The Effect of Minor Addition of Ni on the Microstructural Evolution and Mechanical Properties of Suction Cast Al-0.14 at. pct Sc Binary Alloy

Aluminum scandium binary alloys represent a promising precipitation-hardening alloy system. However, the hardness of the binary alloys decreases with the rapid coarsening of Al₃Sc precipitate during high-temperature aging. In the current study, we report a new approach to compensate for the loss of mechanical properties by combining rapid solidification with very small ternary addition of transition metal Ni. This addition yields dispersion, and at a critical concentration improves the mechanical properties. We explore additions of a maximum of 0.06 at. pct of Nickel to a binary Al-0.14 at. pct Sc alloy, which yield nickel-rich dispersions. We report two kinds of biphasic dispersions containing AlNi₂Sc/Al₉Ni₂ and α-Al/Al₉Ni₂ phase combinations. The maximum improvement in mechanical properties occurs with the addition of 0.045 at. pct Ni with a yield strength of 239 ± 7 MPa for an aging treatment at 583 K (310 °C) for 15 hours.     

Preparation and thermal stability of Zr-Ti-Al-Ni-Cu amorphous powders by mechanical alloying technique

This study examined the amorphization feasibility of Zr_70−x−y Ti _x Al _y Ni₁₀Cu₂₀ alloy powders by the mechanical alloying (MA) technique. According to the results, after 5 to 7 hours of milling, the mechanically alloyed powders were amorphous basically in the ranges of 0 to 12.5 at. pct Ti and 2.5 to 17.5 at. pct Al. These ranges are larger than those of bulk amorphous alloys prepared by a squeeze mold casting technique. Most of the amorphous mechanically alloyed powders exhibited a wide supercooled liquid region of more than 60 K before crystallization. The glass-transition and crystallization temperatures of mechanically alloyed samples were different from those prepared by squeeze casting. It is suspected that different thermal properties arise from the introduction of impurities during the MA process. The amorphization behavior of Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ was examined in detail. The X-ray diffraction and extended X-ray absorption fine structure (EXAFS) results show the fully amorphous powders formed after 5 hours of milling. A kinetically modified thermodynamic phase transformation process was observed for the glass-transition behavior in the Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ amorphous powder.     

Ball-milling-induced crystallization and ball-milling effect on thermal crystallization kinetics in an amorphous FeMoSiB alloy

Microstructure evolution in a melt-spun amorphous Fe_77.2Mo_0.8Si₉B₁₃ alloy subjected to high-energy ball milling was investigated by means of X-ray diffraction (XRD), a transmission electron microscope (TEM), and a differential scanning calorimeter (DSC). It was found that during ball milling, crystallization occurs in the amorphous ribbon sample with precipitation of an α-Fe solid solution, and the amorphous sample crystallizes completely into a single α-Fe nanostructure (rather than α-Fe and borides as in the usual thermal crystallization products) when the milling time exceeds 135 hours. The volume fraction of material crystallized was found to be approximately proportional to the milling time. The fully crystallized sample with a single α-Fe nanophase exhibits an intrinsic thermal stability against phase separation upon annealing at high temperatures. The ball-milling effect on the subsequent thermal crystallization of the amorphous phase in an as-milled sample was studied by comparison of the crystallization products and kinetic parameters between the as-quenched amorphous sample and the as-milled partially crystallized samples. The crystallization temperatures and activation energies for the crystallization processes of the residual amorphous phase were considerably decreased due to ball milling, indicating that ball milling has a significant effect on the depression of thermal stability of the residual amorphous phase.     

Evolution of microstructure and tensile strength of rapidly solidified Al-4.7 pct Zn-2.5 pct Mg-0.25 pct Zr-X wt pct Mn alloys

Analytical transmission electron microscopy and thermal analysis of as-extruded Al-4.7 pct Zn-2.5 pct Mg-0.2 pct Zr-X wt pct Mn alloys, with Mn contents ranging from 0.5 to 2.5 wt pct, were carried out to elucidate the microstructural change and accompanying mechanical properties during subsequent heat treatments. The as-extruded alloy was fabricated from rapidly solidified powder and consisted of a fine, metastable manganese dispersoid and the ternary eutectic T phase (Al₂Mg₃Zn₃). Solution heat treatment resulted in the formation of the stable Al₆Mn phase and complete dissolution of the T phase. Formation of stable Al₆Mn was made by two routes: by phase transition from metastable Mn dispersoids which already existed, and from the supersaturated solid solution by homogeneous nucleation. The density of the Al₆Mn phase increased with the addition of manganese, while the shape and average size remained unchanged. A significant increase in the hardness was observed to coincide with the formation of the Al₆Mn phase. Similarly, the tensile strength increased further after the aging treatment, and the increment was constant over the content of Mn in the alloy, which was explained by the contribution from the same amount of precipitates, MgZn₂. Results of thermal analysis indicated that the dissolution of the T phase started near 180 °C and that formation of Al₆Mn occurred at about 400 °C, suggesting that further enhancement of strength is possible with the modification of the heat-treatment schedule.     

Phase equilibria of the ternary Al-Cu-Ni system and interfacial reactions of related systems at 800 °C

A series of Al-Cu-Ni alloys of various compositions were made and annealed at 800 °C. The equilibrium phases were studied by metallography, X-ray diffraction (XRD) analysis, and electron probe microanalysis. The isothermal section of the ternary Al-Cu-Ni system at 800 °C was then determined based on these experimental results and the available phase relationship knowledge of the three constituent binary systems. No ternary compound was found. All three phases, AlNi₃, AlNi, and Al₃Ni₂, have very high ternary solubility, especially the AlNi phase, which almost reaches the binary Al-Cu side. However, no continuous solid solution was formed between the AlNi phase and any of the binary Al-Cu phases. Interfacial reactions of Al/Ni, Al/Cu, Al-Cu/Ni, and Al-Ni/Cu at 800 °C were investigated by using reaction couple techniques. The results showed that Al₃Ni and Al₃Ni₂ phases were formed in the Al/Ni couples; β-AlCu₄, γ ₁-Al₄Cu₉, and ɛ ₂-Al₂Cu₃ phases were formed in the Al/Cu couples. As for the results in the Al-2 at. pct Ni/Cu, Al-5 at. pct Ni/Cu, and Al-2 at. pct Cu/Ni, Al-4.5 at. pct Cu/Ni, and Al-6 at. pct Cu/Ni were similar to those in the binary Al/Cu and Al/Ni couples, respectively. A different reaction path was found in the Al-7.5 at. pct Cu/Ni couples, and an AlNi solid solution layer was formed instead of the Al₃Ni and Al₃Ni₂ phases.     

Structural study of electrodeposited aluminum-manganese alloys

Aluminum-manganese alloys with compositions ranging between 0 and 27 wt pct Mn were electrodeposited at 150°C onto copper substrates from a chloroaluminate molten salt electrolyte with a controlled addition of MnCl₂. The specimens were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The addition of small amounts of Mn results in the formation of a supersaturated fcc solid solution of Mn in Al. At the higher Mn content, an amorphous phase is established. The highly faceted crystalline surface of pure Al and Al−Mn solid solution becomes smooth and nearly specular when the amorphous phase is present. The amorphous phase appears in the form of rounded grains and has a lower limit of Mn concentration close to the Al₆Mn composition. There is a concentration discontinuity between the above limit and the higher Mn concentration limit of the fcc phase (about 9 wt pct). Appearance of the amorphous phase in the alloy results in a decrease in the Mn concentration in solid solution to about 2 wt pct. Crystallization of the amorphous phase starts at the fcc-amorphous phase interface at 230°C. As a result of treatment at 230 °C to 340 °C, the amorphous phase completely transforms into Al₆Mn, while the fcc phase is unaffected. Prior to crystallization, the amorphous phase shows a modification that could be interpreted as the formation of a fine-grained icosahedral phase. The formation and distribution of phases by electrodeposition and rapid solidification are discussed.     

Compositional analysis of the icosahedral phase in rapidly quenched Al-Mn and Al-V alloys

The formation ranges and alloy compositions of icosahedral phases in rapidly quenched Al-Mn and Al-V alloys containing 12.5 to 25 at. pct Mn and V, respectively, were examined by X-ray diffractometry and analytical transmission electron microscopy. The icosahedral phase was found to appear in a wide range of compositions below about 23 at. pct Mn and below about 18 at. pct V, but the formation of the icosahedral single phase was limited only in the vicinity of about 22.5 at. pct Mn. The analytical solute concentration in the icosahedral phase is not always constant and increases continuously from about 17 to 23 at. pct Mn and about 18 to 21 at. pct V with increasing nominal solute concentration. Thus, the icosahedral phase in rapidly quenched Al-Mn and Al-V alloys can be approximately formulated to be Al₄Mn and A1₄V with a maximum deviation of about 3 at. pct Mn or 2 at. pct V from the stoichiometric ratio.     

Microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 Wt pct Cu-2.0 wt pct Mn alloys

The microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 pct Cu-2.0 pct Mn alloy specimens solidified at various cooling rates were investigated. The equilibrium phases Al₆Mn and θ-Al₂Cu, which are observed in the conventionally solidified alloy in the as-cast condition, were not detected in rapidly solidified (melt-spun) material. Instead, the ternary compound Al₂₀Cu₂Mn₃ was present in addition to the α phase, which was present in all cases. The morphological and kinetic nature of corrosion was investigated metallographically and through potentiostatic techniques in 3.5 wt pct NaCl aqueous solution. Corrosion of the as-cast material was described by two anodic reactions: corrosion of the intermetallic phases and pitting of the α-Al solid solution. The corrosion rate increased with cooling rate from that for the furnace-cooled alloy to that for the copper mold-cast alloy and, subsequently, decreased in the rapidly solidified alloy. In the heat-treated material, corrosion could be described by two anodic reactions: corrosion of Al₂₀Cu₂Mn₃ precipitate particles and pitting of the α-Al matrix. S.M. Skolianos, formerly Graduate Student, Department of Metallurgy, University of Connecticut     

Investigation of the Effects of Ni, Fe, and Mn on the Formation of Complex Intermetallic Compounds in Al-Si-Cu-Mg-Ni Alloys

The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples, and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases was measured using the image analysis technique. The results show that Ni mainly participates as Al₃Ni, Al₉FeNi, and Al₃CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al₉FeNi the only Ni-rich phase, and Al₁₂(Fe,Mn)₃Si₂ appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents.     

Alloying evolution and stability of Al65Cu20Ti15 during process of amorphisation by high energy ball milling

Abstract

Mechanical alloying of Al₆₅Cu₂₀Ti₁₅ powder blend has been carried out by high energy vibrating ball mill. The process of amorphisation in the mechanically alloyed Al₆₅Cu₂₀Ti₁₅ powder and the stability of the amorphous phase during ball milling were investigated. Almost completely amorphous powder was achieved after 25 h ball milling. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the amorphisation process was controlled by the transformation of both Al based solid solution and intermetallic compounds (Al₂Cu, Cu₉Al₄ and AlCu₂Ti). However, that prolonging the ball milling time to 30 h led to the appearance of Cu₉Al₄, the Al₆₅Cu₂₀Ti₁₅ composite comprising nanocrystalline and amorphous phases could be stable after 50 h ball milling.     

Amorphization of Al50(Fe2B)30Nb20 Mixture by Mechanical Alloying

An amorphous Al₅₀(Fe₂B)₃₀Nb₂₀ powder mixture was prepared by mechanical alloying in a high-energy planetary ball-mill under argon atmosphere. Morphologic, microstructural, and structural changes during the milling process were followed by scanning electron microscopy and X-ray diffraction. Rietveld analysis of X-ray diffraction patterns was used to follow the solid-state amorphization transformation during the milling process of the prepared powder. The reaction between elemental Al, Fe₂B, and Nb powders leads to the formation of the Al(Fe,B) and Al(Fe,Nb,B) solid solutions after 4 and 6 hours of milling, respectively. An amorphous structure is achieved after 20 of milling. These amorphous powders are crystallized on further milling time (36 hours). The observation by scanning electron microscope shows a phenomenon of fracturing followed by compaction of the powder particles.     

Development of Ni-Al2O3In-Situ Nanocomposite by Reactive Milling and Spark Plasma Sintering

In the present study, Ni-30 vol pct Al₂O₃ in-situ nanocomposite was developed by reactive milling of NiO-Al-Ni powder mixture followed by spark plasma sintering (SPS). During milling, fcc to hcp transformation was observed in Ni(Al) phase and it transformed back to fcc phase around 773 K (500 °C). The hardness and yield strength of Ni-30 vol pct Al₂O₃ nanocomposite are approximately two times higher than that of pure Ni of similar grain size. The improved mechanical properties of nanocomposite are attributed to the presence of alumina particles of nanometer size.     

Structure of mechanically alloyed Ti-Al-Nb powders

Ti-Al-Nb ternary powder mixtures containing 24Al-11Nb, 25Al-25Nb, 37.5Al-12.5Nb, and 28.5Al-23.9Nb (at. pct) were mechanically alloyed in a SPEX 8000 mixer mill using a ball-to-powder weight ratio of 10:1. The structural evolution in these alloys was investigated by X-ray diffraction and transmission electron microscopy techniques. A solid solution of Al and Nb in Ti was formed at an early stage of milling, followed by the B2/body-centered cubic (bec) and amorphous phases at longer milling times. The stability of these phases and their transformation to other phases have been investigated by heat treating these powders at different temperatures. The B2/bcc phase transformed into an orthorhombic (O-Ti₂AlNb) or a mixture of the orthorhombic (O) and hexagonal close-packed (α₂-Ti₃Al) phases, the proportion of phases being dependent on the powder composition. Milling beyond the amorphous phase formation resulted in the formation of an fee phase in all the powders, which appears to be TiN, formed as a result of contamination of the powder. Formerly Graduate Student, University of Idaho     

Solubility of hydrogen in liquid Fe−Co−Ni alloys

The solubility of hydrogen in the Fe−Co−Ni ternary has been determined by the Sieverts' method over the temperature range 1500° to 1700°C. The solubility of hydrogen at 1600°C and 1 atm hydrogen pressure is 0.00264 wt pct in iron, 0.00224 wt pct in cobalt, and 0.00448 wt pct in nickel. Hydrogen follows Sieverts' law for all alloy compositions. The solubility surface rises smoothly from the Fe−Co binary to the nickel corner of the ternary, and when expressed as the free energy of hydrogen solution the surface is planar. The enthalpy of hydrogen solution is 8.0 kcal per g-atom H in iron, 8.5 kcal per g-atom H in cobalt, and 5.2 kcal per g-atom H in nickel and is planar for the entire ternary. Interaction parameters with hydrogen for Al, Cu, and Mn were established: ɛ _H ^Al =2.0, ɛ _H ^Cu , and ɛ _H ^Mn and are constant for the entire Fe−Co−Ni ternary. This paper is based on a portion of a thesis submitted by R. G. BLOSSEY in partial fulfillment of the requirements for the degree of Doctor of Philosophy at The University of Michigan.     

Structural evolution in mechanically alloyed Al-Fe powders

The structural evolution in mechanically alloyed binary aluminum-iron powder mixtures containing 1, 4, 7.3, 10.7, and 25 at. pct Fe was investigated using X-ray diffraction (XRD) and electron microscopic techniques. The constitution (number and identity of phases present), microstructure (crystal size, particle size), and transformation behavior of the powders on annealing were studied. The solid solubility of Fe in Al has been extended up to at least 4.5 at. pct, which is close to that observed using rapid solidification (RS) (4.4 at. pct), compared with the equilibrium value of 0.025 at. pct Fe at room temperature. Nanometer-sized grains were observed in as-milled crystalline powders in all compositions. Increasing the ball-to-powder weight ratio (BPR) resulted in a faster rate of decrease of crystal size. A fully amorphous phase was obtained in the Al-25 at. pct Fe composition, and a mixed amorphous phase plus solid solution of Fe in Al was developed in the Al-10.7 at. pct Fe alloy, agreeing well with the predictions made using the semiempirical Miedema model. Heat treatment of the mechanically alloyed powders containing the supersaturated solid solution or the amorphous phase resulted in the formation of the Al₃Fe intermetallic in all but the Al-25 at. pct Fe powders. In the Al-25 at. pct Fe powder, formation of nanocrystalline Al₅Fe₂ was observed directly by milling. Electron microscope studies of the shock-consolidated mechanically alloyed Al-10.7 and 25 at. pct Fe powders indicated that nanometer-sized grains were retained after compaction.     

Isothermal section of the ternary Sn-Cu-Ni system and interfacial reactions in the Sn-Cu/Ni couples at 800 °C

The isothermal section of the Sn-Cu-Ni system at 800 °C has been experimentally determined. There is no ternary compound. A solid solution with a very wide compositional range, the γ phase is formed between the Ni₃Sn(H) phase and Cu₄Sn(H) phase; however, both of these two binary phases are not stable at 800 °C. The binary Ni₃Sn₂ phase also has extensive ternary solubility. The homogeneity ranges of both the γ and Ni₃Sn₂ phases are very large in parallel to the Cu-Ni side, but relatively narrow along the Sn direction. This phenomenon indicates that Cu and Ni are exchangeable in both phases. Three kinds of reaction couples, Sn-55 at. pct Cu/Ni, Sn-65 at. pct Cu/Ni, and Sn-75 at. pct Cu/Ni, were prepared and reacted at 800 °C for 5 to 20 minutes. The reaction paths are liquid/Ni₃Sn₂/γ/Ni₃Sn(L)/Ni for the Sn-55 at. pct Cu/Ni and Sn-65 at. pct Cu/Ni couples, and the reaction path is liquid/γ/Ni₃Sn(L)/Ni for the Sn-75 at. pct Ni couples.     

Microstructure and Thickness of 55 pct Al-Zn-1.6 pct Si-0.2 pct RE Hot-Dip Coatings: Experiment, Thermodynamic, and First-Principles Study

The microstructure and thickness of 55 pct A1-Zn-1.6 pct Si-0.2 pct RE coatings during continuous hot-dip on Q235 steel were investigated in this work. The experimental results revealed that the intermetallic layer was composed of the Fe₂Al₅, FeAl₃, and α-FeAlSi phases. The results of thermodynamic calculations with Pandat software package (CompuTherm, LLC, Madison, WI) indicated that FeAl₃ and α(β)-FeAlSi phase precipitated during the period of temperature cooling, which was consistent with experimental result. Then, the thickness of intermetallic layer was characterized. It was shown that the thickness of intermetallic layer decreased after 0.2 wt pct RE was added. Finally, a first-principles calculation was performed to interpret the effect mechanism of RE on the thickness of intermetallic layer. The results indicated that La substitution in Fe₂Al₅ and FeAl₃ phases could grab electronic charges from Al atoms and weaken the formation of Fe-Al compounds.     

Microstructure,crystallization, and coercivity of rare earth-iron-boron amorphous alloy ribbons

Amorphous alloys of rare earth-iron-boron develop high coercivity when crystallized around 650 °C to 700 °C. These alloys are located in the iron-rich corner of the ternary system, and the alloys contain 10 to 15 at. pct rare earth (R). In the amorphous state, isomorphous substitution of different rare earth atoms occurs. The short-range Fe-Fe and R-Fe environments in amorphous ribbons are similar to those in Fe₃B and R₆Fe₂₃ (within 6 Å), respectively. Beyond 6 Å, the R-Fe environment appears similar to R₂Fe₁₄B. On nonisothermal heating of these alloy ribbons, a stress-relieving process occurs around 460 °C. The crystallization of α-Fe and R₂Fe₁₄B occurs at around 520 °C and near 600 °C, respectively. The Fe₃B and R₆Fe₂₃ phases crystallize next. Depending on the alloy composition, the Fe₃B crystallizes between 600 °C and 650 °C, and R₆Fe₂₃ crystallizes between 650 °C and 680 °C. The presence of rare earth atoms, 10 to 15 at. pct, significantly raises the crystallization temperatures of a-Fe and Fe₃B. The favorable short-range Fe-Fe and R-Fe environments may be responsible for the nucleation and growth (crystallization) of Fe₃B and R₆Fe₂₃ in the ternary alloys. The high coercivity of the annealed ribbons containing 10 at. pct Tb, Dy, and Ho is related to the single magnetic domain nature of the small crystallized grains of Fe₃B and R₆Fe₂₃. For the annealed alloy ribbons with 12 to 15 at. pct rare earth, the high coercivity is related to the ternary hard phase, R₂Fe₁₄B.     

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500 °C, and metallography. Solid-state phase equilibria at 900 °C are determined for alloys containing ≤75 at. pct aluminum and at 600 °C for alloys containing >75 at. pct Al. A reaction scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for ≤50 at. pct aluminum is dominated by the primary crystallization field of bcc β(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L1₂-type phase τ forms in a peritectic reaction p _max at 1393 °C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + α(Ti,Al) = TiAl changes into an eutectic L = α(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition reactions and ternary peritectics to end in the binary eutectic L = Cr₇Al₄₅ + (Al).     

Mechanical properties of Ir-Nb alloys containing Ni and Al

Two alloys made by adding 5 or 10 at. pct, respectively, of Ni-18.9 at. pct Al to an Ir-15 at. pct Nb alloy were investigated. The microstructure and compressive strength at temperatures between room temperature and 1800 °C were investigated to evaluate the potential of these alloys for ultra-high-temperature use. Their microstructural evolution indicated that the two alloys formed fcc and L1₂-Ir₃Nb two-phase structures. The fcc and L1₂ two-phase structures were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The 0.2 pct flow stresses were above 1000 MPa at temperatures up to 1200 °C, about 150 MPa at 1500 °C, and over 100 MPa at 1800 °C. The strength of the quaternary Ir-base alloys at 1200 °C was even higher than that of Ir-base binary and ternary alloys. And the strength of quaternary Ir-Nb-Ni-Al was equivalent to that of the Ir-15 at. pct Nb binary alloy at 1800 °C. The compressive ductility of quaternary (around 20 pct) was improved drastically compared with that of the Ir-base binary alloy (lower than 10 pct) and the ternary Ir-base alloys (about 11 pct). An excellent balance of high-temperature strength and ductility was obtained in the alloy with 10 at. pct Ni-18.9 at. pct Al. The effect of Ni and Al on the strength of the Ir-Nb binary alloy is discussed.