Claims:We claim:
1. A method for preparation of a multiphase steel sample for Electron Back Scattered Diffraction (EBSD), the method comprising:
cutting a multiphase steel sample;
mechanically polishing the multiphase steel sample;
electropolishing the multiphase steel sample with a suitable electrolyte; and
polishing the multiphase steel sample by colloidal silica for 30 seconds to 120 seconds.
2. The method as claimed in claim 1, wherein the mechanical polishing comprises grinding.
3. The method as claimed in claim 2, wherein the mechanical polishing further comprises post grinding is cloth polishing.
4. The method as claimed in claim 1, wherein the multiphase steel sample is conductively mounted.
5. The method as claimed in claim 1, wherein the suitable electrolyte is acetic acid + perchloric acid (90:10) mixture.
6. The method as claimed in claim 1, wherein voltage maintained during electropolishing is 30-40 V.
7. The method as claimed in claim 1, wherein time maintained during electropolishing is 20-40 seconds.
8. The method as claimed in claim 1, wherein temperature maintained during electropolishing is 5-8 °C.

, Description:METHOD FOR PREPARATION OF A MULTIPHASE STEEL SAMPLE FOR ELECTRON BACK SCATTERED DIFFRACTION
TECHNICAL FIELD
[0001] The present disclosure, in general, relates to the field of metal processing and, more particularly, to a method for preparation of a multiphase steel sample for Electron Back Scattered Diffraction (EBSD).

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
[0003] Electron Back Scattered Diffraction (EBSD) technique is a surface sensitive technique. In this technique, the diffraction signal comes from the top few nanometers of the crystal lattice. Hence, the top layer needs to be devoid of oxidation, contamination, and damage. This makes the specimen preparation highly significant for acquiring good EBSD data. Besides, the need to tilt the sample up to high angles (typically 70°) for acquisition, it is essential to maintain the sample surface topography to a minimum as well.
[0004] The above demands thus make the normal sample preparation technique inadequate for EBSD and special/final stage polishing technique is a must to obtain good quality EBSD pattern.
[0005] There are several techniques for EBSD sample preparation. The techniques are also depended on the samples under consideration. For examples, there are some samples which do not need any special polishing whereas some samples needed very intense high-quality sample preparation.
[0006] The typical EBSD sample preparation techniques are described briefly herein below:
[0007] Mechanical Polishing: Mechanical polishing is important and done for virtually all samples. The mechanical polishing is an ideal sample preparation technique for multiphase materials, ceramic or geological materials. This process involves the following steps:
(i) Mounting:
Depending on the nature of the sample, mounting should or should not be done for EBSD. In an aspect, a conductive mounting medium can be used to minimize any drift or charging when using insulators. However, materials such as geological minerals will expand and possibly fracture when hot mounting processes are used.
(ii) Grinding:
Grinding is the first mechanical stage of the specimen preparation to remove the deformation layer created during cutting of sample. Typically, Silicon Carbide (SiC) paper is used for this grinding process. Nonetheless, since different materials exhibit different abrasion characteristics, grinding material and conditions are selected specifically to a given sample.
(iii) Polishing:
Polishing eliminates most of the damage caused by grinding. For polishing, different types of abrasive and suspension mediums are available. Diamond polishing compounds or slurries are suitable for preliminary stages for most of the materials. Typically, the polishing is begun on a hard cloth with a coarser abrasive and ended on a softer cloth with a finer abrasive.
After this stage, most samples are ready for the final polishing. However, minor deformation remaining after mechanical preparation is removed by Vibratory Polishing, which is engineered for high-quality polished surface preparation on many different materials and applications.
Nonetheless, there are several final polishing techniques which are briefly described below.
[0008] Colloidal Silica: Colloidal silica is normally used as a final polishing step for the EBSD analysis. It should not be long and be just adequate to obtain the required surface finish without causing excessive relief. Sometime colloidal silica polishing is done in a vibratory polisher. The unique vibratory action yields less deformation, flatter surfaces, and minimizes edge rounding. It also produces a stress-free surface.
[0009] Electropolishing: Electropolishing is another final polishing step suited to prepare samples for many metallic materials. In this process, the top deformed material is removed by the electrolytic process. The selection of the appropriate electrolyte solution and working voltage, current and temperature are crucial for a successful outcome.
[0010] Ion Milling: Ion milling can be used as another final polishing technique. In this process, samples are normally thinned by mechanical means and then bombardment with energetic ion (normally Ar ions) in a selected area of the sample surface is done under vacuum. The bombardment erodes the surface, but can also damage the surface by ion implantation.
[0011] All the above processes listed are quite sensitive to materials and perfection is achieved mainly by trial and error method. Obtaining a perfect sample also depends on a number of other factors; such as phases present and their mutual properties, composition, hardness, etc. For example, it is difficult to get a good sample of multiphase steel than a single-phase steel by electropolishing method because of preferential etching while it is quite useful for single phase soft material such as aluminum (Al), Copper (Cu), and the like.
[0012] Various researches are going on in multiphase steels comprising of different phases such as ferrite, austenite, martensite, bainite, carbides, etc. The properties of these steels depend on the morphology, distribution, size and volume fraction of these phases. However, these changes also pose a problem for EBSD sample preparation. This becomes more significant when the sample has a softer and a harder phase and when there are strain/dislocations in the samples, such as rolled samples. In that case, even prolonged colloidal silica may not yield a good sample, rather may deteriorate.
[0013] Considering the state of the art, there is a requirement to develop a method to obtain a good sample for EBSD which is fast and are suitable for any kind of steels, single phase or multiphase.

OBJECTS OF THE DISCLOSURE
[0014] In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0015] It is an object of the present disclosure to propose a novel and fast process for steel sample preparation for Electron Back Scattered Diffraction (EBSD) study.
[0016] It is another object of the present disclosure to propose a novel and quick method to prepare a sample of multiphase steel for EBSD study.
[0017] It is a further object of the present disclosure to improve the quality of EBSD pattern for multiphase steels.
[0018] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0019] This summary is provided to introduce concepts related to a method for preparation of a multiphase steel sample for Electron Back Scattered (EBSD). The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0020] The present disclosure relates to a method for preparation of a multiphase steel sample for Electron Back Scattered (EBSD). The includes cutting a multiphase steel sample; mechanically polishing the multiphase steel sample; electropolishing the multiphase steel sample with a suitable electrolyte; and polishing the multiphase steel sample by colloidal silica for 30 seconds to 120 seconds.
[0021] In an aspect, the mechanical polishing includes grinding.
[0022] In an aspect, the mechanical polishing further includes cloth polishing after the grinding.
[0023] In an aspect, the method includes conductively mounting the multiphase steel sample.
[0024] In an aspect, the suitable electrolyte is acetic acid + perchloric acid (90:10) mixture.
[0025] In an aspect, voltage maintained during electropolishing is 30-40 V.
[0026] In an aspect, time maintained during electropolishing is 20-40 seconds.
[0027] In an aspect, temperature maintained during electropolishing is 5-8 °C.
[0028] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[0029] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0030] FIG. 1 illustrates a method for preparation of a multiphase steel sample for Electron Back Scattered Diffraction (EBSD), in accordance with an embodiment of the present disclosure;
[0031] FIG. 2 illustrates a scanning electron microscopy (SEM) micrograph showing a lath structure of a steel sample;
[0032] FIG. 3 illustrates an X-ray powder diffraction (XRD) peak profile of the sample showing the presence of fcc-austenite and bcc-ferrite/martensite structure;
[0033] FIGS. 4A and 4B illustrate Inverse Pole Figure (IPF) and Image Quality (IQ) maps of the sample obtained after Process 1; and
[0034] FIGS. 4C and 4D illustrate Inverse Pole Figure (IPF) and Image Quality (IQ) maps of the sample obtained after Process 3.

DETAILED DESCRIPTION
[0035] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0036] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0038] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0039] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0040] FIG. 1 illustrates a method 100 of a sample for Electron Back Scattered Diffraction (EBSD) study for steel, in accordance with an embodiment of the present disclosure. The method 100 is suitable for both single-phase as well as multiphase steels. The order in which the method 100 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 100, or an alternative method.
[0041] In the present disclosure, a multiphase medium Manganese (Mn) steel is chosen for this study. The steel has a lath-like structure, consisting of annealed martensite and austenite. Some amount of ferrite may also present in the steel. Due to the processing, the material has a lot of remnant dislocations inside its structure. The scanning electron microscopic (SEM) microstructure and X-ray powder diffraction (XRD) peak analysis for this sample are shown in FIGS. 2 and 3, respectively. As can be seen from FIG. 3, XRD peak analysis shows the presence of ~ 6 % austenite in the microstructure.
[0042] At block 102, the method 100 includes cutting a multiphase steel sample. For this, the steel sample was cut into 20 x 10 mm2 area, with the longer axis parallel to the rolling direction. In an aspect, the steel sample is mounted in a conductive mount. In the said aspect, depending on the sample size, conductive mounting can be done.
[0043] At block 104, the method 100 includes mechanically polishing the multiphase steel sample. The mechanical polishing includes steps of grinding followed by cloth polishing. In an aspect, the multiphase steel sample is mounted in a conductive mount, ground with 400, 600, 800 and 1200 grit emery papers followed by cloth polishing using 3 µm and 1 µm diamond paste.
[0044] After the cloth polishing at block 104, the different final polishing techniques were employed for EBSD study. The different final polishing techniques include two conventional and the third one by a current procedure. The processes are described briefly herein below:
Process 1. Colloidal Silica Polish: Steel Sample is polished with colloidal silica for 5-30 minutes. However, the quality of the EBSD is not good.
Process 2. Electropolishing: Steel Sample is electropolished with a 90:10 acetic acid-perchloric acid solution for 20-40 seconds at a voltage of 30-40 V and temperature of 5-8 °C. However, after several permutation combinations, the desired surface finish could not be achieved. Unfortunately, no EBSP could be generated from this process.
Process 3. First, the steel sample is electropolished using the method described in Process 2 (electropolished with a 90:10 acetic acid-perchloric acid solution for 20-40 seconds at a voltage of 40 V and temperature of 5-8 °C) followed by 30 - 120 seconds of colloidal silica polish. The EBSP obtained as per Process 3 is much improved.
[0045] The results obtained by Process 1 and Process 3 are shown below in Table 1:
Table 1: Average Confidence Index (CI) and austenite volume fraction of the sample obtained after Process 1 and Process 3
Process 1: Colloidal Silica Process 3: Electropolishing & Colloidal Silica
Ferrite CI 0.13 0.48
Austenite CI 0.03 0.23
% Austenite < 2 % ~ 4.7 %

[0046] Accordingly, at block 106, the method 100 includes electropolishing the multiphase steel sample with a suitable electrolyte. In an aspect, the suitable electrolyte may include acetic acid + perchloric acid (90:10) mixture. In an aspect, voltage maintained during electropolishing is 30-40 V, time maintained during electropolishing is 20-40 seconds, and the temperature maintained during electropolishing is 5-8 °C. In another aspect, the voltage, time and temperature for electropolishing can be established for the given composition/grade of steel first by standard practice. Once it is established, the same voltage-current-temperature condition can be used for all the samples irrespective of their phase distribution and alloy partitioning.
[0047] After the electropolishing, the sample may or may not be suitable for further EBSD analysis. Accordingly, at block 108, the method 100 polishing the multiphase steel sample by colloidal silica for 30 seconds to 120 seconds.
[0048] The sample prepared by the method 100 proposed herein is suitable for EBSD analysis and generate good EBSP patterns.
[0049] FIGS. 4A and 4B illustrate the Inverse Pole Figure (IPF) and Image Quality (IQ) maps of the sample obtained after Process 1; and FIGS. 4C and 4D illustrate Inverse Pole Figure (IPF) and Image Quality (IQ) maps of the sample obtained after Process 3.
[0050] As can be seen from FIGS. 4A-4D, the image quality, and CI both are much better in Process 3 than Process 1. The CI value increased from 0.13 to 0.48 and 0.03 to 0.23 for bcc-martensite and austenite, respectively. Also, the structure is significantly clear as can be seen in FIG. 4D. The increase in CI value indicates sample preparation is better. This is also reflected in the measured austenite volume fraction. The austenite volume fraction obtained after Process 3 is 4.7%, closer to the fraction obtained by XRD. However, after Process 1, austenite fraction obtained was much lower, < 2%. This is because proper Kikuchi lines could not be obtained from austenite in the latter case due to imperfect sample preparation. The multiphase nature of the present sample, smaller austenite size, and presence of dislocations, is responsible for this difficulty and colloidal silica polish for 1-2 minutes is not sufficient to remove the deformed layer introduced during sample cutting and polishing techniques. When colloidal silica polish was done for more than 2 minutes, the process itself introduced deformation into the original sample.
[0051] Moreover, due to the presence of a soft (austenite) and hard phase (martensite), deformation introduced during polishing (normal cloth as well as colloidal) are mainly segregated in the austenite phase. This results in difficulty to get a good EBSP from the austenite phase. This is clearly revealed as in both the cases the CI value is lower in the Austenite phase (FIGS. 4A-4D).
[0052] In contrast, in Process 3, the first electropolishing step efficiently removed the deformed layer but selectively etched the grain boundaries and the phases [2]. This made the top surface uneven and not fit for EBSD study. However, when this was followed by a short (< 120 second, preferably 20-30 seconds) colloidal silica polish the topography became smooth without introducing much deformation. This process thus gives a simpler and better sample preparation experience for EBSD study.
[0053] Furthermore, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0054] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0055] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.