Tadahisa Nakamura

Cavity Formation at the Interface of a Spherical Inclusion in a Plastically Deformed Matrix

Abstract A new theory for cavitation at the interface of a spherical inclusion in a plastically deformed matrix under uniaxial tensile stress is proposed. It is based on the energy calculation in and around the inclusion following Eshelbys transformation problem. It is shown that there is a size below which the fracture strain is inversely proportional to the square root of the particle size. There is also a size above which the applied stress causes cavitation without plastic strain.

The effects of applied stress on the intergranular phosphorus segregation in a chromium steel

Abstract The mean Auger peak ratio (APR) of phosphorus, averaged over the intergranular fracture surface of each sample, has been measured on smooth and notched types of specimens, which were subjected to stress agings at 773 K for times up to 15 h under given stresses of tension or compression after a long term aging at 773 K under no stress. When the stress level for aging was smaller than a critical value, the mean APR of P of the smooth specimen under tension rapidly increased during the first l h aging and then decreased to around the initial value in 15 h of aging, whereas that of the compressed specimen decreased, nearly by the same magnitude as in the case of tension, during the first l h and then similarly approached to the initial value in 15 h of aging. The mean P-APR in the vicinity of the notch root was significantly small compared with those at positions distant from the notch root in a stress aged notched specimen.

Distribution of temperature, strain rate and strain in plastically deforming metals at high strain rates

Abstract A method of calculating the distribution, and its time dependence, of temperature, strain rate and strain in plastically deforming metals is presented. It is assumed that the strain rate y depends on stress T and temperature T as γ = (const) Tm exp (-E/RT) where m, E and R are constants. It is found that the heat generated by deformation causes a significant inhomogeneous plastic deformation associated with the inhomogeneous temperature distribution in a specimen at high strain rates. The flow stress decrease arising from the inhomogeneous deformation is calculated; it is greater at lower temperatures, at higher strain rates and for longer specimens. The temperature rise in slip bands is also considered. Calculations are carried out for aluminium at temperatures above 100°C. Some of the results are compared with experimental observations.

Simulation of the hot working of 5083 aluminium alloy by means of the torsion test

Abstract This paper reports work in which a typical industrial hot-rolling process is simulated by means of an interrupted torsion test, using 5083 aluminium alloy as the test material. In addition, the effect of soaking time on the hot workability of the material is explored, where it is shown that the resistance to deformation of the alloy when soaked for 24 hours is as much as 20% less than that when soaked for 4 hours. Improvement of the hot workability is shown to depend upon the reduction of the denuded zone around the dendritic cast structure and on the refining of the precipitated second phases that occurs with increasing deformation. The results of both qualitative and quantitative microscopy are presented.

A model for the applied stress effects on the Intergranular Phosphorus Segregation in ferrous materials

Abstract A model has been presented in terms of which the facts observed in a previous paper can be successfully explained. It is based on the assumption that phosphorus atoms migrate along grain boundaries so as to decrease the strain energy in the grain boundaries more stressed under normal traction. The change in the intergranular phosphorus concentration (IPC) due to this solute migration during the first aging of At, at a grain boundry normal to the applied stress, is given by ∼ φχ p 0 D p g VσΔt / s 2 RT , where χ p 0 is the initial value of IPC prior to stress aging, D p p the diffusion coefficient of P along grain boundaries, V the specific volume of the alloy, s half the grain diameter, φ a numerical factor of the order of unity, RT has the usual meaning and σ is an apparent traction at the grain boundary, being more than 4 ∼ 5 times as large as the applied stress.

Orientation relationships between individual bundles in FeCrNi alloy with austenite and ferrite phases

Abstract Orientation relationships between adjacent bundles within a packet martensite have been investigated in the FeCrNi alloy with austenite and ferrite. All bundles has a twin relationship at −50°C, while there occurs a deviation from the twin relationship by 0,5,9,15,19,29 and 35 degrees at −196°C, −150°C and −102°. At −196°C, −150°C and −102°C the percentage of approximately twin-related bundles, which are 0 and 5 degrees away from the twin relationship, is 70 %. The fact that the fracture elongation is in the maximum at −50°C may be due to the twin-related bundles. The presence of such bundles is substantiated by the twin-operation on the stereographic projection figure and twin-related variants expected from the Nishiyama variants.

Evaluation of the hot workability of 5083 alloy by the torsion test, using tubular specimens

Abstract Hot torsion tests were conducted on 5083 aluminium alloy with a cast structure under conditions of a shear strain-rate range from 0.1 to 75 s −1 and a temperature range from 400°C to 500°C. The materials that had been solution-treated in two stages exhibited a superior hot workability compared to those that had been solution-treated in a single stage. The results of an electron mictoprobe analysis made it possible to identify the composition and the relative quantity of the constituent elements in the precipitated intermetallic compounds which were responsible for an observed decrease in the ductility of the alloy. The intermetallics were composed of such elements as Fe, Mn, Cr and Si.

The relationship between the occurrence of twin-related laths and the fracture elongation in the two-phase (?+?) Fe-Cr-Ni stainless steel

The relationship between the occurrence of twin-related laths and fracture elongation has been studied in two-phase (α+γ) Fe-Cr-Ni stainless steel. The percentage of adjacent twin-related lath martensites increased as the deformation temperature increased from −196 to −50° C. The appearance of these twin-related laths, having the accommodation effect, contributed to the increase in elongation.

Transformation-induced plasticity in two-phase (α+γ) Fe-Cr-Ni alloys

The relationship between the fracture elongation and the value of α′ martensite per unit tensile strain has been studied for the two-phase (α + γ) Fe-Cr-Ni alloys containing 10%, 35% and 52% 7. The elongation has a peak in the elongation-test temperature curve. The peak elongation is dependent upon both the delay of necking and a suitable value of α′ martensite per unit tensile strain.

The occurrence of stress-induced α′ martensite in an (α+γ) Fe-Cr-Ni alloy

The interaction of an applied stress with the displacive shear during the martensitic transformation determined theK-S variants which formed in three types of tensile specimens, with tensile directions of 0°, 45° and 90° to a rolling direction respectively. The 3–6, 4–5 and 1–3 variants in a 0°-specimen, 1–5 and 4–5 variants in a 45°-specimen and 4-4 and 3–6 variants in a 90°-specimen are chosen asK-S variants which have the maximum value ofU/σ in respective tensile directions. These variants are related to the occurrence of α′ martensite with particular orientations as (100)α, (110)α and (211)α.