Diffraction Line Profile Research Articles

Strain anisotropy models for refined diffraction line profile analysis in cubic metals

Abstract The present work examined the anisotropy magnitudes obtained from different elastic models of cubic metals (Cu, 5383 Al alloy, FCC austenite steel and BCC steel) to explore the origin of strain anisotropy. The results showed that stable intersections were observed from the modeled and experimental plots of the reciprocal elastic modulus (1/Ehkl) and orientation parameter (Γ). The effectiveness of quasi elasto-plastic model based method in correcting strain anisotropy was further verified in cold-worked specimens. For the important input parameters in dislocation model based diffraction line profile analysis methods, the average diffraction contrast factors of dislocations were observed to depend on elastic constants. Interesting intersections were found from linear dependence of on Γ. The conventional input values indicated distinct dependencies on given elastic constants in diffraction line profile analysis. Accordingly, a refined approach was proposed by adopting the optimized intersections as input values, by which more reliable results could be obtained in practical applications.

The Certification of Standard Reference Material 1979: Powder Diffraction Line Profile Standard for Crystallite Size Analysis.

This rather long-standing project has resulted in a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for the analysis of crystallite size from a consideration of powder diffraction line profile broadening. It consists of two zinc oxide powders, one with a crystallite size distribution centered at approximately 15 nm, and a second centered at about 60 nm. These materials display the effects of stacking faults that broaden specific hkl reflections and a slight amount of microstrain broadening. Certification data were collected on the high-resolution powder diffractometer located at beamline 11-BM of the Advanced Photon Source, and on a NIST-built laboratory diffractometer equipped with a Johansson incident beam monochromator and position sensitive detector. Fourier transforms were extracted from the raw data using a modified, two-step profile fitting procedure that addressed the issue of accurate background determination. The mean column lengths, 〈L〉area and 〈L〉vol, were then computed from the Fourier transforms of the specimen contribution for each reflection. Data were also analyzed with fundamental parameters approach refinements using broadening models to yield 〈L〉area and 〈L〉vol values. These values were consistent with the model-independent Fourier transform results; however, small discrepancies were noted for the 〈L〉area values from both machines and both crystallite size ranges. The fundamental parameters approach fits to the laboratory data yielded the certified lattice parameters.

Microstructure evolution and densification during spark plasma sintering of nanocrystalline W-5wt.%Ta alloy

ABSTRACT The present work reports the effect of Ta on densification and microstructure evolution during non-isothermal and spark plasma sintering of nanocrystalline W. Nanocrystalline W-5wt.%Ta alloy powder was synthesised using mechanical alloying. The nanocrystalline powder was characterised thoroughly using X-ray diffraction line profile analysis. Furthermore, the shrinkage behaviour of nanocrystalline powder was investigated during non-isothermal sintering using dilatometry. Subsequently, the alloy powder was consolidated using spark plasma sintering up to 1600°C. The role of Ta on stabilising the microstructure during spark plasma sintering of nanocrystalline W was investigated in detail using electron backscatter diffraction. The average grain size of spark plasma sintered W-5wt.%Ta alloy was observed as µm.

Experimental study of micro-deformation of structural steel under simulation of operating conditions

Diagnostics of the load bearing capacity of machines and structures, service properties of structural materials are carried out by destructive and non-destructive methods. In the system of non-destructive methods of diagnosing and monitoring of the service properties of materials and products, radiation technologies are of particular importance, since they have instrumental capabilities for diagnosing and controlling changes in the soundness of a solid body at different structural levels. The X-ray diffractometry method provided determination of the stability of the stress-strain state of structural steel samples subjected to prolonged (over 5 years) static loads not exceeding the yield strength of the material. The purpose of the study is to determine experimentally the effect of continuous (since 2013) elastic stress and climatic factors on the change in the half-width of the diffraction line profile. It is shown that the straight-line dependence of the half-width of the diffraction line profile is maintained in the range of elastic stresses not exceeding 0.5σt. The results of changes in the microstructural state (micro-strains) identified by the characteristics of the diffraction lines profile are presented and discussed. The results of the experimental study of the effect of small steady elastic stresses reveal that periodic annual fluctuation of temperatures (2013 – 2018) does not cause a significant change in the properties of the diffraction line profile of the 08ps structural steel samples. On the contrary, low climatic temperatures contributed to the elimination of individual instrumental errors attributed to design conditions of the experiment. A sharp change in the true half-width of the diffraction line profile at the stress values σ > 0.5σt, probably indicates the minimum margin of safety of 08ps structural steel when setting the permissible stress value (σ). The revealed changes in microplastic deformation observed in structural steels in the range of elastic stresses corresponding to real operational loads require further study and analysis.

Numerical and experimental investigations on new jar designs for high efficiency planetary ball milling

The internal shape of planetary ball mill jars was modified to increase the efficiency of the milling process. Four new jar designs are presented, where obstacles on the surface of a traditional cylindrical jar modify the ratio of normal-to-tangential transferred mechanical action, thus improving the comminution of the mill charge and reducing the process time. Multibody dynamics simulations, validated by operando video recordings of the process, were employed to investigate modified ball motion regimes promoting the increase of the number of high-energy impacts. Moreover, experimental grinding of calcium fluoride powder was performed to assess the effect of milling time and jar-to-plate velocity ratio, through the evaluation of size and microstrain of the end product deduced from X-ray diffraction line profile analysis.

An alternative neutron diffractometer performance for strain/stress measurements

An alternative neutron diffractometer performance, which documents the feasibility of using a high-resolution three-axis neutron diffractometer for elastic and plastic deformation studies of bulk metallic polycrystalline samples, is presented. Contrary to the conventional double-axis setting, the suggested alternative consists of an unconventional three-axis set-up employing a bent perfect crystal monochromator and an analyzer with a polycrystalline sample in between. Though the alternative is, for measurements, much more time-consuming, its sensitivity to the change of the diffraction angle of the sample is, however, substantially higher and permits also plastic deformation studies on the basis of analysis of the diffraction line profiles. Moreover, much larger widths (up to 10 mm) of the irradiated gauge volumes can be investigated when just slightly affecting the angular resolution properties of the experimental setting.

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Changes in the Characteristics of the Profiles of X-Ray Diffraction Lines of Structural Steels in the Elastic Stress Field

The problems of improving operating procedures and diagnosing the bearing capacity of metal structures designed and operating in the Arctic and subarctic regions of the country with a long period of low climatic temperatures remain unresolved. The paper notes that the development of digital methods of non-destructive testing, primarily X-ray diffractometry methods, can provide technical diagnostics of structures by identifying the features of the deformation of the crystalline structure of structural materials in an elastic stress-strain state. It is shown that the application of the method of X-ray diffractometry of complex polycrystalline structural steels has sufficient resolution to detect changes in the fine structure under the elastically stressed state of the samples. The broadening of the diffraction line (B) profile characterizes the effect of the elastically stressed state of steel samples 08 ps and 09Г2С on the course of microdeformation processes in the surface layers of the metal. The effect of periodic annual temperature fluctuations on the profile characteristics of the diffraction lines of 08 ps structural steel samples was studied experimentally. It is established that low climatic temperatures contribute to the elimination of individual instrumental errors due to the design conditions of the experiment. A sharp change in the true half-width of the profile of diffraction lines (В) at stresses σ ≥ 0.5 σтindicates the minimum possible value of the allowable stress [σ] for structural steel 08 ps.

The Use of X-Ray Diffraction Peaks Profile Analysis to Define the Structural Condition of Elastically Stressed 09G2S Steel

By using X-ray diffractometry, it was determined how short-term stresses, being within the limits of the offset yield strength σs, influence changes in the diffraction line profile characteristics resulting from static tension in plate specimens of 09G2S (09Г2С) structural steel. Microstructural changes in the surface of 09G2S steel specimens considered in this work were studied at different levels of elastic stress. The special aspects of changes in the diffraction line profile characteristics are presented and discussed, specifically, a broadening of the profile maximum half-width (B), as a response to the external mechanical impact on the surface layers.

Experimental Investigations on the Effect of Severe Plastic Deformation Through End Milling on X-Ray Peak Broadening and Microcrystalline Characteristics of Nimonic 263

In the present work, the quantitative contributions of severe plastic deformation (SPD) through machining on the microcrystalline features and fatigue life of SPD processed Nimonic 263 have been investigated. X-ray diffraction line profile analysis (XRDLPA) has been executed to compute the likely makeover of microcrystalline characteristics such as crystallite size, lattice strain and dislocation density using full width at half maximum of diffraction peak, and additionally, the influences of these characteristics on fatigue life of the SPD processed samples have been analyzed. To deconvolute these characteristics, Williamson–Hall methods such as uniform deformation model, uniform energy density deformation models (UEDM) and uniform stress deformation model (USDM) are employed. The XRDLPA of machined samples has confirmed a significant broadening of peaks, due to lattice distortions and grain refinement during machining, and a plot of root mean square (RMS) of lattice strain (erms) versus lattice strain (e) has resulted in no inconsistency related to the lattice plane and crystallographic direction. Further, other related physical parameters such as uniform stress, Young’s modulus and energy density are also evaluated using UEDM and USDM models. As a result of the study, it is clear that the substantial influence comes from tool nomenclature over machining parameters.

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Characterization of Microstructures by X-Ray Diffraction Line Profile Analysis

Influence of carbon concentration and magnetic transition on the austenite lattice parameter of 30Mn-C steel

In this study, the effects of carbon concentration and magnetic transition on the austenite lattice parameter of Fe-30Mn-xC alloys were assessed. A linear relationship was obtained between the carbon content and the lattice parameter determined by neutron diffraction and neutron Bragg-edge transmission imaging for austenitic steels bearing 0.007–1.20 mass% C. The results obtained through both methods showed good agreement. In addition, carbon partitioning was evaluated in artificially piled-up discs with different carbon contents in order to develop a new technique for advanced multi-phase steels. The analysis of asymmetry and broadening of the diffraction line profile revealed that the carbon partitioning could be determined. In addition, the Néel temperature was determined by in situ neutron diffraction upon heating and cooling with magnetic diffraction peaks and the change in the lattice parameter with temperature being monitored. The temperature dependence of the austenite lattice parameter was found to become smaller below the Néel temperature. In conclusion, the results presented herein expand the current knowledge on the properties of high Mn austenite.

Virtual diffraction analysis of dislocations and dislocation networks in discrete dislocation dynamics simulations

This work proposes a data-analytics-based method to correlate diffraction peak broadening to dislocation density in relaxed dislocation networks. The model relies on two key developments: the generation of virtual diffraction signatures of dislocated crystals and the development of a surrogate model to predict dislocation density from diffraction profiles. First, two algorithms are introduced for the generation of diffraction profiles from discrete dislocation dynamics (DDD) simulations. Both algorithms leverage the full-field spectral computation of the elastic strain fields generated in the presence of dislocations. However, the two algorithms differ in their treatment of correlations in the elastic strain field; the impact of this difference on the shape of diffraction peaks is emphasized. A database containing 220 virtual diffraction profiles is generated from networks of dislocations in Al using the correlation-dependent algorithm. This dataset is employed to train and test a surrogate model. Predictions consistently yield dislocation densities within a 90% confidence interval of +30% to −41%, which is an improvement over prior dislocation density prediction methods. It is thus demonstrated that the simultaneous use of virtual diffraction and data analytics can yield alternative models for the analysis of diffraction line profiles in which uncertainty can be quantified for complex dislocation networks.

Data-Driven Analysis of Neutron Diffraction Line Profiles: Application to Plastically Deformed Ta

Data-Driven Analysis of Neutron Diffraction Line Profiles: Application to Plastically Deformed Ta

An experimental investigation on the effect of radial rake angle and machining conditions during end milling on wear resistance and residual stress of nimonic 263 alloy

The tribological and mechanical protection offered to end milled nimonic 263 alloy by the Severe Plastic Deformation (SPD) through machining has been undertaken in the current work. The dry milling of Nimonic 263 alloy has been carried out with a TiAlN coated tungsten carbide tool using vertical machining center. In this study, the surfaces of end milled nimonic 263 are analyzed through x-ray Diffraction Line Profile Analysis (XRDLPA) to evaluate the possible transformation on residual stress using measured interplanar distance between two parallel atomic planes. The quantifiable contributions of machining conditions such as tool nomenclature and machining parameters on the provoked beneficial residual stress on the top surface of the machined samples are evaluated. The SPD processed samples through machining have exposed a significant increment in residual stress which leads to increase the hardness and wear resistance compared to the nascent sample. Further, it reveals that the tool nomenclature has a great extent on the wear resistance followed by machining parameter. Additionally, this study has been carried out to obtain significant machining parameter and tool nomenclature which reflects higher wear resistance of Nimonic 263.

Forming, fracture and corrosion behaviour of stainless steel 202 sheet formed by single point incremental forming process

This work aims to determine the forming limit of stainless steel 202 sheet having 0.8 mm thickness during Single Point Incremental sheet metal Forming (SPIF) process. A L18 orthogonal array was designed using taguchi method for performing SPIF. The process parameters used were spindle speed, feed rate and vertical step down having three levels each and ball diameter having two levels. A straight groove test was conducted for 18 samples and strain based Forming Limit Diagrams (FLD) and stress based FLDs were plotted. Stress triaxiality and strain triaxiality were determined. The fractographs were analyzed and dislocation density was measured from x-ray diffraction line profile analysis. The corrosion behaviour of both undeformed sample and deformed sample were also studied. It was found that the formability is increased with increasing the spindle speed, decreasing the vertical step down and feed rate. The sum of strain was found to be 0.91 which is twice greater than that of conventional forming process. It is also found that the dislocation density is 2.35 times greater for the sample possesses higher formability than the sample possesses least formability. The goodness of fit in strain based FLD and stress based FLD are found to be 0.989 and 0.968 respectively.

Effect of variation in behavioural changes during end milling on Nimonic 263 elastic constants

Machining of aerospace alloy such as nimonic 263 is a challenging task due to its intrinsic characteristics. In this study, the effect of Severe Plastic Deformation (SPD) through machining on its inherent characteristics such as young modulus, bulk modulus, etc have been investigated. The machining has been done using vertical machining center with the help of tungsten carbide tool with PVD coated TiAlN. X-ray diffraction line profile analysis is used to determine the changes in crystallite size and dislocation density on deformed samples through machining. Furthermore, ultrasonic wave method through pulse echo technique has confirmed the changes in elastic constants and lattice stability of machined samples, due to Severe Plastic Deformation (SPD) on machined sample. Quantitative contributions of machining parameter, tool nomenclature effect on surface modification, elastic constants and intrinsic characteristics of machined sample are evaluated and found that the machining have exposed a significant enhancement in elastic constants and hardness compared to the nascent sample. Further, it reveals that the tool nomenclature has a higher influence on the enhancement in material properties followed by machining parameter. The results portray that the significant contribution comes from dislocation density and disorder followed by crystallite size.

Study on formability and dislocation density in forming of hemispherical cup

The aim of this work is to study formability and dislocation density in the plastically deformed cup by both punch and die forming process and single point incremental forming (SPIF) process. The stainless steel grade 202 (SS 202) sheet metal was used for this study. The formability from forming limit diagram (FLD) and dislocation density by X-ray diffraction line profile analysis (XRDLPA) were determined for the cup formed by both forming processes and compared with each other. The amount of strain induced transformation (SIT) was also found from microstructure for the cup formed by both forming processes and compared. The cup with hemispherical shape was formed by SPIF process and its amount of deformation and dislocation density was also found.

Influence of dislocations and grain boundaries on diffraction line profiles of nano-crystalline materials: A numerical study

In the present paper, the contributions of dislocations and grain boundaries to the broadening of diffraction line profile have been delineated. Contribution of each factor is studied on single as well as poly crystalline ‘virtual samples’ containing different dislocation configurations generated by molecular dynamics and evaluating the simulated X-ray diffraction line profiles of these samples. Individual contributions to diffraction line profiles by different sample features, such as domain size, dislocations, grain boundaries, have been isolated by deconvoluting the evaluated diffraction line profiles. The diffraction line profiles exhibited significant asymmetry and peak splitting in the case of dislocations with predominantly edge character. It has been shown that splitting of diffraction peaks carries information about the magnitude of Burger’s vectors of the dislocations. Application of the variance method based on single peak fitting and Wilkens method based on whole powder pattern fitting of line profile analysis on the computed diffraction line profiles, showed that while accurate domain size estimation was possible, there was an under estimation of dislocation density at the high dislocation density and small grain size regime considered in the present study.