| Description |
In this dissertation, the process-structure-property relationships of titanium alloys, specifically Ti-6Al-4V, produced via hydrogen sintering and phase transformation (HSPT) is investigated. HSPT is a low-cost, blended elemental (BE), press-and-sinter process for producing titanium alloys that have mechanical properties that are competitive with wrought titanium alloys. Throughout this dissertation, the wrought-like microstructures that are possible by utilizing HSPT with other low-cost postsintering thermal processes, such as solution treatment and ageing (STA) heat treatments, are discussed. Additionally, the exceptional mechanical properties that result from the range of microstructures produced are presented. Currently, wrought processing is the state of the art for producing titanium alloys with the mechanical properties necessary for critical applications. However, wrought processing employs multiple steps of energy-intensive thermomechanical processing (TMP) to both form the shaped products and refine the microstructure. In fact, the majority of cost associated with many titanium products on the market today stems from TMP. Powder metallurgy (PM) has long been sought as a low-cost alternative to wrought processing, owing to its near-net-shape capabilities. However, traditional PM titanium has mechanical properties that are insufficient for many critical applications. In this dissertation, it is shown that HSPT is capable of producing wrought-like microstructures and mechanical properties without resorting to energy-intensive processes such as pressure-assisted sintering or TMP, which is compulsory for other processing routes. The as-sintered microstructure and mechanical properties of HSPT Ti-6Al-4V are discussed and compared with wrought and traditional PM Ti-6Al-4V. Additionally, the as-sintered HSPT Ti-6Al-4V was processed with a range of low-cost thermal processing techniques to produce a range of wrought-like microstructures and mechanical properties. Therefore, it is shown that HSPT is capable of producing different microstructures that have been engineered to meet the application-tailored demands for mechanical properties of titanium alloys. Additionally, the physical metallurgical principles and mechanisms behind these capabilities are discussed. The impetus for this research was the development of a low-cost process to produce high-performance titanium alloys. Therefore, a quantitative energy model, which was developed by the author, of the HSPT process is also presented. |
