Masters Theses

Date of Award

12-2014

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Claudia J. Rawn

Committee Members

George M. Pharr, Hahn Choo

Abstract

Titanium and titanium diboride (TiB2) are two materials that have attracted interest for application in armor systems. Titanium exhibits a high strength-to-weight ratio and good corrosion resistance while TiB2 exhibits high hardness and stiffness. Combining these into a titanium metal matrix composite would allow the superior ballistic properties to be taken advantage of in one composite material and lead to an improved armor system. The main obstacle behind doing so is the detrimental in situ reaction during processing between the Ti matrix and the TiB2 reinforcing particles that converts TiB2 into TiB. It was hypothesized that a protective coating on the TiB2 particulates would protect and prevent the in situ reaction. Two protective designs were investigated: depositing a carbon layer on the particle surface and also nitrogenizing the particle surface to create a boron nitride (BN) coating. TiB2 particulates were coated using fluidized bed chemical vapor deposition. Powders were blended and then produced either by pressing and firing or by hot pressing. Three separate experiments were performed: variable time, variable temperature, and hot pressing experiments. Samples were characterized using X-ray diffraction and microscopy focusing on phase identification and the coating’s effectiveness in preventing TiB formation. Impact testing using half-size charpy bars cut from the hot pressed plate samples also allowed investigation of impact behavior. The nitrogenizing of the particle surface was shown to be unsuccessful in preventing the conversion of TiB2 into TiB. Reaction between the Ti matrix and TiB2 readily occurs if the particles are not coated. The carbon coating was proven successful in preventing the conversion of TiB2 particles into TiB up to dwell times of 2 h at 1370 °C while also providing complete protection in a sample hot pressed at 1200°C. The carbon coating design presented was proven successful through a range of processing conditions in preventing the in situ conversion of TiB2 into TiB providing a route to produce a metal matrix composite wherein the TiB2 reinforcing particles remain intact and unconverted after processing. This material could lead to the production of an improved armor system.

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