| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | March 27, 2014 |
| Latest Amendment Date: | March 27, 2014 |
| Award Number: | 1404920 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Steve Schmid
CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | April 1, 2014 |
| End Date: | March 31, 2017 (Estimated) |
| Total Intended Award Amount: | $80,000.00 |
| Total Awarded Amount to Date: | $80,000.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
3124 TAMU COLLEGE STATION TX US 77843-3124 (979)862-6777 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Mechanical Engineering-3123 TAMU College Station TX US 77843-3123 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Manufacturing Machines & Equip |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
This collaborative research award supports fundamental research on machining of ultra-fine grained pure titanium for biomedical applications. The research will test the hypothesis that machining induces microstructure changes in severe plastic deformation-processed ultra-fine grained metals, which affects their functionality and cell-material interaction performance. Specifically, key research activities include fabricating bulk ultra-fine grained titanium using equal channel angular extrusion, characterizing the machining-induced microstructure change and functionality variation in terms of grain size, dislocation density, residual stress, and corrosion behavior, and investigating machining-induced cell-material interaction alterations in terms of osteoblast cell adhesion and proliferation. Ultra-fine grained titanium bars will be studied because of titanium's promising use for medical implants and prosthetics.
Research results will provide knowledge and understanding of machining-induced material property variations and functionality alterations of severe plastic deformation-processed bulk ultra-fine grained titanium. The methodology will contribute to the adoption of ultra-fine grained metals in the healthcare industry requiring high strength and corrosion resistance and the automobile industry requiring high strength-to-weight ratios. This collaborative research project features a unique collaboration among materials processing, machining, and biomedical manufacturing researchers. The research activities will promote advanced manufacturing for healthcare applications as well as disciplinary education in materials, materials processing, and manufacturing through curriculum development. The research will also positively impact the participation of diverse groups and promotion of Science, Technology, Engineering, and Mathematics activities at the University of Florida, Texas A&M, and Georgia Tech.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The high strength, low weight, and outstanding corrosion resistance of pure titanium (Ti) and Ti alloys have led to a wide and diverse range of successful medical applications. Unfortunately, the alloying elements aluminum and vanadium in the widely used Titanium alloy Ti64 are toxic to the human body, so this alloy and others are much less biocompatible than pure Ti. If the strength of pure Ti could be increased by reducing the grain size to a submicron level, it could be an attractive substitute for Ti alloy implants. Fortunately, severe plastic deformation (SPD)-processed pure Ti has an ultra-fine grained (UFG) microstructure and shows much promise in replacing Ti alloy implant material because its yield strength can be comparable to that of Ti alloys. Microstructures in SPD-processed UFG materials are metastable, so microstructural changes can occur at the elevated temperatures reached during machining, a common manufacturing process used to shape materials. It is of interest to understand how the machinability of SPD-processed UFG materials changes and how machining may alter their properties, particularly the functionality of machined UFG pure Ti parts for medical applications.
This study has investigated the machining of UFG Ti, which has been prepared using equal channel angular extrusion (ECAE), a typical SPD process. During ECAE, a round or square workpiece bar is pressed through two intersecting channels so that the material is subjected to very intense plastic strain during pressing (extrusion). To characterize the machinability of multipass ECAE-processed UFG Ti, machining chips were fabricated and the chip morphology and chip formation mechanisms identified using metallographic analyses together with high speed imaging and hardness measurements. The observations have been compared with those during machining of coarse-grained (CG) Ti. The chip formation mechanism of ECAE-processed UFG Ti transitions from cyclic shear localization within the low cutting speed regime to uniform shear localization within the moderately high cutting speed regime. The shear band spacing is found to increase as the cutting speed increases and is always lower than that of the CG counterpart. Specifically, during machining of ECAE-processed UFG Ti, if the shear strain-rate distribution varies temporally in the chip flow direction, the chip morphology appears saw-tooth, and cyclic shear localization is the governing chip formation mechanism. If no such temporal variation occurs, the chip formation is considered continuous, and uniform shear localization is the governing chip formation mechanism. Chip hardness measurements corroborate these observations, showing that localized hardness peaks occur when cyclic shear localization is the governing chip formation mechanism, whereas uniform shear localization results in relatively constant hardness. Furthermore, the machined UFG Ti samples have been evaluated in terms of biological cell adhesion and proliferation. While ECAE-processed UFG Ti has unique chip formation mechanisms, there is no pronounced effect of typical machining conditions on the behavior of fibroblasts growing on the machined surface.
The resulting machinability knowledge helps to better machine SPD-processed UFG materials for various applications including those for medical implants. Two graduate students have been involved in this research study, and the resulting machining knowledge has been integrated into a graduate-level advanced manufacturing course and the preparation of three journal papers.
Last Modified: 07/26/2017
Modified by: Karl T Hartwig
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