Abstract
The effect of nano grain surface layer generated by ultrasonic impact on the fatigue behaviors of a titanium alloy Ti3Zr2Sn3Mo25Nb (TLM) was investigated. Three vibration strike-numbers of 24,000 times, 36,000 times and 48,000 times per unit are chosen to treat the surface of TLM specimens. Nanocrystals with an average size of 30 nm are generated. The dislocation motion plays an important role in the transformation of nanograins. Ultrasonic surface impact improves the mechanical properties of TLM, such as hardness, surface residual stress, tensile strength and fatigue strength. More vibration strike numbers will cause a higher enhancement. With a vibration strike number of 48,000 times per square millimeter the rotating-bending fatigue strength of TLM at 107 cycles is improved by 23.7%. All the fatigue cracks initiate from the surface of untreated specimens, while inner cracks appear after the fatigue life of 106 cycles with the ultrasonic surface impact. The crystal slip in the crack initiation zone is the main way of growth for microcracks. Crack cores are usually formed at the junction of crystals. The stress intensity factor of TLM titanium alloy is approximately 7.0 MPa·m1/2.
Highlights
As a kind of advanced multifunctional material, biomedical materials can be used to diagnose, cure, repair or replace human tissues, organs or enhance their functions
A kind of titanium alloy with no toxic element, high strength and low elastic modulus has been the main subject for researchers
The microstructure characterizations of the severe plastic deformation (SPD) layers are usually described by means of Transmission electron microscopy (TEM)
Summary
As a kind of advanced multifunctional material, biomedical materials can be used to diagnose, cure, repair or replace human tissues, organs or enhance their functions. Their unique efficacy is irreplaceable by drugs. In view of the high strength-to-weight ratio and excellent corrosion resistance, titanium and its alloys are widely used in medical instruments and biomedical implants. The large difference between these titanium alloys (more than 100 GPa) and bones (3–40 GPa) causes stress shielding [3]. A kind of titanium alloy with no toxic element, high strength and low elastic modulus has been the main subject for researchers. Nearly 20 new titanium alloys have been successfully developed. The reason is that the elements molybdenum, Materials 2020, 13, 2107; doi:10.3390/ma13092107 www.mdpi.com/journal/materials
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