Main factors affecting the mechanism of structure formation and improvements in the ductility properties of hypereutectoid silumins in three-roll rotary rolling

A study is made of the effect of different metal-shaping methods (extrusion and rotary rolling) on the structure and ductility properties of semifinished products made of hypereutectoid silumins with 17–23% Si. It is established that the degree of fragmentation of the silicon crystals in the semifinished products depends on their degree of deformation by different metal-shaping methods. The article also examines the effect of the type of stress-strain state present during extrusion and rotary rolling and the kinematics of these processes on the mechanism of structure formation in hypereutectoid silumins. __________ Translated from Metallurg, No. 4, pp. 69–75, April, 2006.     

Effect of the main parameters of helical rolling on the ductility properties of hypereutectic silumin alloys

The author examines how the number of cycles in which the work rolls of a rotary rolling mill load semifinished products made of hypereutectic silumin alloys depends mathematically on the degree of deformation ε and feed angle in three-roll rotary rolling. Another mathematical model is proposed to describe the dependence of the dispersity (dimensions) of the silicon crystals (one of the two phases in the structure of hypereutectic silumins that adversely affects the ductility properties of these alloys) on the number of load cycles N_c, the feed angle α, and the deformation ε. The proposed models adequately describe the experimental data, differing from the latter by no more than 5–7% and remaining within the permissible error. __________ Translated from Metallurg, No. 5, pp. 72–74, May, 2006.     

Mathematical model of the movement of layers of metal during the rotary rolling of semifinished products made of hypereutectic silumins

A mathematical model has been constructed to describe the kinematics of the movement of metal on the surface of semifinished products made of hypereutectic silumin alloys as they undergo rotary rolling. The model is based on the dependence of the pitch of the helical lines of metal flow on the deformation ε of the product and the feed angle α. The pitch is minimal when ε = 50–55%, regardless of the feed angle α. The degree of deformation ε = 50–55% is optimum for ensuring that the unit number of cycles in which the semifinished product is loaded by the work rolls is such as to produce a fine-grained structure and maximize the ductility characteristics of hypereutectic silumins. __________ Translated from Metallurg, No. 6, pp. 57–59, June, 2006.     

The microstructure of rapidly solidified Ti-Fe melt-spun ribbons

Ti-Fe binary alloys were rapidly solidified by the melt-spinning technique, and four compositions were examined: Ti-5 wt pct Fe, which is the critical composition for theβ to ω athermal transformation; Ti-10 wt pct Fe, which represents a hypoeutectoid composition; the eutectoid composition Ti-15 wt pct Fe; and Ti-20 wt pct Fe, as an example of a hypereutectoid alloy. The Ti-5 wt pct Fe rapidly solidified ribbons are composed of two different structures. The first consists of α′-martensite plates inβ matrix and the second, athermal ω particles inβ matrix. The Ti-10, 15, and 20 wt pct Fe alloys are also composed of two structures. These areβ grains and isothermal-like ω particles inβ matrix. A solidification model is suggested which explains the existence of two different microstructures at the same composition and the for-mation of two kinds of ω particles.     

Composition dependence of young’s modulus in Ti-V, Ti-Nb, and Ti-V-Sn alloys

The Young’s modulus of Ti-V and Ti-V-Sn alloys quenched from the β-phase region after solution treatment and cold rolling was investigated in relation to alloy compositions, microstructures, and constituent phases. The composition dependence of the Young’s modulus for quenched Ti-V binary alloys shows two minima of 69 GPa at Ti-10 mass pct V and 72 GPa at Ti-26 mass pct V. Between the two compositions, athermalω or stress-induced ω is introduced in retainedβ phase and increases Young’s modulus. That is, a low Young’s modulus is attained unless alloys undergoω transformation. In Ti-5 and -8 mass pct V, which under goα′ (hcp) martensitic transformation on quenching, the Young’s modulus further decreases by cold rolling, which can be reasonably explained by the formation ofα′ rolling texture. Comparing Young’s modulus in Ti-V binary alloy with that in Ti-Nb binary alloy, it is found that Young’s modulus is remarkably increased by athermal- or stress inducedω phase, and it shows a minimum when both martensitic andω transformation are suppressed during quenching in metastableβ alloys. The Sn addition to Ti-V binary alloy retards or suppresses athermal and stress-inducedω transformation, thereby decreasing Young’s modulus. Young’s modulus exhibits minimum values of 51 GPa in quenched (Ti-12 pct V)-2 pct Sn and of 57 GPa in cold-rolled (Ti-12 pct V)-6 pct Sn.     

Alloying behavior of the rare earth metals with manganese

General features of the phase equilibria for binary and ternary systems formed by rare earth metals (REM or R) with Mn and other d-metals and p-elements (Me) are described and reviewed. On passing from the R−Mn alloys of the light REM to those of the heavy ones, a progressive change in the shape of the phase diagrams and an increasing stability of the intermediate phases (RMn₂, RsMn₂₃, and RMn₁₂) is noticed. In particular, no compounds and a miscibility gap in the liquid state can be observed for La and Ce (which in this case behave like the alkaline earths). In the Pr−Mn and Nd−Mn systems no intermediate phases are stable down to room temperature. The peculiar trend of the R−Mn alloys is, moreover, compared with that exhibited by systems of transition metals close to manganese in the Periodic Table. In the ternary systems R−Mn−Me (the R−Mn−Al, R−Mn−Si and R−Mn−Ge ones were considered) and R−R′−Mn the dependence of the main phase equilibrium characteristics on the atomic radii of REM was observed, too. For the R−R′−Mn alloys a comparison is made between the experimental data (literature data and the authors' results) and those which can be predicted on the basis of the general alloying behavior of REM. Dipartimento di Chimica e Chimica Industriale, Sezione di Chimica Inorganica e Metallurgia, via Dodecaneso, 31-I-16146 Genova, Italy. Published in Poroshkovaya Metallurgiya, Nos. 3–4(394), pp. 1–12, March–April, 1997.     

Electron microscopic determination of orientation

The martensites of titanium binary alloys, containing 1, 2, and 5.3 wt pct Cu, were studied by transmission electron microscopy techniques. Roughly parallel plates with different variants of the orientation relationship, as well as colonies of identical variant plates, prevail in the structures. A stereographic projection analysis of super-imposed diffraction patterns from two adjacent plates is shown to be sufficient for the deduction of the orientation relationship that existed during transformation, which is found to be the Burgers’ relationship -(110)_β∥ (0001)_α′; 〈111〉_β∥ 〈2110〉_α′. A graphical method was developed for the derivation of the habit plane and its particular variant, in spite of the absence of retained β phase in quenched Ti-Cu alloys. The habit plane of Ti-Cu martensite is found to be (1079)_β with 4 deg accuracy, and to best agree with Class A (α^- ω⁺) solution of the Bowles and Mackenzie theory, rather than with (α⁺ ω⁺) or with Class B solutions.     

Determination of the elastic moduli of a directionally solidified nickel-based TaC eutectic

Measurements of ultrasonic wave velocities in a polycrystalline directionally solidified nickel based eutectic alloy are used to evaluate the three independent single crystal elastic moduli at temperatures between 298 to 925 K. The C_u and C₄₄ moduli are obtained directly from high frequency wave propagation along the D.S. axis, corresponding to <100>. Evaluation of C₁₂ requires measurements at lower frequencies to obtain (C₁₁ −E _<100>). The elastic anisotropy and temperature dependence of the elastic moduli are almost identical to those reported for pure Ni, indicating that neither TaC fiber reinforcement nor γ′ precipitate have strong effects on elastic properties of Ni based turbine blade alloys.     

Characterization of microstructure in laser-surface-alloyed layers of aluminum on nickel

In order to obtain basic understanding of microstructure evolution in laser-surface-alloyed layers, aluminum was surface alloyed on a pure nickel substrate using a CO₂ laser. By varying the laser scanning speed, the composition of the surface layers can be systematically varied. The Ni content in the layer increases with increase in scanning speed. Detailed cross-sectional transmission electron microscopic study reveals complexities in solidification behavior with increased nickel content. It is shown that ordered B2 phase forms over a wide range of composition with subsequent precipitation of Ni₂Al, an ordered ω phase in the B2 matrix, during solid-state cooling. For nickel-rich alloys associated with higher laser scan speed, the fcc γ phase is invariably the first phase to grow from the liquid with solute trapping. The phase reorders in the solid state to yield γ′ Ni₃Al. The phase competes with β AlNi, which forms massively from the liquid. The β AlNi transforms martensitically to a 3R structure during cooling in solid state. The results can be rationalized in terms of a metastable phase diagram proposed earlier. However, the results are at variance with earlier studies of laser processing of nickel-rich alloys.     

Shear Stresses and their Dependence on Different Process Parameters in the Helical Rolling of Solid Semifinished Products

An analysis of the results obtained from modeling the two- and three-roll helical rolling of solid semifinished products with tension permits the following conclusions: • despite the change in the scheme of deformation of the semifinished product (from two- to three-roll), the pattern of distribution of the shear stresses and the overall distribution of the positive and negative stresses remain similar to the cases of two- and three-roll helical rolling with thrust; • despite this, comparison of two-roll rolling with thrust T_b = 60 kN and with tension T_f = 40 kN shows that that the positively directed components of the shear stresses which develop in the part of the cross section of the semifinished product outside the zone of contact with the work rolls are greater with thrust than with tension. Conversely, the application of the maximum possible amount of tension (T_f = 80 kN) to the front end of the semifinished product results in greater positive shear stresses on the same part of the cross section than does the application of the maximum possible amount of thrust (T_b = 120 kN); • in the three-roll scheme, an increase in tension increases the intensity of the negative shear stresses in the zones not in contact with the rolls, while an increase in thrust increases the positive shear stresses in the same zones; • the absolute values of the shear stresses in the two-roll scheme with tension fluctuate within the range 104–113 MPa, i.e., they are nearly independent of the amount of tension applied; in the three-roll scheme, the shear stresses created with different amounts of tension are within the range 90–97 MPa, i.e., the shear stresses in the three-roll scheme are also nearly independent of the amount of tension or thrust that is applied. Curves are constructed to describe the dependence of the shear stresses on the combined action of thrust and tension. The results collectively show that shear stresses may not be the main reason for the formation of internal cavities in semifinished products during the rolling operation. __________ Translated from Metallurg, No. 7, pp. 45–54, July, 2005.     

Structural states of the material of compacts and sheets made from an Al-Cu-Li alloy with silver

The structure of hot-rolled sheets of V-1469 alloy of the Al-Cu-Li system with silver is studied. The sheets are prepared from ingots 70 mm in diameter by the ingot-pressed strip-hot-rolled sheet scheme. The texture of the pressed strips is characterized by the set of orientations (Bs, S, Cu) typical of thin pressed strips of aluminum alloys. During subsequent hot rolling, the Bs orientation weakens and the Cu and S orientations become more intense. This behavior indicates that a change in the crystallite orientations in the material of the sheets is controlled by a β-skeleton line in the Euler rectangle. According to the data of electron microscopic study, the main contribution to hardening during aging is made by the T₁ and Θ′ phases and the role of δ′-phase precipitates is insignificant. No precipitates of the T₂ phase are observed. The significant anisotropy of the yield stress in the 45°-direction with respect to the rolling direction is associated with T₁ and Θ′-phase precipitates.     

Control of ordered structure and ductility of (Fe,Co, Ni)3V alloys

This study is directed toward improvement of the ductility of long-range ordered alloys through control of their ordered crystal structure. A series of ordered alloys was prepared with a base composition of Co₃V, where Co was partially replaced with Fe and Ni. The stability and structure of the ordered phases in these (Fe,Co,Ni)₃V alloys were characterized by various metallurgical methods. The results indicate that the ordered structure in this alloy system can be controlled by adjusting the electron density, and that the L1₂ type cubic ordered structure (α′) is stable in the alloys with electron density less than 7.888. The phase relation in the cubic ordered alloys depends on the Fe concentration. For the alloys containing <20 pct Fe, the disordered α solid solution transforms to the cubic α′ ordered on the fcc lattice at temperatures below 1000°C. For the alloys containing >20 pct Fe, the α′ is formed through a peritectoid reaction, namely, α+σ→α′. Tensile tests indicate that the alloys with multilayered hexagonal ordered structure are very brittle, while the alloys with the cubic ordered structure are ductile at room temperature. The ductility of the cubic ordered alloys increases with decreasing Co content. The alloys with <55 pct Co showed dimple type ductile rupture with elongation over 40 pct at room temperature. The correlation of ductility with ordered structure is discussed.     

On the decomposition of β phase in some rapidly quenched titanium-eutectoid alloys

The decomposition of the β phase in rapidly quenched Ti-2.8 at. pct Co, Ti-5.4 at. pct Ni, Ti-4.5 at. pct, and 5.5 at. pct Cu alloys has been investigated by electron microscopy. During rapid quenching, two compctitive phase transformations, namely martensitic and eutectoid transformation, have occurred, and the region of eutectoid transformation is extended due to the high cooling rates involved. The β phase decomposed into nonlamellar eutectoid product (bainite) having a globular morphology in Ti-2.8 pct Co and Ti-4.5 pct Cu (hypoeutectoid) alloys. In the near-eutectoid Ti-5.5 pct Cu alloy, the decomposition occurred by a lamellar (pearlite) type, whereas in Ti-5.4 pct Ni (hypereutectoid), both morphologies were observed. The interfaces between the proeutectoid α and the intermetallic compound in the nonlamellar type as well as between the proeutectoid α and the pearlite were often found to be partially coherent. These findings are in agreement with the Lee and Aaronson model proposed recently for the evolution of bainite and pearlite structures during the solid-state transformations of some titanium-eutectoid alloys. The evolution of the Ti₂Cu phase during rapid quenching involved the formation of a metastable phase closely related to an “ω-type” phase before the equilibrium phase formed. Further, the lamellar intermetallic compound Ti₂Cu was found to evolve by a sympathetic nucleation process. Evidence is established for the sympathetic nucleation of the proeutectoid a crystals formed during rapid quenching.     

The effects of composition and γ′/γ lattice parameter mismatch on the critical resolved shear stresses for octahedral and cube slip in NiAlCrX alloys

Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the γ′ phase, and about 3 at. pct of X in the γ′. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 °C, which is about the peak strength temperature. The CRSS_Oct and CRSS_cube are discussed in relation to those of Ni₃ (Al, X) γ′ alloys taken from the literature and the γ′/γ lattice mismatch. The CRSS_Oct of the γ+γ′ alloys reflected a similar compositional dependence to that of both the CRSS_Oct of the γ′ phase and the γ′/γ lattice parameter mismatch. The CRSS_cube of the γ+γ′ alloys also reflected the compositional dependence of the γ′/γ mismatch, but bore no similarity to that of CRSS_cube for γ′ alloys since it is controlled by the γ matrix. The ratio of CRSS_cube/CRSS_Oct was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSS_cube/CRSS_Oct was related to the degree in which elements partition to the γ′ rather than the γ phase.     

Effects of cold work on precipitation in Al-Cu-Mg-(Ag) and Al-Cu-Li-(Mg-Ag) alloys

A study has been made of the effects of cold work prior to aging on precipitation hardening in selected Al-Cu-Mg-(Ag) and Al-Cu-Li-(Mg-Ag) alloys. General aging characteristics have been determined by differential scanning calorimetry, and response to hardening has been correlated with microstructure using transmission electron microscopy (TEM), selected area electron dif-fraction (SAED), and quantitative stereology. Particular attention has been given to the phases Ω andT ₁ that form on the {111 }_α planes, although information on the precipitates θ′,S′ (orS), and δ′ is also reported. Although Ω andT ₁, have similar morphologies and habit planes, their response to cold work prior to aging is different. Deformation promotesT ₁ formation at the expense of the δ′ phase in Al-Cu-Li alloys and at the expense of δ′, θ′, andS′ in Al-Cu-Li-Mg-Ag alloys. On the other hand, in Al-Cu-Mg-Ag alloys, deformation assists precipitation of θ′ at the expense of Ω phase, and some decrease is recorded in the hardening response. Prior cold work is also found to reduce the response during natural aging in most alloys. These results are discussed in terms of the role of particular alloying additions. Formerly Research Fellow, Department of Materials Engineering, Monash University     

Rapidly solidified P/M X2020 aluminum alloys

X2020 aluminum alloys were produced with variations in the Li/Cu ratio by the ultrasonic gas atomization process. In alloy 68 (Al-4.9Cu-l.2Li) and 69 (Al-4.4Cu-l.55Li) alloys, the Θ′ and T₁, phases are dominant with evidence of the T_B phase. In the 70 (Al-3.5Cu-2.8Li) alloy, the δ′ phase is dominant with a trace of T₁. It was found that Θ′ andT ₁ are effective strengtheners whereas δ′ provides excellent fatigue crack initiation resistance. Overall results indicate that the fracture behavior of three RS-PM X2020 alloys is closely related to alloy production route as well as to the phases present in the alloys. Formerly Research Assistant, Massachusetts Institute of Technology.     

Thermodynamic consideration of formation mechanism of α1 plate in βCu-base alloys

For the possible ordering structures of the parent phase β′—i.e., B2 in Cu-Zn alloys, DO₃ in Cu-Al alloys, and B2 and L2, in Cu-Zn-Al alloys—the driving forces for the a, plate formation have been calculated for the three βCu-base alloys. The driving force, ΔG, is larger than zero for the β′ →α₁ shear mechanism and less than zero for the β′ → β′₁ + α₁ diffusional mechanism. Furthermore, the equilibrium temperature, T_o, between the parent β′ phase and the α in, plate has been evaluated to be much less than the experimental start temperature, B_s, of the α₁ plate formation. Therefore, the a! plate formation cannot be initiated by a diffusionless β′ → α₁ shear reaction without other causative factors such as stress field, defects, etc. However, the α₁ plate can be formed through a diffusional β′ → β′₁ +α₁ reaction. Results in Cu-Al alloys also show that the composition of the α₁ plate produced in the diffusional reaction has to deviate from that of the parent phase to a certain extent. For some compositions of Cu-Zn-Al alloys, ΔG^{α1(dis.)→α1(ord.)} < 0 within a temperature range. Thus, the fresh α₁, plate produced after the diffusional reaction may further transform into the ordered α₁ plate within this temperature range. Calculated driving forces for the disordered parent phase reveal that the ordering of the parent phase resists the α₁ formation in Cu-Zn and Cu-Zn-Al alloys and enhances it in Cu-Al alloys. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18–22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Effects of carbon content and ausaging on γ ↔ α′ transformation behavior and reverse-transformed structure in Fe-Ni-Co-Al-C alloys

The effects of carbon content and ausaging on austenite γ ↔ martensite (α′) transformation behavior and reverse-transformed structure were investigated in Fe-32Ni-12Co-4Al and Fe-(26,28)Ni-12Co-4Al-0.4C (wt pct) alloys. TheM _s temperature, the hardness of γ phase, and the tetragonality of α′ increase with increasing ausaging time, and these values are higher in the carbon-bearing alloys in most cases. The γ → α′ transformation behavior is similar to that of thermoelastic martensite; that is, the width of α′ plate increases with decreasing temperature in all alloys. The αt’ → γ reverse transformation temperature is lower in the carbon-bearing alloys, which means that the shape memory effect is improved by the addition of carbon. The maximum shape recovery of 84 pct is obtained in Fe-28Ni-12Co-4Al-0.4C alloy when the ausaged specimen is deformed at theM _s temperature and heated to 1120 K. There are two types of reverse-transformed austenites in the carbon-bearing alloy. One type is the reversed y containing many dislocations which were formed when the γ/α′ interface moved reversibly. The plane on which dislocations lie is (01 l)_γ if the twin plane is (112)_α′. The other type of reverse-transformed austenite exhibits γ islands nucleated within the α′ plates.     

Damping characteristics of Ti50Ni49.5Fe0.5 and Ti50Ni40Cu10 ternary shape memory alloys

The damping characteristics of Ti₅₀Ni_49.5Fe_0.5 and Ti₅₀Ni₄₀Cu₁₀ ternary shape memory alloys (SMAs) have been systematically studied by resonant-bar testing and internal friction (IF) measurement. The damping capacities of the B19′ martensite and the B2 parent phase for these ternary alloys are higher than those for the Ti₅₀Ni₅₀ binary alloy. The lower yield stress and shear modulus of these ternary alloys are considered to be responsible for their higher damping capacity. For the same ternary alloy, the B19/B19′ martensite and R phase also have a higher damping capacity than does the B2 parent phase. In the forward transformations of B2 → R, R → 519′, and B2 → 519′ for Ti₅₀Ni₅₀ and Ti₅₀Ni_49.5Fe_0.5 alloys, the damping capacity peaks appearing in the resonant-bar test are attributed to both stress-induced transformation and stress-induced twin accommodation. The lattice-softening phenomenon can promote the stress-induced transformation and enhance the damping capacity peaks. The Ti₅₀Ni₄₀Cu₁₀ alloy had an unusually high plateau of damping capacity in the B19 martensite, which is considered to have arisen from the easy movement of twin boundaries of B19 martensite due to its inherently very low elastic modulus. The peaks appearing in the IF test for the Ti₅₀Ni₄₀Cu₁₀ alloy are mainly attributed to the thermal-induced transformation due to T ⊋ 0 during the test.     

Structure of phases in the δ-AI2O3 fiber studied by convergent beam electron diffraction

The phases in the δ-Al₂O₃ fibers were investigated using the methods of transmission electron microscopy (TEM): convergent beam electron diffraction (CBED) and high-resolution electron microscopy (HREM). A phaseγ′-Al₂O₃ discovered previously by Vewerly in oxide layers with an fcc structure was found and new atomic positions are proposed. A new structure ofδ-Al₂O₃ was also observed. It has aPmma space group and lattice parameters ofa _δ = 2a _γ′,b _δ = l.5a _γ′, andc _δ ≈a _γ′ The correlation of the observed A1₂O₃ lattices to the spinel lattice is discussed and translation of atom positions during theγ′ →γ →δ transformation is studied. All anions must change their positions by a small amount; one-third of the cation positions inγ′ and more than 90 pct of cation positions inδ experience a large translation during that transformation. This implies that for theγ′ it→γ} →δ transformation, the positions of cations in both lattices are important. The results are discussed in relation to the fiber-matrix interaction under spinel formation during thermal loading ofδ-Al₂O₃-fiber-reinforced aluminum piston alloys.