Solid Solution Softening Research Articles

Solid solution softening and strain-rate sensitivity of Fe-Re and Fe-Mo alloys

The resolved shear stress and strain-rate sensitivity of Fe-Mo and Fe-Re alloys, well within the solid solution range, were measured versus temperature and compared with previous results for Fe-Ti alloys. The strain-rate sensitivity-temperature curves shifted systematically to lower temperatures as solute was added. The resolved shear stress was divided into two parts, a dynamic part which is a function of strain-rate and a static part which is not. The strain-rate sensitivity data were inverted to give the dynamic part of the flow stress and this was subtracted from the resolved shear stress to give the static part of the flow stress. Significant solid solution softening occurred in the dynamic part of the flow stress at 166 and 196 K. This is due to intrinsic effects and not to scavenging of im-purities. The static part of the flow stress is made up of two parts, a peaking effect super-imposed on normal solid solution hardening.

水素を吸収したFe-1.5%Ti合金単結晶の引張変形

Single crystals of Fe-1.5wt% Ti alloy were grown by single-pass zone melting. As grown crystals and the crystals quenched from hydrogen atmosphere at 800°C were deformed in tension between room temperature and -196°C at a strain rate of 1.67×10-4 sec-1. The quenched crystals showed a prominent yielding phenomenon and localized deformation. At room temperature the yield stress of the crystals quenched from hydrogen atmosphere was approximately twice as that of as-grown crystals.The yielding phenomenon, subsequent work softening, and solid solution softening were discussed as the effect of the hydrogen clusters around substitutional Ti atoms.A low temperature aging test was done in order to obtain the information about the yielding phenomenon and hardening mechanism. The yield stress of the crystals quenched from hydrogen atmosphere was decreased rapidly by the low temperature aging process.It was concluded that hydrogen clusters around substitutional Ti atoms cause these phenomena.

Solid solution softening and hardening

The bases for models of solid-solution softening and hardening are discussed. Conclusions of these discussions are presented which show that most intrinsic mechanisms cannot be applied to solution softening in Ta and Nb alloys. Scavenging-like mechanisms, related to effects that solute interactions have on the strain center density, strength or distribution in materials which are effectively ternary alloys, offer the only realistic explanation of solution softening in Ta and Nb alloys. In other materials, the evidence is not all in, because the systematic experments with respect to purity and secondary solute additions done on Ta and Nb alloys have not been performed. The results of a few investigations on other metals to date, the generality of behavior demanded of all metals by intrinsic'' theories of solution softening and the obvious exceptions to this behavior by Ta and Nb, all strongly suggest that if a single mechanism of solute softening exists, it must be a scavenging/solute interaction mechanism. (JRD)

Solid solution softening and solid solution hardening

A mechanism explaining both solid solution softening and solid solution hardening has been developed by examining the motion of a screw dislocation through a combined field of Peierls potential and misfit strain centers. It was found that the strain centers, which assist the double kink nucleation by a couple force exerted on the screw dislocation, impede the sideward motion of the kinks. Therefore, the energies for these two processes must be considered in order to describe the total dislocation motion. The results of the present calculation generally predict a hardening effect at the higher temperature range and a softening effect at the lower temperature range in the same solid solution specimen.

On the solid solution softening in Fe-2.86at%Ni and Fe-2.94at%Si

A consistent theory for the solid solution softening has not yet been established. An important question is whether or not the solid solution softening results from the same cause for all binary alloys. Arsenault (10) concluded that the solid solution softening in TaNb and TaW can be accounted for by a change in the Peierls stress due to a change in the modulus of the alloy. In the case of FeNi and FeSi, the changes in the moduli are too small to account for the observed large decrease in activation enthalpy. However, if the change in shear modulus, lattice constant and critical kink length are taken into consideration, decrease in activation enthalpy seems to be fairly well accounted for on the basis of the Peierls mechanism. Solid solution softening in FeNi may be interpreted in terms of electron configuration or cross slip. This interpretation can not, however, be applied to FeSi. Therefore, it is quite dangerous to derive the general conclusion on the cause of solid solution softening from the information of one alloy alone. The comparison between FeNi and FeSi is a good example to show it.

The effects of phosphorus on the mechanical properties of low-carbon iron

Fe-P alloys with nominal compositions of 0.05, 0.1, 0.2, and 0.6 wt pet P were deformed in compression at temperatures between 77 and 295 K at strain rates between 2.5 x 10-4 and 3.5 x 10-2 per sec. The effect of grain size on the yield strength was investigated over a range of about ASTM 7 to 3.5. The results show that the yield strength of iron is increased 40 to 50 pet in the 0.05 and 0.1 P alloys at 295 K without affecting the notch impact transition temperature. At temperatures of 200 K and below solid solution softening occurs in all the alloys except for 0.6 pet P. The degree of softening at a given temperature is a function of the strain rate and grain size, being more pronounced at higher strain rates and larger grain sizes.

Iron and its dilute substitutional solid solutions

The new results of an extensive study of the effects of alloying elements upon the properties of iron are presented, including lattice parameters, elastic constants, the effect of temperature on strength, solid solution strengthening and softening, work hardening, strain aging, hot working and toughness.

Solid-solution softening and thermally activated flow in alloys of Fe with 3at.% Co, Ni or Si

Iron and its binary alloys with 3 at.% Co, Ni or Si were deformed at temperatures between 77 and 295°K at a strain rate of 2.5 × 10 −5/ sec. The thermal ( σ ∗ ) and athermal ( σ i ) components of the flow stress and the activation parameters for yielding ( V ∗ and ΔH ∗ ) were determined from analyses of double strain-rate cycling and premacroyield tests. Solid-solution softening occurs in Fe-3Si and Fe-3Ni at temperatures between 77 and 200°K. Nickel and Si decrease σ ∗ and ΔH ∗ in this temperature range. Solid-solution softening was not observed in Fe-3Co; σ ∗ and ΔH ∗ for this alloy between 77 and 295°K are essentially those for Fe. For all these materials, at temperatures of 200°K and below, the relations of σ ∗ with T, ΔH ∗ and V ∗ are consistent with the predictions of the lattice-hardening theory of Dorn and Rajnak. The component of stress attributable to solid-solution hardening appears to remain constant between 77 and 295°K. This component is about ten times greater in Fe-3Ni and Fe-3Si (15–20 ksi, 103–138 MN/m 2) than in Fe-3Co (1–2 ksi, 6.9–13.8 MN/m 2). Solid-solution hardening in these alloys can be related to solute atom size misfit, as indicated by lattice parameter measurements. The results suggest that solid-solution softening is greater in alloys which show pronounced solidsolution hardening at temperatures near 295°K; therefore, solid-solution softening also appears to be determined by solute atom size misfit. Solid-solution softening by Ni and Si appears to be most readily explained in terms of promotion of kink nucleation on screw dislocations as a result of relatively strong solute atom-dislocation interactions. The absence of solid-solution softening in Fe-3Co is attributed to the small atomic misfit of Co which results in negligible interactions between dislocations and solute atoms.

The temperature dependence of the yield stress and solid solution softening in FeNi and FeSi alloys

The yield stress and thermal activation parameters of fully aged, purified iron, Fe-1.36 a/o Ni, Fe-2.86 a/o Ni and Fe-2.94 a/o Si and quenched FeC, Fe-1.36 a/o Ni-C and Fe-2.86 a/o Ni-C were measured as a function of temperature. In the fully aged condition, purified Fe showed the strongest temperature dependence of the yield stress followed by FeNi and FeSi. The addition of Ni and Si caused both solid solution hardening at room temperature and solution softening at low temperatures. The activation energy for yielding is smaller for FeNi and FeSi than for purified Fe. Interstitial C caused both athermal solid solution hardening at room temperature and apparent solid solution softening at low temperatures in unalloyed iron. Interstitial C has no effect on the temperature dependence of the yield stress in FeNi and FeSi alloys. These observations rule out the impurity hardening theory proposed by Fleischer and the “scavenging effect”. The hardening is explained by the Mott and Nabarro alloy hardening theory and a reduction of the kink formation energy.

Solid solution softening in BCC metal alloys

Solid solution softening in BCC metal alloys

Comments on “Solid solution softening in B.C.C. alloys”

Comments on “Solid solution softening in B.C.C. alloys”

The double-kink model for low-temperature deformation of B.C.C. metals and solid solutions

The energy of formation of a double kink was calculated as a function of stress, for various boundary conditions, values of elastic constants, and for different dislocation lengths. Once a double kink has formed, its lateral motion is an athermal process. The interaction energies between the kinks and between the kinks and the remaining portions of the dislocations were found to be small compared to the formation energy of the double kink. There is agreement between the calculated activation energies and the experimental values. The potential energy versus displacement curve for the formation of successive double kinks was calculated for a dislocation of finite length. The potential energy was found to go through a series of local maxima and minima before decreasing to an absolute minimum and then increasing monotonically as the displacement increases. This potential energy profile was used to explain low-temperature internal friction data. The means by which solute atoms can effect the Peierls' stress, and the resulting change in activation parameters and yield and flow stress were examined. The significant effect of the change in the Peierls' stress due to solute atoms is the occurrence of solid solution softening effect.