Fatigue and fracture of a Ni–P amorphous alloy thin film on the micrometer scale

Abstract

A B S T R A C T Fracture and fatigue tests have been performed on micro-sized specimens for microelectromechanical systems (MEMS) or micro system technology (MST) applications. Cantilever beam type specimens with dimensions of 10 × 12 × 50 µm 3 , approximately 1/1000th the size of ordinary-sized specimens, were prepared from a Ni-P amorphous thin film by focused ion beam machining. Fatigue crack growth and fracture toughness tests were carried out in air at room temperature, using a mechanical testing machine developed for micro-sized specimens. In fracture toughness tests, fatigue pre-cracks were introduced ahead of the notches. Fatigue crack growth resistance curves were obtained from the measurement of striation spacing on the fatigue surface, with closure effects on the fatigue crack growth also being observed for micro-sized specimens. Once fatigue crack growth occurs, the specimens fail within one thousand cycles. This indicates that the fatigue life of micro-sized specimens is mainly dominated by a crack initiation process, also suggesting that even a micro-sized surface flaw may be an initiation site for fatigue cracks which will shorten the fatigue life of micro-sized specimens. As a result of fracture toughness tests, the values of plane strain fracture toughness, K IC , were not obtained because the criteria of plane strain were not satisfied by this specimen size. As the plane strain requirements are determined by the stress intensity, K , and by the yield stress of the material, it is difficult for micro-sized specimens to satisfy these requirements. Plane-stressand plane-strain-dominated regions were clearly observed on the fracture surfaces and their sizes were consistent with those estimated by fracture mechanics calculations. This indicates that fracture mechanics is still valid for such micro-sized specimens. The results obtained in this investigation should be considered when designing actual MEMS/MST devices.

Fracture toughness testing of nanocrystalline alumina and fused quartz using chevron-notched microbeams

“…Once the method was perfected, these often gave data consistent with data from macroscopic tests of the same material (Si notably) [2,13,19,[37][38][39][40]. Finally, some authors have used fatigue of notched microspecimens to create precracks in metallic specimens (prone to largescale yielding, however) [41][42][43], and also in silicon [44].…”

Fatigue life and plastic deformation behavior of electrodeposited copper thin films

“…On fatigue properties of thin films, there is only little work [8,[21][22][23][24][25][26][27][28][29], mainly due to difficulties in performing fatigue tests and measuring fatigue behavior. Normally, compressive load cannot be applied to film specimens and fatigue testing is usually performed under tension-tension loading conditions.…”

Failure assessment of a hard brittle coating on a ductile substrate subjected to cyclic contact loading

“…caused by fatigue damage [17][18][19][20]; however, such a coating has a brittle characteristic nature and might not be sensitive to cyclic fatigue damage (compared with a ductile metal). On the other hand, the substrate was ductile stainless steel, which often undergoes cyclic plastic deformation [11,[21][22][23][24] This result will be discussed later.…”