Small Plastic Deformation Research Articles

Effect of carbon, silicon, and cobalt on structure and properties of steels for cold deformation

1. Additional alloying of steel 8Kh4V2S2MF with silicon and cobalt leads to an increase of the resistance to small plastic deformation due to intensification of secondary hardening processes and strengthening of the matrix. With addition of more than 3% Mo the toughness and the bending strength are lower than in steels additionally alloyed with silicon alone, which can be explained by the more heterogeneous decomposition during tempering. 2. Steel of the Kh4V2F2M type alloyed with 3–4% Si has a good combination of resistance to compression σ 0.5 comp ∼ 250 kg/mm2, σ 0.5 comp ≥ 300 kg/mm2 and bending strength σbend ∼ 380 kg/mm2 and can be used for dies operating under pressures up to 250 kg/mm2.

Effect of pretreatment on microdeformation development in hcf polycrystals of substitutional solid solutions

The effect of small plastic deformation and subsequent free-state aging even under a load on microplastic deformation development in hcp polycrystals of substitutional solid solutions is investigated on Cu-Al and Cu-Ni alloys. It is established that in the temperature interval 77–300°K the effect of deformation pretreatment on subsequent microdeformation development is independent of the temperature at which it occurs, but is determined only by the temperature of secondary deformation. At the same time a clear correlation is observed between the change in the macroscopic elasticity limit and the shape of the microdeformation curve. If the macroscopic elasticity limit (σ″)after deformation pretreatment is larger than the friction strain (σF), the stress-strain diagram is a second-order parabola, as in the case of annealed alloys. If the macroscopic elasticity limit after deformation pretreatment equals the friction strain, the shape of the curveσ=f (ɛ) changes considerably. A stage of plastic deformation, on which the linear dependence ofσ on ɛP is conserved, is observed on the stress-strain curves after the range of elastic deformation. The mechanism of microplastic deformation development in predeformed alloys is treated by the statistical theory of microdeformation of polycrystals.

Increasing the fatigue life of steel 40KhNMA by tempering under stress

1. Tempering of quenched steel 40KhNMA under stress increases its resistance to small plastic deformations and the fatigue strength in tests for more than 106 cycles. 2. The effect of tempering under stress on the fatigue strength is evidently due to the longer period required for development of the fatigue crack. 3. Tempering under stress can be used as a strengthening treatment for machine parts.

Climb Behavior of Dislocations during Small Plastic Deformation at Low Temperature

The climb behavior of dislocations during stage I was studied in specially prepared crystals of two types: (a) Copper crystals virtually free of super-saturated vacancies and their condensation products were grown at a rate of 2.5 to 3 cm/hr by passing a molten zone through 99.999% copper samples kept in a high vacuum at ambient temperatures within a few degrees of their melting point, then slow cooling them so as to minimize vacancy supersaturations (b) Crystals prepared as above were reheated to near their melting point in evacuated quartz tubes, then removed from the furnace and air cooled. According to earlier results a substantial fraction of the supersaturated vacancies arising during air cooling were expected to precipitate out in the form of very small voids which on slight straining would be collapsed by dislocations) while at the same time causing the dislocations to tangle and “mushroom”).

Energy scattering of vibrations in aluminum after plastic deformation and annealing

1. At an amplitude of 3·10−4 small plastic deformations (3–4%) reduce the damping capacity of recrystallized or partly recrystallized aluminum. High-purity aluminum (A-999) retains higher values of the decrement with plastic deformations up to 6% than aluminum A-99. 2. Annealing of partially recrystallized aluminum at temperatures corresponding to the development of recrystallization processes favors an increase of the energy scattering of vibrations. 3. The change in the damping capacity of aluminum with plastic deformation and annealing conforms with the dislocation theory of damping.

Effect of small plastic deformation on the fatigue strength

1. The reduction of the fatigue limit as the result of small plastic deformation of prepared fatigue samples occurs not only with deformation by tension but also by compression. The reduction of the fatigue limit depends on the atomic-crystalline structure of the metal. The larger reduction occurs in α titanium alloys with a hexagonal lattice and the smaller in bcc metals, with no reduction for fcc metals. 2. For metals with a hexagonal lattice the fatigue limit begins to decrease with e=1.5% and remains low up to e=5.6%, while for bcc metals the fatigue limit is minimal after preliminary deformation of 1–3%. There is little change in the fatigue limit of fcc metals. 3. Removal of a thin surface layer by etching or chemical polishing of prepared samples after preliminary deformation or tempering at 250°C does not restore the fatigue limit; tempering at 600 and 450° after preliminary deformation completely restores the fatigue limit. 4. Small plastic deformation of blanks from which fatigue samples are prepared leads to a slight reduction of the fatigue limit. Evidently the condition of the surface layer changes in the process of preparing the fatigue samples, the hardening and residual stresses almost compensating the reduction of the fatigue limit that occurs in prepared samples subjected to preliminary deformation. 5. The reduction of the fatigue limit as the result of small plastic deformation of prepared fatigue samples is explained by the occurrence of oriented residual microstresses — the “peak” microstresses in “weakened” microvolumes reduce the fatigue limit determined in standard fatigue tests regardless of the sign of the microstresses.

Effect of microadditions of magnesium on the properties of cold-worked spring bronzes

1. The addition of magnesium to bronzes OF6.5-0.15 and KMts3-1 in amounts of 0.1 and 0.2% respectively substantially increases their resistance to small plastic deformation, particularly under long-term static and cyclic stress. 2. The effect of magnesium is due to its surface activity in copper-base alloys. The adsorption of magnesium on internal surfaces sharply inhibits grain growth, resulting in a fine-grained structure, and also induces the formation of segregates at defects in the crystal structure.

Resistance of heat-treated structural steels to small plastic deformation and cold brittle failure

1. The mechanical properties of hardened low-alloy structural steels reach their optimum values during the development of the ferrite matrix polygonization process. 2. The optimum properties of 15G2SF steel σ0.2≥50 kg/mm2, σb≥60 kg/mm2, σ0.01/σ0.2≈0.95, δ5≫=16%,an−60°C ≥3 kg-m/cm2, T50≤−40°C) after tempering at 600–650°C.

Effect of preliminary deformation on the hardening of commercial iron during natural aging

1. The variation of the hardening effect during aging with the degree of deformation depends essentially on the type of deformation if the initial concentration of impurity atoms in the solid solution falls within the limits of 10−4 to 10−3%. With deformation by elongation the effect of hardening increases with the degree of deformation, while with deformation by rolling it varies in a complex manner. 2. A change in the initial concentration of impurity atoms within limits of 10−4 to 10−3% and the ferrite grain size has a quantitative influence on the hardening effect during aging in relation to the degree of deformation. This influence decreases with the transition to hardening associated with resistance to small plastic deformation. 3. With an initial concentration of impurity atoms of approximately 10−2% the variation of hardening during aging with the degree of preliminary deformation by elongation changes qualitatively — with increasing deformation the hardening effect first decreases and then increases.

Recovery of ultrasonic third harmonic amplitude changes in sodium chloride following small plastic deformation

Abstract A recovery with time of the amplitude of an ultrasonic third harmonic wave in single crystal NaCl after applying a static deforming stress has been investigated. The recovery is found to be temperature dependent with an activation energy of 0·32 ev. Simultaneous measurements of the attenuation of the fundamental wave revealed a similar recovery for which an activation energy has also been measured. A recovery of the third harmonic amplitude has also been observed following the eventual removal of the deforming stress. The kinetics of the recovery of the third harmonic amplitude and also of the fundamental wave attenuation are found to obey a t⅓ ageing law.

High-strength nickel steels

1. In steels with 0.25–0.35% C and 10–14% Ni the mechanical properties after quenching (cooling in air) are approximately the same as for carbon-free maraging steels: σb=190−200 kg/mm2; δ=10–12%; ψ=45–50%;an=6–7 kg-m/cm2;ap=1.7–2.2 kg-m/cm2. Small cold plastic deformation (2–5%) substantially increases the strength characteristics: ΔσT=50−60 kg/mm2, Δσb=20−30 kg/mm2. 2. The high plasticity and resistance to crack propagation of the steels investigated are due to the fact that nickel increases dislocation mobility and promotes relaxation processes, which are necessary to prevent crack nucleation and propagation and brittle fracture.

Properties of aluminum bronze after cross rolling

1. With rolling of bronze strips in the direction perpendicular to the first rolling the diagram of the variation of the elastic limit, hardness, and ultimate strength with the orientation of the samples is as if turned 90°, while the anisotropy of the number of bends remains unchanged. 2. By combining first rolling (with large reduction) with a second rolling (with small reduction) in the transverse direction one can obtain a combination of high strength and, especially, resistance to small plastic deformation and ductility in the same direction.

Remanenz und Ummagnetisierungsbeginn in Nickeleinkristallen

The hysteresis, especially the remanence, and the magnetostriction of nickel single crystal rods of 〈110〉, 〈111〉, 〈100〉 and medium orientation are measured at room temperature in a magnetic joke and their dependence on plastic deformation is investigated. In undeformed crystals the nucleation of reverse domains needs a negativeH-field several times the coercivity, thus causing an “overshooting” of the hysteresis. Very small plastic deformations initiate the formation of the reverse domains and destroy the overshooting. Similar to polycrystals, the remanence of the single crystals — except those with 〈100〉 as axis — falls steeply at the beginning of plastic deformation to about 40% of its initial value. The magnetization reversal and the role of nucleation processes are discussed for the different orientations.

Effect of small plastic deformation on the mechanical properties of steel 38Kh5MSFA

1. After small plastic deformation (0.2\2-1.2%) and aging, steel 38Kh5MSFA is susceptible to strain aging, which is manifest in an increase of the ultimate strength and yield strength and decrease of elongation. The yield strength increases more than the ultimate strength. At a deformation of 0.6% and higher, followed by aging, σ0.1/σb is close to unity. The effect of strain aging on the mechanical properties is manifest in the different original conditions after low- and high-temperature tempering. However, the effect is stronger after low-temperature tempering. 2. Strain aging occurs at room temperature but is more evident at higher aging temperatures up to 300\dgC. 3. Strain aging raises the cold-brittleness threshold but has little effect on the work of crack propagation.

Strengthening steel by deformation at martensitic transformation temperatures

1. Deformation of steel in the martensitic transformation range of temperatures is greatly facilitated by the existence of austenite in the structure, which has a high plasticity and low strength. 2. By comparison with cold working of martensite, deformation of steels in the martensitic transformation range produces a better combination of strength and ductility with less variation in the mechanical properties. 3. The absence of a maximum on the strength-tempering temperature curves indicates precipitation of carbon during deformation in the MS-Mf range. 4. The combination of the deformation of austenite at temperatures above the martensitic transformation range (HTTMT, LTTMT) and deformation in the martensitic transformation range after either one produces both high strength and elevated resistance to small plastic deformation. 5. HTTMT + strain in the MS-Mf range produces higher ductility at the same strength and also high "reversibility" of the properties on repeated rapid quenching with intermediate tempering.

Stress Relaxation in Single Crystals of Copper and α-Brasses

Stress relaxation at constant strains has been studied in crystals of copper and α-brasses containing 10, 20, or 30 at.-% zinc at 77,200, and 291° K after consecutive small plastic deformations. Close to the yield point the relaxation was generally within 1% of the applied stress, but at large deformations, notably within the third stage of work-hardening, it attained ∼ 10%. Any given relaxation was observed for ∼ 1000 sec, over most of which period the decay of the stress was logarithmic in time. Energy barriers of the activated process were from ∼ 0.08 eV for copper and 0.2–0.3 eV for brasses. Their significance is discussed in terms of a model in which unpinning of dislocations from rows of solute atoms is the principal process determining the relaxation rate.

Recovery of thermo-electric power and electrical resistivity of gold following small plastic deformation at −195°C

The isochronal recovery of the thermoelectric power of gold wires was measured, following a small plastic deformation at 78°K. In the stage III recovery range a fine structure was observed. In one of the substages we observed by simultaneous measurements of the resistivity and thermo-electric power: ΔS/Δp = 1.2 ± 0.4 V/°KΩ cm . A comparison with the known value of this parameter for quenched gold gives some support to ascribe this stage to vacancy diffusion.

The bauschinger effect in transition from rolling to bending

It is found that suppression of the Bauschinger effect is responsible for the sharp growth in resistance to small plastic deformations in bending in low-temperature annealing of material previously deformed by rolling.

Recovery of Ultrasonic Attenuation in Copper Single Crystals Following Small Plastic Deformation

Migration of deformation-produced defects to dislocations was studied by means of an ultrasonic technique. Copper single crystals of 3N and 4N nominal purity were deformed about 0.3% in tension at temperatures between 40° and 90°C. After deformation the stress was released and the change in ultrasonic attenuation was measured continuously at the deformation temperature. The recovery of the ultrasonic attenuation fits the predictions of the Granato, Hikata, and Lücke theory. This indicates the validity of the Cottrell—Bilby ``t2/3'' strain-aging law for stress-assisted diffusion of point defects to dislocations in copper. A single mobile defect was detected, and its migration energy was measured as 0.67±0.06 eV. The defect was identified as the divacancy. The divacancy concentration after about 0.3% deformation was estimated as 5×10−8.

Properties of alloyed Ni?Be alloys

1. In Ni−Be spring alloys alloyed with Mo, Mo+B, W, and V the resistance to small plastic deformation increases. 2. The strengthening of Ni−Be alloys containing Mo, W, or V is due to the precipitation of a greater number of particles of the β'-phase because of the decrease in the solubility of Be in the nickel solid solution. The addition of Co has the same effect and this leads to a decrease of the resistivity of the alloys as compared to that of the Ni−Be alloy. 3. Alloying of Ni−Be alloys with Mo and B or W and V increases the heat resistance of the alloys.