From the days of the Moh hardness scale, technological advances have enabled quicker and more accurate determinations to be made. The Brinell scale represented the first advance towards supplanting scratching techniques with more accurate and precise indentation techniques. Later on, the Vickers technique was developed which allowed hardness determinations to be made on smaller pieces with less force.
This increased sensitivity brought about by Vickers testing can be understood by considering the geometry of the indenter. With a hemispherical indenter, such as Brinell’s, more force is required to obtain an indentation with sufficient resolution than with a pyrimidal Vickers indenter. The small force required allows for smaller devices and greater range. For this reason, the Vickers technique has become very popular in determining hardness in recent years.
Modern Vickers hardness testers have become integrated with electronics to further increase accuracy. Many new Vickers devices have a USB port which allows monitor viewing as well as motors which rotate the nosepiece, changing between the microscopic objective lenses and the indenter. An independent review company has recently reviewed five different Vickers hardness testers and the results can be seen here.
The highest rated Vickers device was the NG-1000. The ‘NG’ stands for the manufacturer, NextGen, ad the 1000 representes the maximum force (in gram force units.) The minimum force is 10 gf, and coupled with the 40X objective, allows hardness determinations to be made on very small objects. The dedicated software greatly simplifies the indentation measurement stage and the cold LED light allows illumination of metal samples without heating (a source of error, as hardness decrease with increasing temperature.)
For certain applications, the NG-5000 may be desired. This model is similar but has a indentation force range of 300 gf to 5000 gf. Both models come with a calibrated test block and meet ATSM standards and a Knoop indenter is optional for very thin specimens. The rubber feet help to isolate vibrations which could interfere with the test and it is recommended that the Vickers device be free standing and not in contact with walls (vibrations).
