Improved Surface Integrity from Cryogenic Machining of Ti-6Al-7Nb Alloy for Biomedical Applications

AbstractTi-6Al-7Nb alloy is emerging as an alternative biomedical material for replacing Ti-6Al-4V alloy used in dental implants and femoral stem prosthesis applications. In cryogenic machining using liquid nitrogen, the surface integrity characteristics of Ti-6Al-7Nb alloy significantly improved compared to dry and flood-cooled machining. This study shows that surface roughness improved in cryogenic machining by 35% and 6.6% respectively, compared with dry and flood-cooled machining. Also, the hardness in the cryogenically-machined surface layer increased, by 33.6% and 14.7%, respectively, compared to dry and flood-cooled machining, with the formation of a severe plastic deformation (SPD) layer with less volume fraction of α-phase

Cryogenic Machining of Biomedical Implant Materials for Improved Functional Performance, Life and Sustainability

AbstractCryogenic cooling is known to provide a very sustainable machining process because of its environmentally benign, and economically and societally-beneficial nature. This keynote paper will focus on recent findings on producing functionally-superior engineered surfaces for improved product quality, performance and sustainability in cryogenically-processed biomedical implants. Results from cryogenic processing of Ti alloys, Co-Cr-Mo alloy, and AZ31B Mg alloy for achieving enhanced surface and sub-surface integrity will be summarized. Experimental results are compared with numerical/analytical simulations. Encouraging findings from this extensive study shows the tremendous potential for challenging broader applications of cryogenic machining technology for biomedical components

Effect of Heat Treatment on the Electrochemical and Mechanical Behavior of the Ti6Al4V Alloy

The effects of heat treatment on the hardness and electrochemical behavior of the Ti6Al4V alloy were studied. Two heat treatments were performed: one below (800 °C) and the other above (1050 °C) its beta transformation temperature (T= 980 ± 20 °C) and cooled using three conditions: water quenching, normalizing, and furnace. A microstructure observed using Optical Microscopy showed dependence on the heat treatment temperature applied; mainly three microstructures were obtained: martensitic, globular, and lamellar. Besides, alpha and beta phases were characterized by X-ray diffraction (XRD) technique. The Berkovich tests were performed to measure the hardness and reduced modulus (E). The Ti6Al4V alloy treated at 1050 °C and air-cooled exhibited hardness values closer to those of the Ti6Al4V as-received alloy. Electrochemical tests were carried out to analyze the electrochemical behavior after 7-day immersion in Hank’s solution at 37 °C and pH 7.40. Open Circuit Potentials (E) showed less negative values for Ti6Al4V and Ti6Al4V alloys, suggesting ennoblement of these materials. Furthermore, these alloys exhibited an outstanding electrochemical behavior compared to the Ti6Al4V as-received alloy by Electrochemical Impedance Spectroscopy (EIS) technique.The authors thank David Pérez-Risco for sharing his experience and useful advice on Berkovich Nano-indenter at the National Metallurgical Research Center (CENIM-CSIC Madrid, Spain), allowing this work to be carried out. Mercedes Paulina Chávez-Díaz thanks the National Science and Technology Council (CONACyT) for a doctoral fellowship to hold a research stay at CENIM-CSIC. This work was supported by the Government of Spain, through the Ministry of Economy and Competitiveness [MAT2015-67750-C3-1]. Elsa Miriam Arce-Estrada and Román Cabrera-Sierra wish to thank the National Research System (SNI) for the distinction of its members and the stipend received