@phdthesis{Xu2020, author = {Xu, Peng}, title = {Enhancement of tensile fracture resistance of metal-injection-molded β titanium alloys biomaterials via diverse sintering pathways}, doi = {10.26127/BTUOpen-5512}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-55126}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {The powder metallurgically produced beta titanium alloys (traditional PM beta Ti-alloys) have long been plagued by high impurities contamination. For binder-based powder technologies, they originate from the sintering atmosphere, the debinding processes and the starting powders. In general, a normal carbon residual of binder-based powder technologies is capable of incurring the formation of aligned TiCx particles along beta grain boundaries (GB-TiCx) in most classes of beta Ti-alloys. Whereas, oxygen atoms are likely to deteriorate the ductility of PM Ti alloys by promoting the formation of diverse brittle phases and/or altering the deformation modes. Such materials exhibiting rather low toughness to strain ratios are not an option for critical structural applications, where catastrophic damage is completely unacceptable. In this study, biotolerant metastable beta Ti-20Nb-10Zr alloys, containing a certain amount of carbon, oxygen residuals originated from materials processing and consequently 0.5 vol.\% in situ synthesized TiCx particles, were fabricated via metal-injection-molding (MIM). With varying yttrium (Y) addition, the effects of Y-induced oxygen scavenging, beta-grain refinement and porosity increment on tensile properties were systematically investigated. To scavenge oxygen from the beta Ti-matrix, the Y elemental powder with a maximum particle size of 15 µm (e.g. <12 µm or 1200 mesh) is more appropriate than the commonly used <45 µm (i.e. 325 mesh) sized powder or larger ones and without significant detrimental effect on the as-sintered density of beta Ti-alloys. A novel toughening strategy was proposed by regulating TiCx precipitation evolution and resultantly adjusting particles distribution pattern. Synchrotron radiation identified that two separate TiCx precipitation-type reactions occurred at the beta phase region and the alpha/beta region. In a narrow temperature range between these two precipitation reactions, dissolution of carbides was observed just below alpha/beta transus. Y addition can postpone TiCx precipitation. On the basis of those mechanisms, adjusting TiCx particle distribution was proposed for the first time, specifically a combination of yttrium addition (Y) and carbide spheroidization reprecipitation annealing (CSRA). As a result, aligned GB-TiCx particles were adjusted to dispersed intragranular TiCx particles. An apparent toughening effect (≈ 113\% increment reaching elongation = 8.3\%) was achieved after TiCx redistribution, while non-optimally aligned TiCx pattern seriously limited tensile toughness of materials. Here, the mechanisms of TiCx redistribution behavior and its toughening are elucidated systematically.}, subject = {Metal-Injection-Molding; Titanium; Carbide; Fracture; Oxygen; Metallspritzguss; Titan; Karbid; Fraktur; Sauerstoff; Biomaterial; Metallspritzguss; Titanlegierung; Carbide; Sauerstoff; Bruchverhalten}, language = {en} }