Doctor of Philosophy

dissertationIn 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

Candidate anode materials for iron production by MOE

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 61-63).Molten oxide electrolysis (MOE) has been identified by the American Iron and Steel Institute (AISI) as one of four possible breakthrough technologies to alleviate the environmental impact of iron and steel production. This process has also been identified by the National Aeronautics and Space Administration (NASA) as a means to produce oxygen gas, as well as iron and silicon raw materials on the Moon. MOE produces iron by electrolysis of an iron oxide containing electrolyte. The electrolysis results in the production of pure iron metal at the cathode and pure oxygen gas at the anode. Because of the low vapor pressure of the electrolyte at temperatures above 1538°C, MOE can be performed above the melting temperature of iron. The production of liquid metal, ready for continuous casting, is a prerequisite for any industrial-scale extractive metallurgical process. Therefore, if an inert anode can be identified, MOE could provide a an industrial process to produce iron from its ore with pure oxygen gas as the only direct emission. The feasibility of MOE as a carbon-neutral process hinges on the identification of an inert anode material. Therefore, the scope of this study was to determine the criteria of an inert anode for MOE, identify candidate materials, and evaluate the performance of these materials. Previous studies of MOE at MIT found iridium, a platinum group metal, to be an excellent candidate for an inert anode. The high cost of iridium makes it an unlikely candidate for a commercial iron production process. However, iridium provides a likely candidate for lunar production of oxygen, or high-purity iron production. Furthermore, the use of iridium on the laboratory-scale provides a widely available inert anode material to facilitate the study of other areas of MOE. Therefore, unique anode morphologies were evaluated as a means to reduce the economical strain of using an iridium anode. In addition to iridium, a wide array of readily available, high-temperature electrode materials were tested. Due to the highly corrosive environment of MOE, none of the readily available materials tested are compatible with the process. It is believed that the most likely candidate for an inert anode lies in an engineered material, composed of a refractory substrate and an oxide passivation layer. Therefore, the criteria for such a material were determined and likely candidates are discussed.by James D. Paramore.S.M

How 'dynasty' became a modern global concept : intellectual histories of sovereignty and property

The modern concept of ‘dynasty’ is a politically-motivated modern intellectual invention. For many advocates of a strong sovereign nation-state across the nineteenth and early twentieth century, in France, Germany, and Japan, the concept helped in visualizing the nation-state as a primordial entity sealed by the continuity of birth and blood, indeed by the perpetuity of sovereignty. Hegel’s references to ‘dynasty’, read with Marx’s critique, further show how ‘dynasty’ encoded the intersection of sovereignty and big property, indeed the coming into self-consciousness of their mutual identification-in-difference in the age of capitalism. Imaginaries about ‘dynasty’ also connected national sovereignty with patriarchal authority. European colonialism helped globalize the concept in the non-European world; British India offers an exemplar of ensuing debates. The globalization of the abstraction of ‘dynasty’ was ultimately bound to the globalization of capitalist-colonial infrastructures of production, circulation, violence, and exploitation. Simultaneously, colonized actors, like Indian peasant/‘tribal’ populations, brought to play alternate precolonial Indian-origin concepts of collective regality, expressed through terms like ‘rajavamshi’ and ‘Kshatriya’. These concepts nourished new forms of democracy in modern India. Global intellectual histories can thus expand political thought today by provincializing and deconstructing Eurocentric political vocabularies and by recuperating subaltern models of collective and polyarchic power.PostprintPeer reviewe

The IDENTIFY study: the investigation and detection of urological neoplasia in patients referred with suspected urinary tract cancer - a multicentre observational study

Objective To evaluate the contemporary prevalence of urinary tract cancer (bladder cancer, upper tract urothelial cancer [UTUC] and renal cancer) in patients referred to secondary care with haematuria, adjusted for established patient risk markers and geographical variation. Patients and Methods This was an international multicentre prospective observational study. We included patients aged ≥16 years, referred to secondary care with suspected urinary tract cancer. Patients with a known or previous urological malignancy were excluded. We estimated the prevalence of bladder cancer, UTUC, renal cancer and prostate cancer; stratified by age, type of haematuria, sex, and smoking. We used a multivariable mixed-effects logistic regression to adjust cancer prevalence for age, type of haematuria, sex, smoking, hospitals, and countries. Results Of the 11 059 patients assessed for eligibility, 10 896 were included from 110 hospitals across 26 countries. The overall adjusted cancer prevalence (n = 2257) was 28.2% (95% confidence interval [CI] 22.3–34.1), bladder cancer (n = 1951) 24.7% (95% CI 19.1–30.2), UTUC (n = 128) 1.14% (95% CI 0.77–1.52), renal cancer (n = 107) 1.05% (95% CI 0.80–1.29), and prostate cancer (n = 124) 1.75% (95% CI 1.32–2.18). The odds ratios for patient risk markers in the model for all cancers were: age 1.04 (95% CI 1.03–1.05; P < 0.001), visible haematuria 3.47 (95% CI 2.90–4.15; P < 0.001), male sex 1.30 (95% CI 1.14–1.50; P < 0.001), and smoking 2.70 (95% CI 2.30–3.18; P < 0.001). Conclusions A better understanding of cancer prevalence across an international population is required to inform clinical guidelines. We are the first to report urinary tract cancer prevalence across an international population in patients referred to secondary care, adjusted for patient risk markers and geographical variation. Bladder cancer was the most prevalent disease. Visible haematuria was the strongest predictor for urinary tract cancer

Stability of Iridium Anode in Molten Oxide Electrolysis for Ironmaking: Influence of Slag Basicity

Molten oxide electrolysis (MOE) is a carbon-neutral, electrochemical technique to decompose metal oxide directly into liquid metal and oxygen gas upon use of an inert anode. What sets MOE apart from other technologies is its potential environmental advantage of no greenhouse gas emissions. Therefore, the primary challenge for carbon-free molten oxide electrolysis is the development of an inert anode. In the quest for an inert anode that can sustain the aggressive conditions of the process, iridium has been evaluated in two different slags for ironmaking. The basicity of the electrolyte proves to have a dramatic effect on the stability of the iridium anode, where iridium corrosion in an acidic slag with high silica content is less pronounced than the corrosion rate in a basic slag with high calcia content

The uses and applications of hydrogen processing for titanium additive manufacturing

Additive manufacturing has shown to be a promising method for reducing the cost and increasing the complexity of titanium components, with the majority of research focusing on beam-based methods (i.e. powder bed fusion and directed energy deposition). However, these processes produce highly complex thermal histories, which can result in highly anisotropic and otherwise undesirable microstructures and mechanical properties. In an effort to mitigate these challenges, the use of hydrogen as a temporary alloying element has been identified as a promising method to prevent unfavorable microstructures and isotropy in AM Ti-6Al-4V. Herein, the powder metallurgy process known as Hydrogen Sintering Phase Transformation (HSPT) used in conjunction with a solid state AM method known as fused filament fabrication (FFF) is discussed

Thermo-hydrogen refinement of microstructure to improve mechanical properties of Ti–6Al–4V fabricated via laser powder bed fusion

This paper describes the main results from an investigation into the consequences of thermo-hydrogen refinement of microstructure (THRM) after laser powder bed fusion (LPBF) of Ti–6Al–4V on the evolution of microstructure and mechanical properties using a set of experimental techniques. Porosity fraction, grain structure, phases, and crystallographic texture per phase are characterized using micro X-ray computed tomography, microscopy, and neutron diffraction. A hierarchical structure of acicular α-phase morphology formed inside the prior β grains by fast cooling during LPBF transforms into fine-grained globular microstructure by THRM, which facilitates homogeneous nucleation and growth of the low temperature phase with some retained β phase. Moreover, hydrogenated material during THRM has low activation energy for diffusion, which in conjunction with the surface energy of pores causes densification of the material, thereby closing porosity formed during LPBF. Such significant microstructural changes induced by the THRM treatment cause brittle material created by LPBF to become ductile. Significantly, the strength and ductility produced by THRM exceed the minimums set forth by the ASTM B348 standard for Ti-6Al-4V. Moreover, the treatment improves fatigue strength of the material. In particular, it improves the endurance limit and reduces the scatter in the measured fatigue strength data. Performance characteristics of the material can be further optimized for specific application requirements by tailoring microstructures using the LPBF and THRM processes