Microindentation Hardness Testing - Paper

IN MICROINDENTATION HARDNESS TESTING (MHT), a diamond indenter of specific geometry is impressed into the surface of the test specimen using a known applied force (commonly called a “load” or “test load”) of 1 to 1000 gf. Historically, the term “microhardness” has been used to describe such tests. This term, taken at face value, suggests that measurements of very low hardness values are being made, rather than measurements of very small indents. Although the term “microhardness” is well established and is generally interpreted properly by test users, it is best to use the more correct term, microindentation hardness testing.


Last Updated on Monday, 11 February 2013 20:15

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Microindentation Hardness Testing - Article

Microindentation hardness testing is a very valuable tool for the materials engineer, but it must be used with care and with a full understanding of potential problems.


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Metallography of Welds

Welding is an important joining technology, and is highly dependent on the process choice, consumables used, operating parameters, and operator proficiency.

Thus, inspection procedures, both nondestructive and destructive, are required to control the process and guarantee quality. Metallographic examination is a key tool in the destructive examination of weldments, both as a process control tool and as a post-mortem examination of failed components. Macrostructure must also be examined, which can be done on sections after grinding or polishing. Macrostructural examination is used to learn about the weld geometry, the depth of weld metal penetration, the magnitude of the heataffected zone, and to detect cracks and voids. Microstructural examination is used to determine the mode of cracking and the cracking mechanism and to identify phases or constituents in the weld metal, heat-affected zone, and base metal including nonmetallic inclusions, as related to governing specifications, fitness for service, or cause of failure.


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Metallography of Precious Metals

Preparation of Precious Metals

For 18-karat gold alloys, and similar highly noble precious metals: it is necessary to use an attack-polish agent in the MasterPrep alumina abrasive step. Mix 10 mL of the attack-polish solution with 50 mL of MasterPrep alumina slurry. The attack-polish agent can be: H2O2 (30% conc.), or aqueous 5-20% CrO3, or aqueous 10% oxalic acid, etc.


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Metallography and Microstructures of Stainless Steels and Maraging Steels

STAINLESS STEELS are complex alloys containing a minimum of 11% Cr plus other elements to produce ferritic, martensitic, austenitic, duplex, or precipitation-hardenable grades. Procedures used to prepare stainless steels for macroscopic and microscopic examination are similar to those used for carbon, alloy, and tool steels. However, certain types require careful attention to prevent artifacts. Because the austenitic grades work harden readily, cutting and grinding must be carefully executed to minimize deformation. The high-hardness martensitic grades that contain substantial undissolved chromium carbide are difficult to polish while fully retaining the carbides. The most difficult to such grades to prepare is AISI 440C. For the most part, preparation of stainless steels is reasonably simple if the basic rules for metallographic preparation arefollowed. However, unlike carbon, alloy, and tool steels, etching techniques are more difficult due to the high corrosion resistance of stainless steels and the various second phases that may be encountered.


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Metallography and Microstructures of Heat-Resistant Alloys

HEAT-RESISTANT ALLOYS cover a wide range of chemical compositions, microstructural constituents, and mechanical properties. This article summarizes metallographic techniques and microstructural constituents for three types of cast and wrought heat-resistant alloys: iron-base, nickel-base, and cobalt-base. The metallographic methods discussed also are suitable for preparing both cast and wrought heat-resistant alloys; microstructural constituents are quite similar except for obvious differences in homogeneity and porosity.
The procedures used to prepare metallographic specimens of cast or wrought heat-resistant grades are quite similar to those for ironbase alloys, especially stainless steels (see the Section “Metallographic Techniques” in this Volume). Aspects particularly significant to the preparation of cast or wrought heat-resistant alloys are emphasized. Tables 1 to 3 list the nominal compositions of Fe-Ni-Cr Alloy Casting Institute H-series alloys and other iron-nickel,
nickel-, and cobalt-base cast and wrought heatresistant alloys, respectively.


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Metallographic Specimen Preparation for Electron Backscattered Diffraction


Electron backscattered diffraction (EBSD) is performed with the scanning electron microscope (SEM) to provide a wide range of analytical data; e.g., crystallographic orientation studies, phase identification and grain size measurements. A diffraction pattern can be obtained in less than a second, but image quality is improved by utilizing a longer scan time. Grain mapping requires development of diffraction patterns at each pixel in the field and is a slower process. The quality of the diffraction pattern, which influences the confidence of the indexing of the diffraction pattern, depends upon removal of damage in the lattice due to specimen preparation. It has been claimed that removal of this damage can only be obtained using electrolytic polishing or ionbeam polishing. However, the use of modern mechanical preparation methods, equipment and consumables does yield excellent quality diffraction patterns without use of dangerous electrolytes and the problems and limitations associated with electropolishing and ion-beam polishing. Basically, if mechanical preparation results in quality polarized light images of noncubic crystal structure elements and alloys (e.g., Sb, Be, Hf, -Ti, Zn, Zr), or color tint etching of cubic, or non-cubic crystal structure elements or alloys produces high-quality color images, then the surface is free of harmful residual preparation damage and EBSD patterns with high pattern quality indexes will be obtained. Because of the acute angle between the specimen and the electron beam (70 – 74 ), exceptional surface flatness is also necessary for best results.


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resourcesThe articles and presentations that can be down-loaded from this web site are based upon work done by GFV while employed at Bethlehem Steel (1967-1983), Carpenter Technology (1983-1996), Buehler Ltd. (1996-2009) and Struers (2009-Present) and from the authors consulting work for companies such as, Latrobe Steel, Scot Forge, etc., and from his litigation work. GFV's bylined articles appearing in various issues of the ASM Handbook series have been listed here courtesy of ASM International, Materials Park, Ohio.

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