Cutting characteristics of bulk metallic glass

The establishment of appropriate machining techniques for bulk metallic glasses (BMGs), which exhibit excellent mechanical, physical and chemical properties, is required to apply the BMGs. In this report, the cutting characteristics of BMGs were examined by turning with different tool materials, nose radii (R-H) and cutting speeds (V). Round bars of Zr65Cu15Ni10Al10 and Pd40Cu30Ni10P20 at% BMGs were used as the workpieces. In order to compare the cuttability of the BMGs with that of crystalline alloys, steel (JIS SGD-400D) and free-cutting brass (JIS C3604) were used. The principal cutting force (F-H) and surface roughness (R-a) of the machined surfaces were measured. X-ray diffraction patterns were also obtained from the machined surfaces. The value of R-a in the BMGs exhibit the upper end of precise finishing level (i.e., R-a = 0.2 mu m), and was remarkably lower compared with the steel and a little lower compared with the free-cutting brass in spite of the value of V. The value became smaller with increasing values of R-n, exhibiting a very low value of 0.08 mu m for an R-n value of 1.2 mm. The values of FH in both BMGs did not show a clear difference and were half that of the steel for a V value less than 40 m/min, even though the tensile strength of the BMGs was twice as large as the steel. The chip of the BMGs showed an ideal flow type with very short and regular intervals, formed by planar slip, and revealed very homogeneous, flat and featureless back surfaces. From these observations of chips, it is presumed that the reason for the excellent cuttability of BMGs is due to a slipping-off mechanism at planes of very short intervals decided only by the maximum shear stress and non-built-up edges caused by a low glass transition temperature.