Development of Ultrafine and Nano-crystalline Grain Structures during Modified Accumulative Roll Bonding of Titanium Alloy,Ti-25Nb-3Zr-3Mo-2Sn.

摘要

Titanium alloys with high strength to weight,excellent toughness,corrosion resistance and biocompatibility are favoured for a wide range of bio-medical applications. The near β Ti-25Nb-3Zr-3Mo2Sn alloy (TLM) is a new biomedical alloy suitable for implant applications. As well as being biocompatible.Ti alloys for surgical implants need to be mechanically compatible. A modified accumulative roll bonding (ARB) process was developed to form a high strength, ultrafine grain version of the alloy. With each ARB cycle,iterative strength improvements lead to an almost doubling of the strength of the alloy after 4 cycles. This is coupled with an initial large drop in the ductility which then showed some recovery in subsequent cycles. A detailed investigation of the evolution of the microstructure was undertaken. There is a large variation in the grain sizes throughout processing and at the completion of 4 cycles the grain sizes range from>1μm to<20nm. Contributing to refinement is a dense network of shear bands made up of UFG grains<20nm in size which form in later cycles.