Effects of high shear deformation from equal channel angular pressing-conform and post thermal mechanical processing on the microstructural and mechanical properties of titanium alloys

Titanium with its high specific strength (i.e. high strength and low density), excellent biocompatibility, and corrosion resistance makes it suitable for aerospace, automotive, sporting, chemical processing equipment, and medical industries. For medical applications, commercial purity titanium, Ti-13Zr, and Ti-6Al-7Nb, are particularly attractive because of their higher biocompatibility than Ti-6Al-4V which is the most widely used titanium alloy. . The main goal of this project was to develop a better understanding of the severe plastic deformation processing and properties of titanium alloys subject to equal channel angular pressing-conform (ECAP-C) and post thermal mechanical processing (TMP). The ECAP-C process uses high-shear deformation to refine the microstructure with the goal of producing an ultrafine grain material with enhanced mechanical properties. Three titanium alloys were studied, commercially pure titanium Grade 4, Ti 13Zr, and Ti-6Al-7Nb, allowing for the systematic investigation of the processing response and strengthening mechanisms resulting from equal channel angular pressing-conform (ECAP-C) plus post thermal mechanical processing (TMP). From this investigation a strengthening model that incorporated individual components of the microstructure was developed to predict the ultimate tensile strength of each material. The predicted values from the strengthening model were within 10-20 percent of the measured values. This model identified that grain boundary strengthening, as a result of the grain size refinement, is the largest contributing factor, with subgrain strengthening also contributing a significant amount. The strength and ductility levels achieved in this investigation were: o CP Ti G4 (first alloy)  YS: 984 MPa, UTS: 1215, elongation to failure: 6.9% o Ti-13Zr  YS: 1300 MPa, UTS: 1400 MPa, elongation to failure: 6.3% o Ti-6Al-7Nb  YS: 1189 MPa, UTS: 1147 MPa, elongation to failure: 20.4% o CP Ti G4 (second alloy)  YS: 1133 MPa, UTS: 1255 MPa, elongation to failure: 20.8% The fabrication of prototype precision ground CP Ti G4 and Ti-13Zr alloy rod 5 mm in diameter and >1 m in length, plus ECAP-C-only processing of the Ti-6Al-7Nb alloy successfully demonstrated the commercial viability of producing a diverse range of ultrafine grain titanium alloys, leading to the commercial adoption of ECAP-C + TMP processing.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Metallurgical and Materials Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2019

Author dc:creator

• Hayne, Mathew L.

Advisor dc:contributor.advisor

• Lowe, Terry C.

Committee members dc:contributor.committeemember

• Olson, D. L. (David LeRoy)
• Rockett, A. (Angus)
• Petrella, Anthony J.

• titanium
• ECAP-C
• ultrafine grain

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Identifier

T 8842

OAI identifier oai:identifier

oai:repository.mines.edu:11124/173982