Papers by Keyword: Orientation Relationship

Abstract: A systematic study has been made on a Cu-40%Zn alloy treated by an electric current pulse (ECP) and by the examination of the microstructure and the crystallographic features of both the parent and the product phases. The β precipitates under ECP show a Kurdjumov Sachs Orientation Relation (K-S OR) in the vicinity of the grain boundaries (GBs), but a Nishiyama Wasserman (N-W) OR within the grains. Along the GBs the {111}_α /<110>_α dislocation arrays were spotted, whereas the {111}_α /<112>_α stacking faults were observed in the grain interiors. A closer examination of the lattice strain required for the phase transformation revealed that the maximum lattice deformation under the K-S OR is a shear on the {111}_α plane in the <110>_α direction. The dislocations arrays existing along the GBs offer the pre-strain that favors the precipitation of β particles obeying the K-S OR. Oppositely, the stacking faults within the grains provide pre-stains for the formation of the β precipitates respecting the N-W OR. This study sheds some light on the mechanisms by which crystal defects initiate phase transformation in a Cu-40%Zn alloy.

Abstract: Structure-texture states in brass rods after hot extrusion and air-cooling have been investigated with the orientation microscopy (EBSD). In the examined samples, a significant concentration of β-phase with the lattice, close to bcc and fcc α-phase, has been detected. The β-phase texture consisted of the main components: two close to {110}<110> and {001}<110>. The α-phase texture consisted of the main components: close to {001}<100> and two close {110}<111>. The analysis of crystallographic relationship of the texture components of β-and α-phases demonstrates that they may all be obtained, in accordance with the orientation relations, which are intermediate between the Kurdjumov-Sachs and Nishiyama-Wasserman types It is assumed that β-α transformation began in β-phase at coincident site lattice Σ3 and Σ33a boundaries.

Abstract: Different types of carbide phases and regions of their precipitation in tempered martensite of austenitic steel have been investigated with orientation microscopy (EBSD) and electron microprobe analysis. The steel structure consisted of large grains of high-temperature ferrite (~ 15%), without visible mesostructured, and martensite packages with a great number of low-angle boundaries. High-angle boundary spectrum with the most prominent coincidence site lattice (CSL) boundaries, Σ3, Σ11, Σ25b, Σ33с Σ41с, is typical for martensite. This spectrum, resulted from austenite transformation by shear mechanism according to orientation relationships (OR), intermediate between Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). In the structure two types of carbide precipitates were observed: large MC [~ NbC] along the boundaries of former austenite grains, and dispersed M₂₃C₆ [~ (W,Mo)₂(Cr,Fe)₂₁C₆] predominantly along the boundaries in martensite packages. It has been shown that under martensite tempering M₂₃C₆ precipitation was mainly at high-angle intergranular boundaries. Carbide almost did not precipitate at low-angle and special CSL Σ3 boundaries. A few carbides were detected at special CSL boundaries, Σ11, Σ25b, Σ33с Σ41с.

Abstract: Most of the studies on phase transformation in metallic materials have focused on transformations during cooling processes due to the easiness of the conservation of the product phase. However, for phase transformation happening during heating processes, the experimental investigations have been indirect if the product high temperature phase could not be preserved to the convenient observation temperature, for example the room temperature. The high density Electric Current Pulse (ECP) treatment allows the phase transformation during heating process and the preservation of the high temperature phase to the room temperature, offering possibilities for direct experimental examinations. Thus, in the present work, a cold-rolled Cu–40%Zn alloy was ECP treated and the microstructure of the product phase and the transformation orientation relationship were investigated. Results show that during the ECP treatment, the high temperature beta phase with BCC structure formed in the parent alpha phase with FCC structure. Especially, two kinds of orientation relationships could be detected between the parent alpha phase and the product beta precipitates. The one is the Kurdjumov-Sachs orientation relationship (K-S OR), and the other is the Nishiyama-Wasserman (N-W). In addition, the amount of beta precipitates obeying the K-S OR is more than that of precipitates obeying the N-W OR. The results of this work provide new fundamental information on phase transformation of metallic materials.

Abstract: Structure-texture states in 18Cr-9Ni austenitic stainless steel after long-term operation of the tube at high temperatures and neutron irradiation have been investigated with orientation microscopy (EBSD). In the examined samples, cut out at the external surface, a significant concentration of α-phase with the lattice close to bcc has been detected. Phase transformation shows prominent crystallographic direction, caused by initial orientation of austenite grains and tensile stress effect, normally directed at a tangent to its external surface. High-angle boundary spectrum with the most prominent coincidence site lattice (CSL) boundaries, Σ3, Σ11, Σ25b, Σ33с Σ41с, is typical for α-phase. Thus, it can be claimed that austenite transformation was carried out by shear (bainite, taking into account high temperature) mechanism, according to orientation relationships (OR), intermediate between Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). Shear γ-α transformation began in austenite on twin boundaries (CSL Σ3), and was carried out in the range determined by initial orientation of γ-phase crystals and effective stress value. Based on high density of CSL boundaries Σ3 in α-phase it has been suggested that its nuclei are represented not by single crystallites, but crystallite couples in twin misorientation.

Abstract: In this work, NiMnGa thin film composed of non-modulated martensite (NM) and seven-layered modulated martensite (7M) was produced. The crystal structure and lattice constants were determined by X-ray diffractometer (XRD). The preferred crystallographic orientation of martensite was determined using the four-circle XRD. SEM/EBSD was employed to verify the crystal structure of the martensite and to reveal its crystallographic features correlated with the microstructure. According to the XRD patterns, the crystal structure of NM and 7M was determined as tetragonal and monoclinic crystal structure, respectively. Pole figures measured by four-circle diffractometer revealed that the NM martensite possesses (004)_NM and (220)_NM preferred plane texture close to the substrate surface, whereas the 7M martensite has (2 0 20)_7M, (2 0 )_7M and (040)_7M preferred plane texture close to the substrate surface. SEM/EBSD analysis shows that the surface layer of the film is mainly composed of NM martensite that is organized in variant groups. In each variant group, all the martensite plates consist of paired lamellar (112)_NM compound twins and there are eight orientation variants in each variant group.

Abstract: In this paper, high resolution electron microscopy (HREM) was used to observe nanosized Fe2M precipitates in M50NiL steel, and crystal structure of which was also investigated by selected area electron diffraction (SAED). At the same time, the orientation relationship between the Fe2M and the martensite matrix was also studied. The results suggested that crystal structure of Fe2M is close-packed hexagonal, and lattice parameters about a=b=0.473nm, c=0.772nm, α=β=90°, γ=120°. The orientation relationship between the nanoprecipitates Fe2M and martensite is and .

Abstract: The effects of cooling rate and austenite structure on bainite formation was investigated by means of electron backscatter diffraction analysis and processing of obtained orientation data. Variant pairing tendency of bainitic ferrite was found to depend on the austenite grain size, austenite plastic deformation and cooling rate. In the bainite formed at low cooling rate the variant pairs having the same Bain axis correspondence are more frequent, while at high cooling rate the variant pairs having the same parallel correspondence of close-packed planes are formed side by side preferably. At the same time, these features are influenced significantly by structural state of parent austenite.

Abstract: In this work, the investigation of transmission electron microscopy has elucidated the morphologies of the interphase precipitated carbides in an experimental Ti-Mo-bearing steel into three types: (1) planar interphase precipitation with regular sheet spacing (designated as PIP), (2) curved interphase precipitation with regular sheet spacing (designated as Regular CIP), and (3) curved interphase precipitation with irregular sheet spacing (designated as Irregular CIP). The planar sheets of carbides have also been analyzed and found to be oriented close to ferrite planes {211}, {210} and {111}; the results of transmission electron microscopy provide strong evidence to suggest that the development of interphase-precipitated carbides can be associated with the growth of incoherent ferrite/austenite interface by the ledge mechanism. The sheet spacing and inter-carbide spacing in the sheet have been measured and estimated in this work. The sheet spacing is found to be finer than the inter-carbide spacing in the sheet for all samples investigated. The result reflects that the distribution of interphase-precipitated carbides is anisotropic and cannot be considered random distribution. The relevance of the Orowan mechanism to the non-random distribution of interphase-precipitated carbides has been considered. The contribution of the dispersion of interphase-precipitated carbides to the yield strength of the steel studied has been estimated. It is revealed that an optimum component about 400 MPa contributed by interphase-precipitated carbides can be achieved, and the finding is consistent with the hardness data. Other examples of the different alloy steels are also addressed.

Abstract: The precipitation of tungsten nitride upon internal nitriding of ferritic Fe-0.5 at.% W alloy was investigated at 610°C in a flowing NH₃/H₂ gas mixture. Different tungsten nitrides developed successively; the thermodynamically stable hexagonal δ-WN could not be detected. The state of deformation of the surface plays an important role for the development of tungsten nitride at the surface. The morphologies of the tungsten nitrides developed at the surface and those precipitated at some depth in the specimen are different. The nitride particles at the surface exhibit mostly an equiaxed morphology (with the size of the order 0.5 µm) and have a crystal structure which can be described as a superstructure derived from hexagonal δ-WN. These nitride particles show a strong preferred orientation with respect to the specimen frame of reference but have no relation with the crystal orientation of the surrounding ferrite matrix. In the bulk, nanosized and finely dispersed platelet-like precipitates grow preferentially along {100}_α-Fe. It is unclear whether these precipitates consist of binary iron nitride α´´-Fe₁₆N₂ or of a ternary Fe-W-N. Additionally to the finely dispersed particles, bigger nitrides at ferrite grain boundaries develop exhibiting platelet-type morphology and possessing a crystal structure which can be also described as a superstructure derived from hexagonal δ-WN. Upon prolonged nitriding assumed discontinuous precipitation of the initially precipitated finely dispersed nitrides starts from the ferrite-grain boundaries resulting in lamellas consisting of alternate ferrite and hexagonal nitride lamellas, whereas the nitride lamellas having a Pitsch-Schrader orientation relationship with the surrounding ferrite matrix. The nitrides precipitated upon nitriding in the bulk were found to be unstable during H₂ reduction at 470°C. Remarkably, upon such low temperature dissolution of the nitrides took place but only the nitrogen from the nitride particles could diffuse out of the nitride platelets and the specimen, leaving W-rich regions (W-clusters) at the location of the original precipitates.