(Zr,Al)-rich intermetallic phase, and ordered B2 phase can occur during heat treatment at 600~1200 °C. The precipitation of BCC2 phase mainly exists in RHEAs with low content of Al, while HCP (Hexagonal Close Packed) precipitates prefer to form in RHEAs with high content of Al. Interestingly, ordered B2 precipitates with fine and basket-weave structure can form in TiNbTa0.5ZrAl0.5 alloy after annealing at 800 °C, producing significant precipitation hardening effect.

Tensile Fractography of Artificially Aged Al6061-SiC+B<sub>4</sub>C Hybrid Composites

In the current work Al6061 hybrid composites reinforced with Silicon Carbide (SiC) and Boron Carbide (B4C) were studied for improvement in hardness and behavior of fracture surface after artificial aging. It was found that after aging at 100 and 200 OC, presence of SiC and B4C particles in the Hybrid Al6061 Matrix Composites showed substantial improvement in hardness compared to that of the base alloy. Behavior of fracture mechanism after tensile strength have been discussed to conclude the factors which impact the mechanism of crack growth. Presence of SiC and B4C reinforcement particulates and artificially aged at 100°C for Al6061-SiC+ B4C hybrid metal matrix composite shows enhancement in hardness by 180% and tensile strength by 80% due to the presence of finer secondary solute rich intermetallic phases of alloying elements. Fractography analysis displays particle interface failure and combination of brittle and ductile mode of failure.

Dry-sliding tribological properties of AlCoCrFeNiTi0.5 high-entropy alloy

High-entropy alloys (HEAs), with a new alloying concept, could possess many unique mechanical and functional properties. The current work investigated whether one such alloy offers potential for bearing surfaces under dry conditions. The dry, reciprocating sliding wear characteristics of AlCoCrFeNiTi0.5 alloy were investigated under various applied loads and sliding speeds. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were utilized to characterize internal structure and wear surfaces of the alloy, respectively. It is found that the AlCoCrFeNiTi0.5 alloy preserves better wear resistance than Fe77Ni23 solid solution alloy, Ti-46Al-2Cr-2Nb intermetallic alloy, or a wear-resistant steel AISI 52100, especially under higher loads. The wear rate increases slowly with the applied loads increasing and keeps steady under different sliding speeds. The wear mechanisms are abrasive wear, adhesive wear and oxidative wear. The nano-sized Fe–Cr solid solution and Al–Ni–Ti rich intermetallic phase precipitated in the dendritic regions and the formation of oxidation play important roles in the good wear resistances of this high-entropy alloy.

Investigating the influence of Ti powder purity on phase evolution during NiTi sintering using in-situ neutron diffraction

The influence of Ti powder purity on phase evolution during the reactive sintering of elemental Ni and Ti powders to form NiTi was studied using differential scanning calorimetry (DSC) and in-situ neutron diffraction. Reaction between the Ni and Ti is not significant until 600 °C. From 600 to 700 °C, Ti2Ni forms in mixtures made from high (HP) and low purity (LP) Ti powder. The Ni3Ti phase also grows in this temperature range in the LP mixture. The most significant phase evolution takes place between 700 and 920 °C. The α to β phase transformation in (Ti) begins at the eutectoid temperature (765 °C) and ends at 820 °C. The highest growth rates for all three intermetallic phases, including NiTi, and the decay rate of the elemental Ni occur in this temperature range. At approximately 1000 °C, all reactants are consumed and homogenization occurs, with NiTi continuing to grow at the expense of the other intermetallic phases. The Ti rich intermetallic phase persists above its melting point, due to the formation of a solid-solution with oxygen (i.e. Ti2Ni(O)). From 1100 to 1200 °C, the microstructure becomes a stable mixture of NiTi with a small fraction of Ti2Ni(O). The phase evolution is similar in the LP and HP mixtures. However, the rate of reaction is higher in the LP mixture due to the influence of impurities (O, Fe and Ni) on the diffusivities in the many phases involved.

Microstructural features associated with the effect of temperature on the dimensional stability of an automotive Al-A319 alloy

In this work an automotive Al-A319 was given a solid solution heat treatment (T4) at 753 K (480 °C) for 4.5 hours and an ageing treatment (T7) at 513 K (240 °C) for various times up to 3.0 h. The alloy in the T4 condition was dilatometrically tested at various temperatures in order to measure its relative dimensional changes. It was found that the dimensional changes are due to both, alloy thermal expansion and nucleation and growth of second phases. In addition, in the T7 condition the alloy strength and ductility were determined as a function of ageing times. Ageing promoted alloy strength but at the expenses of a rather poor alloy ductility (down to 1%). Apparently, Cu rich intermetallic phases and regions provided a brittle path for fracturing. In particular, microstructural characterization using high resolution transmission electron microscopy indicated that not all the Cu in the matrix was dissolved during the T4 treatment. Hence, after ageing (T7) these Cu-rich regions seemed to coarsen into spherical particles.

Effect of Cerium Addition and Cooling Rate on Microstructure of ADC12 Eutectic Cast Alloy

This research was to determine the effect of Cerium and cooling rate on the microstructure of eutectic Al-11Si-Cu-Mg cast alloy. The Cerium was added to produce Al-11Si-Cu-Mg-1.5Ce alloys. The microstructure was characterized by optical microscope. The Si structure was modified with the increase of the cooling rate, where smaller area was achieved. Ce formed rich intermetallic phase, such as Al-Si-Ce.

Effect of iodine on the corrosion of Au–Al wire bonds

Corrosion study was performed on Au–Al wire bonds, thin layers of sputter deposited Au and Al, and Au–Al intermetallic nuggets. The test environment was iodine-vapour in air (1mg/L) at 85°C with varying relative humidity, and 500mg/L of KI in water. GDOES, XRD, SEM EDS, wire bond shear, and electrochemical testing were used to characterize the samples. Failures of Au–Al wire bonds were found to be primarily attributed to the corrosion of Al via formation of Al iodides and consequent formation of Al oxides and/or hydroxides. Most susceptible to corrosion are Al metallization and Al rich intermetallic phases.

Unraveling EDTA corrosion inhibition when interleaved into Layered Double Hydroxide epoxy filler system coated onto aluminum AA 2024

To entrap a corrosion inhibitor agent into a host matrix and avoid its possible weakening/plasticizing toward an organic coating as well as in enabling its progressive release under stimuli, Layered Double Hydroxide (LDH) framework is here selected as its role as a coating filler to provide a barrier effect due to its associated aspect ratio. To protect aluminum alloy AA 2024 ethylenediaminetetraacetic acid (EDTA) was chosen because of its interaction with copper rich intermetallic phases. Characterization of the inorganic–organic (I/O) hybrid phase confirms the formation of LDH-type sheets with an unusual high charge density. LDH/EDTA is evaluated as corrosion inhibitor agent in the presence of aggressive chloride anions and compared to chromate, carbonate and chloride interleaved LDH anions.The mechanism of inhibitor release from the inorganic LDH container is studied by X-ray diffraction and its efficiency when embarked into an epoxy-based coating is characterized by Electrochemical Impedance Spectroscopy (EIS) and DC-Polarization experiments using Tafel plot refinements. The possible corrosion mechanisms are discussed as a function of the EDTA/LDH action under such particular conditions and the associated protection is scrutinized evolving diadochy, buffering and possible complexing reaction against electrolyte salt concentration versus exposure time. Counter intuitively the deleterious role of released EDTA in inhibiting the corrosion process is here demonstrated, however underlining the benefit of the LDH platelets.

INFLUENCE OF INTERMETALLIC PHASE’S ON THE FRACTURE SURFACES IN SECONDARY ALUMINIUM CAST ALLOY

The contribution describes changes of the character of fracture surfaces depending on the morphology of intermetallic phases in secondary aluminium cast alloy. Morphology changes of intermetallic phases in recycled (secondary) aluminium cast alloy were depended on age-hardening. For study was used age-hardening. The age hardening consist of solution treatment at temperature 515°C with holding time 4 hours, water quenching at 40°C and artificial aging by different temperature 130°C, 170°C and 210°C with different holding time 2, 4, 8, 16 and 32 hours. Recycled (secondary) aluminium cast alloys containing more of additional elements that form various intermetallic phases in microstructure. It is therefore necessary to study structure of recycled aluminium alloy and influence of intermetallic phases. Intermetallic phases were observed by using of combination different analytical techniques (scanning electron microscopy - SEM upon black-white etching, deep etching and energy dispersive X-ray analysis - EDX) in microstructure. Heat treatment led to gradual disintegration, shortening and thinning of Fe- rich intermetallic phases, the dissolution of precipitates and the precipitation of finer hardening phase (Al 2 Cu). The changes of the morphology of intermetallic phases led to changes of fracture surface in recycled (secondary) aluminium cast alloy.

Influence of Solution Heat Treatment Temperature and Time on the Microstructure and Mechanical Properties of Gas Induced Semi-Solid (GISS) 6061 Aluminum Alloy

The influence of solution heat treatment (SHT) temperature and time on the microstructure and mechanical properties of semi-solid 6061 aluminum alloy has been investigated in this study. Microstructure of the as-cast 6061 aluminum alloy mainly consisted of globular α-Al matrix and eutectic phase (α-Al + Mg2Si) at the grain boundary (GB). Iron rich intermetallic phase was also observed at the grain boundary. Eutectic phase started to dissolve after solution heat treatment. The dissolution of eutectic phase increased with increasing solution treatment time, however, the amount of remaining eutectic phase was found to be slightly changed after solution treating longer than 1 h at 550 °C and 2 h at 530 °C. Hardness and tensile results of specimens after artificial aging were utilized to compare and select the optimum solution heat treatment condition cooperating with the microstructural observation. The optimum solution heat treatment condition of the alloy in this study was at 530 °C for 2 h.

Effect of solution annealing temperature on precipitation in 2205 duplex stainless steel

In the present study, effect of solution annealing temperature (1050 °C and 1100 °C) and isothermal ageing (700 °C: 15 min to 6 h) on the microstructural changes in 2205 duplex stainless steel has been investigated systematically. Scanning electron microscopy and X-ray diffraction were adopted to follow the microstructural evolution, while an energy dispersive spectrometer attached to scanning electron microscope was used to obtain localised chemical information of various phases. The ferritic matrix of the two phase 2205 duplex stainless steel (~ 45% ferrite and ~ 55% austenite) undergoes a series of metallurgical transformations during ageing—formation of secondary austenite (γ2) and precipitation of Cr and Mo rich intermetallic (chi-χ and sigma-σ) phases. For solution annealing at 1050 °C, significant amount of carbides were observed in the ferrite grains after 1 h of ageing at 700 °C. χ Phase precipitated after the precipitation of carbides—preferentially at the ferrite–ferrite and also at the ferrite–austenite boundaries. σ Phase was not observed in significant quantity even after 6 h of ageing. The sequence of precipitation in samples solution annealed at 1050 °C was found to be carbides → χ → σ. On the contrary, for samples solution annealed at 1100 °C, the precipitation of χ phase was negligible. χ Phase precipitated before σ phase, preferentially along the ferrite–ferrite grain boundaries and was later consumed in the σ phase precipitation. The σ phase precipitated via the eutectoid transformation of ferrite to yield secondary austenite γ2 and σ phase in the ferrite and along the ferrite–austenite grain boundaries. An increase in the volume fraction of γ2 and σ phase with simultaneous decrease in the ferrite was evidenced with ageing.

Changes in Structural Characteristics of Hypoeutectic Al-Si Cast Alloy after Age Hardening

The contribution describes influence of the age-hardening consist of solution treatment at 515 °C with holding time 4 hours, water quenching at 40 °C and artificial aging at different temperature 150 °C, 170 °C and 190 °C with different holding time 2, 4, 8, 16 and 32 hours on mechanical properties (tensile strength and Brinell hardness) and changes in morphology of eutectic Si, Fe-rich and Cu-rich intermetallic phases in secondary (recycled) AlSi9Cu3 cast alloy. A combination of different analytical techniques (light microscopy upon black-white and colour etching, scanning electron microscopy (SEM) upon deep etching and energy dispersive X-ray analysis (EDX)) were therefore been used for the identification of the various phases. Quantitative study of changes in morphology of eutectic Si, Cu-rich and Fe-rich phases was carried out using Image Analyzer software NIS-Elements. Mechanical properties were measured in line with EN ISO. Age-hardening led to changes in microstructure include the spheroidization and coarsening of eutectic silicon, gradual disintegration, shortening and thinning of Fe- rich intermetallic phases, the dissolution of precipitates and the precipitation of finer hardening phase (Al 2 Cu) further increase in the hardness and tensile strength in the alloy. DOI: http://dx.doi.org/10.5755/j01.ms.18.3.2430

Experimental measurements of the heats of formation of Fe3Pt, FePt, and FePt3 using differential scanning calorimetry

Using differential scanning calorimetry (DSC), the heats of formation of Fe3Pt, FePt, and FePt3 were determined from the reaction of sputter deposited Fe/Pt multilayer thin-films with a periodicity of 200 nm but different overall compositions. Film compositions were measured by energy dispersive x-ray spectrometry. The phases present along the reaction path were identified by x-ray diffraction. For the most Fe-rich phase, namely, Fe3Pt, the measured enthalpy of formation was −9.3 ± 1.3 kJ/mol in a film with a composition of 70.4:29.6 (±0.2 at. %) Fe:Pt. For FePt, the measured enthalpy of formation was −27.2 ± 2.2 kJ/g-atom in a 49.0:51.0 (±0.5 at. %) Fe:Pt film. For FePt3, which is the most Pt rich intermetallic phase, the measured enthalpy of formation was −23.7 ± 2.2 in a film with a composition of 22.2:77.8 (±0.6 at. %) Fe:Pt. The reaction enthalpies for films with Fe:Pt compositions of 44.5:55.5 (±0.3 at. %) and 38.5:61.5 (±0.4 at. %) were −26.9 ± 1.0 and −26.6 ± 0.6 kJ/g-atom, respectively, which taken together with the value for the 49.0:51.0 film demonstrate the relative insensitivity of the reaction enthalpy to film composition over a broad composition range in the vicinity of the equiatomic composition. The experimental heats of formation are compared with two sets of reported first-principles calculated values for each of the three phases at exact stoichiometry.

The Influence of Yttrium Rich Intermetallic Phases and Heat Treatment on the Microstructure, Hardness and Wear Properties of Al-15%Mg<sub>2</sub>Si Composite

This study was undertaken to investigate the effect of different concentrations of Yttrium (0.1, 0.3, 0.5, 1.0 wt.%) and heat treatment on the microstructure, hardness and wear resistance of an in-situ cast composite (Al-15%Mg2Si ). The microstructural study of the composite before and after solution and ageing showed both primary and secondary Mg2Si phases in all specimens and intermetallics containing Y (Al2Y) were visible after Solution at 520 °C for 4 hours. Hardness measurement demonstrates that the addition of Y increases the hardness gradually but a reduction in the hardness of heat treated specimen’s occurs with the addition of Y ( 0.5%Y).Wear tests were performed using a pin on disk apparatus. The MMCs were rubbed against a carbon steel pin under a load of 10 and 20 N at a sliding velocity of 0.1 ms−1; track length of 1500 m. The degree of improvement in dry sliding wear resistance brought about by Y addition is strongly dependent on the formation of Yttrium rich intermetallic phases as well as heat treatment influence and the wear behavior determined through the precise measurement of weight loss of the samples and wear rates. Worn surfaces were analyzed by scanning electron microscopy (SEM).

A facile route to produce Fe–Al intermetallic coatings by laser surface alloying

This work studies the feasibility of obtaining iron aluminide coatings on pure iron substrate by means of laser surface alloying (LSA). Pure Al was plasma spray coated on pure Fe substrate and subsequently laser alloyed by using multi mode continuous wave Nd-YAG laser at different output power and scanning rates. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. Detailed optical, SEM–EDX and XRD investigations were performed to characterize the phases formed during laser alloying. At 300 W laser output power, Al rich intermetallic phases mainly FeAl3, Fe2Al5 had formed with scanning rate in the range of 100–400 mm/min. However, at high power outputs (500 W) Fe–Al intermetallic phase had formed, which was found to have sound and crack free interface with the substrate.

Stability of Haynes 242 as metallic interconnects of solid oxide fuel cells (SOFCs)

Haynes 242 is a unique Ni based alloy for interconnect application of solid oxide fuel cells (SOFCs), due to its low CTE (coefficient of thermal expansion) value which matches other fuel cell components over its peer of other Ni based alloys, together with very excellent oxidation resistance, and electrical conductive nature of the thermally grown oxide scales. A Ni–Mo rich intermetallic phase was observed to precipitate in this alloy during the thermal exposure in the SOFC environments and cause stability issue. This paper examined the stability of Haynes 242 in terms of oxidation resistance, electrical property, and oxidation kinetics as interconnects of solid oxide fuel cells. Results indicated that the precipitation helped significantly towards formation of NiO to reduce the Cr evaporation, and influenced little on oxidation resistance and electrical property.

The influence of Cu rich intermetallic phases on the microstructure, hardness and tensile properties of Al–15% Mg 2Si composite

This study was undertaken to investigate the effect of different concentrations of copper (0.1, 0.3, 0.5, 1.0, 3.0, and 5.0 wt.%) on the microstructure, hardness and tensile properties of an in situ cast composite (Al–15% Mg 2Si). The microstructural study of the composite showed both primary and secondary Mg 2Si phases in all specimens and intermetallics containing Cu ( Q and θ phases) were visible at high Cu contents. Hardness and tensile tests demonstrate that the addition of Cu increases both hardness and ultimate tensile strength (UTS) values. But that a reduction in elongation occurs with the addition of Cu (≥1% Cu). A study of the specimen's fracture surfaces via scanning electron microscope (SEM) revealed that all specimens with large facets of primary Mg 2Si particles succumb to brittle fracture. These brittle phases can initiate cracks, but Cu rich intermetallics phases, produced from the segregation of Cu on eutectic cell boundaries, appear to be the favored path for crack propagation.

Microstructure and Mechanical Properties of Mg-Al-Ca Alloys with Yttrium Addition

The aims of this study are to investigate the effect of Y (yttrium) addition in the Mg-Al- Ca alloys on microstructure and mechanical properties. In additions, the alloys were solution treated in order to achieve a better understanding of the precipitation mechanisms. The as-cast microstructure of Mg-5Al-3Ca alloy and Mg-5Al-3Ca-xY alloys contains dendritic α-Mg matrix and eutectic intermetallic compound at grain boundary. The hardness values of Mg-Al-Ca alloy with Y additions were slightly increased than that of Mg-Al-Ca with no Y addition. It is because of reduction of α-Mg phase and presence of (Mg,Al)2Ca and Al-Y rich intermetallic phase at grain boundary and α-Mg matrix grains. Also, hardness value of yttrium (Y) containing alloys was increased with increasing Y contents. Compared to Mg-5Al-3Ca alloy, maximum strength and yield strength of the alloys with Y additions have slightly increased with increasing Y additions in the case of as-cast samples.