Publication Date

2010

Document Type

Thesis

Committee Members

Ravi Penmetsa (Committee Member), Raghavan Srinivasan (Advisor), Seshacharyulu Tamirisakandala (Committee Member)

Degree Name

Master of Science in Engineering (MSEgr)

Abstract

Boron-modified Ti-6Al-4V alloys have shown increased performance in mechanical properties over unmodified alloys and are currently of interest for use in turbine engine applications. These alloys offer up to 40% increase in ultimate tensile strength, up to 30% increase in stiffness, and favorable damage characteristics while maintaining a ductility greater than 10%. These attractive properties are attributed to small additions of boron that refine the microstructure and form strong and stiff TiB whiskers. Previous research has found that these modified alloys compare favorably in fatigue. Samples machined from a powder-metallurgy forging with nominal composition Ti-6Al-4V-1B, were tested in fully-reversed bending at room temperature using a vibration based step test method to determine the 106 fatigue strength. This method simulates fatigue failure modes for high speed turbomachinery more accurately and produces high-cycle fatigue results much faster than traditional tensile testing methods. Results were compared with data generated in a similar fashion for Ti-6Al-4V, as well as traditional methods. Additionally, failure mode and damage characteristics were identified using fractographic analysis.

The fatigue strengths at 106 cycles compared poorly in comparison to both tensile and bending data for Ti-6Al-4V. This poor performance was attributed to inclusions of foreign material that were smaller than the theoretical maximum powder dimension. Fatigue damage characteristics were found to be consistent with previous research, with the most severe damage modes having little influence from the TiB whiskers.

Page Count

176

Department or Program

Department of Mechanical and Materials Engineering

Year Degree Awarded

2010

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