Kurdjumov-Sachs Relationship Research Articles

Interpretation of the epitaxial orientation relationship at bcc(110)/fcc(111) interfaces

By using a simple interaction potential, the interfacial energy between bcc(110) and fcc(111) surfaces was calculated. Energy minima appear at specific values of the atomic diameter ratio of bcc to fcc for the Nishiyama-Wassermann orientation relationship (NW), [1 1 0] fcc|[001] bcc, and the Kurdjumov-Sachs relationship (KS), [1 1 0] fcc|[1 1 1] bcc. The reason for the appearance of energy minima is well understood by considering the relative atomic arrangements of the two lattices at the interface. From the calculation and from geometrical considerations, one can predict the preferred orientation relationship for epitaxy, namely the NW, and KS or a new [2 1 1 ] fcc|[001] bcc relationship, from the variation of the atomic diameter ratio of bcc to fcc.

鉄基板上にヘテロエピタキシャル成長した電析ニッケル膜の構造

With special attention to the fine structure of Ni film and the structure of Ni/α-Fe interface, the hetero-epitaxial growth of Ni electrodeposits on polycrystalline α-Fe has been studied mainly by transmission electron microscopy. Results obtained are: (1) Ni grows hetero-epitaxially even under such a high current density as 500 A/m2 on a cleaned substrate surface. (2) The crystallographic orientation relationship between Ni deposits and the substrate α-Fe is almost the same as that of the Kurdjumov-Sachs relationship i.e. (110)α\varparallel(111)Ni, [1\bar11]α\varparallel[1\bar10]Ni. (3) the Ni hetero-epitaxial film consists of columnar crystals which grow in the 〈110〉 direction and contains dislocations and stacking faults with high density. (4) These defects are introduced in order to decrease the elastic strain caused by the misfit between Ni and α-Fe at the interface, and the number of defects decreases with increasing film thickness.

Orientation relationships in graphitic cast irons

Ferrite/graphite and martensite/graphite interfaces in three commercial cast irons have been analyzed using transmission electron microscopy. Two recurring orientation relationships have been found to account for over 60 pct of the ferrite/graphite interfaces analyzed. A similar pair of relationships discovered in martensitic material strongly suggests that the prior austenite/graphite interface was also ordered. The same relationships were prominent in gray and ductile irons. One of the relationships observed can be transformed through the Kurdjumov-Sachs relationship to a previously-reported austenite/graphite relationship.

Formation of α-γ-α Transformation Texture in Sheet Steel

For the purpose of investigating the formation mechanism of the texture which is developed by ferrite (α)→austenite (γ)→ferrite (α) transformation, the effects of heating and cooling rates during phase transformation and specimen thickness on the transformation texture have been studied by using an extra low carbon sheet steel with the initial texture of {111}.The results obtained are summarized in the following:(1) A weak {100} and {111} texture was formed in the surface layer of the specimen transformed by rapid heating and rapid cooling.(2) By rapid heating and subsequent slow cooling, a texture with {110} orientations and orientations 20-30 deg shifted away from {100} was obtained in the surface layer.(3) Slow heating and slow cooling produced a distinct {100} texture in the surface layer.(4) There was a marked difference in texture between surface and midsection of thick specimen: In the midsection, the texture similar to that described in (1) was formed, independent of the heating and cooling rates. While, the specimen surface exhibited the texture as mentioned in (1) to (3) on each condition.(5) Those results were consistently explained on the assumptions that the orientation relationship between bcc and fcc follows the Kurdjumov-Sachs relation, and that during a slow progress of α→γ→α transformation the orientation change proceeds preferentially by operation of such variants that generate a larger elastic work in the normal direction of a sheet surface.

The morphology and crystallography of Ferrous lath martensite. Studies of Fe-20%Ni-5%Mn—II. Transmission electron microscopy

This investigation reports a transmission electron microscopy study of the isothermal lathtype martensite in an Fe-20%Ni-5%Mn alloy. All laths showed the Kurdjumov-Sachs orientation relationship: single isolated laths as well as adjacent laths in a packet. Trace analysis shows that the martensite-austenite interfaces are near A , in agreement with optical microscopy, although the boundary is frequently stepped. Adjacent martensite laths in a packet were found to have the same orientation, variant of the Kurdjumov-Sachs relation and habit plane. In all cases (isolated and adjoining laths) the lath substructure consisted of three sets of 〈111〉 screw dislocations in a cross-grid arrangement similar to that previously observed in the untwinned regions of plate martensite in Fe-Ni alloys. Dislocations at the tips of laths and at the lath-lath interfaces were of the same type and arrangement as those found within the laths. No internal twins were observed in the laths.

薄鋼板におけるα→γ→α変態による集合組織形成

For the purpose of investigating the formation mechanism of the texture which is developed by ferrite (α)→austenite (γ)→ferrite (α) transformation, the effects of heating and cooling rates during phase transformation and specimen thickness on the transformation texture have been studied by using an extra low carbon sheet steel with the initial texture of {111}.The results obtained are summarized in the following:(1) A weak {100} and {111} texture was formed in the surface layer of the specimen transformed by rapid heating and rapid cooling.(2) By rapid heating and subsequent slow cooling, a texture with {110} orientations and orientations 20-30 deg shifted away from {100} was obtained in the surface layer.(3) Slow heating and slow cooling produced a distinct {100} texture in the surface layer.(4) There was a marked difference in texture between surface and midsection of thick specimen: In the midsection, the texture similar to that described in (1) was formed, independent of the heating and cooling rates. While, the specimen surface exhibited the texture as mentioned in (1) to (3) on each condition.(5) Those results were consistently explained on the assumptions that the orientation relationship between bcc and fcc follows the Kurdjumov-Sachs relation, and that during a slow progress of α→γ→α transformation the orientation change proceeds preferentially by operation of such variants that generate a larger elastic work in the normal direction of a sheet surface.

薄鋼板のα→γ→α変態集合組織に及ぼす初期方位の影響

By using low and extra low carbon sheet steels with the initial texture of {111}, {110}, or {100}, the effect of transformation condition has been investigated on the texture developed by ferrite (α)→austenite (γ)→ferrite (α) transformation. (1) In specimens with the {111} texture, slow heating to transformation temperature produced {100} texture, whereas rapid heating gave the texture consisting of {110} and orientations shifted away 20 to 30 degrees from {100}. (2) Rapid heating gave {100} texture as far as transformation was performed for long-duration of time as high temperature. (3) The before-mentioned results did not change with variation in annealing atomosphere. (4) In specimens with the {100} texture, slow heating and rapid heating produced respectively {100} texture and the texture consisting of {110} orientation and that shifted away 20 to 30 degrees from {100}. (5) In specimens with the {110} texture, slow heating produced {110} texture, while rapid heating gave {100} texture. (6) To explain these experimental results explicitly and consistently, the new theory on the transformation texture was proposed: Such variants with the Kurdjumov-Sachs relation that undergo larger elastic work in normal direction of sheet tend to operate preferentially with decreasing rate of traransformation.

Analytical electron microscopy study of the plessite structure in four IIICD iron meteorites

Electron optical techniques were employed to investigate the plessite structure and composition of four IIICD fine octahedrites. These meteorites have a similar thermal history and differences in plessite structure can be ascribed to varying bulk Ni content and/or localized differences in carbon content. Microdiffraction patterns from regions as small as 20 nm dia. were obtained for the first time from plessite structures. It was established that transformation twins in clear taenite I have the conventional fcc twin relationship, individual kamacite and taenite cells in the cloudy zone have the Kurdjumov-Sachs orientation and fine γ rods in the decomposed martensite zone display both the Nishiyama and Kurdjumov-Sachs relation with the matrix-α. All the IIICD irons contain cloudy zone and martensitic plessite. Except for Dayton, martensitic plessite shows further decomposition into α + λ at low temperatures. Using STEM X-ray microanalysis with a spatial resolution of ~ 50 nm, Ni composition profiles in taenite from all the IIICD irons showed a maximum of ~48 wt% Ni. The structural and compositional data indicate that plessite formation occurs at quite low temperatures (~ 200–300°C) during the cooling history of the IIICD irons.

Spontaneous hydride formation in β-phase niobium zirconium alloys

A spontaneous transformation has been observed in thin foils of metastable β-phase (b.c.c.) niobium 16–60% zirconium alloys during electro-polishing. The product has a f.c.c. crystal structure and a plate-like morphology. The transformation is governed by the concentration of both hydrogen, which has to exceed a critical value and zirconium. Consequently the spontaneously formed plates are only stable at room temperature in foils where the zirconium concentration exceeds 40%. The hydride plates have a habit plane close to {133} β and contain either slip dislocations, stacking faults or fine twins on {111} h planes or mixtures of these. The orientation relationship between the hydride plates and the β-matrix corresponds closely with the Kurdjumov-Sachs relationship. Complex interactions between plates result in a further transformation which has been interpreted as a reverse transformation (f.c.c. → b.c.c.). The results have been considered in terms of the phenomenological crystallographic theory for martensite formation. Satisfactory agreement between theory and experiment has been established.

Precipitation Behavior in Fe–Ni–Mn Martensitic Alloys

The object of this study is to investigate precipitation behavior during aging of age-hardenable Fe–Ni–Mn martensitic alloys by means of specific heat measurement, thermal differential analysis, electron microscopic observation, and X-ray and electron diffractions. The as-quenched structure before aging is lath martensite. In the initial stage of aging, very fine zones with high solute concentration are homogeneously formed due to the two-phase decomposition. Subsequently the zone acts as a nucleus of the fct NiMn phase. As the zone changes to the fct NiMn particle the hardness of the alloys increases up to its maximum value. The main cause of the age-hardening is considered to be the strain hardening due to the coherency strain between zone or NiMn particle and matrix. In the over-aging and softening processes, NiMn particles grow into disc-like platelets on the (100) planes of the matrix, and the crystallographic orientation relationship with respect to the matrix is determined to be (011)α′4°(111)NiMn, [\bar1\bar11]α′8°[\bar101]NiMn. In the final equilibrium state, NiMn particles disappear and the structure is microduplex lamellae consisting of austenite and ferrite (or martensite) phases. The Kurdjumov-Sachs relationship holds between the austenite and ferrite.