Stacking Fault Probability Research Articles

Microstructure and Stacking-Fault Probability in CoNi Magnetic Shape-Memory Alloys

Microstructure and Stacking-Fault Probability in CoNi Magnetic Shape-Memory Alloys

Microstructural Characterization of Electrosynthesized ZnTe Thin Films

Thin films of zinc telluride (ZnTe) were electrosynthesized on tin oxide coated conducting glass substrates at various bath temperatures. The deposited films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The structure was found to be cubic with preferential orientation along (111) plane. X-ray line profile analysis technique by the method of the variance has been used to evaluate the microstructural parameters. The variation of different microstructural parameters such as, crystallite size, RMS strain, dislocation density and stacking fault probability affecting the fraction of planes with film thickness and bath temperatures were studied. The experimental observations are discussed in detail.

Microstructural Characterization of Electrosynthesized ZnTe Thin Films

Thin films of zinc telluride (ZnTe) were electrosynthesized on tin oxide coated conducting glass substrates at various bath temperatures. The deposited films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The structure was found to be cubic with preferential orientation along (111) plane. X-ray line profile analysis technique by the method of the variance has been used to evaluate the microstructural parameters. The variation of different microstructural parameters such as, crystallite size, RMS strain, dislocation density and stacking fault probability affecting the fraction of planes with film thickness and bath temperatures were studied. The experimental observations are discussed in detail.

Effect of Nitrogen Addition on Shape Memory Characteristics of Fe-Mn-Si-Cr Alloy

Nitrogen-microalloying and partial substitution of Cr for Mn have been employed to enhance the shape memory effect and corrosion resistance of Fe–Mn–Si based alloys. Typically, the tested alloys with nominal composition Fe–25Mn–6Si–5Cr–(0.12–0.14)N in mass% exhibit perfect shape recovery for a 3% pre-strain after only one cycle of thermomechanical training. The related mechanism has been discussed, taking account of the effect of nitrogen on the stacking fault energy (SFE) or the stacking fault probability ( Psf) of the alloy and the strengthening of the austenite matrix. Thermodynamic calculation and Psf measurement showed that the SFE increases with increasing N-content in the concentration range investigated, e.g. less than 0.3 mass%. Thus, the critical stress for the formation of stress-induced martensite increases with N-content. It is believed that the interstitial strengthening of the matrix by nitrogen predominantly contributes to the improvement of shape memory effect. Besides, nitrogen-microalloying remarkably improves the corrosion resistance of the alloys in aqueous solutions containing NaOH and NaCl, but not in HCl solution as indicated by the long-term immersion tests.

Electrical, Optical, and Scanning Tunneling Microscopic Studies on Layer Type CdIn2S4-xSex (1.75 ≤ x ≤ 2.75)

The present paper deals with the microstructural parameters calculated from X-ray diffraction data, electrical and optical investigations, and scanning tunneling microscopy (STM) studies on ZnIn2S4 IIIa layer type CdIn2S4-xSex (1.75 ≤ x ≤ 2.75) quaternary chalcogenides. Microstructural parameters such as dislocation density, root-mean-square strain, stacking fault probability, crystallite size anisotropy, and layer disorder parameters of these compounds have been calculated. The temperature variation of electrical conductivity (25−400 °C) confirmed semiconducting behavior. The band gaps of all these compounds obtained from STM and optical measurements are in the range 1.57−1.77 eV and are comparable to each other irrespective of the technique used.

Thermodynamic calculation of stacking fault energy in Fe–Mn–Si shape memory alloys

Based on thermodynamic considerations together with measurement of the stacking fault probability ( Psf) by X-ray diffraction profile analysis, the stacking fault energy (SFE, γ) of austenite in Fe–Mn–Si shaped memory alloys can be estimated. For instance, the stacking fault energy of an fcc(γ) phase in an Fe–30.3Mn–6.06Si was calculated as 7.8 mJ/m 2. Compositional dependence of stacking fault energy in these alloys with certain composition range has also been derived as SFE(γ)=180.54+7.923 wt.% Mn–46.38 wt.% Si (J/mol), showing that the stacking fault energy increases with the addition of Mn and decreases with the addition of Si.

Characterisation of Microstructure of Isothermally Transformed Martensite in Low Temperature in Powder and Bulk State of Fe–23Ni–3.6Mn (mass%) Alloy by Rietveld's Method

The present study concerns X-ray characterisation of the microstructures of the martensites of Fe–23Ni–3.6Mn alloy, transformed isothermally at low temperature. Along with the austenized powder and bulk forms of the alloy, coldworked powders have also been analysed. The methodology adopted is Rietveld's whole profile fitting technique which incorporates correction for preferred orientation of the crystallites. The results reveal important information on the crystallite (domain) sizes, residual microstrains, preferred orientation, stacking and compound fault probabilities, dislocation density etc., for both the austenite and martensite phases of the alloy. The martensite has smaller crystallite sizes and larger microstrain values, both of which are isotropic in nature for the transformed bulk and the austenized powders but anisotropic for the coldworked powders. The transformed matrix revealed high percentage of martensites in coldworked powder and bulk whereas annealed powder revealed about 8% volume fraction of martensites. The dislocation density values evaluated from the respective crystallite sizes and r.m.s. strain values are high (∼1011 cm/cm3) in the martensitic phase by almost an order of magnitude compared to their respective austenite phase. The coldworked powder reveals high propensity of faulting. The hardness value of transformed bulk (191 kg/mm2) is more than double the value for the austenite bulk (95 kg/mm2). The results have been compared and correlated with those in two previous studies on the same alloy system having 3.3 and 3.8 mass% of Mn.

Martensitic transformation in Fe-Mn-Si based alloys

The stacking fault energy (SFE) or the stacking fault probability plays an important role in the determination of the critical driving force ΔGγ→e for the martensitic transformation fcc(γ)→hcp(e) in ternary Fe-Mn-Si alloys, ΔGγ→e increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of Ms in ternary Fe-Mn-Si alloys is established. The fcc(γ)→hcp(e) martensitic transformation in Fe-Mn-Si is semi-thermoelastic and the nucleation process does not strongly depend on soft modes. Nucleation of e-martensite is not dominated by a pole mechanism. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)hcp planes is required when d111≠d0002. The derived principal strains for the Bain distortion are smaller, i.e. more reasonable than the values given by Christian. Alloying elements which strengthen the austenite, lower the SFE of the γ phase and reduce the TγN temperature may be beneficial to the shape memory effect (SME) of Fe-Mn-Si based alloys.

X-ray diffraction and electron microscopic studies on selenium substituted indium intercalation compounds of tungsten disulphide

Selenium substituted indium intercalation compounds of tungsten disulphide, In 1/3WS 2− x Se x (0≤ x≤2) have been studied for microstructural characterization using X-ray line profile analysis to find out information about crystallite size, r.m.s. strain, dislocation density, variability of interlayer spacing, fraction of planes affected by such defects, stacking fault probability, crystallite size anisotropy etc. Scanning electron microscopic (SEM) and scanning tunneling microscopic (STM) studies are also reported herewith. These results have also been compared with respect to the pure WS 2− x Se x (0≤ x≤2).

X-ray studies on microstructural characterization of tantalum substituted tungsten mixed molybdenum diselenide; W0·65Mo35−x Ta x Se2 (0≤x≤0·35)

The wide angle X-ray diffraction on W0·65Mo5−x Ta x Se2 (0≤x≤0·35) compounds have been used for calculation of the crystallite size by method of variance and Fourier technique and for microstructural parameters purposes. The crystallite size showed the decreasing trend with increasing composition up tox=0·15 and after that it increased sharply. On the contrary, mean fractional change in interlayer spacing, fractions of the planes affected by defects, dislocation density, and root mean square strain showed the opposite trend. The crystallite size anisotropy and stacking fault probability showed 1:1 correspondence in their variation with composition. The radial distribution analysis have also been employed to find out the information about the inter atomic distances, coupling constants and mean square displacements for different pairs of atoms. These results have been interpreted in terms of difference in packing of layers in these compounds.

Variation of stacking fault energy with austenite grain size and its effect on the MS temperature of γ→ε martensitic transformation in Fe–Mn alloy

Abstract The change in MS temperature of γ→e martensitic transformation with austenite grain size (AGS) has been investigated in relation to the stacking fault energy (SFE) in an Fe–18%Mn alloy. With increasing AGS, the MS temperature increases steeply up to 35 μm, and gradually increases in larger grains. The SFE, on the other hand, decreases abruptly until 35 μm, over which it is slightly lowered. A good linear relationship is established between MS temperature and inverse of SFE, i.e. stacking fault probability (SFP). This result suggests that the variation of MS temperature with AGS depends strongly on the change in SFE.

Nonhydrostatic compression of elastically anisotropic polycrystals. II. Direct compression and plastic deformation

The effects of nonhydrostatic conditions on the compression behavior of elastically anisotropic polycrystals have been studied by energy-dispersive x-ray diffraction of a foil of ${\mathrm{Cu}}_{3}\mathrm{Au}$ compressed directly between diamond anvils. A volume expansion between 0.3 and 1 GPa is explained to result from the introduction of dislocations. A volume incompressibility accompanied by saturation in stress, strain, and the stacking fault probability between 1 and 2 GPa is due to work hardening. A complete pressure cycle, including repressurization after pressure release, and the compression of ${\mathrm{Cu}}_{3}\mathrm{Au}$ previously deformed by filing demonstrate that mutual repulsion between lattice defects also contributes to the volume incompressibility. The pressure region of incompressibility terminates at a discontinuity which occurs when the yield strength of the plastically deformed material is exceeded. The compression above this point is elastic and isotropic. The yield strength is estimated from the offset of the measured compression curves from the hydrostat.

Solid Nitrogen Confined in Porous Glass

N 2 condensed into nanoporous glass has been investigated by X-ray diffraction and adsorption/filling isotherms. The material in the pores consists of an amorphous layer at the pore walls and quasi–bulk material in the center of the pores. The freezing temperature of the bulk component is reduced. Its structure is hcp down to lowest temperatures with a stacking fault probability as large as 0.3. Thus the transition hcp–Pa3 of the bulk solid is suppressed.

Effect of stacking fault probability on γ– ε martensitic transformation and shape memory effect in Fe–Mn–Si based alloys

As an important parameter in Fe–Mn–Si based shape memory alloys, the stacking fault probability of γ-phase, P sf, has been determined by means of X-ray diffraction profile analysis and connected with some macro-behavior such as the starting temperature of the thermo-induced γ→ ε transformation, M s, the critical stress required for inducing ε-martensite, σ M, the strain-hardening exponent, n, etc. It is revealed that a linear relationship between M s and the reciprocal of P sf is established as M s=372−0.113/ P sf, and also between σ M and the reciprocal of P sf, as σ M=29+0.212/ P sf. It is shown that the strain-hardening exponent n changes monotonically with P sf. Adding Cr or N, and increasing the content of Mn in a Fe–30Mn–6Si alloy will decrease P sf, resulting in the reducing of M s and n, and the increasing of σ M. The existence of quenched-in vacancies will promote the enhancement of P sf, that leads to the increase in M s. The variation of γ-grain size has no obvious effect on P sf, so that it does not affect the M s temperature. The thermo-mechanical cycling will increase P sf, in turn will lower σ M and increase n, so that the shape memory effect is improved. The possible mechanism is discussed.

Studies on layer disorder, microstructural parameters and other properties of tungsten-substitued molybdenum disulfide, Mo 1− xW xS 2 (0≤ x≤1)

The present paper deals with the preparation of tungsten-substituted molybdenum disulfide, Mo 1− x W x S 2 (0≤ x≤1) compounds and their characterization by various physicochemical methods. X-ray studies confirmed that these compounds crystallized in a layer type of hexagonal structure. X-ray line profile analysis techniques such as the method of variance and Fourier analysis have been used for microstructural characterization of these compounds to find out information about particle size, r.m.s. strain, variability of interlayer spacing, fraction of planes affected by such defects, dislocation density, stacking fault probability and radial distribution function analysis for calculating coupling constants and mean-square displacements, etc. Room-temperature magnetic susceptibility measurements and thermoelectric power experiments and temperature variation of conductivity (25–350°C) confirmed, respectively, diamagnetic n- and p-type semiconducting behaviour for Mo 1− x W x S 2. Thermal stability behaviour of these compounds in air and inert atmosphere has also been carried out up to 1000°C. These studies indicated that the compounds are nearly stable up to 1000°C in inert atmosphere, whereas, in air, oxidative degradation of these compounds started at 400°C. The nature of the oxidized products has also been studied by X-ray analysis. Scanning electron micrograph studies are also reported here.

An X-ray diffraction (XRD) study of vapor deposited gold thin films on aluminum nitride (A1N) substrates

The promise of aluminum nitride (A1N) as a substrate material for highly thermally-conductive electronics packages has fostered a number of efforts to develop adherent metallization systems for A1N. In this study, thin films of Au have been thermally evaporated onto polycrystalline A1N substrates under a variety of conditions, and studied using X-ray diffraction (XRD), in conjunction with transmission electron microscopy (TEM). It has been shown that the root mean squared strain obtained from the Warren-Averbach method based on X-ray peak broadening offers a qualitative non-destructive measure of interfacial adhesion between the Au film and the A1N substrate. Interfacial adhesion between Au and A1N has been shown to improve with increasing substrate surface roughness, improving deposition vacuum, increased substrate surface cleanliness, and when a Cr or Al 2O 3 inter-layer is present between the film and the substrate. A method based on X-ray line shift data was utilized to calculate stacking fault probabilities in the Au films. It was found that the density of stacking faults increased with improving interfacial adhesion for a given substrate surface roughness. TEM revealed numerous twins steeply inclined to the film/foil surface, although the twinning probability calculated via XRD based on peak asymmetry was small, suggesting a low twin density parallel to the film surface. All the films studied had similar grain sizes (∼ 50–70 nm), and possessed a weak {111} fiber texture with the fiber axis normal to the substrate surface. The in-plane grain size and film texture were found to have little dependence on the substrate surface preparation, although variations in the crystallite sizes measured by XRD suggested that the through-thickness grain size may depend on interfacial adhesion.

Characterization of laser deposited CdTe and Hg 1− xCd xTe thin films

CdTe and Hg 1− x Cd x Te narrow-gap semiconductor materials were deposited as thin films on optical glass, by the laser-assisted physical vapor deposition (LAPVD) process. A pulsed CO 2-TEA laser was used to vaporize the studied materials in a vacuum chamber. The Fourier analysis of the (111) CdTe X-ray diffraction profile was used to determine the average effective crystallite size, the root mean square of the microstrain, the stacking fault probability within the crystallites and the dislocation density for CdTe films of various thicknesses. The X-ray diffraction pattern of the Hg 1− x Cd x Te films contains (100) reflection, indicating highly textured films with [100] direction of the HgTe type structure. Photoacoustic (PA) measurements were done to establish the absorption edge of the CdTe and Hg 1− x Cd x Te thin films. The PA spectra were fitted with an exponential function obtaining 1.45 eV absorption threshold photon energy for CdTe films and around 0.3 eV for Hg 1− x Cd x Te, which corresponds to a x = 0.3 alloy fractional composition.

Residual stress, strain and faults in nanocrystalline palladium and copper

Nanocrystalline Pd and Cu, prepared by inert-gas condensation and warm compaction, were studied using X-ray diffraction techniques. A sample of Cu with submicrometer grain size produced by severe plastic deformation was also examined. The Warren-Averbach technique was used to separate the line broadening due to grain size, t.m.s. strain and faults. Peak shifts and asymmetry were used to determine the long-range surface stresses, stacking-fault probability and twin probability. Young's modulus for a Pd sample was determined by an ultrasonic technique and compared with the coarse-grained, fully dense value.

Powder diffraction analysis of an interstratified marcasite/pyrite structure

A synthetic catalyst precursor formed by sulfiding ferrihydrite (Fe3+O(OH)) in the presence of a hydrogen donor produces X-ray diffraction patterns resembling a mixture of both naturally occurring FeS2 polymorphs marcasite and pyrite. The diffraction peaks display a differential broadening, however, wherein only those peaks coincident to both marcasite and pyrite are strong and sharp, a feature that cannot be accounted for by a simple physical mixture. The broadening is analogous to that found in hexagonal cobalt, where occasional stacking faults produce interstratification of the hexagonal and cubic close-packed forms, resulting in strongly coherent diffraction only along the stacking direction. The crystal structures of marcasite and pyrite are virtually identical if viewed perpendicular to the (101) and (001) planes, respectively. Calculation of diffraction patterns based upon models of interstratifying marcasite and pyrite layers along these planes demonstrates that a sequence with marcasite-to-pyrite and pyrite-to-marcasite stacking fault probabilities of 0.22 provides a good fit to the experimental pattern. This interstratified material is a precursor to a species that shows catalytic activity for cleaving C-C bonds between aromatic rings and benzylic carbon atoms at low (<350 °C) temperatures.

Microstructural features of Cd0·8Zn0·2Te thin films studied by X-ray diffraction and electron microscopy

Thin films of synthesized Cd0·8Zn0·2Te have been deposited on glass substrate at different substrate temperatures. Different microstructural parameters like crystallite size, rms strain, dislocation density, stacking fault probability and stacking fault energy are determined by XRD, SEM, TEM and TED. XRD and XPS have been used to determine the composition. Variations of the microstructural parameters with film thickness and substrate temperature have been studied in order to obtain optimum growth condition for maximum particle size and least microstructural defects. An effort has been made to correlate the experimental results.