Optimizing the hot-forging process parameters for connecting rods made of PM titanium alloy

In order to optimize the processing parameters of a new low-cost titanium alloy connecting rod made of powder forging, the deformation behavior of an α + β type Ti–1.5Fe–2.25Mo (wt%) alloy produced by elemental powder metallurgy (PM) route was studied using isothermal compression tests. The constitutive equations and a processing map were established to characterize the flow behavior and predict the optimum deformation parameters. The calculated apparent activation energy was 257.73 kJ/mol for deformation in the α + β phase region and 378.01 kJ/mol in the β phase region. Two deformation mechanism domains were found: α + β → β phase transformation and dynamic recrystallization. The results show that the optimum deformation parameters for the present alloy are (700–800 °C, 10^−1.7–1 s⁻¹) and (800–900 °C, 10⁻²–10 s⁻¹). Based on these results, a finite element method (FEM) simulation of the hot-forming of a connecting rod was conducted, and the simulated results have been successfully used in an industrial forging of the connecting rod.     

Processing maps for Fe–24Ni–11Cr–3Ti–1Mo superalloy

Hot deformation characteristics of a Fe-base superalloy were studied at various temperatures from 1000–1200°C under strain rates from 0·001–1 s^− 1 using hot compression tests. Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate and interpreted by a dynamic materials model. Hot deformation equation was given to characterize the dependence of peak stress on deformation temperature and strain rate. Hot deformation apparent activation energy of the Fe–24Ni–11Cr–1Mo–3Ti superalloy was determined to be about 499 kJ/mol. The processing maps obtained in a strain range of 0·1–0·7 were essentially similar, indicating that strain has no significant influence on it. The processing maps exhibited a clear domain with a maximum of about 40–48% at about 1150°C and 0·001 s^− 1.     

Enhancement of the plasticity of aluminum alloys under the action of electrohydraulic pulses and thermal loads

For tubes of AD1 and AMg3 aluminum alloys, we demonstrate the possibility of attaining a level of deformation that is greater than the relative elongations attained in the process of stepwise deformation to 0.55–0.65 of the relative elongations by applying the method of electrohydraulic pulses combined with thermal treatment. It is shown that the intensity of hardening of AMg3 alloy increases with the level of deformation. It is shown that the intensity of hardening of AMg3 alloy increases with the level of deformation, whereas for AD1 alloy, it is practically constant. In the case of deformation caused by a single electrohydraulic pulse, we detected an anomalously high level of deformation which was greater than the relative elongation by a factor of 1.31–1.34. Translated from Problemy Prochnosti, No. 5, pp. 135–142, September–October, 1997.     

Risk analysis of fracture and failure

 This paper is inspired by the work of Professors Heinz Wilsdorf and Doris Kuhlmann-Wilsdorf on fundamental aspects of ductile fracture mechanism. Risk – a measure of the probability and severity of adverse effects – is introduced and related to the consequences associated with elastic (reversible) deformation, plastic (irreversible) deformation, and catastrophic deformation (total failure). Cost-benefit-risk trade-off analysis is discussed. Received: 25 February 1998 / Accepted: 10 March 1998     

The effects of austenite phase deformation on microstructure and magnetic properties in Fe–13.4%Mn–5.2%Mo alloy

The effects of austenite phase deformation on martensitic transformations and magnetic properties in Fe–13.4%Mn–5.2%Mo have been investigated by scanning electron microscopy, transmission electron microscopy, and M?ssbauer Spectroscopy. The increase of plastic deformation rates on austenite phase created considerable changes in amounts of ε (h.c.p.) and α′(b.c.c.) martensite, and austenite grains size decreased. Analysis of microstructure and M?ssbauer spectra show that the amount of ε martensite increased at low deformation rates whereas it decreased at high deformation rate. Besides, M?ssbauer spectra of the alloy reveal a ferromagnetic character with a broad sextet for α′ martensite phase and a paramagnetic character with a singlet for the γ (f.c.c.) austenite and ε martensite phases. In the other hand, the magnetic character of the alloy exhibits a different magnetic order depending on strain rates.     

Effect of cold rolling on microstructure and magnetic properties in a metastable lean duplex stainless steel

Microstructural and magnetic properties changes of a metastable ferritic–austenitic stainless steel due to cold rolling were studied together with the possibility to develop a new ferritic–martensitic stainless steel. In order to reduce costs low-Ni content was maintained in the lean duplex stainless steel considered, making it more susceptible to strain-induced martensitic transformation. In this study a practically complete γ → α′ transformation was found for 80% of thickness reduction, resulting a new two-phase ferritic–α′ martensitic stainless steel. To investigate the structural evolution different values of thickness reduction were applied. Light optical and scanning electron microscopy were performed to characterize the morphology and grain refining of the structure after each rolling step. Martensitic transformation and work hardening were detected and analyzed by studying of magnetic properties (saturation magnetic polarization, relative magnetic permeability, coercivity). Additionally, hardness tests were performed. The results highlighted a strong grain refining and increase in martensitic phase and hardness with increasing cold deformation. A direct relationship between microstructure and magnetic properties was revealed. In particular the reciprocal of relative magnetic permeability and the coercivity increased with martensite content and the amount of cold deformation. Therefore, the possible application of magnetic measurements as non-destructive tests to study microstructural evolution during cold rolling was shown for the steel considered.     

The effect of metastability on room temperature deformation behavior of β and α + β titanium alloys

The deformation behavior of single-phase metastable β-titanium alloys and two-phase α+metastable-β alloys strongly depends on the degree of stability of the β-phase. Recently, it has been shown that the tensile deformation behavior, as well as the creep deformation behavior at low temperatures (<0.25T _m), is strongly influenced by the degree of metastability. For example, the titanium β-alloy Ti–13.0wt%Mn, which has higher stability than the titanium β-alloy Ti–14.8wt%V, deforms by slip only; whereas the latter deforms by slip and twinning. In addition to the mechanical properties, the deformation mechanisms also depend on the degree of metastability. Further, the deformation mechanisms of a given metastable β-alloy depend on whether the β-phase is present by itself as a single-phase alloy, or in the presence of α-phase in the form of a two-phase alloy. For example, it was found that a metastable Ti–V alloy deforms by slip and twinning when it is in the form of a single-phase alloy, but deforms by slip and martensitic transformation when the same metastable β-phase is present in a two-phase α + β alloy. The mechanical properties of the metastable β alloys in turn depend on these deformation mechanisms. These recent developments are reviewed in this article.     

Construction of Constitutive Relationships of the Deformation Theory for Simple in Noll's Sense Hardening Materials with Elastoplastic Behavior

Based on the theory of simple hardening materials with elastoplastic behavior, the general constitutive relationships of the deformation theory of plasticity are mathematically strictly constructed for arbitrary continuous, piece-wise continuously differentiable deformation trajectories, any strains and symmetry types of the material properties. Two conditions under which this is possible are considered. The approaches to a strict specialization of general constitutive relationships of the deformation theory of plasticity have been developed by imposing restrictions on the material strains, deformation processes and properties. In this case, the restrictions on the properties of materials formalize the data obtained in the experimental investigations. A series of both new and known constitutive relationships have been constructed that are arranged into a hierarchy according to the level of complexity of the response to deformation. The area of applicability of the derived physical equations has been defined. Special attention has been given to the modeling of finite and infinitesimal strains of isotropic materials. __________ Translated from Problemy Prochnosti, No. 6, pp. 35 – 49, November – December, 2005.     

Texture evolution during hot-rolling and recrystallization in B2-type FeAl, NiAl and CoTi intermetallic compounds

The texture evolution during the hot-rolling and the recrystallization of B2-type Fe–48Al, Ni–50Al and Co–50Ti (expressed by at.%) intermetallic compounds were investigated. By hot-rolling at 973 K, Fe–48Al showed a microstructure with coarse grains elongated along rolling direction, while Ni–50Al and Co–50Ti showed a deformed microstructure featured by the heavily distorted (elongated) grains and/or the deformation bands. The hot-rolling texture of Fe–48Al was composed of {111}<uvw>, while those of Ni–50Al and Co–50Ti were composed of {111}<110> and {111}<112>, respectively. After annealing, the recrystallized grains were preferentially nucleated at the grain boundaries for Fe–48Al, and in the heavily distorted regions or the deformation bands for Ni–50Al and Co–50Ti. The orientations of the recrystallized grains were similar with those of the deformed matrix, especially for Ni–50Al and Co–50Ti. The recrystallization textures were generally more dispersive than the hot-rolling texture. Based on these results, the texture evolution during the hot rolling and the recrystallization of the B2-type intermetallic compounds were discussed.     

Development of a new system of alloying of high-strength titanium alloys for welded structures

On the basis of the accumulated experimental data on the redistribution of alloying elements between the α-and β-phases in the process of phase transformation and the well-known concept of necessity of guaranteeing equal molybdenum equivalents in the cast state in different parts of the grains in the β-phase, which is attained by complex alloying of titanium with β-stabilizing elements whose distribution coefficients are greater and lower than one, we choose an alloying complex and specify its limits ensuring the high strength and good weldability of the material. On the basis of the Ti-Al-Mo-V-Nb-Fe-Zr system, we propose the composition of a new high-strength titanium alloy with good weldability and develop new modes of its hot deformation, welding, and thermal treatment. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 65–70, May–June, 2006.     

A method for predicting fracture resistance of material in cyclic loading under viscoelastoplastic deformation and neutron irradiation conditions

We analyze the available methods for prediction of fatigue fracture resistance, which allow for material creep in a deformation cycle and neutron irradiation. Benefits and drawbacks of the available methods are discussed. We present a new method for the fatigue fracture strength prediction, which suffers no disadvantages inherent to the well-known methods. The proposed method has been verified on austenitic steels tested at elevated temperatures. Translated from Problemy Prochnosti, No. 6, pp. 5–24, November–December, 2008.     

Hot deformation behavior of Ti-15-3 titanium alloy: a study using processing maps,activation energy map,and Zener–Hollomon parameter map

The hot deformation behavior of Ti-15-3 titanium alloy was investigated by hot compression tests conducted in the temperature range 850–1150 °C and strain rate range 0.001–10 s⁻¹. Using the flow stress data corrected for deformation heating, the activation energy map, processing maps and Zener–Hollomon parameter map were developed to determine the optimum hot-working parameters and to investigate the effects of strain rate and temperature on microstructural evolution of this material. The results show that the safe region for hot deformation occurs in the strain rate range 0.001–0.1 s⁻¹ over the entire temperature range investigated. In this region, the activation energy is ~240 ± 5 kJ/mol and the ln Z values vary in range of 13.9–21 s⁻¹. Stable flow is associated with dynamic recovery and dynamic recrystallization. Also, flow instabilities are observed in the form of localized slip bands and flow localization at strain rates higher than 0.1 s⁻¹ over a wide temperature range. The corresponding ln Z values are larger than 21 s⁻¹. The hot deformation characteristic of Ti-15-3 alloy predicted from the processing maps, activation energy map, and Zener–Hollomon parameter map agrees well with the results of microstructural observations.     

Tensile impact behavior and deformation mechanism of duplex TiAl intermetallics at elevated temperatures

Investigations are made on the effects of strain rates on the tensile behavior and deformation modes of Duplex Ti–46.5Al–2Nb–2Cr (DP TiAl) at temperatures ranging from room temperature to 840 °C and under strain rates of 0.001, 320, 800, and 1350 s⁻¹. The dynamic strength is higher than quasi-static strength but does not change much over the high strain rate range. Yield stress anomaly is not found. Brittle-to-ductile transition temperature (BDTT) increases with the increased strain rates. A Zerilli–Armstrong constitutive model with appropriate coefficients is chosen to describe the high strain rate flowing behavior. TEM analysis indicates that both ordinary dislocations and superdislocations are found and dislocation pile-up only appears in samples deformed under quasi-static loadings at elevated temperatures. The deformation twins are common in equiaxed grains and the proportion of twinned grains increases with the increased strain rate from 46–72% under quasi-static loadings to 69–95% under high strain rate loadings. No deformation twins are found in lamellar colonies.     

Procedure for the determination of torsional deformation relationships for anisotropic materials

The paper presents a procedure for the determination of torsional deformation relationships for prismatic specimens made of anisotropic material and construction of deformation curves under these conditions Translated from Problemy Prochnosti, No. 3, pp. 116–123, May–June, 2009.     

Modeling of the sorption deformation of glassy polymer sorbents in interaction with gases in a high-pressure region

Based on the phenomenological-thermodynamics method, a model of sorption deformation of a glassy polymer sorbent — polycarbonate — in interaction with carbon dioxide in a high-pressure region has been proposed. The possibility of describing sorption equilibrium for this system has been analyzed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 175–179, September–October, 2006.     

Microstructure evolution of Mg-3%Al-1%Zn alloy tube during warm bending

Microstructure evolution and deformation mechanisms of AZ31 magnesium alloy tubes during bending have been investigated. Dislocation slip appears to be the main deformation mechanism, along with a few {10–12} [−1011] extension twins at the outer bend radius which undergoes tensile deformation. In contrast, the material in the tube wall at the inner bend radius of the tube, which undergoes compression, deforms mainly by extension twinning. This understanding of deformation mechanisms has explain the optimum bending temperature of 150–200 °C for the AZ31 tubes where both slip and twinning are active.     

Deformation behavior of spray-formed hypereutectic Al–Si alloys

The deformation behavior of spray-formed hypereutectic aluminum–silicon alloys—AlSix (x = 18, 25, and 35 wt%)—has been studied by means of compression test at various temperatures and strain rates. The flow stress of the spray-formed Al–Si alloys increases with decreasing compression temperature and increasing strain rate. Higher silicon content in the alloys also leads to higher flow stress during deformation. The flow curves determined from the compression tests exhibit that the deformation of the materials is controlled by two competing mechanisms: strain hardening, and flow softening. Particle damage during the deformation may have an influence on the flow curves of the alloys with large silicon particles. Based on the flow curves obtained from the compression tests and knowledge of aluminum extrusion, the spray-formed hypereutectic Al–Si alloy billets have been hot extruded into wires with a high area reduction ratio around 189. Since primary silicon particles were greatly refined and uniformly distributed in the spray-formed materials, the heavy deformations of the spray-formed Al–Si alloys containing high amount of silicon were successfully performed.     

Prediction of fracture characteristics of metals from high-frequency test data

A method is proposed for the prediction of cyclic crack resistance characteristics of metallic materials under low-frequency loading from high-frequency test data, which is based on a model of development of local plastic deformation regions during the accumulation of fatigue damages and fatigue crack growth with allowance for cyclic loading rate. We performed a comparative analysis of the results of prediction of fatigue fracture diagrams with test data for VT22, VT18U, VNS-25, and AMg6N alloys in a frequency range of 20 Hz–10 kHz. Report on International Conference “Dynamics, Strength, and Life of Machines and Structures” (1–4 November 2005, Kiev, Ukraine). __________ Translated from Problemy Prochnosti, No. 2, pp. 121–128, March–April, 2007.