Fatigue Strength in Nanocrystalline Ti- and Cu-Based Bulk Metallic Glasses

Abstract

Fatigue tests were carried out on nanocrystalline Tiand Cu based bulk metallic glasses (BMGs) for which there are still no reports on fatigue strength. Test alloy rods with a diameter of 2 mm were prepared in nanocrystalline Ti 41.5 Zr 2.5 Hf 5 Cu 42.5 Ni 7.5 Si 1 at and Cu 60 Zr 30 Ti 10 at systems by copper mold casting. Nanocrystals were dispersed in the metallic glassy phase in both BMGs. The tensile strength (s B ) in the nanocrystalline Tiand Cu based BMGs were 2.04 GPa and 2.00 GPa, and Young's modulus were 95 GPa and 114 GPa, respectively. The test specimens were machined to hourglass shape type (the radius in axial direction; 4.45 mm, the minimum diameter; 0.9 mm), and after machining the specimen surfaces were electropolished by 50～ 100 mm. The specimens were tested at a stress ratio of 0.1 and a frequency of 5 8 Hz. The fatigue limit (s w ) (half a total stress amplitude) and fatigue ratio (s w /s B ) in the nanocrystalline Tiand Cu based BMGs showed very large values (Ti based alloy; 806 MPa and 0.40, Cu based alloy; 490 MPa and 0.25). This experimental result indicated a possibility that the nanocrystal dispersed BMGs have higher fatigue strength than the high strength crystalline alloys with high fatigue strength (e.g. Cr Mo steel, s w 500 MPa). (Received February 16, 2006; Accepted August 7, 2006) Keywords: fatigue, fatigue limit, bulk metallic glass, bulk glassy alloy, amorphous, nanocrystal

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

“…However, as discussed below, it is the characteristic dimensions of this second phase compared with pertinent mechanical length scales that is the key to attaining good fatigue properties in metallic glass materials. Indeed, very recent studies on Ti-and Cu-based BMGs (33,34) reinforced with nanocrystalline dispersions provide phenomenological evidence to support this notion, because the finer second-phase A B Fig. 1.…”

Review on the Research and Development of Ti-Based Bulk Metallic Glasses

“…Yamaura et al [198] and Fujita et al [199] have investigated the fatigue behavior of Ti 40 Table 6 lists the fatigue properties of Ti-based BMGs together with other typical BMGs and Ti-6Al-4V alloy [198][199][200][201][202]. Compared with the Ti-6Al-4V alloy, Ti 40 Zr 10 Cu 34 Pd 14 Sn 2 BMG, which is a typical representative of biomedical Ti-based BMG, exhibits higher fatigue strength although the fatigue ratio is lower.…”

Comparison of Fatigue Strengths of Bulk Metallic Glasses Produced by Tilt Casting and High-Pressure Casting

“…Figure 10(a) shows an overview of a fatigue-fractured surface, and Figure 10(b) presents a magnified image of the fatigue-fractured region of the tilt-cast BMG with the fatigue conditions of Dr = 1000 MPa and N = 4.2 9 10 3 . Fatigue-crack initiation probably occurred by a shear slip near the surface, [23] as shown in Figure 10(c). Further, it is noteworthy that clear striation-like marks can be observed all over the fatigue-crack-propagation region, and the clear boundary between the fatigue-fractured and overloaded regions can be seen, as shown in Figures 10(d) and (e), respectively.…”