Stereomicroscopy is a variation of optical microscopy specific for low level magnification in the range of 5X. For Apollo-Clad, stereomicroscopy is routinely used to evaluate the quality of the surfaces of our coatings. This form of imaging is also used for level magnification images of cross sections of laser welds to observe penetration and degree of fusion as well as cross sections of laser clad coatings to observe the quality of metallurgical bonding.
For high magnification imaging, Apollo is equipped with an optical microscope capable of 1000X magnification. At these levels, features at the sub millimeter scale such as precipitates, microstructural phases, grain size, inclusions, and porosity can be observed and measured. Apollo’s analysis capabilities include differential interference contrast (DIC) imaging, which allows for enhanced image contrast for superior photomicrographs. Shown below are some sample micrographs of dissimilar material laser clad layers applied to steel and nickel-based materials.
Apollo-Clad offers two types of hardness testing: macro indentation with Rockwell hardness testing and Vickers microhardness testing. Both work on the principle of resisting permanent deformation of an indenter under an applied load: softer materials result in a larger indent (reduced resistance to the load for a standard period of time) and harder materials produce smaller indents (higher resistance). These two types of hardness testing are described below:
Rockwell Hardness Testing
Rockwell hardness testing is the industry standard for measuring representative bulk hardness. From a metallurgical perspective, Rockwell hardness testing occurs over a relatively large area capturing a large scale or “macro” region of the sample. A Rockwell indentation combines the resistance of many grains, phases, and/or secondary particles in the sample revealing their overall contribution to the bulk hardness. The test is performed on a flat, polished surface, and a minimum of 3 points are taken to report an average value. Apollo’s machine uses both the “B” Scale (HRB) to test softer materials along with the higher hardness “C” scale to evaluate our wear and corrosion resistant products produced through laser cladding and laser heat treating.
Vickers Microhardness Testing
Microhardness testing is an essential tool for measuring hardness of individual, microscopic aspects of a material microstructure such as individual grains or reinforcing particles. Tests are typically gram force (gf) loads and the resulting indents from the test must be measured using a microscope. Vickers microhardness testing is also used to map hardness transitions from a treated surface or through dissimilar materials. The size of microstructurally susceptible regions such as the heat affected zone (HAZ) of a weld can be mapped by regular spacing of microhardness indents. This procedure is a standard for laser cladding, laser heat treating and laser welding processes revealing typical heat affected zone sizes of less than a millimeter and superior hardness of surface layers from the fast cooling rates of laser processes.
It is typical that a sample hardness evaluation will include both Vickers microhardness testing for a surface treatment and Rockwell hardness testing to evaluate the average base material hardness. View a sample report for a typical case depth analysis >