Commercial introduction of the Scanning Electron Microscope (SEM) in 1965, and its subsequent rapid development and implementation in metallographic laboratories, has had a profound influence on failure studies. The chief advantage of the SEM is its great depth of field in comparison of the light microscope. Observations can be made over a much wider range of magnifications including those above the range for light microscopes (and those below the range of TEM replicas). Examination of fracture features by SEM is much simpler than through the study of replicas with the Transmission Electron Microscope, TEM. A further advantage of the SEM is the chemical analytical capability of spectrometers that can be attached to the microscope, Energy-dispersive Spectrometers (EDS) being the most common.

The study of fractures with the unaided eye has been practiced since antiquity chiefly for controlling the quality of metals production. R. A. F. de Réammur may have been the first to examine and publish drawings of fractures examined at high magnifications, at least 100X, in 1722. R. Mallet appears to have been the first to link fracture appearance to service performances in a study of failed cannon barrels published in 1856. Adolf Martens may have been the first to study both fracture surfaces and the underlying microstructures in 1878 followed by the first description of fracture surface features in 1887 when he showed that these lineal features could be traced backward to identify the fracture origin.

The metallographic laboratory is a relatively safe working environment; however, there are dangers inherent to the job. Included in these dangers is exposure to heat, acids, bases, oxidizers and solvents. Specimen preparation devices, such as drill presses, shears and cutoff saws, also present hazards. In general, these dangers can be minimized if the metallographer consults documents such as ASTM E 2014 (Standard Guide on Metallographic Laboratory Safety) and relevant Material Safety Data Sheets (MSDS) before working with unfamiliar chemicals. Common sense, caution, training in basic laboratory skills, a laboratory safety program, access to safety reference books – these are some of the ingredients of a recipe for laboratory safety.

Safe working habits begin with good housekeeping. A neat, orderly laboratory promotes safe working habits, while a sloppy, messy work area invites disaster. Good working habits include such obvious, commonsense items as washing the hands after handling chemicals or before eating. Simple carelessness can cause accidents. For example, failure to clean glassware after use can cause an accident for the next user. Another common problem is burns due to failure to properly clean acid spills or splatter. 

The accident at Unit No. 2 of the Three Mile Island nuclear reactor (TMI-2) on March 28, 1979 was the worst nuclear accident in US history and crippled the nuclear industry. It was not possible to remove specimens from the lower head until January – March 1990. Fourteen of the fifteen specimens removed by electrical discharge machining were from under the debris pile that accumulated on the lower head due to melting of ~19,000 kg (~45%) of the core. Specimens were previously cut from the lower head of a cancelled reactor of very similar size and design destined for Midland, Michigan. These specimens were subjected to controlled heating cycles with peak temperatures from 800 to 1100°C for periods of 1 to 100 minutes. The writer examined both sets of specimens and employed selective etching followed by quantitative metallography (by image analysis) to obtain a far more detailed description of the thermal exposure experienced than had been obtained previously. 

Grain size measurement by electron backscattered diffraction (EBSD) has several unique advantages over the traditional measurement of etched specimens by the light optical microscopy (LOM) approach as defined in ASTM E 112. This is most evident when trying to measure the grain size of twinned face-centered cubic (FCC) metals where two major problems are encountered.

First, in many cases, it is difficult to reveal a very high percentage of the grain boundaries by etching. Secondly, nearly all etchants for twinned FCC metals do reveal the twin boundaries and one must ignore the twin boundaries when measuring the grain size by LOM. The notable exception to this experience is electrolytic etching of the 300 series of austenitic stainless steels where Bell and Sonon’s aqueous 60% nitric acid ^[1], using a platinum cathode and a voltage no greater than 1.5 V DC will reveal nearly 100% of the grain boundaries and virtually none of the twin boundaries. Another significant problem that affects EBSD results somewhat more than LOM etching results is the greater difficulty in preparing the highly ductile FCC metals to the perfection needed to get a very high percentage of the pixels to be indexable. Specimen preparation ^[2-4] is a very critical step in getting a very high percentage of indexable pixels in the field of view. This is not a trivial matter.

Revealing the prior-austenite grain boundaries in heat treated steel is probably the most difficult, and frustrating task, faced by the metallographer or metallurgist. Grain boundaries, regardless of the type, are generally impossible to see in cast metals, as they solidify dendritically and segregation is present and often substantial. After deformation and annealing, if recrystallization occurs, grain boundaries in the product may be visible, but they are not necessarily prior-austenite grain boundaries.

In a deformed, partially recrystallized specimen, it is usually possible to see both recrystallized and non-recrystallized grain boundaries. But, prior-austenite grain boundaries are those of the steel when it was austenitized prior to quenching and tempering. If the steel’s microstructure is fully martensitic after hardening, or contains some retained austenite or lower bainite, the prior-austenite grain boundaries may be revealed. They can often be revealed in specimens isothermally processed to obtain fully lower bainitic microstructures; but they cannot be revealed if the transformation microstructure consists of upper bainite, pearlite and/or ferrite. Composition also is important in trying to reveal the prior-austenite grain boundaries, as is the tempering temperature. In general, steels with low carbon contents and low phosphorous contents are very difficult subjects.  This article summarizes the state-of-the-art in revealing prior-austenite grain boundaries.

Experiments were conducted using three-step preparation procedures for titanium and its alloys.  For CP titanium and alpha-titanium alloys, use of an attack-polishing agent in the third step was required to obtain good results.  The experiments defined optimum surfaces for each step and operating conditions.  Two-phase, α-ß alloy specimens are significantly easier to prepare than a single-phase α specimen. The method does yield perfect polarized light response with α-phase alloys, such as commercial-purity titanium.

Titanium and its alloys have become quite important commercially over the past fifty years due to their low density, good strength-to-weight ratio, excellent corrosion resistance and good mechanical properties.  On the negative side, the alloys are expensive to produce. Titanium, like iron, is allotropic and this produces many heat treatment similarities with steels.  Moreover, the influences of alloying elements are assessed in like manner regarding their ability to stabilize the low temperature phase, alpha, or the high temperature phase, beta.  Like steels, Ti and its alloys are generally characterized by their stable room temperature phases – alpha alloys, alpha-beta alloys and beta alloys, but with two additional categories: near alpha and near beta.