HYDROGEN ENHANCED ATOMIC TRANSPORT: CREATING HARD TITANIUM/TITANIUM HYDRIDE BROWN BODIES AT AMBIENT PRESSURE AND TEMPERATURE GREATER THAN 650 DEGREES CENTIGRADE

Abstract

This thesis introduces a simple, low-temperature method called Hydrogen Enhanced Atomic Transport (HEAT) for creating metallic bonded brown bodies on the order of 40% bulk density in molds of designed shape from titanium (Ti) metal particles. In this initial study, 40 µm Ti particles were poured into graphite molds and heated for four hours to temperatures greater than 650 ˚C in a flowing ambient pressure gas mixture containing some hydrogen, which led to brown body formation that closely mimicked the mold shape. The brown bodies were shown to be hard, and consisted of primarily Ti metal and some titanium hydride. It is postulated that hydrogen is key to the sintering mechanism: it enables the formation of short-lived volatile titanium hydride species that lead to sintering via an Ostwald Ripening mechanism. Data consistent with this postulate includes finding that brown bodies formed with hydrogen present (HEAT process) had mechanical properties like metal, such that they plastically deformed at high pressure (ca. 5000 atm). In contrast, brown bodies made in identical conditions but without hydrogen were brittle and broke into micron-scale particles under pressure. HEAT appears to have advantages relative to existing titanium metal additive manufacturing methods, such as particle injection molding, which requires many more steps, particularly debonding, and other methods, such as laser sintering, which are slower and require expensive hardware and expert operation.