A Metallographic Preparation Method for Three-Dimensional Microstructural Characterization of Machining Chips

Chip formation is an important indicator of machining processes. Statistical characterization of machining chips’ geometric features can offer crucial information for evaluating the stability and productivity of the machining processes. In abrasive machining processes, an abundance of small chips are produced by the vast number of abrasives exposed to the cutting surfaces. Geometric features of abrasives, such as shape, dimension, and distribution, may be hierarchically passed on to the chips. Similar to those of the abrasives, geometric features of the chips may also vary to a certain extent and conform to some statistical distribution. To verify these characteristics, a metallographic preparation method in connection with chips formed in abrasive machining processes is proposed in this study. Challenges in collecting and segmenting chips have been successfully overcome through several steps using ultrasonic bath cleaning and powder cold embedding methods. Finally, a considerable amount of chips was formed and uniformly embedded in a resin mold, ready for microscopic characterization.

Propriedades mecânicas das fases ferrita e austenita de aço inoxidável duplex

Aços inoxidáveis duplex apresentam elevada resistência mecânica e resistência à corrosão, propriedades requeridas pelas indústrias petroquímicas. Esta combinação tem ampliado a utilização destes aços, e motivado diversas pesquisas. Os aços inoxidáveis duplex recebem este nome, devido à microestrutura ser formada por aproximadamente 50% de austenita e 50% de ferrita. Sabe-se que a dureza está diretamente relacionada à resistência mecânica, e que esta propriedade pode variar de acordo com a microestrutura do material. O objetivo do presente trabalho é avaliar e comparar a dureza das fases austenita e ferrita presentes nos aços duplex. Uma amostra foi preparada metalográficamente, sendo posteriormente atacada com a solução Behara pela técnica de “color etching”. Após o ataque químico as amostras foram submetidas a ensaios de microdureza Vickers, apresentando 247,8±35,1 HV0,1 e 263,22±11,6 HV0,1 para a ferrita e austenita, respectivamente. Após analise estatística dos resultados, concluiu-se que as fases ferrita e austenita possuem durezas similares. Duplex stainless steels have high mechanical strength and corrosion resistance properties required by the petrochemical industry. This combination has expanded the use of these steels, and motivated many studies. The duplex stainless steels are named because of the microstructure is formed by about 50% to 50% austenite and ferrite. It is known that the hardness is directly related to mechanical strength, and that this property can vary depending on the microstructure of the material. The objective of this study is to evaluate and compare the hardness of austenite and ferrite phases present in the duplex stainless steels. A sample was prepared by metallographic preparation techniques, and was then attacked with the solution BEHARA with technique of color etching. After etching the samples were tested for Vickers microhardness, with 247.8 ± 35.1 HV0, 1 and 263.22 ± 11.6 HV0, 1 for ferrite and austenite, respectively. After statistical analysis of results showed that the ferrite and austenite phases have similar hardness.

Patience Alone is not Enough – A Guide for the Preparation of Low-Defect Sections from Pure Copper

The preparation of metallographic sections from soft metals such as pure copper constitutes a particular challenge: the high degree of ductility promotes the formation of preparation artifacts and complicates the preparation of homogeneous, low-deformation surfaces. A metallographic preparation routine is therefore presented which has proven effective for pure copper and which can also be applied to additionally soft annealed samples. The subsequent removal of fine crystalline deformation layers is discussed and different setups for electropolishing and its optimization are presented.

Experimental Analysis of Microhardness Changes of Subsurface Areas Affected by WEDM

The influence of the surface area by the impact of high temperatures after wire electric discharge machining (WEDM) is a known fact. However, the affected parameters also include a change in microhardness. In order to further investigate this statement, 5 different metallic and non-metallic materials were selected, from which three samples were always made with different settings of machine parameters (gap voltage, pulse on and off time, wire feed and discharge current). This examined not only the effect of the machining itself on the material but also whether the change in the microhardness of the material is affected by the setting of the machine parameters. In order to measure the microhardness of the subsurface layer, a metallographic preparation was made from each sample, which enabled accurate measurements always in the same area. Subsequent evaluation revealed that the microhardness may not be affected at all and everything depends only on the type of material being machined. The changes in microhardness affected by setting machine parameters are negligible.

Preparation Methods for Lower Bainite after a Continuous Austempering Treatment of Thin Sheets of the Eutectoid Cold Work Steel 80CrV2 (1.2235)

Strip material with a thickness of 0.85 m was austempered in a suitable continuous hardening furnace for the further development of blade body steels used for thin-cutting circular and band saw blades. This work also comprised the search for a rather straightforward metallographic preparation procedure allowing for a reliable identification of the microstructure and microstructural constituents. The prepared microstructure can be revealed using Nital or Beraha and LePera etching solutions. None of the three etchants allows a reliable and reproducible distinction of the microstructural constituents of the extremely fine-grained lower bainite using light-optical techniques. Only the use of the scanning electron microscope at higher magnifications allows a reliable identification of the characteristic bainite fiber bundles. For this examination, etching with Nital is recommended.

Metallographic Preparation of Single Powder Particles

This work developed a systematic method for a metallographic preparation of single powder particles with diameters of approx. 20 to 40 μm. It was motivated by the objective of understanding additive manufacturing processes such as Laser Powder Bed Fusion. A fundamental aspect of the relationship between manufacturing, structure, and properties is the correlation of rapid solidification and resulting microstructure. During powder-based additive manufacturing processes, cooling rates up to 1 MK/s are attained. A thermal analysis determining the characteristics of solidification at such rapid cooling rates can be performed with the aid of chip sensor-based, dynamic Differential Fast Scanning Calorimetry, DFSC. For this purpose, the heat flow during the solidification of single powder particles is measured and, for instance, the solidification onset temperature is evaluated as a function of cooling rate. It is thus possible to estimate the undercooling which has a significant impact on the resulting structure. Subsequently, cross sections of single powder particles must be prepared for the analysis of the resulting structure.

Decipher Ultrasonic Signals from Defects in Thick Aluminum Extrusions to Identify Type and Origin of Defects

Manufacturing of thick seamless pipes of age-hardenable aluminum alloys are a specialized technology since their application is limited to specific hi-tech areas. Quality criteria for their inspection are propriety items of the very few production facilities that develop these criteria in-house. Present study relates ultrasonic signals reflecting back from non-continuities in the thickness of seamless pipes with their microstructural features. Detailed study of defects leads to the source of their formation and will ultimately help to systematically control them. Signals from ultrasonic testing trace defects as UT waves reflect back from discontinuities in the material. Defective sections of seamless pipes were cut with precision to reveal the defects. The sectioned surfaces were subjected to metallographic preparation and revealed defects were studied using Optical and Field Emission Scanning Electron Microscopes (FESEM). Defects are grouped based on the shape of UT signals as well as the defect morphology as revealed by microscopic studies. Most of the observed cracks are found to grow in the direction of extrusion. Energy Dispersive Spectroscopy (EDS) analysis was conducted to determine the composition of inclusions in the vicinity of the defects. Data from elemental analysis is used to identify the potential sources. The study recommends measures to control the defects and improve the yield.

An Additively Manufactured Titanium Alloy in the Focus of Metallography

Additive manufacturing processes allow the production of geometrically complex lightweight structures with specific material properties. However, by contrast with ingot metallurgy methods, the manufacture of components using this process also brings about some challenges. In the field of microstructural characterization, where mostly very fine structures are analyzed, it is thus indispensable to optimize the classic sample preparation process and to furthermore implement additional preparation steps. This work focuses on the metallography of additively manufactured Ti‑6Al‑4V components produced in a selective laser melting process. It offers a guideline for the metallographic preparation along the process chain of additive manufacturing from the metal powder characterization to the macro- and microstructural analysis of the laser melted sample. Apart from developing preparation parameters, selected etching methods were examined with regard to their practicality.

Particularities of metallographic preparation for the analysis of thin layers and coatings. Foundry production and metallurgy

The article deals with the issues of determining the thickness of layers and coatings for various purposes in metallographic research. The role of the material for filling metallographic sections in determining the layer thickness is demonstrated. It is shown that when filling the sample with plastic masses, the error in determining the layer thickness can be 0.2...0.4 microns, which is significant for thin layers. Sample preparation options for determining the thickness of titanium nitride layers with a thickness of 1 microns or less are considered. It is shown that with the optimal method of sample preparation, it is possible to visualize a layer less than 1 microns thick, and also determine its thickness in the image processing program.