Titanium Alloys for Demanding Applications: Sintering and Synthesis of Titanium Alloys
Program Organizers: Jean Stewart, ATI Powder Metals; F. Dax, Retired; Andrzej Wojcieszynski, ATI Powder Metals
Wednesday 8:00 AM
October 10, 2012
Room: Room 409
Location: David L. Lawrence Convention Ctr
Session Chair: Jean Stewart, ATI Powder Metals
8:00 AM
Hydrogen Sintering of TiH2–A Novel Method for Powder Metallurgy Titanium: Zhigang Fang1; Pei Sun1; 1The University of Utah
Powder metallurgy (PM) is a promising low cost approach for manufacture of titanium components. Conventional PM method relies on sintering of titanium metal powders in high vacuum in order to achieve high density and low oxygen. Sintered titanium materials usually have coarse grain size. In this paper, a new approach--Hydrogen Sintering and Phase Transformation (HSPT) of TiH2--is designed to take advantage of both enhanced densification using TiH2 and phase transformations induced by hydrogen to produce fully densified titanium with fine or ultrafine grain microstructure. This method is a three-step process including hydrogen sintering, eutectoid transformation and dehydrogenation. Sintering behaviors of titanium in hydrogen, phase transformations, and mechanical properties are studied. Results of tensile tests and chemical analysis show that PM Ti by HSPT has low impurity levels and superior mechanical properties. This presents a promising approach for producing PM Ti materials with superior mechanical properties at minimum cost.
8:40 AM
The Effect of Hydrogen as Sintering Atmosphere on Densification and Microstructural Features of Powder Metallurgy Titanium: Pei Sun1; Zhigang Fang1; 1The University of Utah
Use hydrogen as the atmosphere for sintering titanium hydride powder is a novel and attractive method to produce fully densified powder metallurgy (PM) titanium materials with fine or ultrafine microstructure. This method includes three steps: hydrogen sintering, eutectoid transformation and dehydrogenation. In this paper, the sintering behavior of titanium hydride powder in controlled hydrogen is compared with that in vacuum-- a typical sintering atmosphere for manufacturing PM titanium materials. Also, microstructural evolution during each step is investigated by X-ray and metallographic examination. Effects of four important parameters (hydrogen ratio in the sintering atmosphere, temperature for eutectoid transformation, temperature and time for dehydrogenation) in the process on the final microstructures and grain size are studied.
9:00 AM
Composite Ti-6Al-4V + Hydroxyapatite Biomedical Implant Materials via Spark Plasma Sintering: Kyle Crosby1; Monica Sawicki1; Leon Shaw1; Claude Estournes2; 1University of Connecticut; 2Carnot Institute
Development of functionally graded composite Ti-6Al-4V + Hydroxyapatite (HA) biomedical implants are hindered by high temperature reactions between the constituents when co-sintered above 1000°C (i.e. the temperature regime required to fully densify Ti-6Al-4V and HA through powder metallurgy sintering). To avoid this detrimental reaction the sintering temperature must be reduced, without compromising the mechanical integrity provided by a fully dense component. Because the sintering process is dependent upon temperature and time, the driving force for diffusion must be enhanced. Fabrication of nanostructured powder precursors promote a change in diffusion mode (i.e. from lattice diffusion limited to grain boundary and free surface diffusion limited), while the spark plasma sintering (SPS) method allows for more rapid heating than traditional tube furnace sintering. Together the augmented diffusion mode and accelerated application of thermal energy allow co-sintering of Ti-6Al-4V + HA below 1000°C to be realized, thus functionally graded composite implants are possible.
9:20 AM Break
9:40 AM
Investigation of the Thermal Pattern at Saturation of Titanium and Its Alloys with Silicon in SHS: Borys Sereda1; Yulija Bondarenko1; Tatjana Vasilchenko1; Dmytro Sereda1; 1ZSEA
The paper presents the results of a study of thermal pattern of SHS (self propagating high temperature synthesis) process. The main factors that have a significant impact on the quality and quantity developed hardened layers in the regime of thermal self-ignition. Found that for the preservation of process conditions in the no degenerate regime the mass ratio of the reacting mixture and the work piece must be at least 3:1. The optimum content of AlF3 in the developed SHS mixture of 2-3%, which is confirmed by metallographic studies. Established that the best quality (uniformity in thickness and continuity) have the coverage obtained in the range of heating rates from 10 to 20° C/min.
10:00 AM Question and Answer Period