Scratch Damage Behavior Of Monocrystalline Silicon And Nickel-Titanium Shape Memory Alloy

Nowadays, the miniaturization trends in the areas of information, biotechnology and advanced manufacturing have greatly promoted the development of microelectromechanical systems (MEMS). However, the surface and size effects have induced the severe adhesion, friction and wear issues in MEMS. Based on their excellent physical and mechanical properties, monocrystalline silicon has been widely used in MEMS as typical structural material. Because of its shape memory effect (SME) and super elasticity (SE), NiTi alloy is the ideal candidate material for microsensors and microactuators. Therefore, the research on their microwear behaviors can not only improve our understanding on nanotribology, but also provide theoretical guidance for high reliability and long-life MEMS.Based on nano-hardness/scratch tester and atomic force microscopy, the scratch behavior of silicon (100) and SME NiTi alloy was studied. Both the load effect and tip radii effect on the scratch behavior of silicon (100) were discussed. The number of scratch cycles effect on the damage behavior of SME NiTi alloy was investigated. The recovery of the scratch scar was characterized by heating to 100°C. The competition of interface friction and plough friction was discussed. The micro-friction mechanism of SME NiTi alloy was analyzed under reciprocating scratches. The main conclusions can be summarized as follows:1. With the increase in load, the scratch damage of silicon (100) has gone through three stages: the formation of upheaval, upheaval co-exist with groove and material removal. As the scratch experiment was performed at low load, the upheaval on silicon (100) was more remarkable than on silicon (111) because of its lower hardness and modulus of elasticity, and the upheaval was higher when the scratch tip's radius is smaller.2. The scratch damage of silicon (100) is closely related to the contact stress and the environment, which suggested that the initial formation of upheaval is induced by friction-chemical action and mechanical deformation.3. The scratch depth of SME NiTi alloy is gradually increasing and tends to stabilize with the increase in the number of cycles. As the scratch experiment was conducted at room temperature, the deformation of SME NiTi is mainly due to the movement of twin boundaries. As the temperature increased above 100°C, the deformation of SME NiTi alloy can be partly recovered due to the transformation from martensite to austenite.4. With the increase in the number of cycles, the interface friction is gradually increasing and tends to stabilize. However, the plough friction and the total friction are gradually decreasing and tend to stabilize.