Behavior of an ultrafine-grained Cu-Zr alloy in heating

The effect of the heating temperature and the initial state (annealed or quenched) of a Cu-0.18% Zr alloy subjected to severe plastic deformation on its microhardness and electrical resistivity is studied. The microhardness distribution along a sample diameter and the dependences of the microhardness and electrical resistivity on the heating temperature in the range from 50 to 550°C are plotted. It is shown that the hardening of Cu-0.18% Zr alloy samples after torsion under hydrostatic pressure is stable up to 400°C irrespective of their initial structure.     

Structure and mechanical properties of boron-doped cubic zirconium trialuminides

Cubic (L1₂) ternary zirconium trialuminides macroalloyed with Cu(Al₅CuZr₂), Mn(Al₆₆Mn₉Zr₂₅), and Cr(Al₆₇Cr₈Zr₂₅) (atomic percent) and doped with 50 and 100 ppm boron were fabricated by induction melting. Their as-cast microstructures are characterized by a small amount of porosity (1 to 2 pct) and second phase (2 to 3 pct). Boron seems to slightly enhance porosity (up to 3.3 pct) in Al₅CuZr₂ +100 ppm B alloy, and it also promotes some compositional inhomo-geneity in Al₆₆Mn₉Zr₂₅ alloy. Vickers microhardness and compressive properties at room temperature (RT), peak strength temperature (500 °C to 600 °C) and 900 °C were investigated. Microcracking development was also investigated in Al₅CuZr₂ +100 ppm boron alloy exhibiting a stepped load-deflection curve. Vickers microhardness strongly depends on load, similarly to boron-free cubic ternary zirconium and titanium trialuminides, and increases in a systematic way with increasing boron content which seems to indicate a solid solution strengthening effect. At RT, 0.2 pct offset yield strength is not increased by the boron doping in most of the alloys studied except for Al₆₆Mn₉Zr₂₅ + 50 ppm B alloy. Permanent deformation (apparent ductility) at ultimate compressive strength is not enhanced by boron doping. In Al₅CuZr₂ +100 ppm B alloy microcracks start nucleating and proliferating in the elastic region of load-deflection curve in characteristic “bursts” accompanied by a “click” sound and the appearance of a discernible step on the load-deflection curve. Pre-existing pores are observed to be active centers of microcracking.     

Microstructure and mechanical behavior of spray-deposited High-Li Al-Li alloys

High-Li alloys, with the composition Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr, were synthesized using a spray deposition technique (wt. pct, X=0∼1.5). The microstructure of the spray-deposited Al-Li alloys consisted of equiaxed grains with an average grain size in the range from 20 to 50 μm. The grain-boundary phases were fine and discrete. The spray-deposited and thermomechanically processed materials were isothermally heat treated at 150 °C and 170 °C to investigate the age-hardening kinetics. It was noted that the spray-deposited Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr alloys exhibited relatively sluggish aging behavior. The peak-aged condition was achieved at 170 °C in the range from 20 to 90 hours. It was noted that Cu increases the hardness of alloys during aging. Moreover, the influence of Cu on age-hardening kinetics is marginal. The mechanical properties of the spray-deposited and extruded Al-Li alloys were studied in the underaged, peak-aged, and overaged conditions. For example, the peak-aged yield strength, tensile strength, and ductility of Al-3.8Li-1.0Cu-1.0Mg-0.4Ge-0.2Zr are 455 MPa, 601 MPa, and 3.1 pct, respectively. Moreover, an increase in the Cu content of the alloy led to improvements in strength, with only slight changes in ductility, for Cu contents up to 1.0 wt pct. Beyond this range, an increase in Cu content led to decreases in both strength and ductility.     

Microhardness and compressive mechanical behavior of L12 titanium trialuminides

Vickers microhardness and compressive mechanical properties of Ll₂ Al₃Ti + X intermetallics, where X = Cr, Mn, Fe, and Cu, were studied. Compressive tests were carried out at the temperature range from room temperature to 900 °C. At room temperature, both Vickers microhardness and yield strength (0.2 pct offset) decrease with increasing the long-range order parameterS. Essentially the same behavior of yield strength is observed at all compressive test temperatures up to 900 °C. In general, apparent compressive ductility (permanent deformation) increases with increasing test temperature, although with different rates, for most of the alloys, except Ll₂ Al₃Ti + Mn (high Ti), which is characterized by the lowest long-range order parameterS. Compressive ductility increases with increasing long-range order at all temperatures, but the highest rate of increase occurs at high temperatures above approximately 600 °C and the rate of increase at room temperature is minimal. At low temperatures, deformation-induced microcracks were formed in large numbers in all of the alloys studied, even in the matrix free of preexisting flaws. These microcracks can propagate catastrophically under tensile deformation conditions at a stress level barely approaching 0.2 pct offset prior to the onset of gross plastic flow, leading to a premature fracture. At high temperatures, the initiation of deformation-induced microcracks is inhibited. The mechanical behavior of L1₂ titanium trialuminides is discussed within a general framework of ductile-to-brittle transition.     

Mechanical alloying of aluminum alloy with nanodiamond particles

The shape, size, and microhardness of composite materials based on an Al-2Cu-1.6Mn-0.4Zr alloy (wt %) reinforced with nanodiamond particles in an amount of 0–10 vol % depending on the duration of mechanical alloying (MA) are investigated. The maximal treatment time in a planetary mill is 15 h. It is shown that, as the MA time increases, the average granule size of composite materials fabricated using chips matrix particles of about 1000 μm in size decreases to 30 μm. During MA, the material microhardness increases to 270–320 HV.     

Quasicrystalline and related crystalline phases in a rapidly solidified 2024-2Li aluminium alloy

The formation and decomposition of quasicrystalline and crystalline phases in as-rapidly solidified and annealed commercial AISI 2024 aluminium alloy containing 2 wt% Li have been investigated by detailed transmission electron microscopy, including a combination of bright field and dark field imaging, selected area diffraction pattern analysis and energy dispersive X-ray microanalysis. The microstructure of as-melt spun 2024-2Li consists of α-Al cell, containing small coherent δ′ precipitates, and particles or a continuous network of the icosahedral phase at the cell boundaries. After annealing at 300°C, the intercellular particles of the icosahedral phase coarsen progressively and assume a more faceted shape; after annealing at 400°C, particles of the decagonal and crystalline O phases precipitate heterogeneously on preexisting particles of the icosahedral phase; and after annealing at 500°C, the icosahedral and decagonal phases dissolve completely, and small particles of the crystalline O phase remain together with newly precipitated plates of the T₁ phase. The icosahedral phase in melt spun and melt spun/annealed 2024-2Li belongs to the Al₆CuLi₃ class of icosahedral phases, with a quasilattice constant of 0.51 nm, a stoichiometry of (Al,Si)₆(Cu, Mn, Fe) (Li, Mg)₃ and an average composition of Al-24.1 at.% Cu-64 at.% Mg-1.7 at.% Si-0.3 at.% Mn-0.5 at.% Fe as melt spun and Al-21.9 at.% Cu-6.3 at.% Mg-1.0 at.% Si-0.5 at.% Fe as-heat-treated. The decagonal phase in melt spun/annealed 2024-2Li belongs to the Al₄Mn class of decagonal phases, with a periodicity of 1.23 nm along the 10-fold symmetry axis, a stoichoimetry of Al₃(Cu, Mn, Fe) and an average composition of Al-10.3 at.% Cu-13.8 at.% Mn-2.3 at.% Fe. The crystalline O phase in melt spun/annealed 2024-2Li has an orthorhombic structure with lattice parameters of a = 2.24 nm, b = 2.35 nm and c = 1.23 nm, a stoichiometry of Al₃(Cu, Mn, Fe), and an average composition of Al-11.0 at.% Cu-14.8 at.% Mn-3.9 at.% Fe. Detailed analysis of selected area diffraction patterns shows a close similarity between the icosahedral, decagonal and crystalline O phases in melt spun and melt spun/annealed 2024-2Li. In particular, the decagonal phase and crystalline O phases have a similar composition, and exhibit an orientation relationship which can be expressed as:

• •[D10]//[001]_o
• •[D2_a]//[100]_o
• •[D2_b]//[010]_o

suggesting that the orthorhombic O phase is an approximant structure for the decagonal phase.     

Cu-Al-Mn-B低温形状记忆合金

研究经不同条件热处理的Cu-8.9Al-12.4Mn-0.07B低温形状记忆合金的结构及相变行为,发现B的添加能细化晶粒,并抑制室温时效过程中Cu9Al4(γ2)相的析出。     

Design and development of an experimental wrought aluminum alloy for use at elevated temperatures

A new wrought aluminum alloy has been designed having high room temperature strength (e.g., 0.2 pct P.S. 520 MPa) combined with improved creep resistance at temperatures in the range 150° to 220 °C. The alloy is A1-6.3 pct Cu-0.5 pct Mg-0.5 pct Ag-0.5 pct Mn-0.2 pct Zr and it is hardened by a new precipitate which forms on the {111} planes and appears to be highly stable at elevated temperatures. Details are given of the principles underlying the development of the alloy and of the preliminary assessment that has been made of mechanical properties. The alloy, or compositions close to it, also has potential for welded applications.     

Effects of temperature on the fatigue crack growth behavior of cast gamma-based titanium aluminides

This article reports the results of an experimental study of the effects of temperature (25 °C, 450 °C, and 700 °C) on the fatigue crack growth behavior of three near-commercial cast gamma titanium aluminide alloys (Ti-48Al-2Cr-2Nb, Ti-47Al-2Mn-2Nb+0.8 pct TiB₂, and Ti-45Al-2Mn-2Nb+0.8 pct TiB₂). The trends in the fatigue crack growth rate data are explained by considering the combined effects of crack-tip deformation mechanisms and oxide-induced crack closure. Faster fatigue crack growth rates at 450 °C are attributed to the high incidence of irreversible deformation-induced twinning, while slower crack growth rates at 700 °C are due to increased deformation by slip and the effects of oxide-induced crack closure.     

An Atom-Probe Tomographic Study of Arc Welds in a Multi-Component High-Strength Low-Alloy Steel

An experimental plate steel with the composition Fe-1.39Cu-2.7Ni-0.58Al-0.48Mn-0.48Si-0.065Nb-0.05C (wt pct) or alternatively Fe-1.43Cu-2.61Ni-1.21Al-0.48Mn-0.98Si-0.039Nb-0.23C at. pct has been recently produced at Northwestern University for use in Naval hull and deck applications—it is designated NUCu-140. To understand the microstructural changes occurring in NUCu-140 steel after gas-metal arc welding (GMAW), a detailed study of the heat-affected and fusion zones was performed throughout the weld cross section using microhardness, metallographic, chemical, and atom-probe tomographic analyses. Local-electrode atom-probe (LEAP) tomography was employed to measure the morphology and compositions of Cu-rich precipitates from each region. The mean radius, number density, volume fraction, and compositions of the precipitates, as well as the interfacial concentration profiles, are measured. The Cu precipitates dissolve partially from the heat-affected zone (HAZ) thermal cycle, and freshly formed sub-nanometer radius Cu-rich precipitates nucleate in both the HAZ and fusion zone (FZ) during cooling; however, the precipitation of Cu during cooling in the HAZ and FZ is not sufficient to restore the lost strength. The precipitation in the FZ is reduced compared to the HAZ due to a mismatched Cu composition of the weld. Multi-pass welding is suggested to restore strength in the GMAW sample by promoting Cu precipitate nucleation and growth in the HAZ and FZ.     

Hillock-free aluminum thin films for electronic devices

The addition of an alloying element was proposed in order to suppress hillocks which grow on the surface of deposited aluminum conductors after they have been subjected to thermal cycling (200°C to room temperature) or high temperature heat treatment (400°C). The alloying element, tin, which has a small diffusion coefficient, a large binding energy with a lattice vacancy and a large atomic diameter, and manganese, which has a relatively small solid solubility into aluminum, were evaluated since they also have proper values of vapor pressure for ease of evaporation with aluminum. Alloy composition was determined to be just above the solid solubility of the element in aluminum at the deposition temperature of 350°C. It was proved experimentally that Al-0.06 wt pct Sn alloy and Al-0.1 wt pct Mn alloy, which had been selected for the abovementioned reason, had a marked effect in suppressing the growth of hillocks.     

Investigation into the Fabrication Possibility of the Boron–Aluminum Sheet Rolling of Increased Strength without Using Homogenization and Quenching

Al–Cu–Mn (Zr) aluminum alloys possess high strength and manufacturability without operations of thermal treatment (TT). In order to investigate the fabrication possibility of the aluminum boron-containing alloy in the form of sheet rolling with an increased strength without TT, Al–2% Cu–1.5% Mn–2% B and Al–2% Cu–1.5% Mn–0.4% Zr–2% B alloys are prepared. To exclude the precipitation of refractory boride particles, smelting is performed in a RELTEK induction furnace providing intense melt stirring. The smelting temperature is 950–1000°C. Pouring is performed into graphite molds 40 × 120 × 200 mm in size. It is established using computational methods (Thermo-Calc) that manganese forms complex borides with aluminum and zirconium at the smelting temperature; herewith, a sufficient amount of manganese remains in liquid, while zirconium is almost absent. The formation of AlB₂Mn₂ complex boride is proven; however, the amount of manganese remaining in the solid solution is sufficient to form the particles of the Al₂₀Cu₂Mn₃ phase in amounts of up to 7 wt %. Boron stimulates the isolation of Al₃Zr primary crystals in the alloy with zirconium; in connection with this, an amount of zirconium insufficient for hardening remains in the aluminum solid solution. The possibility of fabricating thin-sheet rolling with a thickness smaller than 0.3 mm with homogeneously distributed accumulations of the boride phase with a particle size smaller than 10 μm is shown. A high strength level (up to 543 MPa) is attained without using quenching and aging due to the precipitation of dispersoids of the Al₂₀Cu₂Mn₃ phase during hot deformation (t = 450°C).     

Age Hardening Behavior and Corresponding Microstructure of Dilute Al-Er-Zr Alloys

The age hardening and the microstructure of dilute Al-Er-Zr alloys were investigated by microhardness tests and TEM. The Al-0.04Er alloy shows a conventional age hardening behavior and obtains a maximum hardness of 410 MPa after aging for 2 h at 523 K (250 °C) due to precipitation of Al₃Er. The addition of Zr to Al-Er alloy can slow down the growth of the precipitates and make the age hardening effect remain for a long time in Al-0.04Er-0.04Zr alloy. Addition of Zr retards the decomposition of Al-Er and the Al-0.04Er-0.08Zr alloy can reach higher peak hardness than that of Al-0.04Er after aging for long time at elevated temperature. The precipitation behavior of Al-Er-Zr system is likely to be a new commercial way to developing creep-resistant aluminum alloy.     

Influence of Aging and Thermomechanical Treatments on the Mechanical Properties of a Nanocluster-Strengthened Ferritic Steel

This study investigated the effect of aging and thermomechanical treatments on the mechanical properties of a nanocluster-strengthened ferritic steel, Fe-1.5Mn-2.5Cu-4.0Ni-1.0Al (wt pct). The effect of thermomechanical treatments on the microhardness and tensile properties were measured at room temperature and correlated with microstructural features. Cu-rich precipitates were characterized by transmission electron microscopy and were found to coarsen slowly during long-time aging. The microhardness measurements indicate a typical precipitation hardening behavior during aging at 773 K (500 °C). Tensile tests showed that thermomechanical treatments can improve the mechanical strength and ductility of the nanocluster-strengthened ferritic steel significantly compared with those without the treatments. Fractography results indicated that the high yield strength resulted from precipitation hardening makes the steel more susceptible to grain-boundary decohesion, which can be suppressed by grain refinement. Atmosphere adsorption and diffusion along grain boundaries were found to intensify brittle intergranular fracture, and this embrittlement can be avoided by vacuum heat treatment.     

Abrasive Wear Behaviors of Light-weight Austenitic Fe-24Mn-7Al-1C Steel and Mn13Cr2 Steel

The impact abrasive wear behaviors of light-weight austenitic Fe-24Mn-7Al-1C steel with increasing impact wear conditions were studied by comparing with the modified Hadfield (Mn13Cr2)steel.Wear tests were performed with the MLD-10 abrasive wear testing machine.Main parameters such as impact energy,impacting frequency and wear time were evaluated.To explore the abrasive wear behaviors under different impact energies,the parameters in-cluding mass loss,wear resistance and hardness were evaluated in detail.The microstructures of the steels were fur-ther analyzed using optical microscopy (OM),scanning electron microscopy (SEM),transmission electron micros-copy (TEM)and X-ray diffraction (XRD).Results showed that the light-weight austenitic Fe-24Mn-7Al-1C steel had a better wear resistance than Mn13Cr2 steel under the impact energy tested.The wear resistance of light-weight austenitic Fe-24Mn-7Al-1C steel was about 1.09-1.17 times as high as that of Mn13Cr2 steel under low and medi-um impact energy (0.5-2.0 J)conditions,and 1.41 times under high impact energy (4.0 J)condition.In Mn13Cr2 steel,the evolution of dislocation substructure with increasing impact energy showed typical stacking fault,interac-tion of twins and dislocations,as well as mechanical twins.The high work-hardening rate in Fe-24Mn-7Al-1C steel was caused by Taylor lattice and high density of dislocation tangles.     

Al-3Si-0.6Mg-(Cu,Mn)合金薄板的组织性能

采用拉伸试验、金相、扫描电镜、透射电镜高分辨组织分析方法,研究了水冷铜模铸造的扁锭轧制的Al-3.0Si-0.6Mg-0.4Cu-0.6Mn-0.18Fe合金薄板经400℃至540℃不同温度保温30 min水淬、室温停放90 d(自然时效)后的组织和性能.结果表明:在6009合金基础上提高Si的质量分数至3%,有提高其强度的作用;该合金薄板经540℃×30 min固溶处理自然时效后屈服强度为180 MPa、抗拉强度为313 MPa、延伸率接近23%,其组织中存在Si结晶相及含Fe、Mn和少量Cu、Si的结晶相,以及尺寸小于0.5μm的以含Mn为主并含少量Si和Fe的弥散相;提高其固溶处理温度至540℃,合金薄板的强度明显提高,其原因是析出强化产物尺寸增大,密度提高了.     

Tempering of Martensite and Subsequent Redistribution of Cr,Mn, Ni,Mo, and Si Between Cementite and Martensite Studied by Magnetic Measurements

Tempering reactions in ternary Fe-2M-0.7C steels (M=Cr, Ni, Mn, Mo, and Si) were studied by correlative dilatometry and magnetic measurements at room temperature. Magnetic measurements were conducted after tempering at progressively higher temperatures. Based on the magnitude of demagnetization in the temperature range associated with the tempering stage I contraction, Mn- and Si-added steels formed the largest and smallest fractions of transition carbides, respectively. Estimation of the magnetization of paraequilibrium cementite indicated that Cr, Mn, and Mo reduced the magnetization while Ni increased it. In the presence of Si, the decomposition of retained austenite and cementite formation were shifted to higher temperatures. At temperatures above approximately 723 K (450 °C), the enrichment of cementite with Mn and Cr significantly reduced the total magnetization. In the Mo-added steel, on the other hand, the magnetization slightly increased implying the formation of ferromagnetic Mo-rich carbides. For the Ni- and Si-added steels, the magnetization remained almost constant indicating minimal redistribution of Ni and Si subsequent to the formation of cementite. The possibility of analyzing the latter redistribution is one of the main advantages of sequential tempering and magnetic measurements at room temperature compared to in situ thermomagnetic measurements.     

Oxidation Processes for Alloys in the Ni – Zr System. Part 2. Phase Composition of Scale Formed on Ni7Zr2

We have used x-ray and metallographic layer-by-layer phase analysis to study the structure and composition of scale formed on the alloy Ni₇Zr₂ during its oxidation in air over a period of 1 h and 10 h in the temperature range 500-1200°C. In the scale we find NiO, the cubic and monoclinic modifications of ZrO₂, and also Ni and Ni₅Zr. The phase components are nonuniformly distributed over the thickness of the scale. The outer scale consists of the oxides NiO and ZrO₂, while the composition of the inner scale includes Ni and Ni₅Zr in addition to monoclinic ZrO₂. Cubic ZrO₂ is formed on the surface of the specimen in the initial stages of its oxidation at 500-700°C. For T ≥ 900°C, on the surface of the scale we find both modifications of ZrO₂, while the nickel phase is itself a solid solution Ni(Zr). We note that the mechanisms for the formation of low-temperature (T ≤ 800°C) and high-temperature (T ≥ 900°C) scales are different. It is hypothesized that these differences are determined mainly by the fact that at high temperatures, diffusion of zirconium ions toward the outer boundary of the scale is superimposed on diffusion of oxygen toward the scale – alloy boundary.     

Influence of zirconium and copper on the early stages of aging in Al-Zn-Mg alloys

The effects of zirconium and copper on the early stages of the precipitation processes in an Al-5.5 wt pct Zn-1.2 wt pct Mg alloy have been studied by differential scanning calorimetry (DSC) thermal analysis. Electron diffraction has been used as a complementary technique to aid in the interpretation of the thermal effects observed in the DSC thermograms. The results show that the initial stages of Guinier-Preston zone I (GP(I)) formation at room temperature are not affected by the presence of zirconium, but the rate of Guinier-Preston zone II (GP(II)) precipitation is slowed down significantly. For aging at 100 °C, the stability of GP zones is reduced by the addition of zirconium, and this leads to a reduction in the amount of η′ produced during aging. The addition of copper to an Al-5.4 wt pct Zn-1.2 wt pct Mg-0.2 wt pct Zr alloy intensifies the electron diffraction spots from GP(I), suggesting that the strong electron-scatterer copper may be incorporated into GP zones. The rate of growth of GP(I) at room temperature is unaffected by the presence of copper, but the rate of formation of GP(II) at room temperature is retarded. For artificial aging at 100 °C, the development of GP(I) and GP(II) is not affected significantly by the presence of copper, but the formation of η′ is stimulated, producing a high number density of very fine η′ precipitates. Preaging at room temperature results in accelerated η′ formation during subsequent aging at 100 °C in the zirconium-containing alloy. However, this acceleration of η′ formation is absent when copper is present in the alloy.     

The influence of overlay coatings on high cycle fatigue of an advanced tantalum carbide strengthened eutectic composite

High cycle fatigue of coated and uncoated NiTaC 3-116A2, a directionally solidified tantalum carbide strengthened eutectic, has been examined over a range of temperatures. In the uncoated condition, the fatigue strength of the alloy increased with temperature from room temperature to 600 °C, but was slightly lower at 900 °C than at 600 °C, which is consistent with the variation in 0.2 pct yield strength with temperature. At room temperature and 600 °C, the influence of several plasma sprayed coatings in reducing the fatigue life was found to be sensitive to the coating composition and alternating stress level. A Ni-20Cr coating resisted fatigue damage on the basis of its ductility and therefore performed better at high cyclic stress levels than at low cyclic stress levels. By contrast, Ni-20Cr-10Al-2Hf-0.1C. and Ni-20Co-20Cr-10Al-2Hf-0.1C coatings were stronger and so exhibited high fatigue strengths at long lives but, because of their limited ductility, cracked readily when tested at high stress levels. At 900 °C the coatings had little effect on fatigue life. On the basis of the present results and the metallographic observations of early crack growth through the coatings, it is concluded that the selection of a mechanically compatible coating requires a knowledge of the fatigue cycle. To ensure a minimum effect on fatigue lives for the anticipated stress cycle, it is necessary to match the coating and substrate mechanical properties as closely as possible. Formerly with Corporate Research and Development